Novel Dock-and-Lock (DNL) Agents Presented at the 2012 Annual Meeting of the American Association for Cancer Research (AACR)
The Impact of Linker's Stability on Efficacy of Antibody-SN-38 Conjugates and Studies on Mechanisms of Action of Epratuzumab Also Presented
CHICAGO, April 2, 2012 (GLOBE NEWSWIRE) -- Immunomedics, Inc. (Nasdaq: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 reported the development of two bispecific, hexavalent antibodies for treating breast, pancreatic and other solid cancers.
Novel Dock-and-Lock (DNL) Agents
The two bispecific antibodies, 1R-(E1)-(E1) and 1R-(15)-(15), were generated using the Company's patented DNL conjugation technology. Both agents comprise intact hR1, a proprietary humanized antibody targeting the type I insulin-like growth factor receptor (IGF-1R). 1R-(E1)-(E1) was created by attaching four antibody fragments of hRS7, a humanized antibody that recognizes the trophoblast cell-surface marker (TROP-2), to hR1, while 1R-(15)-(15) utilized fragments from hMN-15, the Company's proprietary antibody against the carcinoembryonic antigen cell adhesion molecule 6 (CEACAM6).
In diverse epithelial cancers, the expression of IGF-1R, TROP-2 and CEACAM6 are elevated, making them attractive targets for antibody-based cancer therapy. The use of two distinct monoclonal antibodies in combination to improve efficacy has produced promising results in some early clinical studies. However, combination therapy may be accomplished without increased toxicity with a single bispecific antibody.
The objective of this preclinical study was to explore the potential of 1R-(E1)-(E1) and 1R-(15)-(15) for treating breast and pancreatic cancers by evaluating their effects on three breast cancer cell lines of varying invasive activities and two pancreatic cancer cell lines. All five cell lines were found to express IGF-1R, TROP-2, and CEACAM6 at various levels.
When tested at 100 mg/mL, 1R-(E1)-(E1) reduced the invasion of a breast cancer cell line to less than 10% of the untreated control, whereas under the same conditions, a more invasive cell line appeared to be resistant and the parental antibodies showed no effect. 1R-(15)-(15) potently reduced the invasion of a pancreatic cancer cell line at the same concentration, but had little effect on breast cancer cells. Additionally, at 10 mg/mL, the anti-CEACAM6/anti-IGF-1R bispecific antibody reduced the invasion of pancreatic cancer cells to less than 10% of untreated cells.
The ability of the DNL-derived bispecific antibody to inhibit anchorage-independent growth was demonstrated, with a statistically significant difference when compared with samples treated with parental antibodies at the same concentrations. Furthermore, cells treated with 1R-(E1)-(E1) produced fewer and much smaller cell colonies, the largest size of which was less than 1/10 of the untreated cells.
"We believe these promising results, as exemplified by 1R-(E1)-(E1) and 1R-(15)-(15), attest to the potential of bispecific hexavalent antibodies for targeted therapy of solid cancers," commented Cynthia L. Sullivan, President and Chief Executive Officer.
Impact of Linker's Stability on Efficacy of Antibody-SN-38 Conjugates
The Company also presented a study examining the impact of linker chemistry on the stability and efficacy of antibody-SN-38 conjugates, using a variety of antibodies that differ in their internalization properties.
SN-38 is the active metabolite of irinotecan, an FDA-approved drug for metastatic colorectal cancer treatment. To increase the amount reaching the tumors and minimize the damage to normal tissues and organs, the Company has previously conjugated SN-38 to monoclonal antibodies for improved selective therapy of cancer. The antibody-drug conjugate (ADC), labetuzumab-SN-38, is currently in a Phase I trial for therapy of advanced colorectal cancer, whereas hRS7 (anti-TROP-2)-SN-38, will enter clinical testing for the potential treatment of certain solid cancers later this year.
The linker that connects SN-38 to the antibody in the two ADCs is CL2A. (Please refer to the Company's press release at www.immunomedics.com/pdfs/news/2010/PR04192010a.pdf for more information). In the current study, a new linker, CL2E, was evaluated and compared with CL2A. CL2E is more stable and only releases free SN-38 inside the tumor cell.
In cancer cell lines and animal models of human cancers, ADCs with the more inert CL2E linker were significantly less efficacious than those employing CL2A. These observations were independent of the internalization rates of carrier antibodies, indicating that purely cellular mechanisms of drug release were inadequate for delivering therapeutic levels of SN-38 to tumor cells. A more labile linker in CL2A provides a better release mechanism extracellularly as well as intracellularly, thereby increasing the bioavailability of the drug. This is the linker being used in the ADC being tested clinically.
Studies on Mechanisms of Action of Epratuzumab
At the same cancer research meeting, the in vitro effects of immobilized epratuzumab on malignant B cells were also presented.
Epratuzumab is a humanized anti-CD22 antibody currently in advanced clinical trials in non-Hodgkin lymphoma (NHL) and systemic lupus erythematosus (SLE) patients. As a single agent, epratuzumab is well tolerated and depletes 30 to 50% of circulating B cells in patients with NHL and SLE. However, the mechanism of action of epratuzumab is still largely unknown.
In vitro, epratuzumab shows moderate antibody-dependent cell-mediated cytotoxicity, but no detectable complement-dependent toxicity, and displays cytotoxicity to CD22-expressing human lymphoma cancer cells only when immobilized onto plastic plates or combined with both an anti-immunoglobulin M antibody and a crosslinking secondary antibody. In this preclinical study, the molecular mechanism underlying the cytotoxic effects of immobilized epratuzumab was elucidated.
Using flow cytometry, immunofluorescence microscopy, and various cell-based assays, immobilized epratuzumab was found to induce many of the intracellular changes that were also observed upon crosslinking of anti-immunoglobulin M antibody, which appears to be crucial for cell death. The process also involved mitochondria by changing the mitochondrial membrane potential and the generation of reactive oxygen species. These findings indicate, for the first time, that immobilized epratuzumab and anti-immunoglobulin M antibody behave similarly in killing malignant B cells by affecting B-cell receptor-mediated signaling.
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 190 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 www.immunomedics.com. The information on our website does not, however, form a part of this press release.
This release, in addition to historical information, may contain forward-looking statements made pursuant to the Private Securities Litigation Reform Act of 1995. Such statements, including statements regarding clinical trials, out-licensing arrangements (including the timing and amount of contingent payments), forecasts of future operating results, potential collaborations, and capital raising activities, involve significant risks and uncertainties and actual results could differ materially from those expressed or implied herein. Factors that could cause such differences include, but are not limited to, risks associated with any cash payment that the Company might receive in connection with a sublicense involving a third party and UCB, which is not within the Company's control, new product development (including clinical trials outcome and regulatory requirements/actions), our dependence on our licensing partners for the further development of epratuzumab for autoimmune indications and veltuzumab for non-cancer indications, competitive risks to marketed products and availability of required financing and other sources of funds on acceptable terms, if at all, as well as the risks discussed in the Company's filings with the Securities and Exchange Commission. The Company is not under any obligation, and the Company expressly disclaims any obligation, to update or alter any forward-looking statements, whether as a result of new information, future events or otherwise.
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