PF645 EXPOSURE‐RESPONSE ANALYSIS & DISEASE MODELING FOR SELECTION OF OPTIMAL DOSING REGIMEN OF ISATUXIMAB AS SINGLE AGENT IN PATIENTS WITH MULTIPLE MYELOMA

Abstract

Background:Isatuximab is an anti‐CD38 monoclonal antibody with multiple modes of action for killing tumor cells through direct tumor targeting and immune cell engagement [1].Aims:Exposure‐Response (E‐R) analysis and disease modelling of tumor burden were performed to evaluate the relationship between isatuximab exposure and efficacy outcome and to support dosing regimen selection for isatuximab as a single agent in relapsed/refractory multiple myeloma (RRMM) patients.Methods:The E‐R analyses were conducted in 194 RRMM patients evaluable for pharmacokinetics (PK) from two monotherapy trials, a phase 1/2 trial (NCT01084252)[2] and a phase 1 trial (NCT02514668). Isatuximab was administered intravenously at doses from 1 to 20 mg/kg once a week or every 2 weeks. Several isatuximab exposure parameters were tested and their association with the probability of achieving an objective response (CR, VGPR or PR) was examined by logistic regression modeling. Baseline covariates were also considered in the model to reduce their potential confounding effects. Disease progression was captured in a subset of 122 evaluable patients with the dynamics of the serum M‐protein and accounted for dropout using a joint model. Trial simulations were then performed to evaluate different dosing regimens of interest using both models.Results:The E‐R relationship was best described by Emax model, in which Ctrough at 4 weeks and percent of bone marrow plasma cells were significant predictors of overall response rate (ORR). Patients with bone marrow plasma cells lower than 50% were more likely to respond. For a given bone marrow plasma cell value, higher probability of response to treatment was obtained with higher Ctrough at 4 weeks. Longitudinal data of M‐protein was adequately described by a tumor growth inhibition model [3,4] and provided more insights into the response of patients over time. Therefore, a high loading dose of 20 mg/kg weekly over 4 weeks was chosen for maximizing the tumor response and a maintenance dose of 20 mg/kg every 2 weeks appeared sufficient to sustain efficacy. Clinical trial simulation demonstrated that this dosing regimen presented a probability of success of 76% to reach 30% ORR (5,000 trials with 100 patients) and would allow 52% reduction of serum M‐protein from baseline at 2 months of treatment. In addition, isatuximab appeared to be well tolerated at this dose level.Summary/Conclusion:Model‐based drug development has been successfully applied to support phase II isatuximab monotherapy dosing regimen selection in RRMM patients. This approach increases both the robustness of dose selection decision making and the chances of success for future clinical trials.