Bristol-Myers Squibb has posted interim data on its IDO1 inhibitor in combination with Opdivo. The early look at data in heavily pretreated bladder cancer patients suggest the cocktail can hold its own against a combination of rival drugs from Incyte and Merck.

IDO1 has emerged as a key battleground in immuno-oncology as companies have sought to block the tumor escape mechanisms that render PD-1 checkpoint inhibitors such as Opdivo ineffective in some patients. Bristol-Myers showed how much value it placed on the combination in 2015 when it offered up to $1.25 billion to buy Flexus and its IDO1 inhibitor.

The Big Pharma subsequently moved the IDO1 inhibitor, now known as BMS-986205, into a phase 1/2a solid tumor trial in combination with Opdivo. Bristol-Myers shared a look at data from the bladder and cervical cancer cohorts this week ahead of its oral presentation at the Society for Immunotherapy of Cancer annual meeting.

In the 25 bladder cancer patients, the combination chalked up objective response and disease control rates (ORR/DCR) of 32% and 44%, respectively. That puts Bristol-Myers’ combination in the same ballpark as that of Incyte’s epacadostat and Merck’s checkpoint inhibitor, which was linked to a 35% ORR in 40 bladder cancer patients earlier this year.

Bristol-Myers reported a lower ORR—14%—in the cervical cancer cohort, although the DCR in this group topped 60%. The trial has also generated evidence CD8+ T cells are proliferating into tumors, suggesting the IDO1 inhibitor is having the desired effect on the tumor microenvironment. 

A lot of work stands between Bristol-Myers and vindication of its claims BMS-986205 looks like a best-in-class IDO1 inhibitor. But with the early clinical data supporting the hypothesis behind the combination without setting off safety alarms, the Big Pharma is moving quickly to set up a clinical trial program that more comprehensively details the drug’s merits.  

Bristol-Myers took a step forward on that front earlier this month when it posted details of a phase 3 trial of BMS-986205 on ClinicalTrials.gov. The 700-patient study will assess whether adding BMS-986205 to Opdivo extends progression-free survival in people with advanced melanoma. Incyte began a phase 3 melanoma trial of its IDO1 inhibitor last year. 

The race for the IDO1 market is taking place against the backdrop of a legal dispute involving an employee who moved from Incyte to Flexus. Incyte has accused the employee of taking intellectual property with him and is taking Flexus and its founders to court in pursuit of upward of $2 billion in damages.