US-based Syros Pharmaceuticals has started dosing patients in a Phase I clinical trial of an oral cyclin-dependent kinase 7 (CDK7) inhibitor SY-5609 to treat solid tumours.

The company studied the drug candidate in various preclinical models of solid tumours, including breast, colorectal, lung and ovarian cancers. SY-5609 demonstrated anti-tumour activity when given in doses below the maximum tolerated dose (MTD).

In these models, sustained responses were observed to be related to the presence of Rb pathway alterations.

A SY-5609 and fulvestrant combination also exhibited anti-tumour activity in oestrogen receptor-positive breast cancer models that were resistant to treatment.

The multi-centre, open-label, dose-escalation Phase I trial is being conducted to assess the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of SY-5609 in around 60 participants.

Patients suffering from advanced breast, colorectal, lung or ovarian cancer, or from any solid tumours expressing Rb pathway alterations will be enrolled into the trial.

The primary aim of the trial is to track the safety and tolerability of escalating doses in order to determine the MTD. In addition, the study will monitor anti-tumour activity, PK, PD and predictive biomarkers.

In the future, the trial will be expanded to include various cohorts to further assess the safety and anti-tumour activity of the drug candidate as a monotherapy and combination therapy.

Syros Pharmaceuticals chief medical officer David Roth said: “Based on this dual mechanism and the exquisite selectivity and preclinical potency of SY-5609, we believe it could provide a profound benefit for patients in dire need of new therapies.

“We have designed our Phase I trial to move efficiently through dose escalation and to increase the chances of seeing early signals of clinical activity by focusing on patient populations we believe are most likely to respond.”

Initial data from the Phase I trial is expected in the fourth quarter of this year, with additional dose-escalation data scheduled for mid-2021.