Thermal Dosimetry Predictive of Efficacy of ¹¹¹In-ChL6 Nanoparticle AMF–Induced Thermoablative Therapy for Human Breast Cancer in Mice

Abstract

Antibody (mAb)-linked iron oxide nanoparticles (bioprobes) provide the opportunity to develop tumor specific thermal therapy (Rx) for metastatic cancer when inductively heated by an externally applied alternating magnetic field (AMF). To evaluate the potential of this Rx, in vivo tumor targeting, efficacy, and predictive radionuclide-based heat dosimetry were studied using ¹¹¹In-ChL6 bioprobes (ChL6 is chimeric L6) in a human breast cancer xenograft model. Methods: Using carbodiimide, ¹¹¹In-DOTA-ChL6 (DOTA is dodecanetetraacetic acid) was conjugated to polyethylene glycol-iron oxide–impregnated dextran 20-nm particles and purified as ¹¹¹In-bioprobes. ¹¹¹In doses of 740–1,110 kBq (20–30 μCi) (2.2 mg of bioprobes) were injected intravenously into mice bearing HBT3477 human breast cancer xenografts. Pharmacokinetic (PK) data were obtained at 1, 2, 3, and 5 d. AMF was delivered 72 h after bioprobe injection at amplitudes of 1,410 (113 kA/m), 1,300 (104 kA/m), and 700 (56 kA/m) oersteds (Oe) at 30%, 60%, and 90% “on” time (duty), respectively, and at 1,050 Oe (84 kA/m) at 50% and 70% duty over the 20-min treatment. Treated and control mice were monitored for 90 d. Tumor total heat dose (THD) from activated tumor bioprobes was calculated for each Rx group using ¹¹¹In-bioprobe tumor concentration and premeasured particle heat response to AMF amplitudes. Tumor growth delay was analyzed by Wilcoxon rank sum comparison of time to double, triple, and quintuple tumor volume in each group, and all groups were compared with the controls. Results: Mean tumor concentration of ¹¹¹In-bioprobes at 48 h was 14 ± 2 percentage injected dose per gram; this concentration 24 h before AMF treatment was used to calculate THD. No particle-related toxicity was observed. Toxicity was observed at the highest AMF amplitude–duty combination of 1,300 Oe and 60% over 20 min; 6 of 10 mice died acutely. Tumor growth delay occurred in all of the other groups, correlated with heat dose and, except for the lowest heat dose group, was statistically significant when compared with the untreated group. Electron microscopy showed ¹¹¹In-bioprobes on tumor cells and cell death by necrosis at 24 and 48 h after AMF. Conclusion: mAb-guided bioprobes (iron oxide nanoparticles) effectively targeted human breast cancer xenografts in mice. THD, calculated using empirically observed ¹¹¹In-bioprobe tumor concentration and in vitro nanoparticle heat induction by AMF, correlated with tumor growth delay.