Superior Efficacy of the Novel Type II, Glycoengineered CD20 Antibody GA101vs. the Type I CD20 Antibodies Rituximab and Ofatumumab

Abstract 3925

GA101 is Type II, glycoengineered CD20 monoclonal antibody currently in PhII/III clinical trials. We have previously shown that GA101 mediates superior in vitro and in vivo activity compared to the Type I CD20 antibody rituximab. By epitope mapping and crystallography we have shown that GA101 recognizes CD20 in a unique way that is different from Type I CD20 antibodies and have proposed that this may be the basis for the Type II character of GA101.

Here we compare for the first time GA101 with rituximab, the standard of care in various clinical settings in NHL and B-CLL in combination with chemotherapy, as well as with the Type I CD20 antibody ofatumumab, which was recently approved for treatment of B-CLL patients refractory to fludarabine and alemtuzumab. The following assays were used to compare the three anti-CD20 antibodies: i) Binding to NHL cell lines Z138 (MCL, ca. 60.000 CD20 binding sites per cell) and SU-DHL4 (DLBCL, ca. 1 Mio CD20 binding sites per cell) assessed by FACS, ii) Cell death induction, detected by AxV/PI staining and FACS, on a panel of NHL cell lines, iii) Antibody dependent cellular cytotoxicity mediated by PBMNCs as effector and Z138, SU-DHL4 as target cells (ADCC, LDH release assay); iv) Complement dependent cytotoxicity with Z138, SU-DHL4 as target cells (CDC, LDH release assay) and v) B-cell depletion (assessed by FACS) in whole blood from healthy donors. Dose-dependent anti-tumoral activity was assessed in a s.c. SU-DHL4 NHL xenograft model in Scid beige mice. Survival experiments in a disseminated Z138 MCL model are ongoing and an update on the results will be included as part of the poster presentation. Ofatumumab (“Arzerra”) was purchased from a local pharmacy, GA101 and rituximab were obtained from Hoffmann La Roche AG, Basel.

First, binding studies confirmed that GA101 shows half-maximal binding to NHL cells relative to rituximab and ofatumumab, a known property of Type II CD20 antibodies. EC50 values of binding were comparable indicating that GA101, rituximab and ofatumumab have apparent binding affinities in the low nanomolar range on NHL cells independent of the level of CD20 expression.

Second, the three CD20 antibodies were compared for their induction of direct cell death as measured by AxV/PI staining. Overall, GA101 mediated superior direct cell death induction compared to rituximab and ofatumumab utilizing a panel of NHL cell lines of different origins.

Immune effector-related mechanisms of action were subsequently compared by ADCC and CDC assays. GA101, a glycoengineered antibody with enhanced affinity for FcgRIIIa, was found to exhibit up to 100-fold higher ADCC potency than rituximab and ofatumumab on Z138 and SU-DHL4 cells. CDC, as expected for a Type II CD20 antibody was ca. 10 to 1,000 less potent compared to the Type I antibodies rituximab and ofatumumab. In order to integrate the different mechanisms of action (direct cell death, ADCC, CDC), autologous ex vivo B-cell depletion assays with whole blood from healthy donors containing natural immune effector cells, human complement and physiological concentrations of human immunoglobulins were performed. These studies showed that GA101 was more potent in terms of EC50 values and more efficacious in terms of absolute B-cell depletion when compared to rituximab and ofatumumab.

Finally, the dose-dependent effects of the three CD20 antibodies was studied on the growth of s.c. SU-DHL4 DLBCL xenografts in SCID beige mice. GA101 induced a dose-dependent anti-tumoral effect including complete tumor remission and was superior to the Type I antibodies rituximab and ofatumumab at saturating antibody doses.

In summary, the preclinical data presented herein demonstrate that the Type II, glycoengineered CD20 antibody GA101 is differentiated from the Type I CD20 antibodies rituximab and ofatumumab by its superior overall activity supporting its further clinical investigation. Of note, in contrast to previous publications, in this series of assays no superior preclinical activity of ofatumumab was observed when compared to rituximab.