Combined modality radioimmunotherapy for human prostate cancer xenografts with taxanes and 90yttrium-DOTA-peptide-ChL6.

Background: Therapy for prostate cancer in the PC3 tumor-nude mouse model with 90yttrium-(90Y)-DOTA-peptide-ChL6 (5.55 MBq;150 microCi) has resulted in durable responses. To make radioimmunotherapy (RIT) more effective, the radiation-enhancing drugs Taxol (paclitaxel) and Taxotere (docetaxel) were tested for synergy with 90Y-DOTA-peptide-ChL6.

Methods: Nude mice bearing human prostate cancer PC3 xenografts were treated with 90Y-DOTA-peptide-ChL6 (2.78 MBq; 75 microCi) and after 24 hr, paclitaxel (300 or 600 microg), or docetaxel (300 microg). Tumor size, survival, blood counts, and pharmacokinetics were monitored to assess efficacy and toxicity.

Results: Docetaxel plus RIT had a 67% cure rate, whereas no mice were cured among the RIT alone, chemotherapy alone, or untreated controls. Paclitaxel (600 microg) plus RIT produced a 100% response rate with 20% cures. Average tumor volume was reduced to a greater degree in the combined modality radioimmunotherapy (CMRIT) groups compared to controls and the anti-tumor response was durable. Myelotoxicity in the combined modality groups (RIT plus paclitaxel or RIT plus docetaxel) were similar to groups receiving the same dose of RIT alone.

Conclusion: In the PC3-tumor nude mouse model, addition of paclitaxel or docetaxel to 90Y-DOTA-peptide-ChL6, in doses clinically achievable in humans, provided therapeutic synergy without increased or excessive toxicity.