Pretargeted radioimmunotherapy of pancreatic cancer xenografts: TF10- 90Y-IMP-288 alone and combined with gemcitabine

Abstract

Pancreatic cancer is a silent disease that most commonly presents in an already metastatic form. Current treatment options provide little survival benefit. Radiolabeled PAM4 IgG, a monoclonal antibody that recognizes a unique epitope associated with a mucin found almost exclusively in pancreatic cancer, has shown encouraging therapeutic effects in animal models and in early clinical testing (90Y-humanized PAM4 IgG, 90Y-clivatuzumab tetraxetan). The studies reported herein examine a new pretargeting procedure for delivering therapeutic radionuclides. Methods: We prepared a humanized, recombinant tri-Fab bispecific monoclonal antibody (bsmAb) (TF10) using specificity for targeting pancreatic cancer of PAM4 and another Fab binding to a hapten (histamine-succinyl-glycine [HSG]) and tested this in a pretargeting setting with a 90Y-1,4,7,10-tetraazacyclododecane-N,N′, N″,N‴-tetraacetic acid-di-HSGpeptide (pretargeted radioimmunotherapy [PT-RAIT]). Nude mice bearing established Capan-1 human pancreatic cancer xenografts were given TF10 and then received the 90Y peptide as a single bolus dose 19 h later, or the therapy cycle was fractionated weekly. Other studies examined different combinations with gemcitabine. Results: PT-RAIT of 18.5 MBq (∼50% of its maximum tolerated dose [MTD]) was as effective as the MTD of 90Y-PAM4 IgG (5.55 MBq). Three monthly doses of 9.25 MBq of PT-RAIT combined with a monthly cycle of gemcitabine (3 weekly, 6-mg doses) significantly enhanced survival, compared with PT-RAIT alone. Adding gemcitabine as a radiosensitizer to 9.25 MBq of PT-RAIT enhanced objective responses. Weekly fractionation of the PT-RAIT, as compared with a single treatment, improved responses. Conclusion: PAM4-based PT-RAIT with 90Y hapten peptide is an effective treatment for pancreatic cancer, with less toxicity than 90Y-PAM4 IgG, in this model. Combinations with gemcitabine and dose fractionation of the PT-RAIT enhanced therapeutic responses. Copyright © 2009 by the Society of Nuclear Medicine, Inc.