Abstract LB-149: Discovery and characterization of fully human monoclonal antibodies that neutralize multiple TGFβ isoforms
Authors: Mirza Amer , Bedinger Daniel , Lao Llewelyn , Khan Shireen , Takeuchi Toshihiko 
Published: May 2015

Abstract
TGFβ levels are elevated in, and can drive the progression of, numerous disease states including advanced metastatic cancer and fibrosis. The exact role of each TGFβ isoform in disease is an area of active research. To help elucidate the therapeutic importance and test the value of inhibiting multiple TGFβ isoforms, we generated antibodies with differing specificities to each of the three TGFβ isoforms. Antibodies that functionally neutralized TGFβ1/2, TGFβ2/3, and TGFβ1/2/3 were characterized in vitro, and in vivo. Two surface plasmon resonance (SPR)-based kinetic methods were used to compare the binding affinities and rate constants of the three antibodies. All three antibodies had single digit nanomolar affinities (KD) or better to the TGFβ isoforms, ranging from 1.7pM to 1400pM. The antibodies were characterized in cell based assays for their ability to effect signaling, cell proliferation, and stimulated cytokine release, and EC50 values for each were obtained. Potency in each of the cell assays directly correlated with the affinity of the antibody for the TGFβ isoform used to elicit the effect.These antibodies were then used to elucidate the role of each of the TGFβ isoforms in more complex systems in vivo. Detroit 562, a human metastatic pharyngeal carcinoma derived cell line, was shown to express all three TGFβ isoforms in vitro and in vivo. 5x106 cells were implanted subcutaneously on the flanks of athymic (nu/nu) mice. Tumors were established to ∼200 mm3, and treatment initiated at day 7 post implant. Groups were treated with 10mg/kg IP twice weekly. At Day 28, blocking all three TGFβ isoforms with a pan reactive TGFβ1/2/3 antibody significantly reduced mean tumor volume (219 ± 38 mm3) compared to a control IgG (1022 ± 241mm3) (n= 12 mice per group). Additionally, dose-ranging studies were performed (1, 3, or 10 mg/kg) to determine the relative potency of the antibodies. We found that tumors in mice treated with either the anti-TGFβ1/2 or the pan anti-TGFβ1/2/3 inhibitor antibody (3mg/kg twice weekly) showed notable and significant (p&lt;0.005) differences in mean tumor volumes and mean tumor weights at day 30 compared to IgG control antibody, with average tumor volume reductions of 63%, and 64% respectively. In this model, inhibition of tumor growth by the anti-TGFβ1/2 antibody was indistinguishable from inhibition by the anti-TGFβ1/2/3 antibody, suggesting that TGFβ3 may not play a role in tumor progression. Conversely, in this model, inhibition of TGFβ2/3 alone was insufficient to significantly impact tumor growth. These data suggest that effective neutralization of TGFβ1/2 function may be sufficient to inhibit tumor growth and that neutralizing all three TGFβ isoforms is not required. Specific and targeted inhibition of select TGFβ isoforms offers a more focused therapeutic approach which has potential for improved safety. Experiments are underway to elucidate the role of the various TGFβ isoforms in key aspects of tumor biology.
Citation Format: Amer Mirza, Daniel Bedinger, Llewelyn Lao, Shireen Khan, Toshihiko Takeuchi. Discovery and characterization of fully human monoclonal antibodies that neutralize multiple TGFβ isoforms. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-149. doi:10.1158/1538-7445.AM2014-LB-149