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Targeted alpha therapy utilizes alpha-emitting radionuclides conjugated to monoclonal antibodies to allow specific irradiation of cancer cells whilst sparing normal, healthy tissues. The mutagenic potential of (213)Bi conjugated to a human melanoma antigen-specific antibody (9.2.27) was examined using an in vivo transgenic mouse model containing multiple copies of a lacZ target gene in every cell, allowing the quantification and comparison of mutagenesis in different organs. Mice received an ip injection of 16.65 MBq of (213)Bi-cDTPA-9.2.27, and were sacrificed at 24 h, 1 w and 4 w post-injection. Pharmacokinetic studies gave the absorbed and effective doses for each organ. The mutant frequency and mutant spectra were analysed for the brain, spleen and kidneys. The brain and spleen did not show significant increases in induced mutation frequencies compared to spontaneous background levels or changes in mutant spectra, these results being independent of p53 status. However, elevated mutation frequencies and persistent size change mutations were observed in the kidneys, but are not significant at the p = 0.05 level. The effect of p53 status was also evident, as p53 heterozygotes displayed higher mutation frequencies than their wild-type counterparts, suggesting a reduction in the p53 gene may lead to an increased susceptibility to mutagenesis. These effects were time dependent and levels returned to those of the controls at 4 w post-irradiation, albeit with a predominant residue of size mutations. These effects were observed at activities very much higher than those expected for the therapy of human patients. As such, the induction of secondary cancer with the (213)Bi-cDTPA-9.2.27 alpha immunoconjugate is not expected to be a significant problem in the clinic.

Control of ovarian cancer (OC) ascites remains a major objective in post-surgical treatment. The aim of this study was to investigate the effect of targeted alpha therapy (TAT) for the control of ascites in an OC ascites mouse model; the biodistribution of (213)Bi-C595 and its long term toxicity.The expression of tumor-associated antigen mucin-1 (MUC-1) in OVCAR3 ascites cells in mice and OC cancer tissues in patients was detected by indirect immmunostaining. The monoclonal antibody (MAb) C595 was labeled with (213)Bi using the chelator cDTPA to form the alpha-immunoconjugate (AIC). Mice were injected with different concentrations of AIC by i.p administration. Changes in tumor progression were assessed by measurement of the circumference of the abdomen.MUC-1 is strongly expressed in 73% of OC tissues. At 9 days post-cell inoculation in mice, a single injection of 355 MBq/kg of (213)Bi-C595 can prolong survival by 25 days. A high tumor: blood ratio (5.8) was found in biodistribution study. The maximum tolerance dose (MTD) was more than 1180 MBq/kg up to 21 weeks.C595 is a specific targeting vector for ovarian cancer cells, which show a high percentage of expression of MUC1. (213)Bi-C595 can effectively target and kill ovarian cancer cells in vitro and in vivo. (213)Bi-C595 is the recommended alpha conjugate for a Phase I clinical trial for ovarian cancer.

The aim of this study was to investigate the effect of targeted alpha therapy for the control of in vitro pancreatic cancer cell clusters and micrometastatic cancer lesions in vivo.The expression of tumor-associated antigen MUC-1 on three pancreatic cancer cell clusters and animal xenografts was detected by indirect immmunostaining. Monoclonal antibodies C595 (test) and A2 (non-specific control) were labeled with 213Bi using the chelator CHX.A" to form the alpha-immunoconjugate (AIC). Cell clusters were incubated with AIC and examined at 48 h. Apoptosis was documented using the TUNEL assay. In vivo, an antiproliferative effect for tumors was tested at two days post-subcutaneous cell inoculation. Mice were injected with different concentrations of AIC by regional or systemic administration. Changes in tumor progression were assessed by tumor size.MUC-1 is strongly expressed on CFPAC-1, PANC-1 and moderate expression was found CAPAN-1 cell clusters and tumor xenografts. The AICs can target and kill cancer cell clusters (100 mm) in vitro. Some 73-81 % of cells were TUNEL positive cells in the clusters after incubation with AIC. At two days post- cell inoculation in mice, a single local injection of 74 and 148 MBq/kg of AIC causes complete inhibition of tumor growth. Systemic injections of 111, 222 and 333 MBq/kg of AIC cause significant tumor growth delay after 16 weeks, compared with the nonspecific control providing 333 MBq/kg after 16 weeks.CFPAC-1, PANC-1 and CAPAN-1 pancreatic cancer cell clusters and pancreatic tumor xenografts show high expression of the MUC-1 target antigen. 213Bi-C595 can specifically target and regress pancreatic cancer cell clusters in vitro, and delay and inhibit tumor growth in vivo. 213Bi-C595 may be a useful agent for the treatment of micrometastatic pancreatic cancer with overexpression of MUC 1 antigen in post-surgical patients with minimal residual disease.

Objectives: Key objectives of the study were to determine the pharmacokinetics and efficacy of the alpha emitting Bismuth-213 labeled 9.2.27 alpha-immunoconjugate (AIC). Methods: Balb/c nude mice were injected with varying doses of AIC to determine the pharmacokinetics of the AIC. The results were normalized to percent counts per minute (CPM) per gram per 3.7 MBq of the AIC (%CPM/g/3.7MBq) for each organ. Efficacy was determined by injected varying doses of AIC to different stages of tumor growth for intra-lesional, systemic and multiple dose TAT. Results: Biodistribution studies showed similar pharmacokinetics for blood and brain, liver, kidneys, spleen, gut, heart, lungs and bone marrow, indicating that there was no retention of AIC. This is particularly important for brain (due to the presence of NG2+ cells) as the antibody 9.2.27 may reach NG2 positive cells. Tumor growth at 2-days post-inoculation was completely inhibited by TAT. The response to TAT was inversely proportional to tumor growth, i.e., a reduction in response was observed with increased tumor burden. A multiple dose regime was found to be more effective than single dose. Conclusions: TAT is effective for the treatment of micrometastatic melanoma, when the tumor is preangiogenic in the form of isolated cells or cell clusters. There is no evidence of retention of AIC in brain, kidneys and other vital organs.