Pretargeted Radioimmunotherapy and Pretargeted ImmunoPET Imaging of Prostate Cancer Also Presented

MIAMI BEACH, FL, USA I June 13, 2012 I Immunomedics, Inc. (IMMU), a biopharmaceutical company primarily focused on the development of monoclonal antibody-based products for the targeted treatment of cancer, autoimmune and other serious diseases, today announced that three studies involving two bispecific antibodies created by the Company’s patented protein conjugation method, Dock-and-Lock (DNL), were presented at the 2012 Annual Meeting of the Society of Nuclear Medicine (SNM). All three presentations were pretargeting studies conducted by the Company’s collaborators at the Department of Nuclear Medicine, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.

Phase I Clinical Study of Pretargeted Radioimmunotherapy in Patients with Colorectal Cancer: An Update

Pretargeted radioimmunotherapy (PRIT) was investigated in this Phase I trial in patients with advanced colorectal cancer (CRC) using TF2, a DNL-bispecific antibody that binds to the carcinoembryonic antigen (CEA or CEACAM5), and the peptide IMP288. The safety, dosimetry and tumor targeting, as well as the therapeutic potential of this pretargeting system were assessed.

Four cohorts of 5 patients were enrolled in this study to receive an imaging cycle with TF2 and indium-111-labeled IMP288, followed by PRIT with TF2 and IMP288 labeled with the therapeutic radioisotope lutetium-177 (177Lu). Two dose levels of TF2 (75 and 150 mg) and IMP288 (25 and 100 microgram), as well as the effect of the interval between TF2 and IMP288 administration were evaluated.

Rapid tumor localization of radiolabeled IMP288 in CRC patients was seen within 1 hour post-injection of the peptide, with excellent tumor-to-normal tissue ratios of greater than 20 at 24 hours. Because TF2 was found to quickly clear from the blood, a short interval between TF2 and IMP288 is preferred. At the time of reporting, no objective therapeutic responses were observed with a single therapy.

High 177Lu-IMP288 doses of up to 7.4 GBq were reported to be safe in CRC patients, with mild hematologic toxicity in most patients, including two having grade 3-4 platelet toxicity, and low absorbed doses of less than 0.5 Gy in the bone marrow.

"These clinical observations are consistent with our preclinical findings that pretargeting, as compared to conventional radioimmunotherapy, has the advantage of delivering higher levels of radioactivity to tumor sites while keeping the toxic side-effects of the treatment to a minimum," remarked Cynthia L. Sullivan, president and Chief Executive Officer of Immunomedics. "The doses delivered, however, are still too low in this early trial to achieve tumor shrinkage," she added.

Pretargeted Radioimmunotherapy of Prostate Cancer with TF12

The other DNL-created bispecific antibody that the Dutch medical researcher team presented at the Annual Meeting is TF12, which has two binding arms targeting the TROP-2 antigen. TROP-2, also known as epithelial glycoprotein-1, EGP-1, is a cancer marker that is expressed at high levels on most human solid cancers, including prostate cancer and its metastases, but with only limited expression in normal human tissues.

In this preclinical study, the efficacy of PRIT with TF12 and 177Lu-IMP288 was studied in a mouse model of human prostate cancer. The therapeutic potential of one or two cycles of PRIT with TF12 and 177Lu-IMP288 was compared to that of conventional RIT with 177Lu-hRS7, the Company’s proprietary humanized anti-TROP-2 antibody, at the maximum tolerated dose.

Treatment with one cycle of PRIT improved median survival from 82 days to 121 days, which could be further extended to more than 160 days when animals were treated with an additional cycle of the pretargeted therapy. Moreover, after 150 days, 70% of the mice treated with two cycles of PRIT were still alive, while none in the control groups survived. These results compare favorably with 177Lu-hRS7, but mice treated with PRIT showed much lower hematologic toxicity. In view of the limited toxicity, additional treatment cycles of PRIT or higher doses of 177Lu-IMP288 are possible.

Pretargeted ImmunoPET Imaging of Prostate Cancer with TF12

TF12 was also the subject of an imaging study presented earlier at this year’s SNM Annual Meeting. The objective of this preclinical study was to evaluate the potential of a pretargeting system based on TF12 and in combination with a radiolabeled peptide for the PET imaging of advanced prostate cancer, using 18F-FDG as a reference.

In an animal model of human prostate cancer, the pretargeting system revealed high uptake in the tumors and rapid blood clearance, producing an excellent tumor-to-blood ratio of 17.4 as early as 1 hour after injection of the radiolabeled peptide. As a result, the tumor can be easily visualized in the PET images with minimal activity in the kidneys. In contrast, tumor uptake of 18F-FDG was significantly lower, with a much lower tumor-to-blood ratio of 3.0 and a threefold higher kidney uptake.

"These encouraging results suggest that pretargeted immunoPET with TF12 could be a rapid and specific imaging method for prostate cancer, showing even better results in this model than 18F-FDG, a conventional PET imaging agent," remarked Cynthia Sullivan.

About Immunomedics

Immunomedics is a New Jersey-based biopharmaceutical company primarily focused on the development of monoclonal antibody-based products for the targeted treatment of cancer, autoimmune and other serious diseases. We have developed a number of advanced proprietary technologies that allow us to create humanized antibodies that can be used either alone in unlabeled or "naked" form, or conjugated with radioactive isotopes, chemotherapeutics, cytokines or toxins, in each case to create highly targeted agents. Using these technologies, we have built a pipeline of therapeutic product candidates that utilize several different mechanisms of action. We also have a majority ownership in IBC Pharmaceuticals, Inc., which is developing a novel Dock-and-Lock (DNL) methodology with us for making fusion proteins and multifunctional antibodies, and a new method of delivering imaging and therapeutic agents selectively to disease, especially different solid cancers (colorectal, lung, pancreas, etc.), by proprietary, antibody-based, pretargeting methods. We believe that our portfolio of intellectual property, which includes approximately 199 patents issued in the United States and more than 400 foreign patents, protects our product candidates and technologies. For additional information on us, please visit our website at The information on our website does not, however, form a part of this press release.

SOURCE: Immunomedics