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Increased Preclinical Efficacy of Irinotecan and Floxuridine Coencapsulated Inside Liposomes Is Associated With Tumor Delivery of Synergistic Drug Ratios

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Whether anticancer drug combinations act synergistically or antagonistically often depends on the ratio of the agents being combined. We show here that combinations of irinotecan and floxuridine exhibit drug ratio-dependent cytotoxicity in a broad panel of tumor cell lines in vitro where a 1:1 molar ratio consistently provided synergy and avoided antagonism. In vivo delivery of irinotecan and floxuridine coencapsulated inside liposomes at the synergistic 1:1 molar ratio (referred to as CPX-1) lead to greatly enhanced efficacy compared to the two drugs administered as a saline-based cocktail in a number of human xenograft and murine tumor models. When compared to liposomal irinotecan or liposomal floxuridine, the therapeutic activity of CPX-1 in vivo was not only superior to the individual liposomal agents, but the extent of tumor growth inhibition was greater than that predicted for combining the activities of the individual agents. In contrast, liposome delivery of irinotecan:floxuridine ratios shown to be antagonistic in vitro provided antitumor activity that was actually less than that achieved with liposomal irinotecan alone, indicative of in vivo antagonism. Synergistic antitumor activity observed for CPX-1 was associated with maintenance of the 1:1 irinotecan:floxuridine molar ratio in plasma and tumor tissue over 16–24 h. In contrast, injection of the drugs combined in saline resulted in irinotecan:floxuridine ratios that changed 10-fold within 1 h in plasma and sevenfold within 4 h in tumor tissue. These results indicate that substantial improvements in the efficacy of drug combinations may be achieved by maintaining in vitro-identified synergistic drug ratios after systemic administration using drug delivery vehicles.
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Keywords: Colorectal cancer; Combination chemotherapy; Floxuridine; Irinotecan; Liposome delivery; Synergy

Document Type: Research Article

Affiliations: 1: Celator Pharmaceuticals Corp., Vancouver BC, V6P 6P2 Canada 2: Celator Pharmaceuticals Corp., Vancouver BC, V6P 6P2 Canada, Celator Pharmaceuticals Inc., Princeton, NJ 08540, USA

Publication date: 2006-08-01

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  • Formerly: Oncology Research Incorporating Anti-Cancer Drug Design
    Oncology Research Featuring Preclinical and Clincal Cancer Therapeutics publishes research of the highest quality that contributes to an understanding of cancer in areas of molecular biology, cell biology, biochemistry, biophysics, genetics, biology, endocrinology, and immunology, as well as studies on the mechanism of action of carcinogens and therapeutic agents, reports dealing with cancer prevention and epidemiology, and clinical trials delineating effective new therapeutic regimens.
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