Coyne CP, Toni Jones and Ryan Bear
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, chemotherapeuticresistance 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 tubulin/ microtubule inhibitor, griseofulvin 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 griseofulvin 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 griseofulvin 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 griseofulvin created increased levels of cytotoxic anti-neoplastic potency that were greater than was attainable with gemcitabine-(C4-amide)-[anti-HER2/neu] or gemcitabine alone.
Conclusion: Gemcitabine-(C4-amide)-[anti-HER2/neu] in dual combination with griseofulvin can produce enhanced levels of cytotoxic anti-neoplastic activity and potentially provide a basis for treatment regimens with a wider marginof- safety. Such benefits would be possible through the collective properties of; [i] selective “targeted” gemcitabine delivery; [ii] relatively lower toxicity of griseofulvin 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 griseofulvin functioning as a tubulin/microtubule inhibitor.
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