Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate comprised of trastuzumab and the cytotoxic agent DM1 (derivative
of maytansine) linked by a stable linker N-succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC). T-DM1
targets an epitope located at subdomain IV of human epidermal growth factor receptor 2 (HER2). Pertuzumab is a monoclonal antibody
that targets an epitope located at subdomain II of HER2, distinct from the epitope recognized by T-DM1. The pharmacokinetics (PK),
safety, and efficacy of T-DM1 combined with pertuzumab were studied in a phase 1b/2 trial in 67 patients with HER2-positive, locally
advanced or metastatic breast cancer (MBC). The therapeutic protein-drug interaction (TP-DI) potential of T-DM1 plus pertuzumab was
evaluated. The PK of T-DM1–related analytes and pertuzumab were compared with historical PK data. The results show that the exposure
of T-DM1 and DM1, as estimated by noncompartmental analyses, was comparable with that reported by historical single-agent studies
in patients with HER2-positive MBC. T-DM1 clearance and volume of distribution in the central compartment, as estimated by population
PK analysis, were also comparable between this study and historical single-agent studies in patients with HER2-positive MBC.
Summary statistics of pertuzumab trough and maximal exposure (concentrations at predose and 15–30 minutes after the end of infusion
at cycle 1 and at steady state) were similar with those observed in a representative historical single-agent study with the same dosing
regimen. The visual predictive check plot by population simulation further confirmed that T-DM1 did not alter pertuzumab PK. Based on
these data and the PK and pharmacodynamic properties of T-DM1 and pertuzumab, the risk of TP-DI appears to be low when T-DM1
and pertuzumab are given together.
Keywords: HER2, metastatic breast cancer, pertuzumab, pharmacokinetics, therapeutic protein-drug interactions, trastuzumab emtansine, Interaction, cytotoxic agent, PK analysis, T-DM1, noncompartmental analyses.
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