Targeted Antisense Radiotherapy And Dose Fractionation Using A Lu-177-Labeled Anti-Bcl-2 Peptide Nucleic Acid-Peptide Conjugate

Introduction: The overall goal of these studies was to test the hypothesis that simultaneous down-regulation of a tumor survival gene and delivery of internally emitted cytotoxic radiation will be more effective than either treatment modality alone. The objectives were to evaluate the therapeutic efficacy of a Lu-177-labeled anti-bcl-2-PNA-Tyr(3)-octreotate antisense conjugate in a mouse model bearing human non-Hodgkin's lymphoma (NHL) tumor xenografts and to optimize targeted antisense radiotherapy by dose fractionation.Methods: In the initial therapy studies, tumor-bearing mice were given saline, nonradioactive DOTA-anti-bc1-2PNA-Tyr(3)-octreotate, Lu-177-DOTA-Tyr(3)-octreotate, Lu-177-DOTA-PNA-peptide alone, or 177Lu-DOTA-PNA-peptide followed by a chase dose of nonradioactive PNA-peptide. The MTD of Lu-177-DOTA-anti-bc1-2-PNA-Tyr(3)octreotate was then determined. Subsequently single dose MTD and four weekly fractionated doses were directly compared, followed by histopathologic evaluation.Results: Antisense radiotherapy using 4.44 MBq of the Lu-177-DOTA-PNA-peptide followed by nonradioactive PNA-peptide was significantly more effective than other low dose treatment regimens. A dose of 18.5 MBq of 177Lu-DOTA-PNA-peptide was determined to be the approximate maximum tolerated dose (MTD). The median times to progression to a 1 cm(3) tumor volume were 32 and 49 days for single dose MTD and fractionated dose (4 x 4.63 MBq) groups, respectively. Histopathology revealed metastases in the single dose groups, but not in the dose fractionation group.Conclusions: Targeted antisense radiotherapy using 177Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate and DOTA-PNA-peptide conjugate effectively inhibited tumor progression in a mouse model of NHL Furthermore, a dose fractionation regimen had a significant advantage over a single high dose, in terms of tumor growth inhibition and prevention of metastasis.Advances in knowledge and implications for patient care: Down-regulating bcl-2, an anti-apoptotic protooncogene, is a mechanism to reverse chemotherapy resistance or failure in humans with NHL. We have developed a 177Lu-DOTA-anti-bcl-2-PNA-Tyr3-octreotate conjugate for targeted antisense radiotherapy, in which down-regulation of bcl-2 and delivery of cytotoxic radiation occur simultaneously. Our previous studies have shown highly specific inhibition of bc1-2 protein, additive in vitro cytotoxic effects on human lymphoma cells, and favorable biodistribution and dosimetric properties. Lutetium-177 targeted antisense radiotherapy demonstrates a significant advantage over conventional 177Lu-peptide receptor radionuclide therapy in a mouse model of NHL Our preclinical studies identified an effective combination of antisense and radionuclide therapy, with the goal of future clinical trials in patients. Published by Elsevier Inc.