Cytotoxic Effects of Diterpenoid Alkaloids Against Human Cancer Cells
Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, Hokkaido University of Science, 4-1, Maeda 7-jo 15-choume, Teine-ku, Sapporo 006-8590, Japan
*
Author to whom correspondence should be addressed.
Molecules 2019, 24(12), 2317; https://doi.org/10.3390/molecules24122317
Submission received: 23 May 2019
/
Revised: 17 June 2019
/
Accepted: 21 June 2019
/
Published: 22 June 2019
(This article belongs to the Special Issue Antitumor and Anti-HIV Agents from Natural Products)
Abstract
:Diterpenoid alkaloids are isolated from plants of the genera Aconitum, Delphinium, and Garrya (Ranunculaceae) and classified according to their chemical structures as C18-, C19- or C20-diterpenoid alkaloids. The extreme toxicity of certain compounds, e.g., aconitine, has prompted a thorough investigation of how structural features affect their bioactivities. Therefore, natural diterpenoid alkaloids and semi-synthetic alkaloid derivatives were evaluated for cytotoxic effects against human tumor cells [A549 (lung carcinoma), DU145 (prostate carcinoma), MDA-MB-231 (triple-negative breast cancer), MCF-7 (estrogen receptor-positive, HER2-negative breast cancer), KB (identical to cervical carcinoma HeLa derived AV-3 cell line), and multidrug-resistant (MDR) subline KB-VIN]. Among the tested alkaloids, C19-diterpenoid (e.g., lipojesaconitine, delcosine and delpheline derivatives) and C20-diterpenoid (e.g., kobusine and pseudokobusine derivatives) alkaloids exhibited significant cytotoxic activity and, thus, provide promising new leads for further development as antitumor agents. Notably, several diterpenoid alkaloids were more potent against MDR subline KB-VIN cells than the parental drug-sensitive KB cells.
1. Introduction
Cancer therapy mainly involves surgery, chemotherapy, radiation therapy, immunotherapy, monoclonal antibody therapy, and hormone therapy. Chemotherapy generally refers to the use of cytotoxic drugs to treat cancer. Plant alkaloids are one major class of chemotherapeutic drugs [1,2,3,4,5,6,7,8,9]. Chemotherapeutic drugs that affect cell division by preventing the normal functioning of micro-tubules include the vinca alkaloids.
Numerous diterpenoid alkaloids have been isolated from various Aconitum, Delphinium, and Garrya (Family Ranunculaceae) species and are classified according to their chemical structures as C18-, C19- or C20-diterpenoid alkaloids (Figure 1) [10,11]. The C19-diterpenoid alkaloids may be divided into six types: aconitine, lycoctonine, pyro (C8=C15 or C15=O), lactone (δ-valerolactone rather than cyclopentyl C-ring), 7,17-seco, and rearranged ones [10,11]. Most of the isolated C19-diterpenoid alkaloids are aconitine- and lycoctonine-types and include aconitine, mesaconitine, hypaconitine and jesaconitine, all of which are extremely toxic. The C20-diterpenoid alkaloids may be divided into ten types: atisine, denudatine, hetidine, hetisine, vakognavine, napelline, kusnezoline, racemulosine, arcutine, and tricalysiamide [10,11]. Most of the isolated C20-diterpenoid alkaloids are atisine-, hetisine-, and napelline-types and include atisine, kobusine, pseudokobusine and lucidusculine, which are far less toxic [12].
The pharmacological properties of the C19-diterpenoid alkaloids have been studied extensively and reviewed [12]. Aconitine is a toxin that exhibits activity both centrally and peripherally, acting predominantly on the cardiovascular and respiratory systems by preventing the normal closing of sodium channels [12]. This extreme toxicity resulted in the use of Aconitum extracts as poisons in hunting and warfare [13], although extracts were also used as traditional medicines by oral and topical routes. For example, the roots of Aconitum plants have been used as “bushi”, an herbal drug in some prescriptions of traditional Japanese medicine for the treatment of hypometabolism, dysuria, cardiac weakness, chills, neuralgia, gout, and certain rheumatic diseases [14]. However, proper processing is essential to reduce the content of toxic alkaloids and avoid inadvertent poisoning [15,16,17]. Such obstacles encourage a good understanding of the relationships between structure and cytotoxic activity of aconitine and related compounds before they can be considered for modification and development as chemotherapeutic agents.
Our previous study demonstrated the effects of various naturally occurring and semi-synthetic C19- and C20-diterpenoid alkaloids on the growth of the A172 human malignant glioma cell line [18]. Antitumor properties and radiation-sensitizing effects of various types of novel derivatives prepared from C19- and C20-diterpenoid alkaloids were also investigated [19]. Two novel hetisine-type C20-diterpenoid derivatives showed significant suppressive effects against the Raji non-Hodgkin’s lymphoma cell line [20]. In addition, the effects of various semi-synthetic novel hetisine-type C20-diterpenoid alkaloids on the growth of the A549 human lung cancer cell line were examined and subsequent structure-activity relationships for the antiproliferative effects against A549 cells were considered [21]. Since 2012, several diterpenoid alkaloid components and their derivatives exhibited antiproliferative activity against human tumor cell lines, including A549 (lung carcinoma), DU145 (prostate carcinoma), MDA-MB-231 (estrogen and progesterone receptor-negative & HER2-negative triple-negative breast cancer), MCF-7 (estrogen receptor-positive, HER2-negative breast cancer), KB (identical to cervical carcinoma HeLa derived AV-3 cell line), and multidrug-resistant (MDR) subline KB-VIN [P-glycoprotein (P-gp) overexpressing vincristine-resistant KB subline]. Among such alkaloids, C19-diterpenoid (e.g., lipojesaconitine, delpheline, and delcosine derivative) and C20-diterpenoid (e.g., kobusine and pseudokobusine derivatives) alkaloids have shown significant antiproliferative activity, as well as provided promising new leads for further development as antitumor agents.
2. Antiproliferative Activity of C19-Diterpenoid Alkaloid Derivatives
2.1. Aconitine-Type C19-Diterpenoid Alkaloids
The tested aconitine-type C19-diterpenoid alkaloids included 21 natural alkaloids, aconitine (1), deoxyaconitine (2), jesaconitine (3), deoxyjesaconitine (4), aljesaconitine A (5), secojesaconitine (6), mesaconitine (8), hypaconitine (9), hokbusine A (10), 14-anisoyllasianine (12), N-deethylaljesaconitine A (13), aconine (14), lipomesaconitine (15), lipoaconitine (16), lipojesaconitine (17), neolinine (18), neoline (19), 14-benzoylneoline (20), isotalatizidine (21), karacoline (22), and 3-hydroxykaracoline (23), isolated from the rhizoma of Aconitum japonicum THUNB. subsp. subcuneatum (NAKAI) KADOTA [22,23,24,25,26,27,28] (Figure 2). Two synthetic aconitine-type C19-diterpenoid alkaloids, 3,15-diacetyljesaconitine (7) [26] and 3-acetylmesaconitine (11) [29] prepared from secojesaconitine (6) and mesaconitine (8), respectively (Figure 2), were also tested.
Eighteen of the 23 tested aconitine-type C19-diterpenoid alkaloids, both natural alkaloids (1~6, 8~10, 12~14, 18~23) and synthetic analogs (7 and 11), were inactive (IC50 > 20 or 40 μM) [27,28,30] (Table 1). Three natural diterpenoid alkaloids (15~17) exhibited cytotoxic activity against five human tumor cell lines (A549, MDA-MB-231, MCF-7, KB, and MDR KB subline KB-VIN) (Table 1). Lipojesaconitine (17) showed significant cytotoxicity against four tested cell lines with IC50 values of 6.0 to 7.3 μM, but weak cytotoxicity against KB-VIN (IC50 = 18.6 μM) [28]. Lipomesaconitine (15) showed moderate cytotoxicity against the KB cell line (IC50 = 9.9 μM), but weak cytotoxicity against the other four human tumor cell lines (IC50 =17.2 ~ 21.5 μM) [27]. Lipoaconitine (16) was weakly cytotoxic (IC50 = 13.7 ~ 20.3 μM) against all five human tumor cell lines [28]. Based on the results, the fatty acid ester at C-8 and the anisoyl group at C-14 found in 17 may be important to the cytotoxic activity of aconitine-type C19-diterpenoid alkaloids.
2.2. Lycoctonine-Type (7,8-diol) C19-Diterpenoid Alkaloids
The tested lycoctonine-type (7,8-diol) C19-diterpenoid alkaloid group included 12 natural alkaloids, namely nevadensine (24), N-deethylnevadensine (25), and virescenine (27), purified from rhizoma of Aconitum japonicum subsp. subcuneatum [27], and 18-methoxygadesine (26), delphinifoline (28), delcosine (34), 14-acetyldelcosine (34–43), and 14-acetylbrowniine (35), purified from root of Aconitum yesoense var. macroyesoense (NAKAI) TAMURA [31,32,33,34], and andersonidine (30), pacifiline (31), pacifinine (32), and pacifidine (33), purified from seeds of Delphinium elatum cv. Pacific Giant [35] (Figure 3). The remaining tested C19-diterpenoid alkaloids from this subtype were synthetic alkaloids, N-deethyldelsoline (29) [18], 1-acetyldelcosine (34-1) [36], 1,14-diacetyldelcosine (34-2) [37], 1-(4-trifluoromethylbenzoyl)delcosine (34-24) [30], delsoline (34-42) [37], 1,14-di-(4-nitrobenzoyl)-delcosine (34-45) [30], 14-acetyl-1-(4-nitrobenzoyl)delcosine (34-46) [30], and 1-acyl or 1,14-diacyldelcosine derivatives (34-3~34-23, 34-25~34-41, 34-44, and 34-47) [38], prepared from delcosine (34) or delsoline (34-42) (Figure 3). These 42 C19-diterpenoid alkaloids were evaluated for antiproliferative activity against four to five human tumor cell lines (A549, DU145, MDA-MB-231, MCF-7, KB, and KB-VIN) [30,38] (Table 2). Several tested lycoctonine-type (7,8-diol) C19-diterpenoid alkaloids, both natural alkaloids (24~28, 30~33) and a synthetic alkaloid (29), were inactive (IC50 > 20 or 40 μM). All tested delcosine derivatives that contain an acetyl or methoxy group, both natural alkaloids (34, 34-43, 35) and synthetic analogs (34-1, 34-2, 34-42), were inactive (IC50 > 20 μM). However, acylation, except with an acetyl group, of the C-1 and/or C-14 hydroxy group of 34 led to various degrees of antiproliferative activity. Among the C-1 esterified alkaloids, the synthetic derivatives 34-6, 34-8, 34-10, and 34-18 exhibited significant potency against all cell lines (average IC50 9.3, 5.3, 5.0, and 6.9 µM, respectively). Also, alkaloids 34-3, 34-16, 34-17, 34-21, 34-25, 34-27, 34-31, 34-32, 34-38, and 34-40 showed moderate potency toward all cell lines (average IC50 12.7−20.7 µM). While alkaloid 34-32 displayed good antiproliferative activity (IC50 8.7 µM) against KB cells, it was much less potent against A549, MDA-MB-231, and KB-VIN cells. Alkaloids 34-5, 34-13, 34-15, 34-29, 34-35, 34-37, and 34-41 exhibited only weak potency against all cell lines (average IC50 22.0−26.5 µM). Finally, alkaloids 34-24, 34-30, and 34-34 were inactive against all five human tumor cell lines, while 34-12, 34-33, and 34-39 showed limited potency.
Among the derivatives esterified at both C-1 and -14, alkaloids 34-19 and 34-20 exhibited significant potency against all five tested cell lines (average IC50 4.9 and 5.0 µM, respectively). Alkaloid 34-9 (average IC50 11.9 µM) showed significant antiproliferative activity against MDA-MB- 231 and KB cells (IC50 4.7 and 5.8 µM, respectively) comparable with 34-19 and 34-20, but was less potent against MCF-7 and A549 (IC50 12.2 and 24.8 µM, respectively) and inactive against KB-VIN. Alkaloid 34-23 exhibited only weak potency toward all cell lines (average IC50 23.7 µM). Alkaloids 34-4, 34-7, 34-11, 34-14, 34-26, 34-36, 34-45, 34-46, and 34-47 were inactive against all five human tumor cell lines, while 34-22 and 34-28 showed limited potency.
Particularly, C-1 monoacylated delcosine derivatives (34-3, 34-6, 34-8, 34-10, 34-13, 34-21, 34-25, 34-27, and 34-35) were significantly more potent compared with corresponding C-1,14 diacylated delcosine derivatives (34-4, 34-7, 34-9, 34-11, 34-14, 34-22, 34-23, 34-26, 34-28 and 34-36). Thus, a C-1 acyloxy group and C-14 hydroxy group are crucial for enhanced antiproliferative activity of 1-derivatives. Regarding alkaloids 34-18 (pentafluorobenzoate at C-1, hydroxy at C-14), 34-19 (pentafluorobenzoate at C-1 and C-14), and 34-20 (pentafluorobenzoate at C-1, acetate at C-14), all three alkaloids were essentially equipotent against three of the five tumor cell lines, while 34-18 was somewhat less potent than the diacylated alkaloids against MCF-7 and KB-VIN cells.
Striking observations from the data in Table 2 were the consistent identities of the most potent alkaloids. Alkaloids 34-8, 34-10, 34-19, and 34-20 exhibited the highest potency against all five tested tumor cell lines with IC50 values ranging from 4.3 to 6.0 µM. The same range of potency was found with alkaloid 34-18 against A549 cells, with alkaloids 34-9 and 34-18 against MDA-MB-231 cells, and with 34-6, 34-9, and 34-18 against KB cells. The potencies of 34-6 and 34-17 (IC50 5.6−11.8 µM) generally ranked somewhat below those of the most potent alkaloids, except against the MCF-7 cell line, where they were even less active.
The identity of the substituent(s) on the acyl group affected the antiproliferative potency. Notably, among the 1,14-diacyl and 1-acyl-14-acetyl derivatives, only alkaloids 34-19 and 34-20 with one or two pentafluorinated benzoyl esters, respectively, showed significant potency against all five tested cell lines. Alkaloid 34-9 with two 3-nitro-4-chlorobenzoyl groups showed good potency against certain cell lines. Similarly, the 1-monoacylated alkaloids with the highest potency against the five tumor cell lines contained 3-nitro-4-chloro- (34-8) and pentafluoro- (34-18) as well as 4-dichloro-methyl- (34-10) benzoyl esters. The chlorinated alkaloids 34-8 and 34-10 as well as 34-6, which has 3,5-dichloro substitution on the benzoate ester, were more potent than 34-5 with only a single chloro group or 34-13 with chloro and fluoro groups. Similarly, alkaloid 34-18 showed increased antiproliferative activity against the five tumor cell lines compared with other fluorinated alkaloids 34-13~34-17, 34-21~34-27. Moreover, with some exceptions against certain cell lines, alkaloids with bromo (34-3 and 34-4), dimethylamino (34-12), dimethoxy (34-29), trimethoxy (34-30), diethoxy (34-31), benzyloxy (34-32), cyano (34-33), methylenedioxy (34-34 and 34-35), nitro (34-45 and 34-46), and ethoxy (34-47) substituted benzoate esters or phenylacetyl (34-37), cinnamoyl (34-38 and 34-39), 1-naphthoyl (34-40), and anthraquinone-2-carbonyl (34-41) esters were less potent or inactive.
Interestingly, the active alkaloids were generally effective against P-gp overexpressing MDR subline KB-VIN, while alkaloids such as vincristine and paclitaxel are ineffective due to excretion from the MDR cells by P-gp. These results suggest that these diterpenoids are not substrates for P-gp.
2.3. Lycoctonine-Type (7,8-methylenedioxy) C19-Diterpenoid Alkaloids
The tested lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids included 19 natural alkaloids, delcorine (36), delpheline (37), pacinine (38), yunnadelphinine (39), melpheline (40), bonvalotidine C (41), N-deethyl-N-formylpaciline (42), N-deethyl-N-formylpacinine (43), isodel-pheline (44), pacidine (45), eladine (46), N-formyl-4,19-secopacinine (47), N-formyl-4,19-secoyunna-delphinine (48), iminoisodelpheline (49), iminodelpheline (50), laxicyminine (51), N-deethyl-19-oxo-isodelpheline (52), N-deethyl-19-oxodelpheline (53), and 19-oxoisodelpheline (54), purified from seeds of Delphinium elatum cv. Pacific Giant [35,39,40,41,42] (Figure 4). The remaining 22 tested C19-diterpenoids were synthetic derivatives (37-1~37-22) [43] prepared from 37 (Figure 4).
All tested lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids were evaluated for antiproliferative activity against human tumor cell lines [30,40,41,42,43] (Table 3). The lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids, both the natural alkaloids (36~54) and synthetic analogs that did not contain a C-6 ester group (37-20 and 37-22), were inactive (IC50 > 20 or 40 μM). Among the C-6 esterified alkaloids, 37-1, 37-17, and 37-18 exhibited the highest average potency toward four tested cell lines (A549, DU145, KB and KB-VIN; average IC50 9.83, 9.57, and 9.41 μM, respectively). Alkaloids 37-3, 37-5~37-7, 37-9, 37-10, 37-12, 37-13, 37-16, and 37-19 showed moderate potency against all tested cell lines (average IC50 13.9−20.8 µM). However, alkaloid 37-13 showed significantly increased cytotoxic activity (IC50 10.2 μM) against A549 cells compared with 37-1, 37-17, and 37-18, but was generally less potent against DU145 and KB cells. While alkaloids 37-12, 37-13, 37-16, and 37-19 displayed good antiproliferative activity (IC50 6.8, 9.1, 6.5, and 4.7 µM, respectively) against KB-VIN cells, they were much less potent against A549, DU145, and KB cells. Alkaloids 37-4 and 37-21 were inactive against all tested cancer cell lines, while 37-2, 37-8, 37-11, and 37-14 exhibited only weak potency toward all cell lines (average IC50 23.0−29.2 µM).
The most noticeable observations from the data in Table 3 were the degree and relative ratio of KB/KB-VIN potency. Among the four cancer cell lines tested, the highest potency was found against the KB-VIN cell line by alkaloids 37-17~37-19 (IC50 4.22, 4.40, and 4.71 μM, respectively), followed by alkaloids 37-16, 37-12, 37-1, 37-13, and 37-9 (IC50 6.50, 6.80, 8.27, 9.10, and 11.9 μM, respectively). Generally, all active alkaloids showed the highest potency against the KB-VIN cell line compared with the other three tested cancer cell lines. Moreover, alkaloids 37-12, 37-16, 37-13, and 37-19 showed over two-fold selectivity between the two cell lines (ratio of IC50 KB/IC50 KB-VIN: 2.15, 2.28, 2.31, and 2.57, respectively). Alkaloids 37-2, 37-5, and 37-17 displayed weak selectivity between the KB and KB-VIN cell lines (ratio of IC50 KB/IC50 KB-VIN: 1.55, 1.36, and 1.62, respectively). Finally, alkaloids 37-1, 37-3, 37-6~37-9, 37-11, 37-14, 37-15, and 37-18 displayed similar potency against the KB and KB-VIN cell lines (ratio of IC50 KB/IC50 KB-VIN: 1.07, 1.17, 1.06, 1.21, 1.04, 1.25, 1.07, 1.07, 1.17, and 1.23, respectively).
The identity of the substituent on the C-6 acyl group affected the cytotoxic potency. For instance, the alkaloids with the highest potency against the KB-VIN cell line contained chloro (37-1), fluoro (37-12, 37-18, and 37-19), trifluoromethyl (37-9, 37-13, and 37-18), ethoxy (37-16), or benzyloxy (37-17) substituents on the acyl group. Against the KB-VIN cell line, alkaloids 37-18 and 37-19 with both fluoro and trifluoromethyl/methyl groups were more potent than 37-9 with only a single trifluoromethyl group and even more potent than 37-2 with a single fluoro group. Similarly, alkaloid 37-13 showed increased cytotoxic activity against most cell lines compared with the related fluorinated alkaloids 37-14 and 37-15. Moreover, alkaloids with nitro, methoxy, phenyl, trifluoromethoxy, trifluoromethythio, and methyl carboxylate groups on a C-6 benzoate ester were generally less potent.
3. Antiproliferative Activity of C20-Diterpenoid Alkaloid Derivatives
3.1. Actaline and Napelline-Type C20-Diterpenoid Alkaloids
One natural actaline-type C20-diterpenoid alkaloid [44], aconicarchamine A (55), isolated from rhizoma of Aconitum japonicum subsp. subcuneatum [30], (Figure 5) and seven natural napelline-type C20-diterpenoid alkaloids, lucidusculine (57), flavadine (58), 12-acetyllucidusculine (59), 1-acetyl-luciculine (60), dehydrolucidusculine (61), dehydroluciculine (62), and 12-acetyldehydroluciduscu-line (63), purified from roots of Aconitum yesoense var. macroyesoense [31,32,33], (Figure 5) were tested. Seven synthetic napelline-type C20-diterpenoid alkaloid derivatives (56-1~56-7) [18,32,45] were prepared from luciculine (56) (Figure 5) and tested also. All tested actaline- and napelline-type C20-diterpenoid alkaloids were evaluated for antiproliferative activity against four to five human tumor cell lines [28,30] (Table 4). Tested actaline- and napelline-type C20-diterpenoid alkaloids, both the natural alkaloids (55 and 57~63) and synthetic analogs (56-1~56-4, 56-6, and 56-7), were inactive (IC50 > 20 or 40 μM). Among the synthetic alkaloids, alkaloid 56-5 exhibited only weak potency toward the tested cell lines (A549, DU145, KB and KB-VIN; average IC50 27.8 μM). Because the related alkaloids 57, 60, 56-2~56-4, 56-6, and 56-7 were inactive against all tested cancer cell lines, a C-1 hydroxy group, C-12 acyloxy group, and C-15 acetoxy group found in 56-5 could be needed for antiproliferative activity of luciculine derivatives.
3.2. Hetisine-Type (Analogs of Kobusine) C20-Diterpenoid Alkaloids
Tested hetisine-type (analogs of kobusine) C20-diterpenoid alkaloids included four natural alkaloids, ryosenamine (64), 9-hydroxynominine (65), and torokonine (66), isolated from rhizoma of Aconitum japonicum subsp. subcuneatum [27,28] (Figure 6) and kobusine (67), purified from roots of Aconitum yesoense var. macroyesoense [31] (Figure 6). Nineteen synthetic derivatives (67-1~67-19) [18,21,30,46,47] (Figure 6) prepared from 67 were tested also.
All tested hetisine-type (kobusine analogs) C20-diterpenoid alkaloids were evaluated for antiproliferative activity against four human tumor cell lines [27,28,30] (Table 5). Fifteen of the 23 alkaloids, both natural (64~67) and synthetic (67-1~67-4, 67-6, 67-9, 67-11, 67-12, 67-15~67-17), were inactive (IC50 > 20 or 40 μM). Kobusine derivatives 67-5, 67-7, 67-10, 67-18, and 67-19 exhibited the highest average potency over the four tested cell lines (A549, DU145, KB and KB-VIN; average IC50 7.8, 6.1, 6.2, 6.8, and 4.7 μM, respectively), and alkaloids 67-8, 67-13, and 67-14 showed moderate potency (average IC50 16.6, 14.3, and 11.6 µM, respectively). However, while alkaloid 67-14 showed good cytotoxic activity (IC50 9.6 μM) against DU145 cells, it was much less potent against A549, KB, and KB-VIN cells.
Among these analogs of 67, esterification of C-15 in addition to C-11 increased potency significantly (compare 67-8 to 67-10) or even converted an inactive to an active alkaloid (compare 67-3 to 67-5, 67-6 to 67-7, 67-16 to 67-18). Consequently, all of the most potent analogs (67-5, 67-7, 67-10, 67-18, and 67-19) of 67 were esterified at both C-11 and C-15.
Striking observations from the data in Table 5 were the degree and comparative ratio of KB/KB-VIN potency. Five alkaloids (67-5, 67-7, 67-10, 67-18, and 67-19) were quite potent (IC50 < 10 µM) against KB-VIN. Indeed, alkaloid 67-19 exhibited a significantly low IC50 value of 3.1 µM. The ratios of KB to KB-VIN (IC50 KB/IC50 KB-VIN) were greater than 0.73 for all active alkaloids, with many alkaloids displaying comparable potency against the two cell lines, in contrast with paclitaxel (ratio of 0.0067). Alkaloid 67-19 showed over 1.3-fold selectivity with the greatest cytotoxic activity against KB-VIN (IC50 KB/IC50 KB-VIN: 1.32).
3.3. Hetisine-Type (Analogs of Pseudokobusine) C20-Diterpenoid Alkaloids
The two tested natural hetisine-type (analogs of pseudokobusine) C20-diterpenoid alkaloids pseudokobusine (68) and 15-veratroylpseudokobusine (68-11) were purified from the roots of Aconitum yesoense var. macroyesoense [31,32] (Figure 7). The 36 tested synthetic derivatives (68-1~68-10, 68-12~68-37) [18,21,30,32,46,47,48,49] (Figure 7) were prepared from 68.
All tested hetisine-type (68 analogs) C20-diterpenoid alkaloids were evaluated for antiproliferative activity against four human tumor cell lines [30] (Table 6). Many alkaloids, both natural alkaloids (68 and 68-11) and synthetic analogs (68-1~68-3, 68-6, 68-8, 68-9, 68-14, 68-16~68-18, 68-21, 68-23, 68-25~68-31, 68-33~68-37), were inactive (IC50 > 20 µM). The pseudokobusine derivatives 68-5, 68-15, 68-19, 68-20, 68-24, and 68-32 exhibited the highest average potency over the tested cell lines (A549, DU145, KB and KB-VIN; average IC50 7.0, 5.2, 5.3, 7.4, 7.1, and 6.1 µM, respectively). Alkaloids 68-7, 68-10, 68-12, 68-13, and 68-22 showed moderate potency over all tested cell lines (average IC50 13.5-16.8 µM). However, although alkaloid 68-10 showed good cytotoxic activity (IC50 8.0 µM) against A549 cells, it was much less potent against DU145, KB, and KB-VIN cells.
Among the analogs of 68, four C-11 mono-substituted alkaloids (68-15, 68-20, 68-24, and 68-32) and two C-11,15 di-esterified alkaloids (68-5 and 68-19) exhibited average IC50 values of less than 10 μM. Certain C-11 (68-7, 68-10, and 68-22), C-6,11 (68-4 and 68-12) and C-6,15 (68-13) esterified alkaloids were generally less potent, while all C-6 (68-3, 68-6, 68-14, and 68-23) and C-15 (68-1, 68-11, 68-16, 68-25, 68-28, and 68-30) mono-substituted alkaloids, as well as the tri-substituted analog (68-18), were inactive. Thus, all more active (IC50 < 10 µM) C20-diterpenoid alkaloids in this classification had an ester or ether group on the C-11 hydroxy and were 11-monoester/11,15-diester analogs of 68 (OH at C-6).
The data in Table 6 led to noticeable observations about the degree and comparative ratio of KB/KB-VIN potency. Six alkaloids (68-5, 68-15, 68-19, 68-20, 68-24, and 68-32) were quite potent (IC50 < 10 µM) against KB-VIN. Indeed, alkaloid 68-32 exhibited a low IC50 value of 5.2 µM. The ratios of KB to KB-VIN (IC50 KB/IC50 KB-VIN) were greater than 0.70 for all active alkaloids, with many alkaloids displaying comparable potency against the two cell lines, in contrast with paclitaxel (ratio of 0.0067). Alkaloids 68-12, 68-13, and 68-20 showed over 1.3-fold selectivity with their greatest cytotoxic activity against KB-VIN (IC50 KB/IC50 KB-VIN: 1.34, 1.48, and 1.44, respectively).
In mechanism of action studies on selected diterpenoid alkaloids, the hetisine-type C20-diterpenoid alkaloid derivatives 68-7 and 68-22 showed important suppressive effects against Raji cells. Further study indicated that 68-22 inhibited extracellular signal-regulated kinase phosphorylation but induced enhanced phosphoinositide 3 kinase phosphorylation, leading to accumulation of Raji cells in the G1 or sub G1 phase [20]. More investigation is certainly warranted.
4. Discussion
We have synthesized acylated derivatives of various C19- and C20-diterpenoid alkaloids. Totally, 199 natural alkaloids and their derivatives were evaluated against four to five human tumor cell lines. Among all alkaloids, 128 alkaloids were non-toxic (IC50 > 20 or 40 µM) and 51 alkaloids showed moderate antiproliferative effects (average IC50 = 10–40 µM). General summaries are described briefly below, and the most active compounds are shown in Figure 8.
Among the aconitine-type C19-diterpenoid alkaloids, the fatty acid ester at C-8 and the anisoyl group at C-14 found in 17 may be important to the cytotoxic activity. Compounds without the fatty acid ester at C-8 were inactive, and compounds with an unsubstituted benzoyl group at C-14 were less potent.
Among the C19-diterpenoid alkaloids, the most active alkaloids were lycoctonine-type C19-diterpenoid alkaloids with two different substitution patterns, C-1 (delcosine derivatives) and C-6 (delpheline derivatives). Delcosine derivatives 34-6, 34-8, 34-10, and 34-18, which are acylated at the C-1 hydroxy, as well as delpheline derivatives 37-1, 37-17, and 37-18, which are acylated at the C-6 hydroxy, exhibited the greatest potency over all tested cell lines, including MDR KB-VIN.
Among the lycoctonine-type (7,8-diol) C19-diterpenoid alkaloids, a C-1 acyloxy group and C-14 hydroxy group were important for improved antiproliferative activity. The C-1,14 diacylated delcosine derivatives were generally less potent than corresponding C-1 monoacylated delcosine derivatives. The 1-monoacylated alkaloids with the highest potency (IC50 4−6 µM) against five tested cell lines contained 3-nitro-4-chloro- (34-8) and pentafluoro- (34-18) as well as 4-dichloromethyl- (34-10) benzoyl esters. Two or one pentafluorinated benzoyl esters were also found in the two most consistently potent alkaloids (34-19 and 34-20) among the 1,14-diacyl and 1-acyl-14-acetyl derivatives.
Among the lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids, none of the tested compound reached the potency levels of the most active 7,8-diol compounds. However, three 6-acylated delpheline derivatives 37-17~37-19 did show significant potency against the KB-VIN cell line (IC50 4.22, 4.40, and 4.71 μM, respectively). Interestingly, the two latter compounds contained fluorinated benzoyl esters. In addition, among 19 tested delpheline derivatives, four compounds (37-12, 37-16, 37-13, and 37-19) showed over two-fold selectivity between the MDR and parental cell lines (ratio of IC50 KB/IC50 KB-VIN: 2.15, 2.28, 2.31, and 2.57, respectively).
None of the 15 tested actaline- and napelline-type C20-diterpenoid alkaloids showed significant antiproliferative potency. Only 12-benzoyllucidsuculine (56-5) with C-1 hydroxy, C-12 acyloxy, and C-15 acetoxy groups showed even weak potency.
Among C20-diterpenoid alkaloids, the most active alkaloids were hetisine-type C20-diterpenoid alkaloids with two different substitution patterns, C-11,15 (kobusine) and C-6,11,15 (pseudo-kobusine). Hetisine-type C20-diterpenoid alkaloids 67-5, 67-7, 67-10, 67-18, 67-19, 68-5, 68-15, 68-19, 68-20, 68-25, and 68-32, which are acylated or tritylated at the C-11 hydroxyl, exhibited the greatest potency over all tested cell lines, including MDR KB-VIN. All five most active kobusine derivatives (67-5, 67-7, 67-10, 67-18, and 67-19) are acylated at both C-11 and C-15. All tested derivatives with a hydroxy group at either C-11 or C-15 were inactive or much less active. All six most active pseudo-kobusine derivatives (68-5, 68-15, 68-19, 68-20, 68-25, and 68-32) contain a free hydroxy group at C-6. The substituent at C-11 is either a benzoyl/cinnamoyl ester (68-5, 68-15, 68-19, 68-20, and 68-25) or a trityl ether (68-32). Finally, the moiety at C-15 is a hydroxy group (68-15, 68-20, 68-25, and 68-32) or benzoyl ester (68-5, 68-19).
Furthermore, previously our study, Antitumor properties and radiation-sensitizing effects of various types of novel derivatives prepared from C19- and C20-diterpenoid alkaloids were also investigated [19]. Two novel hetisine-type C20-diterpenoid derivatives (68-7 and 68-20) showed significant suppressive effects against the Raji non-Hodgkin’s lymphoma cell line [20].
5. Conclusions
We have synthesized acylated derivatives of various C19- and C20-diterpenoid alkaloids. All alkaloids and their derivatives were screened against four to five human tumor cell lines. Alkaloids 37-2, 37-9, 37-17, 37-18, 56-5, 67-7, 67-14, 67-19, 68-4, 68-12, 68-20, 68-22, 68-24, and 68-32 showed comparable potency against KB and KB-VIN cancer cell lines, and some alkaloids showed tumor- selective activity. Alkaloids 37-12, 37-13, 37-16, and 37-19 exhibited greater inhibitory activity against drug-resistant KB-VIN cells (2.15~2.57-fold) than the parental KB cells. These results demonstrate that modified lycoctonine-type C19-diterpenoid alkaloids and hetisine-type C20-diterpenoid alkaloids are not substrates of P-gp and could be effective against P-gp overexpressing MDR tumors. These promising new lead alkaloids merit continued studies to evaluate their potential as antitumor agents, particularly with enhanced resistant tumor selectivity. In addition, our results from modification-based antitumor activity studies can be used for further development of anticancer drugs overcoming an MDR phenotype.
Funding
This study was supported in part by NIH grant CA177584 from the National Cancer Institute awarded to K.H.L. as well as the Eshelman Institute for Innovation, Chapel Hill, North Carolina, awarded to M.G.
Acknowledgments
The author gratefully acknowledges Lee, K.H., Goto, M., Morris-Natschke, S.L., Ohkoshi, E., Zhao, Yu., Li, K.P., Bastow, K.F., Natural Products Research Laboratories, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill; and Mizukami, M., Kaneda, K., Suzuki, Y., Shimizu, T., Kusanagi, N., Takeda, K., Haraguchi, M., Abe, Y., Kuwahara, N., Suzuki, S., Terui, A., Masaka, T., Munakata, N., Uchida, M., Nunokawa, M., Chiba, R., Kanazawa, R., Matsuoka, K., Suzuki, M., Ikuta, M., Asakawa, E., Tosho, Y., Nakata, A., Hasegawa, Y., Katoh, M., Kokubun, A., Uchimura, A., Mikami, S., Takeuchi, A., Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, Hokkaido University of Science, for their helpful advice and support throughout this work.
Conflicts of Interest
The authors declare no conflict of interest.
References
- Dzubak, P.; Hajduch, M.; Vydra, D.; Hustova, A.; Kvasnica, M.; Biedermann, D.; Markova, L.; Urban, J.; Sarek, J. Pharmacological activities of natural triterpenoids and their therapeutic implications. Nat. Prod. Rep. 2006, 23, 394–411. [Google Scholar] [CrossRef]
- Cragg, G.M.; Newman, D.J. Nature: A vital source of leads for anticancer drug development. Phytochem. Rev. 2009, 8, 313–331. [Google Scholar] [CrossRef]
- Kingston, D.G. Tubulin-interactive natural products as anticancer agents. J. Nat. Prod. 2009, 72, 507–515. [Google Scholar] [CrossRef]
- Lee, K.H. Discovery and development of natural products-derived chemotherapeutic agents based on a medicinal chemistry approach. J. Nat. Prod. 2010, 73, 500–516. [Google Scholar] [CrossRef]
- Grothaus, P.G.; Cragg, G.M.; Newman, D.J. Plant natural products in anticancer drug discovery. Curr. Org. Chem. 2010, 14, 1781–1791. [Google Scholar] [CrossRef]
- Kinghorn, A.D.; Pan, L.; Fletcher, J.N.; Chai, H. The relevance of higher plants in lead compound discovery programs. J. Nat. Prod. 2011, 74, 1539–1555. [Google Scholar] [CrossRef]
- Dall’Acqua, S. Natural products as antimitotic agents. Curr. Top. Med. Chem. 2014, 14, 2272–2285. [Google Scholar] [CrossRef]
- Hussain, M.; Khera, R.A.; Iqbal, J.; Khalid, M.; Hanif, M.A. Phytochemicals: Key to effective anticancer drugs. Mini-Rev. Org. Chem. 2019, 16, 141–158. [Google Scholar] [CrossRef]
- Agarwal, G.; Carcache, P.J.B.; Addo, E.M.; Kinghorn, A.D. Current status and contemporary approaches to the discovery of antitumor agents from higher plants. Biotechnol. Adv. 2019. [Google Scholar] [CrossRef]
- Wang, F.P.; Chen, Q.H. The diterpenoid alkaloids. The Alkaloids: Chemistry and Biology; Cordell, G.A., Ed.; Academic Press: San Diego, CA, USA, 2010; Volume 69, pp. 1–577. [Google Scholar]
- Wang, F.P.; Chen, Q.H.; Liu, X.Y. Diterpenoid alkaloids. Nat. Prod. Rep. 2010, 27, 529–570. [Google Scholar] [CrossRef]
- Benn, M.H.; Jacyno, J.M. The toxicology and pharmacology of diterpenoid alkaloids. In Alkaloids: Chemical and Biological Perspectives; Pelletier, S.W., Ed.; Wiley-Interscience: New York, NY, USA, 1983; Volume 1, pp. 153–210. [Google Scholar]
- Bock, J.H.; Norris, D.O. Introduction to forensic plant science. In Forensic Plant Science; Elsevier Academic Press: Boston, MA, USA, 2016; pp. 1–22. [Google Scholar]
- Amiya, T.; Bando, H. Aconitum alkaloids. In The Alkaloids; Brossi, A., Ed.; Academic Press: San Diego, CA, USA, 1988. [Google Scholar]
- Chan, T.Y.K. Aconite poisoning. Clin. Toxicol. 2009, 47, 279–285. [Google Scholar] [CrossRef]
- Chan, T.Y.K. Aconite poisoning following the percutaneous absorption of Aconitum alkaloids. Forensic Sci. Int. 2012, 223, 25–27. [Google Scholar] [CrossRef]
- Povšnar, M.; Koželj, G.; Kreft, S.; Lumpert, M. Rare tradition of the folk medicinal use of Aconitum spp. is kept alive in Solčavsko, Slovenia. J. Ethnobiol. Ethnomed. 2017, 13, 45. [Google Scholar] [CrossRef]
- Wada, K.; Hazawa, M.; Takahashi, K.; Mori, T.; Kawahara, N.; Kashiwakura, I. Inhibitory effects of diterpenoid alkaloids on the growth of A172 human malignant cells. J. Nat. Prod. 2007, 70, 1854–1858. [Google Scholar] [CrossRef]
- Hazawa, M.; Wada, K.; Takahashi, K.; Mori, T.; Kawahara, N.; Kashiwakura, I. Suppressive effects of novel derivatives prepared from Aconitum alkaloids on tumor growth. Invest. New Drugs 2009, 27, 111–119. [Google Scholar] [CrossRef]
- Hazawa, M.; Wada, K.; Takahashi, K.; Mori, T.; Kawahara, N.; Kashiwakura, I. Structure-activity relationships between the Aconitum C20-diterpenoid alkaloid derivatives and the growth suppressive activities of non-Hodgkin’s lymphoma Raji cells and human hematopoietic stem/progenitor cells. Invest. New Drugs 2011, 29, 1–8. [Google Scholar] [CrossRef]
- Wada, K.; Hazawa, M.; Takahashi, K.; Mori, T.; Kawahara, N.; Kashiwakura, I. Structure-activity relationships and the cytotoxic effects of novel diterpenoid alkaloid derivatives against A549 human lung carcinoma cells. J. Nat. Med. 2011, 65, 43–49. [Google Scholar] [CrossRef]
- Bando, H.; Kanaiwa, Y.; Wada, K.; Mori, T.; Amiya, T. Structure of deoxyjesaconitine. A new diterpene alkaloid from Aconitum subcuneatum Nakai. Heterocycles 1981, 16, 1723–1725. [Google Scholar]
- Mori, T.; Bando, H.; Kanaiwa, Y.; Wada, K.; Amiya, T. Studies on the constituents of Aconitum Species. II. Structure of deoxyjesaconitine. Chem. Pharm. Bull. 1983, 31, 2884–2886. [Google Scholar] [CrossRef]
- Wada, K.; Bando, H.; Mori, T.; Wada, R.; Kanaiwa, Y.; Amiya, T. Studies on the constituents of Aconitum Species. III. On the components of Aconitum subcuneatum Nakai. Chem. Pharm. Bull. 1985, 33, 3658–3661. [Google Scholar] [CrossRef]
- Bando, H.; Wada, K.; Watanabe, M.; Mori, T.; Amiya, T. Studies on the constituents of Aconitum Species. IV. On the components of Aconitum japonicum Thunb. Chem. Pharm. Bull. 1985, 33, 4717–4722. [Google Scholar] [CrossRef]
- Bando, H.; Wada, K.; Amiya, T.; Fujimoto, Y.; Kobayashi, K. Structures of secojesaconitine and subdesculine, two new diterpenoid alkaloids from Aconitum japonicum Thunb. Chem. Pharm. Bull. 1988, 36, 1604–1606. [Google Scholar] [CrossRef]
- Yamashita, H.; Takeda, K.; Haraguchi, M.; Abe, Y.; Kuwahara, N.; Suzuki, S.; Terui, A.; Masaka, T.; Munakata, N.; Uchida, M.; et al. Four new diterpenoid alkaloids from Aconitum japonicum subsp. subcuneatum. J. Nat. Med. 2018, 72, 230–237. [Google Scholar] [CrossRef]
- Yamashita, H.; Miyao, M.; Hiramori, K.; Kobayashi, D.; Suzuki, Y.; Mizukami, M.; Goto, M.; Lee, K.H.; Wada, K. Cytotoxic diterpenoid alkaloid from Aconitum japonicum subsp. subcuneatum. J. Nat. Med. 2019, submitted. [Google Scholar]
- Wada, K.; Bando, H.; Kawahara, N.; Mori, T.; Murayama, M. Determination and quantitative analysis of Aconitum japonicum by liquid chromatography atomospheric pressure chemical ionization mass spectrometry. Biol. Mass Spectrom. 1994, 23, 97–102. [Google Scholar] [CrossRef]
- Wada, K.; Ohkoshi, E.; Zhao, Y.; Goto, M.; Morris-Natschke, S.L.; Lee, K.H. Evaluation of Aconitum diterpenoid alkaloids as antiproliferative agents. Bioorg. Med. Chem. Lett. 2015, 25, 1525–1531. [Google Scholar] [CrossRef]
- Wada, K.; Bando, H.; Amiya, T. Two new C20-diterpenoid alkaloids from Aconitum yesoense var. macroyesoense (NAKAI) TAMURA. Structures of dehydrolucidusculine and N-deethyldehydrolucidusculine. Heterocycles 1985, 23, 2473–2477. [Google Scholar]
- Bando, H.; Wada, K.; Amiya, T.; Fujimoto, Y.; Kobayashi, K.; Sakurai, T. Studies on Aconitum Species. V. Constituents of Aconitum yesoense var. macroyesoense (Nakai) Tamura. Heterocycles 1987, 26, 2623–2637. [Google Scholar]
- Wada, K.; Bando, H.; Kawahara, N. Studies on Aconitum species. XI. Two new diterpenoid alkaloids from Aconitum yesoense var. macroyesoense (Nakai) Tamura V. Heterocycles 1989, 29, 2141–2148. [Google Scholar]
- Wada, K.; Kawahara, N. Diterpenoid and norditerpenoid alkaloids from the roots of Aconitum yesoense var. macroyesoense. Helvetica Chimica Acta 2009, 92, 629–637. [Google Scholar] [CrossRef]
- Wada, K.; Yamamoto, T.; Bando, H.; Kawahara, N. Four diterpenoid alkaloids from Delphinium elatum. Phytochemistry 1992, 31, 2135–2138. [Google Scholar] [CrossRef]
- Wada, K.; Ishizuki, S.; Mori, T.; Bando, H.; Murayama, M.; Kawahara, N. Effects of alkaloids from Aconitum yesoense var. macroyesoense on cutaneous blood flow in mice. Biol. Pharm. Bull. 1997, 20, 978–982. [Google Scholar]
- Wada, K.; Mori, T.; Kawahara, N. Application of liquid chromatography−atmospheric pressure chemical ionization mass spectrometry to the differentiation of stereoisomeric C19-norditerpenoid alkaloids. Chem. Pharm. Bull. 2000, 48, 660–668. [Google Scholar] [CrossRef]
- Wada, K.; Goto, M.; Shimizu, T.; Kusanagi, N.; Lee, K.-H.; Yamashita, H. Structure-activity relationships and evaluation of esterified diterpenoid alkaloid derivatives as antiproliferative agents. J. Nat. Med. 2019. [Google Scholar] [CrossRef]
- Bando, H.; Wada, K.; Tanaka, J.; Kimura, S.; Hasegawa, E.; Amiya, T. Two new alkaloids from Delphinium pacific giant and revised 13C-NMR assignment of delpheline. Heterocycles 1989, 29, 1293–1300. [Google Scholar] [CrossRef]
- Wada, K.; Chiba, R.; Kanazawa, R.; Matsuoka, K.; Suzuki, M.; Ikuta, M.; Goto, M.; Yamashita, H.; Lee, K.H. Six new norditerpenoid alkaloids from Delphinium elatum. Phytochem. Lett. 2015, 12, 79–83. [Google Scholar] [CrossRef]
- Wada, K.; Asakawa, E.; Tosho, Y.; Nakata, A.; Hasegawa, Y.; Kaneda, K.; Goto, M.; Yamashita, H.; Lee, K.H. Four new norditerpenoid alkaloids from Delphinium elatum. Phytochem. Lett. 2016, 17, 190–193. [Google Scholar] [CrossRef]
- Yamashita, H.; Katoh, M.; Kokubun, A.; Uchimura, A.; Mikami, S.; Takeuchi, A.; Kaneda, K.; Suzuki, Y.; Mizukami, M.; Goto, M.; et al. Four new C19-diterpenoid alkaloids from Delphinium elatum. Phytochem. Lett. 2018, 24, 6–9. [Google Scholar] [CrossRef]
- Wada, K.; Ohkoshi, E.; Morris-Natschke, S.L.; Bastow, K.F.; Lee, K.H. Cytotoxic esterified diterpenoid alkaloid derivatives with increased selectivity against a drug-resistant cancer cell line. Bioorg. Med. Chem. Lett. 2012, 22, 249–252. [Google Scholar] [CrossRef] [Green Version]
- Wang, F.P.; Liang, X.T. C20-Diterpenoid alkaloids. In The Alkaloids: Chemistry and Biology; Cordell, G.A., Ed.; Academic Press: San Diego, CA, USA, 2002; Volume 59, pp. 1–280. [Google Scholar]
- Wada, K.; Mori, T.; Kawahara, N. Application of liquid chromatography-atmospheric pressure chemical ionization mass spectrometry to the differentiation of stereoisomeric diterpenoid alkaloids. Chem. Pharm. Bull. 2000, 48, 1065–1074. [Google Scholar] [CrossRef]
- Wada, K.; Ishizuki, S.; Mori, T.; Fujihira, E.; Kawahara, N. Effects of Aconitum alkaloid kobusine and pseudokobusine derivatives on cutaneous blood flow in mice. Biol. Pharm. Bull. 1998, 21, 140–146. [Google Scholar] [CrossRef] [PubMed]
- Wada, K.; Ishizuki, S.; Mori, T.; Fujihira, E.; Kawahara, N. Effects of Aconitum alkaloid kobusine and pseudokobusine derivatives on cutaneous blood flow in mice; II. Biol. Pharm. Bull. 2000, 23, 607–615. [Google Scholar] [CrossRef] [PubMed]
- Wada, K.; Bando, H.; Kawahara, N. Studies on Aconitum Species. XIII. Two new diterpenoid alkaloids from Aconitum yesoense var. macroyesoense (Nakai) Tamura VI. Heterocycles 1990, 31, 1081–1088. [Google Scholar] [CrossRef]
- Wada, K.; Bando, H.; Wada, R.; Amiya, T. Analgesic activity of main components from Aconitum yesoense var. macroyesoense (Nakai) Tamura and pseudokobusine derivatives. Shouyakugaku Zasshi 1989, 43, 50–54. [Google Scholar]
Figure 1.
Classifications, general structures and numbering systems for C18-, C19-, and C20-diterpenoid alkaloids.
Figure 1.
Classifications, general structures and numbering systems for C18-, C19-, and C20-diterpenoid alkaloids.
Figure 2.
Chemical structures of aconitine-type C19-diterpenoid alkaloids 1–23.
Figure 3.
Chemical structures of lycoctonine-type (7,8-diol) C19-diterpenoid alkaloids 24–35.
Figure 4.
Chemical structures of lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids 36-54.
Figure 4.
Chemical structures of lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids 36-54.
Figure 5.
Chemical structures of actaline and napelline-type C20-diterpenoid alkaloids 55~63.
Figure 6.
Chemical structures of hetisine-type (analogs of kobusine) C20-diterpenoid alkaloids 64~67-19.
Figure 6.
Chemical structures of hetisine-type (analogs of kobusine) C20-diterpenoid alkaloids 64~67-19.
Figure 7.
Chemical structures of hetisine-type (analogs of pseudokobusine) C20-diterpenoid alkaloids 68~68-37.
Figure 7.
Chemical structures of hetisine-type (analogs of pseudokobusine) C20-diterpenoid alkaloids 68~68-37.
Figure 8.
Most potent tested diterpenoid alkaloids & structure-activity correlations.
Table 1.
Cytotoxic activity data for aconitine-type C19-diterpenoid alkaloids and derivatives 1–23.
| Cell Line/IC50 (μM) 1 | ||||||
|---|---|---|---|---|---|---|
| Alkaloids | A549 | DU145 | MDA-MB-231 | MCF-7 | KB | KB-VIN |
| Aconitine (1) | >20 | >20 | - | - | >20 | >20 |
| Deoxyaconitine (2) | >20 | >20 | - | - | >20 | >20 |
| Jesaconitine (3) | >20 | >20 | - | - | >20 | >20 |
| Deoxyjesaconitine (4) | >20 | >20 | - | - | >20 | >20 |
| Aljesaconitine A (5) | >20 | >20 | - | - | >20 | >20 |
| Secojesaconitine (6) | >20 | >20 | - | - | >20 | >20 |
| 7 | >20 | >20 | - | - | >20 | >20 |
| Mesaconitine (8) | >20 | >20 | - | - | >20 | >20 |
| Hypaconitine (9) | >20 | >20 | - | - | >20 | >20 |
| Hokbusine A (10) | >20 | >20 | - | - | >20 | >20 |
| 11 | >20 | >20 | - | - | >20 | >20 |
| 14-Anisoyllasianine (12) | >40 | - | >40 | >40 | >40 | >40 |
| N-Deethylaljesaconitine A (13) | >40 | - | >40 | >40 | >40 | >40 |
| Aconine (14) | >40 | - | >40 | >40 | >40 | >40 |
| Lipomesaconitine (15) | 17.2 ± 2.3 | - | 20.0 ± 0.2 | 19.0 ± 1.0 | 10.0 ± 3.3 | 21.5 ± 0.9 |
| Lipoaconitine (16) | 17.4 ± 1.1 | - | 15.5 ± 0.5 | 16.0 ± 0.3 | 13.7 ± 1.3 | 20.3 ± 1.1 |
| Lipojesaconitine (17) | 7.3 ± 0.3 | - | 6.0 ± 0.2 | 6.7 ± 0.2 | 6.0 ± 0.2 | 18.6 ± 0.9 |
| Neolinine (18) | >40 | - | >40 | >40 | >40 | >40 |
| Neoline (19) | >20 | >20 | - | - | >20 | >20 |
| 14-benzoylneoline (20) | >20 | >20 | - | - | >20 | >20 |
| Isotalatizidine (21) | >40 | - | >40 | >40 | >40 | >40 |
| Karacoline (22) | >20 | >20 | - | - | >20 | >20 |
| 3-Hydroxykaracoline (23) | >40 | - | >40 | >40 | >40 | >40 |
| PXL2 (nM) | 4.8 ± 0.6 | 5.9 ± 1.9 | 8.4 ± 0.8 | 10.2 ± 0.9 | 5.8 ± 0.2 | 2405.4 ± 44.8 |
1 Values are means ± standard deviation; 2 Paclitaxel (PXL; nM) was used as an experimental control.
Table 2.
Cytotoxic activity data for lycoctonine-type (7,8-diol) C19-diterpenoid alkaloids and synthetic analogs of delcosine 24~35.
Table 2.
Cytotoxic activity data for lycoctonine-type (7,8-diol) C19-diterpenoid alkaloids and synthetic analogs of delcosine 24~35.
| Cell Line/IC50 (μM) 1 | ||||||
|---|---|---|---|---|---|---|
| Alkaloids | A549 | DU145 | MDA-MB-231 | MCF-7 | KB | KB-VIN |
| Nevadensine (24) | >40 | - | >40 | >40 | >40 | >40 |
| N-Deethylnevadensine (25) | >40 | - | >40 | >40 | >40 | >40 |
| 18-Methoxygadesine (26) | >20 | >20 | - | - | >20 | >20 |
| Virescenine (27) | >40 | - | >40 | >40 | >40 | >40 |
| Delphinifoline (28) | >20 | >20 | - | - | >20 | >20 |
| N-Deethyldelsoline (29) | >20 | >20 | - | - | >20 | >20 |
| Andersonidine (30) | >20 | >20 | - | - | >20 | >20 |
| Pacifiline (31) | >20 | >20 | - | - | >20 | >20 |
| Pacifinine (32) | >20 | >20 | - | - | >20 | >20 |
| Pacifidine (33) | >20 | >20 | - | - | >20 | >20 |
| Delcosine (34) | >20 | >20 | - | - | >20 | >20 |
| 34-1 | >20 | >20 | - | - | >20 | >20 |
| 34-2 | >20 | >20 | - | - | >20 | >20 |
| 34-3 | 20.6 ± 0.3 | - | 19.4± 1.0 | 17.9 ± 0.3 | 14.6 ± 0.6 | 17.1 ± 0.8 |
| 34-4 | >40 | - | >40 | >40 | >40 | >40 |
| 34-5 | 18.7 ± 0.1 | - | 29.1 ± 1.6 | 25.8 ± 1.4 | 19.6 ± 0.3 | 21.1 ± 1.5 |
| 34-6 | 7.7 ± 0.9 | - | 8.6 ± 6.0 | 15.8 ± 4.2 | 5.6 ± 1.2 | 8.6 ± 1.9 |
| 34-7 | >40 | - | >40 | >40 | >40 | >40 |
| 34-8 | 4.5 ± 0.5 | - | 5.0 ± 0.1 | 5.9 ± 0.3 | 5.4 ± 0.3 | 5.6 ± 0.4 |
| 34-9 | 24.8 ± 0.1 | - | 4.7 ± 0.1 | 12.2 ± 0.3 | 5.8 ± 0.4 | >40 |
| 34-10 | 4.8 ± 0.3 | - | 4.8 ± 0.7 | 5.7 ± 0.4 | 4.3 ± 0.5 | 5.3 ± 0.4 |
| 34-11 | >40 | - | >40 | >40 | >40 | >40 |
| 34-12 | 26.5 ± 0.3 | - | >40 | 40.6 ± 2.5 | 27.8 ± 1.7 | 28.1 ± 3.0 |
| 34-13 | 20.8 ± 1.7 | - | 32.4 ± 1.8 | 25.9 ± 2.4 | 23.0 ± 2.4 | 21.5 ± 1.3 |
| 34-14 | >40 | - | >40 | >40 | >40 | >40 |
| 34-15 | 21.7 ± 1.6 | - | 30.2 ± 2.7 | 26.9 ± 1.4 | 20.7 ± 1.2 | 21.5 ± 3.6 |
| 34-16 | 14.4 ± 2.1 | - | 20.1 ± 0.7 | 16.4 ± 2.1 | 13.6 ± 1.1 | 15.7 ± 0.8 |
| 34-17 | 11.4 ± 1.4 | - | 10.4 ± 1.7 | 22.5 ± 1.5 | 10. 8 ± 1.9 | 11.8 ± 3.2 |
| 34-18 | 4.7 ± 0.1 | - | 5.3 ± 0.2 | 9.2 ± 0.4 | 5.8 ± 0.6 | 9.5 ± 0.5 |
| 34-19 | 4.9 ± 0.1 | - | 4.9 ± 0.1 | 5.3 ± 0.3 | 4.7 ± 0.1 | 4.9 ± 0.1 |
| 34-20 | 4.8 ± 0.1 | - | 4.6 ± 0.3 | 6.0 ± 0.1 | 4.8 ± 0.4 | 4.9 ± 0.4 |
| 34-21 | 20.8 ± 2.1 | - | 21.5 ± 0.6 | 21.4± 0.3 | 18.6 ± 1.7 | 15.0 ± 0.1 |
| 34-22 | >40 | - | >40 | >40 | >40 | 39.1 ± 2.0 |
| 34-23 | 23.8 ± 2.0 | - | 25.2 ± 1.0 | 23.3 ± 1.1 | 23.7 ± 1.1 | 22. 6 ± 0.3 |
| 34-24 | >20 | >20 | - | - | >20 | >20 |
| 34-25 | 20.6 ± 1.2 | - | 21.3 ± 1.3 | 22.4 ± 1.2 | 20. 8 ± 2.1 | 18.0 ± 1.0 |
| 34-26 | >40 | - | >40 | >40 | >40 | >40 |
| 34-27 | 18.6 ± 2.6 | - | 19.7 ± 2.0 | 20.6 ± 1.2 | 22.2± 1.8 | 19.8 ± 1.9 |
| 34-28 | 33.0 ± 2.1 | - | 32.4 ± 1.7 | 31.1 ± 0.8 | 23.2 ± 1.1 | 40.0 ± 1.0 |
| 34-29 | 23.8 ± 2.6 | - | 33.4 ± 1.7 | 29.8 ± 1.2 | 22.8 ± 1.7 | 22.6 ± 2.4 |
| 34-30 | >40 | - | >40 | >40 | >40 | >40 |
| 34-31 | 17. 3 ± 2.2 | - | 23. 1 ± 0.5 | 20.0 ± 0.7 | 16.2 ± 1.8 | 17.4 ± 1.9 |
| 34-32 | 16.5 ± 1.3 | - | 22.5 ± 0.8 | - | 8.71 ± 0.7 | 15.8 ± 0.8 |
| 34-33 | 40.9 ± 5.3 | - | >40 | >40 | 36.3 ± 1.0 | 29.3 ± 0.6 |
| 34-34 | >40 | - | >40 | >40 | >40 | >40 |
| 34-35 | 21.2 ± 0.1 | - | 24.8 ± 1.6 | 24.6 ± 1.0 | 18.7 ± 1.2 | 21.7± 0.6 |
| 34-36 | >40 | - | >40 | >40 | >40 | >40 |
| 34-37 | 23.8 ± 0.5 | - | 32.9 ± 1.0 | 22.6 ± 1.5 | 21.2 ± 0.1 | 19.2 ± 0.1 |
| 34-38 | 11.2 ± 0.7 | >20 | - | - | 21.1 ± 3.9 | 19.5 ± 8.2 |
| 34-39 | 29.7 ± 0.7 | - | 43.2 ± 1.8 | 32.0 ± 0.6 | 36.0 ± 0.4 | 45.1 ± 3.4 |
| 34-40 | 18.5 ± 0.5 | - | 17.9 ± 0.5 | 15.5± 0.6 | 13.7± 0.1 | 14.2 ± 0.5 |
| 34-41 | 22.9± 0.5 | - | 20.7 ± 2.1 | 20.5 ± 1.0 | 21.6 ± 0.1 | 24.4 ± 0.5 |
| 34-42 | >20 | >20 | - | - | >20 | >20 |
| 14-Acetyldelcosine (34-43) | >20 | >20 | - | - | >20 | >20 |
| 34-44 | >20 | >20 | - | - | >20 | >20 |
| 34-45 | >20 | >20 | - | - | >20 | >20 |
| 34-46 | >20 | >20 | - | - | >20 | >20 |
| 34-47 | >20 | >20 | - | >20 | >20 | >20 |
| 14-Acetylbrowniine (35) | >20 | >20 | - | - | >20 | >20 |
| PXL2 (nM) | 4.8 ± 0.6 | 5.9 ± 1.9 | 8.4 ± 0.8 | 10.2 ± 0.9 | 5.8 ± 0.2 | 2405.4 ± 44.8 |
1 Values are means ± standard deviation; 2 Paclitaxel (PXL; nM) was used as an experimental control.
Table 3.
Cytotoxic activity data for lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids and synthetic analogs of delpheline 36~54.
Table 3.
Cytotoxic activity data for lycoctonine-type (7,8-methylenedioxy) C19-diterpenoid alkaloids and synthetic analogs of delpheline 36~54.
| Cell Line/IC50 (μM) 1 | KB/KB-VIN Ratio | |||||
|---|---|---|---|---|---|---|
| Alkaloids | A549 | DU145 | MDA-MB-231 | KB | KB-VIN | |
| Delcorine (36) | >40 | - | >40 | >40 | >40 | - |
| Delpheline (37) | >20 | >20 | - | >20 | >20 | - |
| Pacinine (38) | >20 | >20 | - | >20 | >20 | - |
| Yunnadelphinine (39) | >20 | >20 | - | >20 | >20 | - |
| Melpheline (40) | >40 | - | >40 | >40 | >40 | - |
| Bonvalotidine C (41) | >40 | - | >40 | >40 | >40 | - |
| N-Deethyl-N-formylpaciline (42) | >40 | - | >40 | >40 | >40 | - |
| N-Deethyl-N-formylpacinine (43) | >40 | - | >40 | >40 | >40 | - |
| Isodelpheline (44) | >40 | - | >40 | >40 | >40 | - |
| Pacidine (45) | >40 | - | >40 | >40 | >40 | - |
| Eladine (46) | >40 | - | >40 | >40 | >40 | - |
| N-Formyl-4,19-secopacinine (47) | >40 | - | >40 | >40 | >40 | - |
| N-Formyl-4,19-secoyunnadelphinine (48) | >40 | - | >40 | >40 | >40 | - |
| Iminoisodelpheline (49) | >40 | - | >40 | >40 | >40 | - |
| Iminodelpheline (50) | >40 | - | >40 | >40 | >40 | - |
| Laxicyminine (51) | >40 | - | >40 | >40 | >40 | - |
| N-Deethyl-19-oxoisodelpheline (52) | >40 | - | >40 | >40 | >40 | - |
| N-Deethyl-19-oxo-delpheline (53) | >40 | - | >40 | >40 | >40 | - |
| 19-Oxoisodelpheline (54) | >40 | - | >40 | >40 | >40 | - |
| 37-1 | 14.8 ± 3.8 | 7.4 ± 1.2 | - | 8.9 ± 2.0 | 8.3 ± 1.6 | 1.07 |
| 37-2 | 38.1 ± 11.8 | 15.6 ± 5.4 | - | 23.3 ± 3.9 | 15.0 ± 6.5 | 1.55 |
| 37-3 | 22.7 ± 0.3 | 17.2 ± 3.3 | - | 20.7 ± 0.9 | 17.7 ± 3.5 | 1.17 |
| 37-4 | >20 | >20 | - | >20 | >20 | - |
| 37-5 | 24.1 ± 2.7 | 17.1 ± 11.4 | - | 23.6 ± 0.4 | 17.4 ± 7.4 | 1.36 |
| 37-6 | 18.7 ± 6.6 | 20.3 ± 7.1 | - | 20.1 ± 7.6 | 18.9 ± 5.0 | 1.06 |
| 37-7 | 21.1 ± 9.2 | 16.6 ± 12.7 | - | 21.7 ± 11.6 | 17.9 ± 4.2 | 1.21 |
| 37-8 | 28.7 ± 13.6 | 28.7 ± 7.2 | - | 24.3 ± 5.7 | 23.3 ± 3.7 | 1.04 |
| 37-9 | 21.2 ± 4.7 | 12.6 ± 3.0 | - | 14.9 ± 4.9 | 11.9 ± 3.3 | 1.25 |
| 37-10 | 20.9 ± 4.3 | 22.7 ± 6.0 | - | 19.1 ± 4.8 | 20.3 ± 2.7 | 0.94 |
| 37-11 | 30.8 ± 13.3 | 28.9 ± 4.7 | - | 29.5 ± 3.5 | 27.5 ± 3.1 | 1.07 |
| 37-12 | 19.9 ± 10.1 | 16.9 ± 6.7 | - | 14.6 ± 7.1 | 6.80 ± 5.0 | 2.15 |
| 37-13 | 10.2 ± 2.6 | 15.1 ± 6.0 | - | 21.0 ± 9.4 | 9.10 ± 1.5 | 2.31 |
| 37-14 | 22.4 ± 7.1 | 22.8 ± 8.5 | - | 25.9 ± 9.3 | 24.2 ± 4.4 | 1.07 |
| 37-15 | 29.7 ± 11.6 | 29.0 ± 5.4 | - | 21.8 ± 1.4 | 18.7 ± 5.2 | 1.17 |
| 37-16 | 20.0 ± 0.9 | 15.6 ± 2.6 | - | 14.8 ± 3.3 | 6.5 ± 2.2 | 2.28 |
| 37-17 | 14.1 ± 2.9 | 13.2 ± 5.7 | - | 6.8 ± 1.7 | 4.2 ± 1.1 | 1.62 |
| 37-18 | 16.5 ± 2.2 | 11.3 ± 7.9 | - | 5.4 ± 1.8 | 4.4 ± 0.8 | 1.23 |
| 37-19 | 25.6 ± 1.2 | 19.8 ± 4.6 | - | 12.1 ± 7.8 | 4.7 ± 1.4 | 2.57 |
| 37-20 | >20 | >20 | - | >20 | >20 | - |
| 37-21 | >20 | >20 | - | >20 | >20 | - |
| 37-22 | >20 | >20 | - | >20 | >20 | - |
| PXL2 (nM) | 4.8 ± 0.6 | 5.9 ± 1.9 | 8.4 ± 0.8 | 5.8 ± 0.2 | 2405.4 ± 44.8 | - |
1 Values are means ± standard deviation; 2 Paclitaxel (PXL; nM) was used as an experimental control.
Table 4.
Cytotoxic activity data for actaline and napelline-type C20-diterpenoid alkaloids 55~63 and synthetic analogs 56-1~56-7 of luciculine.
Table 4.
Cytotoxic activity data for actaline and napelline-type C20-diterpenoid alkaloids 55~63 and synthetic analogs 56-1~56-7 of luciculine.
| Cell Line/IC50 (μM) 1 | ||||||
|---|---|---|---|---|---|---|
| Alkaloids | A549 | DU145 | MDA-MB-231 | MCF-7 | KB | KB-VIN |
| Aconicarchamine A (55) | >40 | - | >40 | >40 | >40 | >40 |
| Lucidusculine (57) | >20 | >20 | - | - | >20 | >20 |
| Flavadine (58) | >20 | >20 | - | - | >20 | >20 |
| 12-Acetyllucidusculine (59) | >20 | >20 | - | - | >20 | >20 |
| 1-Acetylluciculine (60) | >20 | >20 | - | - | >20 | >20 |
| Dehydrolucidusculine (61) | >20 | >20 | - | - | >20 | >20 |
| Dehydroluciculine (62) | >20 | >20 | - | - | >20 | >20 |
| 12-Acetyldehydrolucidusculine (63) | >20 | >20 | - | - | >20 | >20 |
| 56-1 | >20 | >20 | - | - | >20 | >20 |
| 56-2 | >20 | >20 | - | - | >20 | >20 |
| 56-3 | >20 | >20 | - | - | >20 | >20 |
| 56-4 | >20 | >20 | - | - | >20 | >20 |
| 56-5 | 23.3 ± 6.1 | 28.1 ± 11.1 | - | - | 31.8 ± 10.5 | 27.8 ± 1.9 |
| 56-6 | >20 | >20 | - | - | >20 | >20 |
| 56-7 | >20 | >20 | - | - | >20 | >20 |
| PXL2 (nM) | 4.8 ± 0.6 | 5.9 ± 1.9 | 8.4 ± 0.8 | 10.2 ± 0.9 | 5.8 ± 0.2 | 2405.4 ± 44.8 |
1 Values are means ± standard deviation; 2 Paclitaxel (PXL; nM) was used as an experimental control.
Table 5.
Cytotoxic activity data for hetisine-type C20-diterpenoid alkaloids 64~67 and synthetic derivatives 67-1~67-19 of kobusine.
Table 5.
Cytotoxic activity data for hetisine-type C20-diterpenoid alkaloids 64~67 and synthetic derivatives 67-1~67-19 of kobusine.
| Cell Line/IC50 (μM) 1 | KB/KB-VIN Ratio | ||||||
|---|---|---|---|---|---|---|---|
| Alkaloids | A549 | DU145 | MDA-MB-231 | MCF-7 | KB | KB-VIN | |
| Ryosenamine (64) | >40 | - | >40 | >40 | >40 | >40 | |
| 9-Hydroxynominine (65) | >40 | - | >40 | >40 | >40 | >40 | |
| Torokonine (66) | >40 | - | >40 | >40 | >40 | >40 | |
| Kobusine (67) | >20 | >20 | - | - | >20 | >20 | |
| 67-1 | >20 | >20 | - | - | >20 | >20 | |
| 67-2 | >20 | >20 | - | - | >20 | >20 | |
| 67-3 | >20 | >20 | - | - | >20 | >20 | |
| 67-4 | >20 | >20 | - | - | >20 | >20 | |
| 67-5 | 8.4 ± 1.4 | 9.3 ± 3.0 | - | - | 6.0 ± 0.8 | 7.5 ± 3.7 | 0.80 |
| 67-6 | >20 | >20 | - | - | >20 | >20 | |
| 67-7 | 6.7 ± 2.4 | 7.1 ± 2.0 | - | - | 5.3 ± 0.3 | 5.2 ± 1.2 | 1.02 |
| 67-8 | 19.5 ± 3.3 | 15.3 ± 5.6 | - | - | 13.9 ± 2.8 | 17.9 ± 1.8 | 0.78 |
| 67-9 | >20 | >20 | - | - | >20 | >20 | |
| 67-10 | 6.9 ± 1.7 | 7.0 ± 2.2 | - | - | 5.3 ± 0.6 | 5.5 ± 0.7 | 0.96 |
| 67-11 | >20 | >20 | - | - | >20 | >20 | |
| 67-12 | >20 | >20 | - | - | >20 | >20 | |
| 67-13 | 17.2 ± 0.9 | 13.2 ± 2.8 | - | - | 12.7 ± 1.1 | 14.1 ± 1.0 | 0.90 |
| 67-14 | 14.1 ± 0.7 | 9.6 ± 2.4 | - | - | 11.7 ± 0.6 | 10.9 ± 0.7 | 1.07 |
| 67-15 | >20 | >20 | - | - | >20 | >20 | |
| 67-16 | >20 | >20 | - | - | >20 | >20 | |
| 67-17 | >20 | >20 | - | - | >20 | >20 | |
| 67-18 | 8.1 ± 4.7 | 6.8 ± 2.0 | - | - | 5.2 ± 0.6 | 7.1 ± 2.6 | 0.73 |
| 67-19 | 5.5 ± 1.9 | 6.2 ± 3.1 | - | - | 4.1 ± 0.7 | 3.1 ± 1.6 | 1.32 |
| PXL2 (nM) | 4.8 ± 0.6 | 5.9 ± 1.9 | 8.4 ± 0.8 | 10.2 ± 0.9 | 5.8 ± 0.2 | 2405.4 ± 44.8 | 0.0067 |
1 Values are means ± standard deviation; 2 Paclitaxel (PXL; nM) was used as an experimental control.
Table 6.
Cytotoxic activity data for hetisine-type C20-diterpenoid alkaloids pseudokobusine (68) and its synthetic analogs 68-1~68-37.
Table 6.
Cytotoxic activity data for hetisine-type C20-diterpenoid alkaloids pseudokobusine (68) and its synthetic analogs 68-1~68-37.
| Cell Line/IC50 (μM) 1 | KB/KB-VIN Ratio | ||||
|---|---|---|---|---|---|
| Alkaloids | A549 | DU145 | KB | KB-VIN | |
| Pseudokobusine (68) | >20 | >20 | >20 | >20 | |
| 68-1 | >20 | >20 | >20 | >20 | |
| 68-2 | >20 | >20 | >20 | >20 | |
| 68-3 | >20 | >20 | >20 | >20 | |
| 68-4 | 19.3 ± 4.5 | 15.3 ± 4.3 | 12.8 ± 1.7 | 10.2 ± 0.9 | 1.25 |
| 68-5 | 8.8 ± 4.5 | 7.6 ± 2.5 | 5.2 ± 1.3 | 6.3 ± 0.6 | 0.83 |
| 68-6 | >20 | >20 | >20 | >20 | |
| 68-7 | 15.4 ± 3.7 | 13.2 ± 2.0 | 11.1 ± 5.5 | 15.7 ± 1.5 | 0.70 |
| 68-8 | >20 | >20 | >20 | >20 | |
| 68-9 | >20 | >20 | >20 | >20 | |
| 68-10 | 8.0 ± 5.1 | 15.3 ± 2.9 | 14.9 ± 3.6 | 20.1 ± 13.5 | 0.74 |
| 15-Veratroylpseudokobusine (68-11) | >20 | >20 | >20 | >20 | |
| 68-12 | 16.0 ± 5.5 | 16.9 ± 7.8 | 19.7 ± 3.1 | 14.7 ± 7.0 | 1.34 |
| 68-13 | 15.2 ± 6.4 | 16.6 ± 7.9 | 18.1 ± 4.3 | 12.2 ± 5.6 | 1.48 |
| 68-14 | >20 | >20 | >20 | >20 | |
| 68-15 | 5.8 ± 0.7 | 7.2 ± 1.9 | 6.4 ± 0.8 | 6.4 ± 1.8 | 1.00 |
| 68-16 | >20 | >20 | >20 | >20 | |
| 68-17 | >20 | >20 | >20 | >20 | |
| 68-18 | >20 | >20 | >20 | >20 | |
| 68-19 | 5.0 ± 1.1 | 5.2 ± 1.8 | 5.6 ± 1.2 | 5.6 ± 2.9 | 1.00 |
| 68-20 | 6.8 ± 0.7 | 7.7 ± 3.8 | 8.9 ± 3.7 | 6.2 ± 1.3 | 1.44 |
| 68-21 | >20 | >20 | >20 | >20 | |
| 68-22 | 17.9 ± 7.2 | 14.5 ± 7.2 | 15.7 ± 4.1 | 13.9 ± 3.3 | 1.13 |
| 68-23 | >20 | >20 | >20 | >20 | |
| 68-24 | 8.4 ± 1.7 | 6.5 ± 0.5 | 7.0 ± 1.3 | 6.4 ± 0.9 | 1.09 |
| 68-25 | >20 | >20 | >20 | >20 | |
| 68-26 | >20 | >20 | >20 | >20 | |
| 68-27 | >20 | >20 | >20 | >20 | |
| 68-28 | >20 | >20 | >20 | >20 | |
| 68-29 | >20 | >20 | >20 | >20 | |
| 68-30 | >20 | >20 | >20 | >20 | |
| 68-31 | >20 | >20 | >20 | >20 | |
| 68-32 | 6.4 ± 1.2 | 6.0 ± 3.3 | 6.6 ± 3.1 | 5.2 ± 1.0 | 1.27 |
| 68-33 | >20 | >20 | >20 | >20 | |
| 68-34 | >20 | >20 | >20 | >20 | |
| 68-35 | >20 | >20 | >20 | >20 | |
| 68-36 | >20 | >20 | >20 | >20 | |
| 68-37 | >20 | >20 | >20 | >20 | |
| PXL2 (nM) | 4.8 ± 0.6 | 5.9 ± 1.9 | 5.8 ± 0.2 | 2405.4 ± 44.8 | |
1 Values are means ± standard deviation; 2 Paclitaxel (PXL; nM) was used as an experimental control.
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Share and Cite
MDPI and ACS Style
Wada, K.; Yamashita, H. Cytotoxic Effects of Diterpenoid Alkaloids Against Human Cancer Cells. Molecules 2019, 24, 2317. https://doi.org/10.3390/molecules24122317
AMA Style
Wada K, Yamashita H. Cytotoxic Effects of Diterpenoid Alkaloids Against Human Cancer Cells. Molecules. 2019; 24(12):2317. https://doi.org/10.3390/molecules24122317
Chicago/Turabian StyleWada, Koji, and Hiroshi Yamashita. 2019. "Cytotoxic Effects of Diterpenoid Alkaloids Against Human Cancer Cells" Molecules 24, no. 12: 2317. https://doi.org/10.3390/molecules24122317
