Monte Carlo calculation of the maximum therapeutic gain of tumor antivascular alpha therapy.

PURPOSE: Metastatic melanoma lesions experienced marked regression after systemic targeted alpha therapy in a phase 1 clinical trial. This unexpected response was ascribed to tumor antivascular alpha therapy (TAVAT), in which effective tumor regression is achieved by killing endothelial cells (ECs) in tumor capillaries and, thus, depriving cancer cells of nutrition and oxygen. The purpose of this paper is to quantitatively analyze the therapeutic efficacy and safety of TAVAT by building up the testing Monte Carlo microdosimetric models. METHODS: Geant4 was adapted to simulate the spatial nonuniform distribution of the alpha emitter (213)Bi. The intraluminal model was designed to simulate the background dose to normal tissue capillary ECs from the nontargeted activity in the blood. The perivascular model calculates the EC dose from the activity bound to the perivascular cancer cells. The key parameters are the probability of an alpha particle traversing an EC nucleus, the energy deposition, the lineal energy transfer, and the specific energy. These results were then applied to interpret the clinical trial. Cell survival rate and therapeutic gain were determined. RESULTS: The specific energy for an alpha particle hitting an EC nucleus in the intraluminal and perivascular models is 0.35 and 0.37 Gy, respectively. As the average probability of traversal in these models is 2.7% and 1.1%, the mean specific energy per decay drops to 1.0 cGy and 0.4 cGy, which demonstrates that the source distribution has a significant impact on the dose. Using the melanoma clinical trial activity of 25 mCi, the dose to tumor EC nucleus is found to be 3.2 Gy and to a normal capillary EC nucleus to be 1.8 cGy. These data give a maximum therapeutic gain of about 180 and validate the TAVAT concept. CONCLUSIONS: TAVAT can deliver a cytotoxic dose to tumor capillaries without being toxic to normal tissue capillaries.

Autonomic activation links CNS oxygen toxicity to acute cardiogenic pulmonary injury.

Breathing hyperbaric oxygen (HBO2), particularly at pressures above 3 atmospheres absolute, can cause acute pulmonary injury that is more severe if signs of central nervous system toxicity occur. This is consistent with the activation of an autonomic link between the brain and the lung, leading to acute pulmonary oxygen toxicity. This pulmonary damage is characterized by leakage of fluid, protein, and red blood cells into the alveoli, compatible with hydrostatic injury due to pulmonary hypertension, left atrial hypertension, or both. Until now, however, central hemodynamic parameters and autonomic activity have not been studied concurrently in HBO2, so any hypothetical connections between the two have remained untested. Therefore, we performed experiments using rats in which cerebral blood flow, electroencephalographic activity, cardiopulmonary hemodynamics, and autonomic traffic were measured in HBO2 at 5 and 6 atmospheres absolute. In some animals, autonomic pathways were disrupted pharmacologically or surgically. Our findings indicate that pulmonary damage in HBO2 is caused by an abrupt and significant increase in pulmonary vascular pressure, sufficient to produce barotrauma in capillaries. Specifically, extreme HBO2 exposures produce massive sympathetic outflow from the central nervous system that depresses left ventricular function, resulting in acute left atrial and pulmonary hypertension. We attribute these effects on the heart and on the pulmonary vasculature to HBO2-mediated central sympathetic excitation and catecholamine release that disturbs the normal equilibrium between excitatory and inhibitory activity in the autonomic nervous system.

Inhibition of micrometastatic prostate cancer cell spread in animal models by 213Bilabeled multiple targeted alpha radioimmunoconjugates.

PURPOSE: To investigate the therapeutic potential of 213Bilabeled multiple targeted alpha-radioimmunoconjugates for treating prostate cancer (CaP) micrometastases in mouse models. EXPERIMENTAL DESIGN: PC-3 CaP cells were implanted s.c., in the prostate, and intratibially in NODSCID mice. The expression of multiple tumor-associated antigens on tumor xenografts and micrometastases was detected by immunohistochemistry. Targeting vectors were two monoclonal antibodies, and a plasminogen activator inhibitor type 2 that binds to cell surface urokinase plasminogen activator, labeled with 213Bi using standard methodology. In vivo efficacy of multiple alpha conjugates (MTAT) at different activities was evaluated in these mouse models. Tumor growth was monitored during observations and local regional lymph node metastases were assessed at the end of experiments. RESULTS: The take rate of PC-3 cells was 100% for each route of injection. The tumor-associated antigens (MUC1, urokinase plasminogen activator, and BLCA-38) were heterogeneously expressed on primary tumors and metastatic cancer clusters at transit. A single i.p. injection of MTAT (test) at high and low doses caused regression of the growth of primary tumors and prevented local lymph node metastases in a concentration-dependent fashion; it also caused cancer cells to undergo necrosis and apoptosis. CONCLUSIONS: Our results suggest that MTAT can impede primary PC-3 CaP growth at three different sites in vivo through induction of apoptosis, and can prevent the spread of cancer cells and target lymph node micrometastases in a concentration-dependent manner. MTAT, by targeting multiple antigens, can overcome heterogeneous antigen expression to kill small CaP cell clusters, thus providing a potent therapy for micrometastases.

Preoperative body composition is influenced by the stage of operable pancreatic adenocarcinoma but does not predict survival after Whipple's procedure.

OBJECTIVES: Cachexia is common in pancreatic cancer and may have an influence on longterm survival but few studies have investigated this in patients with operable tumours. Therefore, this study was carried out to document body composition status in patients with pancreatic adenocarcinoma (PCa) presenting for a Whipple's procedure (WP) and to relate the findings to histopathology and longterm survival. METHODS: Body composition was measured 1 day before a WP for ductal PCa in 36 patients (15 men, 21 women) aged 41-81 years. Results for total body nitrogen (TBN), nitrogen index (NI), total body water (TBW), fat mass (FM) and total body potassium (TBK) were compared with results in 73 age- and sex-matched controls. Patients' survival and details from histopathology synoptic reports were documented. RESULTS: Patients undergoing WPs had low TBK values (P < 0.001) and females had lower body fat (P = 0.007) compared with controls. Five of 36 presented with significant protein deficiency, but this was not associated with a prolonged length of stay or reduced survival. The 12 patients who had involved surgical margins had larger tumours and reduced weight (P = 0.015), FM (P = 0.001), TBN (P = 0.045), TBK (P = 0.014) and survival (P = 0.036). However, multivariate Cox's regression analysis only included FM along with vascular invasion and margin status as independent predictors of survival. CONCLUSIONS: PCa patients undergoing a WP have reduced body fat and TBK compared with community controls while those with stage III tumours had greater deficits of fat, TBK and protein stores. However, preoperative body composition was a poor predictor of postoperative survival after pathological data were considered.

Radioimmunotherapy of Pancreatic Ductal Adenocarcinoma: A Review of the Current Status of Literature.

Pancreatic ductal adenocarcinoma (PDAC) has long been associated with low survival rates. A lack of accurate diagnostic tests and limited treatment options contribute to the poor prognosis of PDAC. Radioimmunotherapy using α- or ß-emitting radionuclides has been identified as a potential treatment for PDAC. By harnessing the cytotoxicity of α or ß particles, radioimmunotherapy may overcome the anatomic and physiological factors which traditionally make PDAC resistant to most conventional treatments. Appropriate selection of target receptors and the development of selective and cytotoxic radioimmunoconjugates are needed to achieve the desired results of radioimmunotherapy. The aim of this review is to examine the growing preclinical and clinical trial evidence regarding the application of α and ß radioimmunotherapy for the treatment of PDAC. A systematic search of MEDLINE® and Scopus databases was performed to identify 34 relevant studies conducted on α or ß radioimmunotherapy of PDAC. Preclinical results demonstrated α and ß radioimmunotherapy provided effective tumour control. Clinical studies were limited to investigating ß radioimmunotherapy only. Phase I and II trials observed disease control rates of 11.2%-57.9%, with synergistic effects noted for combination therapies. Further developments and optimisation of treatment regimens are needed to improve the clinical relevance of α and ß radioimmunotherapy in PDAC.

Two faces of nitric oxide: implications for cellular mechanisms of oxygen toxicity.

Recent investigations have elucidated some of the diverse roles played by reactive oxygen and nitrogen species in events that lead to oxygen toxicity and defend against it. The focus of this review is on toxic and protective mechanisms in hyperoxia that have been investigated in our laboratories, with an emphasis on interactions of nitric oxide (NO) with other endogenous chemical species and with different physiological systems. It is now emerging from these studies that the anatomical localization of NO release, which depends, in part, on whether the oxygen exposure is normobaric or hyperbaric, strongly influences whether toxicity emerges and what form it takes, for example, acute lung injury, central nervous system excitation, or both. Spatial effects also contribute to differences in the susceptibility of different cells in organs at risk from hyperoxia, especially in the brain and lungs. As additional nodes are identified in this interactive network of toxic and protective responses, future advances may open up the possibility of novel pharmacological interventions to extend both the time and partial pressures of oxygen exposures that can be safely tolerated. The implications of a better understanding of the mechanisms by which NO contributes to central nervous system oxygen toxicity may include new insights into the pathogenesis of seizures of diverse etiologies. Likewise, improved knowledge of NO-based mechanisms of pulmonary oxygen toxicity may enhance our understanding of other types of lung injury associated with oxidative or nitrosative stress.

Phosphodiesterase-5 inhibitors oppose hyperoxic vasoconstriction and accelerate seizure development in rats exposed to hyperbaric oxygen.

Oxygen is a potent cerebral vasoconstrictor, but excessive exposure to hyperbaric oxygen (HBO(2)) can reverse this vasoconstriction by stimulating brain nitric oxide (NO) production, which increases cerebral blood flow (CBF)-a predictor of O(2) convulsions. We tested the hypothesis that phosphodiesterase (PDE)-5 blockers, specifically sildenafil and tadalafil, increase CBF in HBO(2) and accelerate seizure development. To estimate changes in cerebrovascular responses to hyperoxia, CBF was measured by hydrogen clearance in anesthetized rats, either control animals or those pretreated with one of these blockers, with the NO inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME), with the NO donor S-nitroso-N-acetylpenicillamine (SNAP), or with a blocker combined with l-NAME. Animals were exposed to 30% O(2) at 1 atm absolute (ATA) ("air") or to 100% O(2) at 4 or 6 ATA. EEG spikes indicated central nervous system CNS O(2) toxicity. The effects of PDE-5 blockade varied as a positive function of ambient Po(2). In air, CBF did not increase significantly, except after pretreatment with SNAP. However, at 6 ATA O(2), mean values for CBF increased and values for seizure latency decreased, both significantly; pretreatment with l-NAME abolished these effects. Conscious rats treated with sildenafil before HBO(2) were also more susceptible to CNS O(2) toxicity, as demonstrated by significantly shortened convulsive latency. Decreases in regional CBF reflect net vasoconstriction in the brain regions studied, since mean arterial pressures remained constant or increased throughout. Thus PDE-5 blockers oppose the protective vasoconstriction that is the initial response to hyperbaric hyperoxia, decreasing the safety of HBO(2) by hastening onset of CNS O(2) toxicity.

The cytokinesis-block micronucleus assay as a biological dosimeter for targeted alpha therapy.

Ionizing radiation causes structural chromosomal aberrations, a proportion of which give rise to chromosome fragments without spindle attachment organelles. When a cell divides, some of these fragments are excluded from the main daughter nuclei and form small nuclei within the cytoplasm. The cytokinesis-block micronucleus assay allows these micronuclei (MN) to be counted, providing an in situ biological dosimeter. In this study, we evaluated the micronucleus frequency in peripheral blood lymphocytes after in vitro incubation with the alpha conjugates (213)BiI(3) and (213)Bi-9.2.27 (AIC). Lymphocytes were inoculated in vitro AIC for 3 h. Further, we report the first MN measurements in melanoma patients after targeted alpha therapy (TAT) with (213)Bi-9.2.27. Patients were injected with 260-360 MBq of AIC, and blood samples taken at 3 h, 2 weeks and 4 weeks post-treatment. Absorbed dose (MIRD) and effective total body dose (PED) were calculated. The MN frequency in lymphocytes was similar for equal in vitro incubation activities of (213)BiI(3) and (213)Bi-9.2.27 (P=0.5), indicating that there is no selective targeting of lymphocytes by the alpha conjugates. After inoculation with 10-1200 kBq mL-1 of AIC, there was a substantial activity-related increase in MN. The number of MN in the blood of treated patients peaked at 3 h post-TAT, slowly returning to baseline levels by 4 weeks. The mean photon equivalent dose (PED) is 0.43 Gy (SD 0.15) and the mean MIRD calculated absorbed dose is 0.11 Gy (SD 0.03), giving an RBE=4+/-0.4 for this study.

Global comparison of targeted alpha vs targeted beta therapy for cancer: In vitro, in vivo and clinical trials.

Targeted therapy for cancer is a rapidly expanding and successful approach to the management of many intractable cancers. However, many immunotherapies fail in the longer term and there continues to be a need for improved targeted cancer cell toxicity, which can be achieved by radiolabelling the targeting vector with a radioisotope. Such constructs are successful in using a gamma ray emitter for imaging. However, traditionally, a beta emitter is used for therapeutic applications. The new approach is to use the short range and highly cytotoxic alpha radiation from alpha emitters to achieve improved efficacy and therapeutic gain. This paper sets out to review all experimental and theoretical comparisons of efficacy and therapeutic gain for alpha and beta emitters labelling the same targeting vector. The overall conclusion is that targeted alpha therapy is superior to targeted beta therapy, such that the use of alpha therapy in clinical settings should be expanded.

Estimation of thigh muscle cross-sectional area by dual-energy X-ray absorptiometry in frail elderly patients.

BACKGROUND: Thigh muscle mass and cross-sectional area (CSA) are useful indexes of sarcopenia and the response to treatment in older patients. Current criterion methods are computed tomography (CT) and magnetic resonance imaging. OBJECTIVE: The objective was to compare thigh muscle mass estimated by dual-energy X-ray absorptiometry (DXA), a less expensive and more accessible method, with thigh muscle CSA determined by CT in a group of elderly patients recovering from hip fracture. DESIGN: Midthigh muscle CSA (in cm(2)) was assessed from a 1-mm CT slice and midthigh muscle mass (g) from a 1.3-cm DXA slice in 30 patients (24 women) aged 81 +/- 8 y during 12 mo of follow-up. Fat-to-lean soft tissue ratios were calculated with each technique to permit direct comparison of a variable in the same units. RESULTS: Baseline midthigh muscle CSA was highly correlated with midthigh muscle mass (r = 0.86, P < 0.001) such that DXA predicted CT-determined CSA with an SEE of 10 cm(2) (an error of approximately 12% of the mean CSA value). CT- and DXA-determined ratios of midthigh fat to lean mass were similarly related (intraclass correlation coefficient = 0.87, P < 0.001). When data were expressed as the changes from baseline to follow-up, CT and DXA changes were weakly correlated (intraclass correlation coefficient = 0.51, P = 0.019). CONCLUSIONS: Assessment of sarcopenia by DXA midthigh slice is a potential low-radiation, accessible alternative to CT scanning of older patients. The errors inherent in this technique indicate, however, that it should be applied to groups of patients rather than to individuals or to evaluate the response to interventions.

Tumour anti-vascular alpha therapy: a mechanism for the regression of solid tumours in metastatic cancer.

Targeted alpha therapy (TAT) is an emerging therapeutic modality, thought to be best suited to cancer micrometastases, leukaemia and lymphoma. TAT has not been indicated for solid tumours. However, several melanoma patients in a phase 1 clinical trial of systemic targeted alpha therapy for melanoma experienced marked regression of subcutaneous and internal tumours. This response cannot be ascribed to killing of all cancer cells in the tumours by targeted alpha therapy. These new observations support the original hypothesis that tumours can be regressed by a mechanism called tumour anti-vascular alpha therapy. This effect depends on the expression of targeted receptors by capillary pericytes and contiguous cancer cells, and on the short-range and high-energy transfer of alpha radiation.

A comparative evaluation of Ac225 vs Bi213 as therapeutic radioisotopes for targeted alpha therapy for cancer.

The Ac225:Bi213 generator is the mainstay for preclinical and clinical studies of targeted alpha therapy for cancer. Both Ac225 (four alpha decays) and Bi213 (one alpha decay) are being used to label targeting vectors to form the alpha immunoconjugate for cancer therapy. This paper considers the radiobiological and economic aspects of Ac225 vs Bi213 as the preferred radioisotope for preclinical and clinical TAT. The in vitro and in vivo evidence and the role of DNA repair processes is examined. The maximum tolerance dose and therapeutic gain are endpoints for comparison. Ac225 has the higher therapeutic gain, when normalised to equal alpha production. However, the slow repair of double strand breaks reduces this advantage. Comparisons are made for the specific energy deposition in targeted and non-targeted cells, for endothelial cells by direct or indirect targeting, the need for sparing agents to save critical organs and cost considerations for preclinical and clinical trials and clinical use. Overall, Ac225 is found to have the better or equal performance to Bi213 at a much lower cost.

Antiepileptic drugs prevent seizures in hyperbaric oxygen: A novel model of epileptiform activity.

Breathing oxygen at sufficiently elevated pressures can trigger epileptiform seizures. Therefore, we tested the hypothesis that pre-treatment with FDA-approved antiepileptic drugs could prevent seizure onset in hyperoxia at 5 atmospheres absolute. We selected drugs from two putative functional categories, Na+-channel antagonists and GABA enhancers, each administered intraperitoneally at four doses in separate groups of C57BL/6 mice. The drugs varied in efficacy at the doses used. Of the five tested Na+-channel antagonists, carbamazepine and lamotrigine more than tripled seizure latency compared to values seen in vehicle controls. Primidone, zonisamide and oxcarbazepine were less effective. Of the four GABA reuptake inhibitors, tiagabine and vigabatrin also increased seizure latency by more than three times control values; valproic acid was less effective, and the GABA synthesis promoter gabapentin was intermediate in effectiveness. We infer that Na+-channel function and GABA neurotransmission may be critical targets in the pathophysiology of CNS O2 toxicity. Because these essential components of neuronal excitation and inhibition are also implicated in the pathogenesis of other seizure disorders, including generalized epilepsy, we propose that, at some level, common pathways are involved in these pathologies, although the initiating insults differ. Furthermore, hyperoxic exposures are not known to cause the spontaneously-recurring seizures that characterize true clinical epilepsy. Nonetheless, experimental studies of hyperbaric oxygen toxicity could provide new insights into molecular mechanisms of seizure disorders of various etiologies. In addition, the neuropathology of hyperbaric oxygen is particularly relevant to the hypothesis held by some investigators that oxidative stress is an etiological factor in clinical epilepsies.

Preclinical studies of bismuth-213 labeled plasminogen activator inhibitor type 2 (PAI2) in a prostate cancer nude mouse xenograft model.

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Cytotoxicity of PAI2, C595 and Herceptin vectors labeled with the alpha-emitting radioisotope Bismuth-213 for ovarian cancer cell monolayers and clusters.

The vectors PAI2, C595 and Herceptin target the membrane-bound uPA, MUC1 and HER2 antigens expressed by cancer cells, respectively. The expression of these receptors was tested in the ovarian cancer cell line OVCAR-3; MUC-1 was strongly expressed (3+), uPA moderately expressed (2+), but HER2 was negative (-). The alpha-emitting radionuclide Bismuth-213 was chelated with these targeting vectors to form alpha conjugates (ACs), the cytotoxicity of which were tested with OVCAR-3 cells. The PAI2 and C595 ACs are highly cytotoxic to the ovarian monolayer cancer cells and cell clusters in a concentration-dependent fashion and cause morphological changes of treated cancer cells, inducing apoptosis. These ACs are potential candidates for the control of ovarian cancer at the minimum residual disease (MRD) stage.

Internal high linear energy transfer (LET) targeted radiotherapy for cancer.

High linear energy transfer (LET) radiation for internal targeted therapy has been a long time coming on to the medical therapy scene. While fundamental principles were established many decades ago, the clinical implementation has been slow. Localized neutron capture therapy, and more recently systemic targeted alpha therapy, are at the clinical trial stage. What are the attributes of these therapies that have led a band of scientists and clinicians to dedicate so much of their careers? High LET means high energy density, causing double strand breaks in DNA, and short-range radiation, sparing adjacent normal tissues. This targeted approach complements conventional radiotherapy and chemotherapy. Such therapies fail on several fronts. Foremost is the complete lack of progress for the control of primary GBM, the holy grail for cancer therapies. Next is the inability to regress metastatic cancer on a systemic basis. This has been the task of chemotherapy, but palliation is the major application. Finally, there is the inability to inhibit the development of lethal metastatic cancer after successful treatment of the primary cancer. This review charts, from an Australian perspective, the developing role of local and systemic high LET, internal radiation therapy.

Cerebral blood flow and brain oxygenation in rats breathing oxygen under pressure.

Hyperbaric oxygen (HBO(2)) increases oxygen tension (PO(2)) in blood but reduces blood flow by means of O(2)-induced vasoconstriction. Here we report the first quantitative evaluation of these opposing effects on tissue PO(2) in brain, using anesthetized rats exposed to HBO(2) at 2 to 6 atmospheres absolute (ATA). We assessed the contribution of regional cerebral blood flow (rCBF) to brain PO(2) as inspired PO(2) (PiO(2)) exceeds 1 ATA. We measured rCBF and local PO(2) simultaneously in striatum using collocated platinum electrodes. Cerebral blood flow was computed from H(2) clearance curves in vivo and PO(2) from electrodes calibrated in vitro, before and after insertion. Arterial PCO(2) was controlled, and body temperature, blood pressure, and EEG were monitored. Scatter plots of rCBF versus PO(2) were nonlinear (R(2)=0.75) for rats breathing room air but nearly linear (R(2)=0.88-0.91) for O(2) at 2 to 6 ATA. The contribution of rCBF to brain PO(2) was estimated at constant inspired PO(2), by increasing rCBF with acetazolamide (AZA) or decreasing it with N-nitro-L-arginine methyl ester (L-NAME). At basal rCBF (78 mL/100 g min), local PO(2) increased 7- to 33-fold at 2 to 6 ATA, compared with room air. A doubling of rCBF increased striatal PO(2) not quite two-fold in rats breathing room air but 13- to 64-fold in those breathing HBO(2) at 2 to 6 ATA. These findings support our hypothesis that HBO(2) increases PO(2) in brain in direct proportion to rCBF.

In vivo studies of pharmacokinetics and efficacy of Bismuth-213 labeled antimelanoma monoclonal antibody 9.2.27.

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.

Intralesional targeted alpha therapy for metastatic melanoma.

UNLABELLED: This paper reports the development and application of intralesional targeted alpha therapy (TAT) for melanoma, being the first part of a program to establish a new systemic therapy. RATIONALE: Labelling the benign targeting vector 9.2.27 with 213Bi forms the alpha-immunoconjugate (AIC), which is highly cytotoxic to targeted melanoma cells. OBJECTIVE: To investigate the safety and efficacy of intralesional AIC in patients with metastatic skin melanoma. FINDINGS: 16 melanoma patients were recruited. All the patients were positive to the monoclonal antibody 9.2.27. AIC doses from 50 to 450 mCi injected into lesions of different sizes resulted in massive cell death, as observed by the presence of tumour debris. The AIC was very effective in delivering a high dose to the tumour while sparing other tissues. There were no significant changes in blood proteins and electrolytes. There was no evidence of a human-antimouse-antibody reaction. Evidence of significant decline in serum marker melanoma-inhibitory-activity protein (MIA) at 2 weeks post-TAT was observed. CONCLUSIONS: Intralesional TAT for melanoma was found to be quite safe up to 450 mCi, and efficacious at a dose of 200 mCi. MIA, apoptosis and ki67 proliferation marker tests all indicated that TAT is a promising therapy for the control of inoperable secondary melanoma or primary ocular melanoma.

In vivo and in vitro inhibition of pancreatic cancer growth by targeted alpha therapy using 213Bi-CHX.A"-C595.

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.