At the MTD of 3.6 mg/kg every 3 weeks, T-DM1 was associated with mild, reversible toxicity and substantial clinical activity in a heavily pretreated population. Phase II and III trials in patients with advanced HER2-positive breast cancer are under way.
Trastuzumab emtansine (T-DM1) is a HER2-targeted antibody-drug conjugate in development for treatment of HER2-positive cancers. T-DM1 has been tested as a single agent in a phase I and 2 phase II studies of patients with heavily pretreated metastatic breast cancer (MBC), with the maximum tolerated dose established at 3.6 mg/kg intravenously for every-3-week dosing. The authors present results from the population pharmacokinetics analysis for T-DM1. Population pharmacokinetics for T-DM1 were characterized using a clinical database of 273 patients from the 3 studies. Pharmacokinetics was best described by a linear 2-compartment model. Population estimates (interindividual variability [IIV]) for pharmacokinetic parameters were clearance, 0.7 L/d (21.0%); central compartment volume (V(c)), 3.33 L (13.2%); peripheral compartment volume (V(p)), 0.89 L (50.4%); and intercompartmental clearance, 0.78 L/d. Body weight, albumin, tumor burden, and aspartate aminotransferase levels were identified as statistically significant covariates accounting for interindividual variability in T-DM1 pharmacokinetics, with body weight having a greater effect on IIV of clearance and V(c) than other covariates. T-DM1 exposure was relatively consistent across the weight range following body weight-based dosing. This analysis suggests no further T-DM1 dose adjustments are necessary in heavily pretreated patients with MBC.
The tiered immunogenicity assay strategy for T-DM1 allowed detection of antitherapeutic antibodies to all components of the ADC in multiple nonclinical and clinical studies. Characterization strategies implemented in clinical studies provided additional insights into the specificity of the immune response.
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