Tusamitamab ravtansine (SAR408701) is an antibody-drug conjugate (ADC), combining a humanized monoclonal antibody (IgG1) targeting carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) and a potent cytotoxic maytansinoid derivative, DM4, inhibiting microtubule assembly. SAR408701 is currently in clinical development for the treatment of advanced solid tumors expressing CEACAM5. It is administered intravenously as a conjugated antibody with an average Drug Antibody Ratio (DAR) of 3.8. During SAR408701 clinical development, four entities were measured in plasma: conjugated antibody (SAR408701), naked antibody (NAB), DM4 and its methylated metabolite (MeDM4), both being active. Average DAR and proportions of individual DAR species were also assessed in a subset of patients. An integrated and semi-mechanistic population pharmacokinetic model describing the time-course of all entities in plasma and DAR measurements has been developed. All DAR moieties were assumed to share the same drug disposition parameters, excepted for clearance which differed for DAR0 (i.e. NAB entity). The conversion of higher DAR to lower DAR resulted in a DAR-dependent ADC deconjugation and was represented as an irreversible first-order process. Each conjugated antibody was assumed to contribute to DM4 formation. All data were fitted simultaneously and the model developed was successful in describing the pharmacokinetic profile of each entity. Such a structural model could be translated to other ADCs and gives insight of mechanistic processes governing ADC disposition. This framework will further be expanded to evaluate covariates impact on SAR408701 pharmacokinetics and its derivatives, and thus can help identifying sources of pharmacokinetic variability and potential efficacy and safety pharmacokinetic drivers.

Tusamitamab ravtansine is an anti-CEACAM5 antibody-drug conjugate indicated in patients with solid tumors. Based on a previous developed semimechanistic model describing simultaneously pharmacokinetic (PK) of SAR408701, two of its active metabolites: DM4 and methyl-DM4 and naked antibody, with integration of drug-to-antibody data, the main objective of the present analysis was to evaluate covariate's impact in patients from phase I/II study (n = 254). Demographic and pathophysiologic baseline covariates were explored to explain interindividual variability on each entity PK parameter. Model parameters were estimated with good precision. Five covariates were included in the final PK model: body surface area (BSA), tumor burden, albumin, circulating target, and gender. Comparison of BSA-adjusted dosing and flat dosing supported the current BSA-based dosing regimen, to limit under and over exposure in patients with extreme BSA. Overall, this model characterized accurately the PKs of all entities and highlighted sources of PK variability. By integrating mechanistic considerations, this model aimed to improve understanding of the SAR408701 complex disposition while supporting key steps of clinical development. Study Highlights WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?Tusamitamab ravtansine (SAR408701) population pharmacokinetics (PKs) has been described by a semimechanistic PK model, characterizing simultaneously PK of SAR408701, two active metabolites: DM4 and methyl-DM4 (MeDM4), and naked antibody (NAB). This model included drug-to-antibody measurements and was successful in describing the PKs of all entities. WHAT QUESTION DID THIS STUDY ADDRESS?This study allowed to evaluate the impact of several demographic and pathophysiologic covariates on SAR408701, DM4, MeDM4, and NAB PKs simultaneously.

2524 Background: SAR439459 (SAR459) is a human anti-TGFβ monoclonal antibody that neutralizes all isoforms of TGFβ. In preclinical models, combining SAR459 with an anti-PD-1 showed improved anti-tumor activity compared to SAR459 single agent. In the dose escalation, acceptable tolerability was observed, the MTD was not reached and the preliminary RP2D was 22.5mg/kg Q3W when combined with cemiplimab (CEMI; S. Williamson et al. J Clin Oncol 39, 2021[suppl 15; #2510]). Reduction of plasma TGFβ was ≥90% at doses ≥0.25mg/kg Q2W, with a trend of a decrease in intra-tumoral TGFβ (D. Robbrecht et al. JITC 2021;9 [suppl 2; #250]). Here we report safety and efficacy results of the dose expansion. Methods: The expansion phase of this open-label, phase 1/1b study aimed to determine the optimal dose of SAR459 (7.5 mg/kg or 22.5 mg/kg Q3W) in patients (pts) with advanced melanoma (MEL) resistant to anti-PD(L)1 therapy (Part 2A); and the ORR (confirmed responses) in all treated pts with SAR459 22.5 mg/kg + CEMI 350 mg Q3W in pts with MEL, Non-small Cell Lung Cancer (NSCLC), or Hepatocellular Carcinoma (HCC), resistant to anti-PD(L)1; as well as in pts with mesenchymal Colorectal Cancer (CRC) or Urothelial Cancer (UC), anti-PD(L)1 naïve (Part 2B). Results: From October 2019 to September 2021, 109 pts with ECOG PS 0-1 enrolled in Part 2A (14) and Part 2B (95). Overall, the median age was 63 years and 83% of pts received up to 3 prior treatment lines for advanced disease (range 1-8). Based on preliminary data, the ORR in Part 2B was 8% (Table). No significant association between clinical response and plasma TGFb level at baseline or modulation upon treatment was observed. The correlation between tumor TGFb level and clinical benefit is inconclusive due to limited number of tumor biopsies. No response was observed in Part 2A. Overall, 100% of pts had at least one treatment emergent adverse event (AE), 67% were G≥3, 34% related G≥3, 17% G5, and 4% related G5. The limited number of patients treated with SAR459 alone at the RP2D did not allow to demonstrate added toxicity due to the combination. Overall, 51 pts (47%) reported hemorrhagic AE of any grade, 8 pts (7%) had G≥3 and 5 pts (5%) had fatal outcome. The rate of bleeding and severe hemorrhagic AE was higher in HCC pts compared to the other cohorts: 11/14 (79%) pts had a hemorrhagic AE, of which 3 (21%) G≥3 and fatal. An exploratory analysis showed a trend for higher frequency of any grade SAR459-related and fatal hemorrhagic AE in patients with higher exposure. Conclusions: The NCT03192345 study was discontinued due to a lack of efficacy, and a high bleeding risk particularly in pts with HCC. Clinical trial information: NCT03192345. [Table: see text]