Menon, Rajeev

Introduction ABBV-383 is a differentiated BCMA x CD3 bispecific antibody (fully humanized IgG4) T-cell engager composed of a bivalent BCMA binding domain with high avidity, a low-affinity CD3-binding domain, and a present but silenced-Fc tail retaining the FcRn binding allowing for an extended half-life and thereby, enabling dosing convenience. ABBV-383 monotherapy has shown promising activity and improved CRS safety profile with modified dexamethasone (Dex) premedication in patients (pts) with RRMM (NCT03933735; Rodriguez et al., JCO 2024;42[suppl 16]:7531). Here, ER and CRS PK/PD analyses supporting the selection of optimal SUD for ABBV-383 are reported. Methods ER-efficacy (N=286) and -safety (N=290) analyses were conducted using logistic regression methodology (R version 4.3.2) combining data from escalation (0.025-120 mg Q3W) and expansion (20, 40, 60 mg Q3W and 60 mg Q4W) cohorts of phase 1 study NCT03933735 and Arm A of phase 1b study NCT05650632 evaluating step-up dose (2 or 4 mg on Day 1) with a full dose (60 mg on Day 4) in pts with RRMM. Pts received modified Dex with full dose in expansion cohorts of 60 mg Q4W and 2/60 mg Q4W. In all other cohorts with or without SUD, pts received low Dex. Based on prior knowledge (JCO 2024;42[suppl 16]:7541), the safety endpoints (CRS: any-grade and ≥ G2) were modeled with Cycle 1 total (unbound + bound to soluble BCMA) Cmax, while objective response rate (ORR) was modeled with free (unbound + partially bound to soluble BCMA) Cavg. CRS ER models included a priori selected Dex (low vs. modified) and SUD (yes vs. no) as predictors. Relevant pt-specific covariates were tested in all models. CRS PK/PD analyses included total PK, IL-6, and CRS data (N=199) from the first 3 cycles of the above phase 1/1b studies. A semi-mechanistic indirect response PK/IL-6 model was developed to correlate total PK and IL-6 (NONMEM 7.5). Maximal IL-6 concentrations were derived using post hoc estimates from the PK/IL-6 model and correlated with CRS events (logistic regression; R version 4.3.2). The models included effects of time-dependent Dex (low vs. modified) and SUD (yes vs. no). The overall modeling approach was assessed by comparing observed and predicted CRS rates. Simulations were conducted for various dosing regimens, including one or two SUD and Dex premedication scenarios to support the selection of the optimal SUD. Results Consistent with clinical observations (separate abstract submission), any-grade CRS model predicted probabilities suggested two key outcomes: 1) premedication with modified Dex improves the CRS safety profile compared to the low Dex (42% vs 69% for 60 mg Q4W); 2) modified Dex with SUD further improves the CRS safety profile of ABBV-383 compared to low Dex with SUD (29% vs 43% for 2/60 mg Q4W). Consistent with prior work, no ER relationship was observed for ≥ G2 CRS (p > 0.05). The ORR model resulted in a predicted probability of 68% ORR (closely matching with overall observed 64% ORR) with no impact of SUD and modified Dex. Only soluble BCMA was selected as a covariate in the ORR ER model. The final semi-mechanistic PK/IL-6 model well captured the observed IL-6 data, and the CRS rates (predicted by the logistic regression models) closely matched with the observed data. The CRS PK/PD analyses findings were consistent with the clinical observations and ER analyses key outcomes 1 and 2. The CRS PK/PD analyses predictions comparing the 1-SUD vs 2-SUD (untested) regimens with modified Dex suggested that 1) among the 2-SUD regimens with modified Dex, the 2/3/60 mg regimen would have the maximum reduction of 4% points in any-grade CRS compared to the 2/60 mg 1-SUD regimen, however, with substantial overlap of confidence intervals and with no decrease in ≥ G2 CRS (< 0.5% point); 2) 4 mg as an intermediate SUD in a 2-SUD regimen would lead to higher any-grade and ≥ G2 CRS rates (~9% and 3% points higher, respectively), compared to the 2/60 mg Q4W regimen. Conclusions ER and CRS PK/PD analyses suggested that modified Dex and SUD improve the CRS safety profile of ABBV-383 with no impact on efficacy (ORR) in pts with RRMM. The CRS PK/PD predictions indicated that implementation of 2-SUDs provide minimal additional or no improvement in CRS safety profile compared to 1-SUD. Overall, the 1-SUD dosing regimen of 2 mg with modified premedication prior to the full dose of 60 mg Q4W showed promising results and can be considered for future evaluation and studies.

7541 Background: ABBV-383 is a fully human, B-cell maturation antigen (BCMA) × CD3 T-cell–engaging IgG4 bispecific with an effector-silenced Fc region, 2 high-affinity BCMA- and a low-affinity CD3-binding domains. ABBV-383 monotherapy has shown promising activity in patients (pts) with RRMM (Blood 2023;142[suppl 1]:3378). Here, exposure-response (ER) analyses of efficacy and safety endpoints supporting the optimal therapeutic ABBV-383 dose selection are reported in alignment with US FDA’s Project Optimus. Methods: Efficacy (n=218) and safety (n=220) data from the phase 1 study (NCT03933735) escalation cohorts of 0.025 - 120 mg Q3W and expansion cohorts of 20, 40, 60 mg Q3W and 60 mg Q4W including objective response rate (ORR), very good partial response or better (≥VGPR), stringent complete response (sCR)/CR, adverse events (≥G3 and serious), infections (≥G3, overall and serious), cytokine release syndrome (CRS; any-grade, G1, G2, and ≥G2) were modeled. Total(unbound + bound to soluble BCMA) and free (unbound + partially bound to soluble BCMA) Cycle 1 AUCinf, Cmax, and Ctrough and population pharmacokinetic model-derived up to the time of event Cavg and avgCtrough metrics were utilized in the ER analyses (logistic regression; R Version 4.2.2). Relevant pt-specific covariates were tested. Dexamethasone premedication (36 vs 10 mg) was included in CRS models. The ER relationships were utilized to predict the probabilities of efficacy and safety endpoints for relevant doses and thereby, support justification of the optimal therapeutic dose selection. Results: Based on overall assessment, ORR, ≥VGPR, sCR/CR and ≥G3 neutropenia strongly correlated with free Cavg; CRS endpoints (any-grade CRS and G1 only CRS) strongly correlated with Cycle 1 total Cmax (p <0.05). No other endpoints had ER relationships (p >0.05). Only MM type (IgG vs Others) was selected in ≥VGPR and sCR/CR models. ER relationships suggested high response rates of >63% ORR, >53% ≥VGPR, and ≥30% sCR/CR for 40, 60 mg Q3W and 60 mg Q4W. Predictions demonstrated that 20 mg Q3W (<39% ORR and ≥VGPR; <13% sCR/CR) and untested 40 mg Q4W (<60% ORR, <45% ≥VGPR and <23% sCR/CR) provide suboptimal efficacy. The 60 mg Q4W with 36 mg dexamethasone in Cycle1 (limited follow-up and data) was predicted to have ~30% sCR/CR and 31% ≥G3 neutropenia (≈ 40 mg Q3W) and substantially lower any-grade CRS events compared with 40 and 60 mg doses with 10 mg dexamethasone in Cycle 1. Conclusions: While ER analyses indicated promising efficacy and acceptable safety profiles for 40, 60 mg Q3W, and 60 mg Q4W, they support 60 mg Q4W as the optimal ABBV-383 therapeutic dose due to its predicted better therapeutic benefit/risk profile (high response rates, improved/equivalent ≥G3 neutropenia, and lower CRS events) and extended dosing interval. ABBV-383 at 60 mg Q4W will be investigated in the registrational phase 3 trial (NCT06158841) in RRMM.

Introduction ABBV-383 is a fully human, silenced Fc region IgG4 monoclonal, BCMA × CD3 T-cell-engaging bispecific antibody with 2 BCMA-binding domains and a low-affinity CD3-binding domain. ABBV-383 has shown promising activity following intravenous (IV) infusion every three weeks (Q3W) as monotherapy in patients (pts) with RRMM in an ongoing phase 1 study (D'Souza A, et al. J Clin Oncol. 2022 Nov 1;40(31):3576-3586; Voorhees et al. Blood 2022;140[suppl 1]:4401). Herein, preliminary pharmacokinetic (PK) and immunogenicity results from Q3W regimens of this study and impact of soluble BCMA (sBCMA) on ABBV-383 PK are reported. Methods In the phase 1 study (NCT03933735), adult pts with RRMM, who were previously exposed to ≥3 prior multiple myeloma agents including ≥1 proteasome inhibitor, immunomodulatory drug, and anti-CD38 monoclonal antibody, received Q3W IV infusion at doses 0.025 - 120 mg in escalation (ESC) phase, and at 20 mg, 40 mg, and 60 mg in expansion (EXP) phase. Serial blood samples for PK characterization were collected in cycles 1, 3, and 6 along with sparse/periodic samples throughout the study. Blood samples were also collected throughout the study to detect anti-drug antibodies (ADAs) for immunogenicity characterization and to determine sBCMA concentrations. Appropriate validated assays were used to determine ‘total’ (unbound and bound to sBCMA) and ‘free’ (unbound and partially bound to sBCMA) ABBV-383 serum concentrations, to detect/determine ADAs/titers, and to determine total sBCMA concentrations. ‘Total’ and ‘free’ ABBV-383 serum concentrations from cycles 1, 3, and 6 were used to calculate individual PK parameters (peak concentration [C max], trough concentration [C trough], area under the concentration-time curve [AUC], terminal phase elimination half-life [t 1/2], clearance [CL], and steady state volume of distribution [V ss]) using non-compartmental analysis in Phoenix WinNonlin Version 8.2. Immunogenicity was summarized using ADA/titer data. Impact of baseline/pre-dose sBCMA concentrations on ‘total’ and ‘free’ ABBV-383 PK parameters from cycles 1, 3, and 6 was explored. Results ‘Total’ and ‘free’ ABBV-383 intensive PK data (cycles 1, 3, and 6) were available from 169 and 157 pts, respectively, representing Q3W regimens in ESC and EXP cohorts and ADA data were available from 186 evaluable subjects. Preliminary PK results suggest that ‘total’ and ‘free’ ABBV-383 exhibited approximately dose-proportional PK between 5.4-120 mg Q3W. Estimated t 1/2 for ‘total’ and ‘free’ ABBV-383 ranged between 11-12 days and 8-11 days, respectively, with steady state achieved by cycle 4 in Q3W EXP cohorts. Estimated CL and V ss were consistent with those of a typical IgG4 antibody in humans. Across EXP Q3W regimens, accumulation (cycle 3 vs. cycle 1) was 30%-60% in C max and 60%-177% in C trough for ‘free’ and ‘total’ ABBV-383. ABBV-383 exposures (AUC tau and C trough) of ‘total’ ABBV-383 were 28-74% higher than those representing ‘free’ ABBV-383 among the EXP Q3W regimens with no/minimal observed differences in C max (≤21%). Higher sBCMA levels prior to treatment appeared to reduce ‘free’ ABBV-383 PK exposures with pronounced reduction at lower doses (e.g., 20 mg) and in cycle 1, however the effect diminished in later cycles (cycles 3 and 5). Preliminary assessment of immunogenicity indicated an ADA incidence of 3.8% (7/186) with low titers ranging between 11.7 and 187 titer units and no impact on PK. Conclusions ABBV-383 exhibited a PK profile with relatively long half-life and low incidence of immunogenicity. Overall, sBCMA impacted (reduced) the ‘free’ ABBV-383 (pharmacologically active component) PK exposures only, with pronounced effect at lower doses and the effect is consistent with understanding of treatment dependent sBCMA dynamics over time. Determination of both ‘total’ and ‘free’ ABBV-383 serum concentrations allowed to demonstrate such underlying impact of sBCMA on PK.

Abstract Venetoclax, a potent BCL‐2 inhibitor, is currently under development for treatment of t(11;14) Multiple myeloma (MM). The objective of this research was to investigate the exposure–response relationships of venetoclax for a phase 1/2 study evaluating venetoclax monotherapy or in combination with dexamethasone in relapsed or refractory MM. A total of 117 patients receiving venetoclax at 300, 600, 800, 900, or 1200 mg were included in the analysis. The impact of venetoclax exposures on efficacy (objective response rate [ORR], progression‐free survival [PFS] and overall survival [OS]) as well as safety (treatment‐emergent adverse effects (grade ≥3) of neutropenia, infection, and any grade of serious treatment‐emergent adverse effects) was evaluated. In the t(11;14)‐positive subpopulation, venetoclax exposure relationships to PFS and OS indicated a trend of longer PFS and OS with higher exposures. Moreover, logistic regression analyses for clinical response (ORR and ≥VGPR rate) demonstrated a statistically significant ( p < 0.05) relationship with exposure. Evaluation of the exposure‐safety relationships demonstrated a lack of a relationship between venetoclax exposures (AUC avg ) and grade ≥3 infections, grade ≥3 neutropenia, grade ≥3 treatment‐emergent adverse events or any grade serious treatment‐emergent adverse events. These findings support further study of venetoclax at 800 mg QD dose in combination with dexamethasone in the t(11;14)‐positive patient population where increased efficacy was observed without an increase in safety events.Clinical Trial: NCT01794520 registered 20 February 2013.