The Responsiveness of Breast Cancer Cells to Varied Levels of Vitamin B12, Cisplatin, and G-CSF.

Supportive agents, such as vitamin B12 (cobalamin, B12) and granulocyte colony-stimulating factor (G-CSF), are widely used during chemotherapy; however, their direct effects on tumor biology are not well understood. We evaluated the impact of pharmacological B12 and G-CSF, alone or in combination with cisplatin, on hormone receptor-positive (MCF-7) and triple-negative (MDA-MB-231) breast cancer cells, conducting in vitro assays of cell viability, cytotoxicity, caspase activation, mitochondrial membrane potential, and cytolytic protein expression. Neither B12 nor G-CSF alone induced cytotoxicity; instead, both promoted proliferation in a dose- and time-dependent manner. When combined with cisplatin, they consistently attenuated drug-induced cytotoxicity, suppressed caspase-3/-8/-9 activation, preserved mitochondrial integrity, and reduced perforin/granzyme expression, exhibiting stronger effects in MCF-7 cells. G-CSF markedly increased proliferation (>130% at 50 ng/mL), while B12 modestly enhanced viability and mitigated cisplatin-induced damage, particularly in triple-negative cells. These findings indicate that B12 and G-CSF can impair cisplatin efficacy by blunting apoptotic signaling and mitochondrial injury in different breast cancer subtypes. These preclinical findings warrant prospective, biomarker-driven in vivo and clinical studies to delineate the clinical contexts in which B12 and G-CSF can be safely integrated into supportive care without compromising antitumor efficacy.