Preclinical Evaluation of the Biodistribution of AuPLU/AlClPc (Gold–Pluronic Associated with Phthalocyanine) in a Novel Murine Model of Gestational Breast Cancer ^†

Introduction: Breast cancer during pregnancy (GBC) is a rare and challenging condition due to the limited availability of safe and effective therapies for both mother and fetus. Moreover, the lack of reliable experimental models hinders translational research. This study proposes an innovative murine model of GBC to investigate the biodistribution of gold–Pluronic F127 nanocomposites conjugated with aluminum chloride phthalocyanine (AuPLU/AlClPc), a photosensitizer for photodynamic therapy. This nanotechnology-based platform aims to enable selective tumor targeting with minimal systemic exposure. Methodology: Pregnant BALB/c mice were orthotopically inoculated with 4T1 mammary tumor cells at gestational days E3.5 or E10.5. Seven days later (E10.5 or E17.5), the nanocomposite AuPLU/AlClPc was administered intravenously. A tumor control group (TC) received PBS and was used as a reference for baseline measurements and biological matrix evaluation. Animals were euthanized 24 h after injection. Organs were lyophilized, digested, and analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to quantify gold distribution. Results: In late-gestation animals (TN3), gold accumulated mainly in the tumor (172.2 ppb), lung (164.6 ppb), heart (102.1 ppb), uterus (83.8 ppb), and spleen (57.5 ppb). In early-gestation animals (TN2), lower gold levels were found in maternal organs, with notable accumulation in the placenta (128.4 ppb). Fetal tissues showed minimal gold in TN3 and none in TN2. Conclusions: AuPLU/AlClPc demonstrated a preliminary maternal–fetal safety profile and a potential for application. The novel GBC model supports further studies in oncogynecology and nanomedicine.