![]() Optimal therapeutic selectivity is achieved only when MSC is administered at least 7 days prior to irinotecan and continued throughout treatment schedule. Treatment with MSC alone resulted in 30% partial response (PR) but 0% CR. The CR rate increased from 10% after irinotecan alone to 60% after the combination treatment in mice bearing A253 xenografts. ![]() In nude mice bearing human FaDu xenografts, sequential combination treatment of MSC (0.2mg/d × 28) and irinotecan (100mg/kg/wk × 4) increased the complete response (CR) rate from 30% after irinotecan alone to 100% after the combination treatment. ![]() Both untreated tumors have similar level of carboxylesterase-2, irinotecan activating enzyme. A253 is well differentiated and null p53. FaDu is poorly differentiated and p53 mutant. FaDu and A253, head and neck squamous cell carcinomas (HNSCC), were previously characterized. However, MSC enhances the anti-tumor activity (cure rates) of irinotecan against FaDu and A253 xenografts. MSC has modest partial response of anti-tumor activity when given alone. Methylselenocysteine (MSC) is a selenium containing compound that is activated by β-lyase into the active metabolite methylselenol. Irinotecan treats multiple solid tumors by targeting topoisomerase I and resulting in double-stranded DNA breaks.
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