Immunomedics Develops New Bispecific Antibodies That Exhibit Potent Anti-Lymphoma Activity

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| Source: Immunomedics, Inc.

-- Two Preclinical Studies Presented at the 54th Annual Meeting of the American Society of Hematology (ASH) --

-- Preclinical Study of Milatuzumab in Graft-Versus-Host Disease also Presented --

ATLANTA, Dec. 12, 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 announced that two new classes of bispecific antibodies were created as the DOCK-AND-LOCK™ (DNL™) complexes using the Company's patented platform technology that enables site-specific conjugation of two self-assembling modules. These bispecific antibodies exhibited potent cell killing activity against lymphoma cell lines in vitro.

Antibodies are large Y-shaped proteins, comprising two identical target-binding arms, each referred to as the fragment, antigen binding (Fab) region, and a tail known as the fragment crystalline (Fc) region. When an antibody is bound to its target via the two Fab arms, interaction of the Fc region with the Fc receptors on blood cells may result in eliminating the tagged target. Other mechanisms of target killing can be achieved with engineered antibodies of various designs, often with enhanced potency compared to the parental antibodies.

Redirecting T cells with a Novel Class of DNLTM Complexes

One advance that the Company presented at the 2012 ASH Annual Meeting is a novel T-cell redirecting agent made as a DNLTM complex by tethering a pair of Fabs that recognize CD19 on B cells to a single-chain variable fragment (scFv) that binds to CD3 on T cells. Referred to as (19)-3s, the prototype potently directs T cells to destroy CD19-expressing B cells by linking them together. Specifically, (19)-3s was shown to bind to T cells and non-Hodgkin lymphoma (NHL) cells simultaneously, and induce T-cell-mediated killing of NHL cells at less than 1 picomolar (pM) concentrations in an ex vivo setting, with maximal activity at 10 pM.

"We expect (19)-3s to have an elimination rate longer than that of blinatumomab, which is made of two scFvs to co-ligate CD19 and CD3," commented Cynthia L. Sullivan, President and Chief Executive Officer. "We are currently evaluating the in vivo activity of (19)-3s, as a prototype, to determine if this novel bsAb offers additional advantages," Ms. Sullivan added. "The slower clearance and the fact that (19)-3s has two binding arms might allow for less frequent dosing, and possibly subcutaneous administration. The modular nature of DNL will allow the rapid production of a large number of related conjugates for redirected T-cell killing of various malignancies, without the need for additional recombinant engineering and protein production," concluded Ms. Sullivan.

A New Class of Hexavalent Bispecific Antibodies and Immunocytokines

Another advance the Company presented at the 2012 ASH Annual Meeting is an improved design of IgG-based DNLTM complexes that have the AD2-sequence fused at the end of the light chain (the CK-format) instead of at the end of the heavy chain (the CH3-format), resulting in superior pharmacokinetic profiles, increased bioavailability in mice and rabbits, and a higher effector functions, as shown with a bsHexAb, referred to as CK-22-(20)-(20), generated by conjugating IgG-AD2 of epratuzumab (anti-CD22) to Fab-DDD2 of veltuzumab (anti-CD20), or with an immunocytokine, referred to as Ck-20-2b, generated by conjugating IgG-AD2 of veltuzumab to DDD2-IFNα2b. Importantly, both CK-22-(20)-(20) and Ck-20-2b demonstrated more potent anti-tumor activity than their CH3-format counterparts in an animal model of human NHL. For example, with a single low dose of 0.25 µg, Ck-20-2b cured 7 of 8 animals, with a median survival time (MST) greater than 189 days, which was statistically significant (P=0.035) when compared with CH3-20-2b (3 of 8 survivors; MST of 134.5 days). With Ck-22-(20)-(20), two injections of 1 mg produced a MST greater than 130 days with 100% survival, which was superior to MST of 71 days with 10% survival obtained with the CH3-counterpart (P<0.001). Furthermore, a low dose treatment of 10 µg x 2 resulted in a MST of 91 days with 2 animals surviving as compared to 50.5 days with no survivors (P=0.001) for the Fc-based construct.

"These new constructs demonstrate further enhancement of two different classes of fusion proteins with already potent anti-lymphoma efficacy," remarked Ms. Sullivan. "The strategy of designing antibody fusion proteins at the C-terminus of the light chain, instead of at the commonly used Fc, may improve the in vivo efficacy of most immunoconjugates in general, and the DNL conjugates in particular," added Ms. Sullivan.

Prevention of Acute Graft-Versus-Host Disease in Human/Mouse Xenogeneic SCID Mouse Model by Humanized Anti-CD74 Monoclonal Antibody, Milatuzumab

Finally, the Company presented results from a preclinical study that shows milatuzumab, the Company's proprietary humanized anti-CD74 antibody, effectively prevents the onset and manifestations of acute graft-versus-host disease in a humanized-mouse model. (For more information on this study, please refer to the Company's earlier press release at www.immunomedics.com/pdfs/news/2012/pr10092012.pdf).

Encouraged by results from this study, the Company plans to respond to investigators who have requested to study milatuzumab for this indication by conducting an initial small clinical trial to evaluate the safety and efficacy of milatuzumab for the control of this challenging disease.

This work was supported in part by Award Number R41AI093082 from the National Institute of Allergy and Infectious Diseases.

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™) method 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 209 active patents 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 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.

Dr. Chau Cheng
Senior Director, Investor Relations & Grant Management
(973) 605-8200, extension 123