Tumor treatment by sustained intratumoral release of cisplatin: Effects of drug alone and combined with radiation

Purpose: The effect of intratumoral delivery of cisplatin to a mouse tumor model (RIF-1) by means of a biodegradable polymer implant with and without radiation was studied. Methods and Materials: The polymer bis (p-carboxyphenoxy)propane-sebacic acid (CPP:SA; 80:20) and its degradation products have been characterized. Polymer rods (8 x 0.5 mm) containing 17% cisplatin by weight were prepared by extrusion, and the in vitro degradation rate measured. The implants were placed into mouse tumors and their effect (with and without radiation) on tumor growth delay studied. The levels of Pt in the mouse kidney, tumor, and blood plasma at selected intervals after implant were also determined. These results were compared with those obtained when cisplatin was delivered systemically. Results: When cisplatin was delivered by the polymer implants, higher levels were present in the tumor for longer time periods (cf. systemic delivery of the drug). For both nonirradiated and irradiated tumors, those treated with the polymer implants had significantly longer tumor growth delays compared to nonimplanted controls and to systematically treated tumors. Conclusions: The results show that intratumoral delivery of cisplatin is more efficient than systemic delivery. Using the biodegradable polymer implant, higher doses of cisplatin can be tolerated by the animal as the drug is localized within the tumor, and the high levels of the drug in the tumor can be maintained for an extended period of time. When radiation is given in conjunction with cisplatin, the tumor response is supraadditive for all modes of cisplatin administration but is potentiated to a greater extent when cisplatin is delivered through the polymer implant. The greatest effect is seen for treatment with cisplatin delivered by polymer implant combined with fractionated radiation. (C) 1997 Elsevier Science Inc.