Mechanistic prediction of first-in-human dose for bispecific CD3/EpCAM T-cell engager antibody M701, using an...

M701 is a bispecific CD3/EpCAM T-cell engager antibody to treat malignant ascites. This study aimed to predict in vivo exposure-cytotoxicity relationship and human pharmacokinetics (PK) characteristics of M701, as well as to design optimal starting dose and effective dose for M701 first-in-human (FIH) study.

Mechanistic in vitro PK/PD model was firstly developed based on in vitro data of M701's cytotoxicity and binding affinities with targeting receptors. The cell killing effect of M701 in vitro was driven by tri-molecular synapse, which formed by binding drug to both CD3 receptor on T cells and EpCAM receptor on tumor cells. Human exposure-response (E-R) curve in ascites was estimated using the same model structure with clinical systemic model parameters. Human PK was predicted by allometrically scaling monkey PK data, which was characterized using a two compartment model. Human PK model was integrated into in vivo synapse-based cell killing model to provide human PK/PD characteristics. Integrated human PK/PD model was applied in FIH dose design. Clinical starting dose and effective dose were suggested as the simulated drug concentration in human ascites that achieved the estimated in vivo minimally anticipated biological effect level (MABEL) and pharmacologically active level. Other approaches including PK-driven and receptor occupancy calculation were also employed in this study to verify the starting dose prediction.

In vitro M701 cytotoxicity curves under 24, 48, 72 h incubations were well captured by mechanistic synapse-based cell killing model. Human E-R curve in ascites was obtained based on in vitro model structure and clinical systematic parameters. We defined 10~20% and 80% of maximum cytotoxicity effect as in vivo MABEL and pharmacologically active level. Human E-R curve indicated in vivo EC₁₀, EC₂₀ and EC₈₀ were 0.56, 1.26 and 31.6 ng/mL. For human PK model, clearance (CL, CL_d), distribution volumes (V_c, V_p) and absorption rate were allometrically scaled using exponent of 0.9, 1 and -0.25. Predicted clearance and volume were 0.53- and 1.19-fold of observed data. Simulated average ascites M701 concentrations (calculated as C_{ave_ ascites} = AUC_τ/τ) were 0.81 and 32.5 ng/mL under dose of 5 and 200 μg within 2-hour i.p. infusion. By integrating human E-R curve and the simulated PK profile in ascites, we suggested 5 and 200 μg within 2-hour i.p. infusion as MABEL dose and pharmacologically active dose (PAD) for M701 FIH study. PK-driven approach predicted a starting dose of 5 μg, which was comparable to that predicted via PK/PD-driven approach.

This study predicted human ascites PK and E-R curve by integrating human PK model into in vivo synapse-based cell killing model. Optimal clinical MABEL dose and PAD of bispecific T cell engager antibody M701 were suggested based on current integrated PK/PD approach.