Short communication: nanoparticle thermotherapy and external beam radiation therapy for human prostate cancer cells.

UNLABELLED: Nanoparticle thermotherapy (NPTT) uses monoclonal antibody-linked iron oxide magnetic nanoparticles (bioprobes) for the tumor-specific thermotherapy of cancer by hysteretic heating of the magnetic component of the probes through an externally applied alternating magnetic field (AMF). The present study investigated the effect of NPTT on a human prostate cancer cell line, DU145. The concept of total heat dose (THD) as a measure for NPTT was validated on a cellular level and THD was correlated to cell death in vitro. The study, furthermore, explored the potential enhancement of the NPTT effect through added external beam radiation therapy (EBRT), because both forms of treatment have a different, and potentially complementary, mechanism of causing cell death. METHODS: Using carbodiimide, (111)In-DOTA-ChL6 was conjugated to dextran iron oxide 20-nm particles with polyethylene glycol COOH groups on the surface and purified as (111)In-bioprobes. NPTT and EBRT were applied alone and combined to cells labeled with the bioprobes. Cell response was monitored by measuring lactate dehydrogenase (LDH), a product of cytolysis, in the medium. This distinct focus on the response to NPTT was possible, since we found in previous studies that the LDH assay was relatively insensitive to the response of cells (without bioprobes) to EBRT in the dose levels given here. RESULTS: NPTT showed a significantly increased cell death at a total calculated heat dose of 14.51 and 29.02 J/g cells (50% and 100% AMF duty, 350 Oe, 136 kHz, 12 cycles, 20 minutes total), compared with AMF exposure in the absence of bioprobes. Adding EBRT to NPTT did not increase cell death, as measured by LDH. However, EBRT given to cells labeled with bioprobes caused significant cell death at radiation doses of 10 Gy and higher. CONCLUSIONS: In human prostate cancer cell cultures, NPTT applied as a single modality caused cell death that correlated with THD estimation; complete cell death occurred at 14.51 J/g cells. Consequently, enhancement of the NPTT effect through the addition of EBRT could not be addressed. Interestingly, EBRT induced cell death on bioprobe-labeled cells at EBRT levels that did not show cell death in the absence of bioprobes; this phenomenon is worth investigating further.

Thermal dosimetry predictive of efficacy of 111In-ChL6 nanoparticle AMF--induced thermoablative therapy for human breast cancer in mice.

UNLABELLED: 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 (111)In-ChL6 bioprobes (ChL6 is chimeric L6) in a human breast cancer xenograft model. METHODS: Using carbodiimide, (111)In-DOTA-ChL6 (DOTA is dodecanetetraacetic acid) was conjugated to polyethylene glycol-iron oxide-impregnated dextran 20-nm particles and purified as (111)In-bioprobes. (111)In doses of 740-1,110 kBq (20-30 muCi) (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 (111)In-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 (111)In-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 (111)In-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 (111)In-bioprobe tumor concentration and in vitro nanoparticle heat induction by AMF, correlated with tumor growth delay.

Application of high amplitude alternating magnetic fields for heat induction of nanoparticles localized in cancer.

OBJECTIVE: Magnetic nanoparticles conjugated to a monoclonal antibody can be i.v. injected to target cancer tissue and will rapidly heat when activated by an external alternating magnetic field (AMF). The result is necrosis of the microenvironment provided the concentration of particles and AMF amplitude are sufficient. High-amplitude AMF causes nonspecific heating in tissues through induced eddy currents, which must be minimized. In this study, application of high-amplitude, confined, pulsed AMF to a mouse model is explored with the goal to provide data for a concomitant efficacy study of heating i.v. injected magnetic nanoparticles. METHODS: Thirty-seven female BALB/c athymic nude mice (5-8 weeks) were exposed to an AMF with frequency of 153 kHz, and amplitude (400-1,300 Oe), duration (1-20 minutes), duty (15-100%), and pulse ON time (2-1,200 seconds). Mice were placed in a water-cooled four-turn helical induction coil. Two additional mice, used as controls, were placed in the coil but received no AMF exposure. Tissue and core temperatures as the response were measured in situ and recorded at 1-second intervals. RESULTS: No adverse effects were observed for AMF amplitudes of < or = 700 Oe, even at continuous power application (100% duty) for up to 20 minutes. Mice exposed to AMF amplitudes in excess of 950 Oe experienced morbidity and injury when the duty exceeded 50%. CONCLUSION: High-amplitude AMF (up to 1,300 Oe) was well tolerated provided the duty was adjusted to dissipate heat. Results presented suggest that further tissue temperature regulation can be achieved with suitable variations of pulse width for a given amplitude and duty combination. These results suggest that it is possible to apply high-amplitude AMF (> 500 Oe) with pulsing for a time sufficient to treat cancer tissue in which magnetic nanoparticles have been embedded.