Multimodality Therapy: Potentiation of High Linear Energy Transfer Radiation with Paclitaxel for the Treatment of Disseminated Peritoneal Disease

Purpose: Studies herein explore paclitaxel enhancement of the therapeutic efficacy of α-particle-targeted radiation therapy. Experimental Design: Athymic mice bearing 3 day i.p. LS-174T xenografts were treated with 300 or 600 μg paclitaxel at 24 h before, concurrently, or 24 h after [213Bi] or [212Pb]trastuzumab. Results: Paclitaxel (300 or 600 μg) followed 24 h later with [213Bi]trastuzumab (500 μCi) provided no therapeutic enhancement. Paclitaxel (300 μg) administered concurrently with [213Bi]trastuzumab or [213Bi]HuIgG resulted in median survival of 93 and 37 days, respectively; no difference was observed with 600 μg paclitaxel. Mice receiving just [213Bi]trastuzumab or [213Bi]HuIgG or left untreated had a median survival of 31, 21, and 15 days, respectively, 23 days for just either paclitaxel dose alone. Paclitaxel (300 or 600 μg) given 24 h after [213Bi]trastuzumab increased median survival to 100 and 135 days, respectively. The greatest improvement in median survival (198 days) was obtained with two weekly doses of paclitaxel (600 μg) followed by [213Bi]trastuzumab. Studies were also conducted investigating paclitaxel administered 24 h before, concurrently, or 24 h after [212Pb]trastuzumab (10 μCi). The 300 μg paclitaxel 24 h before radioimmunotherapy (RIT) failed to provide benefit, whereas 600 μg extended the median survival from 44 to 171 days. Conclusions: These results suggest that regimens combining chemotherapeutics and high linear energy transfer (LET) RIT may have tremendous potential in the management and treatment of cancer patients. Dose dependency and administration order appear to be critical factors requiring careful investigation.