The combination of topotecan and [(131)I]MIBG compared with either treatment alone gave rise to greater than additive DNA damage, clonogenic cell kill, and tumor growth delay. These effects were dependent on the scheduling of the two agents.

These results indicate that the telomerase promoters have the capacity to drive the expression of the NAT. The potency of [(211)At]MABG is approximately three orders of magnitude greater than that of [(131)I]MIBG. Spheroids composed of only 5% of cells expressing NAT under the control of the RSV or hTERT promoter were sterilised by radiopharmaceutical treatment. This observation is indicative of bystander cell-kill.

TMS provide a useful model for assessment of the effectiveness of targeted radiotherapy in combination with gene therapy when less than 100% of the target cell population is expressing the NAT transgene. Further, this novel model offers the unique opportunity to investigate radiation-induced bystander effects and their contribution to cell cytotoxicity in radiotherapy and other gene therapy applications.

No abstract

Targeted radiotherapy using radiolabelled meta-iodobenzylguanidine (MIBG) is a promising treatment option for bladder cancer, restricting the effects of radiotherapy to malignant cells thereby increasing efficacy and decreasing morbidity of radiotherapy. We investigated the efficacy of a combined gene therapy and targeted radiotherapy approach for bladder cancer using radiolabelled MIBG. The effectiveness of alternative radiohalogens and alternative preparations of radiolabelled MIBG for this therapeutic strategy were compared. Bladder cancer cells, EJ138, were transfected with a gene encoding the noradrenaline transporter (NAT) under the control of a tumour specific telomerase promoter, enabling them to actively take up radiolabelled MIBG. This resulted in tumour-specific cell kill. Uptake and retention of radioactivity in cells transfected with the NAT gene were compared with that obtained in cells transfected with the sodium iodide symporter (NIS) gene. Substantially greater uptake and longer retention of radioactivity in NAT-transfected cells was observed. Carrier-added (c.a.) [131I]MIBG, no-carrier added (n.c.a.) [131I]MIBG, and [211At]-labelled benzylguanidine (i.e. [211At] meta-astatobenzylguanidine (MABG)) were compared with respect to efficiency of induction of cell kill. N.c.a[(131)I]MIBG was more cytotoxic than c.a.[131I]MIBG. However, the alpha-emitter [211At]MABG was, by three orders of magnitude, more effective in causing tumour cell kill than the beta-emitter [131I]MIBG. We conclude that NAT gene transfer combined with the administration of n.c.a.[131I]MIBG or [211At]MABG, is a promising novel treatment approach for bladder cancer therapy.

For gene therapy to be efficacious in the treatment of cancer, therapeutic transgenes must be limited in their expression to tumor cells and must be expressed at sufficiently high transcriptional levels. Moreover, the inadequacy of gene delivery must be overcome by induction of toxicity to neighboring nontargeted cells. Combining targeted radionuclide therapy with gene therapy using human telomerase promoters has shown promise in these respects, and the efficacy of this scheme has been assessed in vitro using transfectant mosaic tumor spheroids. To enable the evaluation of targeted radiotherapy combined with gene transfer in vivo, we have developed a transfectant mosaic xenograft (TMX) model. Methods: Human telomerase promoters were used to drive expression of the noradrenaline transporter (NAT) transgene in 2 human cell lines (UVW and EJ138). Promoter activity was assessed in xenografts in nude mice by determination of the uptake of the radiopharmaceutical 131 I-metaiodobenzylguanidine ( 131 I-MIBG) and by measurement of tumor growth. The efficacy of 131 I-MIBG treatment was also assessed in TMXs to determine the delay in growth of tumors composed of various proportions of NAT-expressing cells-a likely clinical scenario after gene delivery in vivo. Results: In terms of induction of the capacity for active uptake of 131 I-MIBG and the resultant inhibition of tumor growth in vivo, both telomerase promoters (hTR and hTERT) were similar in potency to the CMV (cytomegalovirus) promoter as controlling elements for the expression of the NAT transgene. In TMXs derived from UVW and EJ138 cells, 131 I-MIBG uptake was proportional to NAT gene expression (r s 5 0.910, P , 0.001 for UVW; r s 5 0.971, P , 0.001 for EJ138). Inhibition of the growth of these tumors correlated with the fraction of NATtransfected cells (r s 5 0.910, P , 0.001 for UVW; r s 5 0.971, P , 0.001 for EJ138), and substantial tumor growth delay was observed when 5% of the xenograft was composed of NATpositive cells. Conclusion: TMXs constitute a suitable model to measure the efficacy of cancer gene therapy strategies when ,100% of the tumor mass can be targeted to express the therapeutic transgene.

No abstract

No abstract