Gemcitabine-(C4-amide)-[anti-HER2/neu] Anti-Neoplastic Cytotoxicity in Dual Combination with Mebendazole against Chemotherapeutic-Resistant Mammary Adenocarcinoma.

INTRODUCTION Gemcitabine is a pyrimidine nucleoside analog that becomes triphosphorylated and competitively inhibits cytidine incorporation into DNA strands. Diphosphorylated gemcitabine irreversibly inhibits ribonucleotide reductase thereby preventing deoxyribonucleotide synthesis. Functioning as a potent chemotherapeutic, gemcitabine decreases neoplastic cell proliferation and induces apoptosis which accounts for its effectiveness in the clinical treatment of several leukemia and carcinoma cell types. A brief plasma half-life due to rapid deamination, chemotherapeutic-resistance and sequelae restrict gemcitabine utility in clinical oncology. Selective "targeted" gemcitabine delivery represents a molecular strategy for prolonging its plasma half-life and minimizing innocent tissue/organ exposure. METHODS A previously described organic chemistry scheme was applied to synthesize a UV-photoactivated gemcitabine intermediate for production of gemcitabine-(C4-amide)-[anti-HER2/neu]. Immunodetection analysis (Western-blot) was applied to detect the presence of any degradative fragmentation or polymerization. Detection of retained binding-avidity of gemcitabine-(C4-amide)-[anti-HER2/neu] was determined by cell-ELISA using populations of chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3) that highly over-express the HER2/neu trophic membrane receptor. Cytotoxic anti-neoplastic potency of gemcitabine-(C4-amide)-[anti-HER2/neu] and the benzimidazole tubulin/microtubule inhibitors, albendazole, flubendazole and mebendazole was established against chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3). Related investigations evaluated the potential for gemcitabine-(C4-amide)-[anti-HER2/neu] in dual combination with mebendazole to evoke increased levels of cytotoxic anti-neoplatic potency compared to gemcitabine-(C4-amide)-[anti-HER2/neu]. RESULTS Covalent gemcitabine-(C4-amide)-[anti-HER2/neu] immunochemotherapeutic and each benzimidazole (n=3) exerted cytotoxic anti-neoplastic potency against chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3). Covalent gemcitabine-(C4-amide)-[anti-HER2/neu] immunochemotherapeutic or gemcitabine in dual combination with mebendazole created increased levels of cytotoxic anti-neoplastic potency that were greater than attained with gemcitabine-(C4-amide)-[anti-HER2/neu] or gemcitabine alone. CONCLUSION Gemcitabine-(C4-amide)-[anti-HER2/neu] in dual combination with benzimidazoles can produce enhanced levels of cytotoxic anti-neoplastic activity and potentially provide a basis for treatment regimens with a wider margin-of-safety. Such benefits would be possible through the collective properties of; [i] selective "targeted" gemcitabine delivery; [ii] relatively lower toxicity of benzimidazoles compared to many if not most conventional chemotherapeutics; [iii] reduced total dosage requirements faciliated by additive or synergistic anti-cancer properties; and [iv] differences in sequelae for gemcitabine-(C4-amide)-[anti-HER2/neu] compared to benzimidazole tubulin/microtubule inhibitors.