Merck & Co has told partner Vertex Pharmaceuticals that it has halted enrolment in clinical trials of the firms’ investigational drug for leukaemia over a cardiovascular safety issue in one patient.

The companies said they suspended studies involving MK-0457, which is also known as VX-680, “pending a full analysis of efficacy and safety data” after preliminary findings revealed that one patient experienced QTc prolongation, an irregularity of the electrical activity of the heart that places patients at risk for ventricular arrhythmias.

MK-0457 is the lead drug in Vertex and Merck’s collaboration to develop Aurora kinase inhibitors. It is being investigated in a Phase II trial in patients with treatment-resistant chronic myelogenous leukaemia, or Philadelphia chromosome-positive acute lymphoblastic leukaemia containing the T315I mutation, as well as an ongoing Phase I study in patients with advanced leukaemias.

Vertex and Merck said patients currently enrolled in these trials may continue to be treated with MK-0457, with additional monitoring for QTc prolongation, but added that they have also suspended a recently-initiated Phase I trial of MK-0457 in combination with dasatinib in those same patient groups.

The firms concluded by noting that they have also discontinued development of their Aurora kinase inhibitor MK-6592 (VX-667) after it failed to meet pharmacokinetic objectives in a Phase I trial.