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Bevacizumab, a humanized anti-VEGF monoclonal antibody has shown promise in various clinical trials. We report the development and testing of Bi-213 (an alpha-emitting radionuclide) labeled bevacizumab for in vitro and in vivo studies using two different chelators viz cDTPA and CHX-A''. The developed labeling method showed high labeling yields of 93.6% and 89.7% for cDTPA and CHX-A'' respectively and the results were reproducible. The in vitro and in vivo stability tests were carried out using Bi-213 and long half-life Bismuth isotope (Bi-205/Bi-206) for pharmacokinetics. The in vitro results showed remarkable stability of the radiolabeled bevacizumab regardless of the chelator. The in vivo pharmacokinetics studies however, showed that the uptake and retention of cDTPA-bevacizumab was significantly higher in kidneys (p-value 0.02) and lower in liver and spleen (p-value0.0001 and 0.0009 respectively). The values for the two conjugates compared well in blood but the longer term data for CHX-A'' conjugate showed slow clearance resulting in a significantly longer blood half-life of the product (211 hours compared to 4 hours for cDTPA-bevacizumab). Preliminary in vivo results showed increased efficacy of the combination therapy compared to bevacizumab only. The tumor area (mm(2)) decreased from 24.8 +/- 3.6 and 12.8 +/- 1.7 for 1 and 3 mg/kg cold bevacizumab only to 6.5 +/- 0.7 and 7.5 +/- 4.8 when single dose of 333 MBq/kg of (213)Bi-bevacizumab was administered as combination therapy. In conclusion it can be said that stable radiolabeled bevacizumab conjugates can be prepared with Bi-213 with either chelators used. The shorter blood half-life with cDTPA-bevacizumab may not be a major concern with Bi-213 as its own half-life is 46 minutes only. The combination therapy proved superior to bevacizumab alone therapy, a phenomenon that can be particularly useful in cancers where bevacizumab alone has shown limited success like prostate cancer.

The aim is to assess toxicity and response of systemic alpha therapy for metastatic melanoma.This is an open-labelled Phase 1 dose escalation study to establish the effective dose of the alpha-immunoconjugate (213)Bi-cDTPA-9.2.27 mAb (AIC). Tools used to investigate the effects were physical examination; imaging of tumors; pathology; GFR; CT and changes in tumor marker. Responses were assessed using RECIST criteria.Twenty-two patients with stage IV melanoma/in-transit metastasis were treated with activities of 55-947 MBq. Using RECIST criteria 50% showed stable disease and 14% showed partial response. One patient (6%) showed near complete response and was retreated because of an excellent response to the initial treatment. Another patient showed response in his tumor on mandible and reduction in lung lesions. Overall 30% showed progressive disease. The tumor marker melanoma inhibitory activity protein (MIA) showed reductions over eight weeks in most of the patients. The disparity of dose with responders is discussed. No toxicity was observed over the range of administered activities.Observation of responses without any toxicity indicates that targeted alpha therapy has the potential to be a safe and effective therapeutic approach for metastatic melanoma.

The plasminogen activator inhibitor type 2 (PAI2) when labelled with (213)Bi forms the (213)Bi-PAI2 alpha conjugate (AC). This AC has been shown to be efficacious in preclinical studies with breast, ovarian, prostate and pancreatic cancers. The objectives of this study were to investigate the pharmacokinetics and in vivo stability of (213)Bi-PAI2 in mice, its toxicity in mice and rabbits; and to determine whether a prior injection of a metal chelator (Ca-DTPA) or lysine can reduce toxicity by decreasing renal uptake.Two chelators (CHX-A"-DTPA and cDTPA) were used for preparation of the (213)Bi-PAI2 conjugate, for intraperitoneal administration in mice and ear vein injection in rabbits. The mice were sacrificed at different time points for pharmacokinetic studies. Blood and organs were collected for toxicity studies for all groups.Both chelators were found to have similar %ID/g in the kidneys over four hours. Mice and rabbits did not show any short term toxicity over 13 weeks at 1420 MBq/kg and 120 MBq/kg (213)Bi-PAI2 respectively. Kidney uptake was decreased three fold by lysine. Radiation nephropathy was observed at 20-30 weeks in mice, leading to severe weight loss, whereas severe and widespread renal tubular necrosis was observed at 13 weeks in rabbits.Radiation nephropathy is the dose limiting toxicity observed in mice and rabbits. Lysine can reduce kidney uptake by three fold. Based on long-term monitoring, the maximum tolerance doses (MTD) are 350 and 120 MBq/kg for mice and rabbits respectively.

The key objective of the study was to determine the single and multiple dose toxicity and efficacy of Bismuth-213 labeled PAI2 based targeted alpha therapy by selectively targeting uPA and uPAR in regressing prostate cancer in a nude mouse model. Targeted alpha therapy (TAT) is an experimental therapeutic modality for cancer. Another objective was to compare the in vivo pharmacokinetics using two different chelators to form the radioisotope-protein construct.The single and multiple intra-peritoneal (IP) dose toxicity and efficacy of 213BiPAI2 was investigated in nude mice and its toxicity in rabbits. CD 31 staining for vasculature and uPA expression were measured at different stages of tumor growth. The pharmacokinetics of the chelators cDTPA and CHX-A'' were measured.All TAT regimes were well tolerated in mice and rabbits on biochemical and haematological examination. Capillaries became evident at six days post-cell inoculation. uPA expression was positive at all stages of tumour growth. No significant differences were observed between cDTPA and CHX-A. '' Inhibition of tumour growth was observed at 947 and 1421 MBq/kg single dose injection at three days post-PC3 cell inoculation. The three day post-inoculation multiple dose regime gave complete tumour growth inhibition at a total dose of 947 MBq/kg given on five successive days. Mice treated at 6, 12 and 18 days post-inoculation showed significantly slower tumour growth compared to controls.The efficacy of single and multiple dose TAT in mice was demonstrated within tolerance limits, the multiple dose regime being no more toxic than the single dose. Either of the two chelators could be used for 213Bi studies.