RG6234: A Novel 2:1 GPRC5D T Cell Bispecific Antibody Exhibits Best in Class Potential for the Treatment of Multiple Myeloma As a Monotherapy and in Combination

With the majority of patients relapsing after multiple lines of diverse treatments, multiple myeloma (MM) remains a largely incurable disease. "Off the shelf" T-cell bispecific antibodies (TCBs) targeting GPRC5D demonstrated promising efficacy in early clinical development. Here we benchmarked RG6234, a novel 2:1 GPRC5D-TCB, versus a 1:1 GPRC5D-TCB and a 2:1 BCMA-TCB in clinically relevant ex vivo and in vivo models confirming its' best in class TCB potential for the treatment of multiple myeloma. First we compared the potency of TCBs using MM patients' immune cells and MM cell lines with a wide range of GPRC5D expression levels. RG6234 exhibited superior potency in T cell activation, cytokine production and proliferation against all GPRC5D+ MM cell lines tested. Particularly on target cells with low expression the potency and efficacy of RG6234 was clearly superior to a conventional 1:1 GPRC5D-TCB. Next we compared the potential of TCBs to drive T cell activation and MM plasma cell (PC) depletion in an autologous ex vivo model of MM using total BM aspirates from newly diagnosed MM patients. RG6234 exhibited superior potency as illustrated by upregulation of CD25 on CD4+ and CD8+ T cells and superior efficacy as demonstrated by lower EC50 MM PC depletion dose of 0.12 nM versus 6.26 nM for 2:1 BCMA-TCB and 41.9 nM for 1:1 GPRC5D-TCB. We next tested the capacity of TCBs to inhibit growth of established NCI-H929 xenograft tumors in humanized mice (huNSG) upon repetitive dosing. Strikingly, RG6234 therapy eradicated tumors at all doses tested (0.1-1-10 mg/kg) whereas no regressions were observed for 1:1 GPRC5D-TCB. Interestingly, despite higher baseline expression of BCMA at treatment start, 2:1 GPRC5D-CD3 TCB was also clearly more efficacious than the 2:1 BCMA-CD3 TCB underlying the best in class TCB potential for treatment of multiple myeloma. To improve mechanistic understanding of the mode of action of RG6234 in a patient relevant setting we next evaluated T cell recruitment, activation and MM PC killing in an orthotopic in vivo model of multiple myeloma in huNSG mice. RG6234 was highly active eliminating multiple myeloma cells in the BM as early as 72h after single dose injection as confirmed by drop in soluble BCMA. GPRC5D-TCB induced CD8 T cell margination in blood 24h after first injection and T cell expansion at 24h after second dosing. Up to 5 fold T cell expansion was observed in BM tumors 72h after first and second dosing indicating efficient cross-linking of T cells at the tumor site. Timing of T cell expansion and tumor cell killing correlated with shift of naïve CD62L+CD45RA+ towards CD4RA-CD62L- effector memory CD8 T cells in blood and in tumor. In line with the proposed TCB mode of action, RG6234 induced release of patient relevant amounts of cytokines immediately after first but not after second dosing, correlating with tumor burden at the given timepoints. Peak concentrations for individual cytokine were detected at 4h (IL-2, MIP1a and GM-CSF), 24h (TNFa, CXCL10, G-CSF and IL-10) and 48h-72h ( INFg, IL-6, IL-8 or sCD25). We next evaluated the therapeutic capacity of RG6234 in combination with daratumumab (Dara) and/or pomalidomide (Pom) in total BM aspirate samples from 10 MM patients with variable frequency of GPRC5D positive MM plasma cells (range 74-98%). RG6234 induced MM PC lysis was seen in all patients and was significantly boosted in combination with Dara or the triple combination with Dara and Pom. Tumor cell killing was correlated with increased expression of CD69, CD25, and CD107a as well as checkpoints CD137 and PD-1 on CD8 T cells. Only combination with Pom but not Dara enhanced T cell activation and cytokine release underpinning the different modes of action of these standard of care agents. To validate synergistic combination activity upon repetitive dosing huNSG mice were engrafted s.c. with RPMI-8226 or OMP-2 tumors and treated with RG6234 in combination with Dara or Lenalidomide (Len), respectively. Antitumoral response of RG6234 was significantly improved in combination inducing tumor stasis with Dara and regressions with Len. Improved efficacy in combination with Len was found to correlate with significant expansion of intratumoral T cells 48h after second injection. In summary, we demonstrate preclinical evidence for best in class potential of the RG6234 antibody format for the treatment of multiple myeloma. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal