4D pharma plc announced that in Part B of its signal finding study of MRx0518 in combination with MSD's anti-PD-1 therapy, KEYTRUDA® (pembrolizumab) in patients with solid tumors that have progressed on a prior immune checkpoint inhibitor (ICI), the renal cell carcinoma (RCC) group has met its primary efficacy endpoint ahead of enrollment completion. The ongoing study is being conducted in heavily pre-treated metastatic patients with solid tumors who have previously experienced clinical benefit on prior ICI therapy and subsequently developed progressive disease. The study is being conducted in collaboration with MSD (Merck & Co.

Inc., Kenilworth, NJ, USA). The primary efficacy endpoint for Part B of the study is more than three out of 30 patients per tumor group achieving clinical benefit, defined as complete response, partial response, or stable disease for at least six months. Part B of the study has to date enrolled 20 patients with RCC, of which four out of the first 16 evaluable patients have achieved clinical benefit, each having achieved at least 6 months of stable disease.

To date, Part B of the study has enrolled 47 patients of up to a total of 120 patients with RCC, non-small cell lung cancer, bladder cancer, and head and neck squamous cell carcinoma. MRx0518 continues to be safe and well tolerated. 4D pharma intends to discuss next steps with partners and its Genitourinary Cancers Advisory Board regarding the development path of MRx0518 and a potentially pivotal study in patients with ICI-refractory RCC.

4D pharma will continue to recruit patients into the ongoing study of MRx0518 and Keytruda in RCC and the three tumor groups, with potential expansion into other types of ICI resistance.