Concentration QTc analysis of giredestrant: Overcoming QT/heart rate confounding in the presence of drug‐induced heart rate changes

Concentration‐QTc (C‐QTc) analysis has become a common approach for evaluating proarrhythmic risk and delayed cardiac repolarization of oncology drug candidates. Significant heart rate (HR) change has been associated with certain classes of oncology drugs and can result in over‐ or underestimation of the true QT prolongation risk. Because oncology early clinical trials typically lack a placebo control arm or time‐matched, treatment‐free baseline electrocardiogram collection, significant HR change brings additional challenges to C‐QTc analysis in the oncology setting. In this work, a spline‐based correction method (QTcSPL) was explored to mitigate the impact of HR changes in giredestrant C‐QTc analysis. Giredestrant is a selective estrogen receptor degrader being developed for the treatment of patients with estrogen receptor‐positive (ER+) breast cancer. A dose‐related HR decrease has been observed in patients under giredestrant treatment, with significant reductions (>10 bpm) observed at supratherapeutic doses. The QTcSPL method demonstrated superior functionality to reduce the correlation between QTc and HR as compared with the Fridericia correction (QTcF). The effect of giredestrant exposure on QTc was evaluated at the clinical dose of 30 mg and supratherapeutic dose of 100 mg based on a prespecified linear mixed effect model. The upper 90% confidence interval of ΔQTcSPL and ΔQTcF were below the 10 ms at both clinical and supratherapeutic exposures, suggesting giredestrant has a low risk of QT prolongation at clinically relevant concentrations. This work demonstrated the use case of QTcSPL to address HR confounding challenges in the context of oncology drug development for the first time.