Pharmacokinetics, dosimetry and toxicity of holmium-166-DOTMP for bone marrow ablation in multiple myeloma.

Abstract

UNLABELLED: In this Phase I clinical trial, six multiple myeloma patients who had not responded to conventional therapy and were scheduled for bone marrow transplantation received a bone-seeking radiopharmaceutical for bone marrow ablation. The pharmacokinetics, dosimetry, and toxicity of this radiopharmaceutical were studied. METHODS: Patients received from 519 mCi to 2.1 Ci (19.2 GBq to 77.7 GBq) of holmium-166 (166Ho) complexed with a bone-seeking agent, DOTMP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylene-phosphonic acid). The reproducibility of pharmacokinetics from multiple injections of 166Ho-DOTMP administered to these myeloma patients was demonstrated from blood (r2 = 0.926) and whole-body retention (r2 = 0.983), which allowed therapeutic parameters to be determined from a diagnostic study. RESULTS: Over 50% of the 166Ho-DOTMP injected dose was excreted within 2-3 hr postinjection, increasing to 75%-85% over a 24-hr period. Rapid blood clearance minimized radiation dose to nontarget tissue: less than 10% of the injected activity was retained in the blood pool at 1 hr postinjection, and less than 2% remained after 5 hr. The total radiation absorbed dose delivered to the bone marrow for the six patients ranged from 7.9 Gy to 41.4 Gy. CONCLUSION: All patients demonstrated severe bone marrow toxicity with a white blood cell (WBC) count < 1,000 cells/microliters, two patients exhibited marrow ablation (WBC count < 100 cells/microliters), and no other toxicity > or = grade 2 was observed in any of the patients.