Inhibrx has concluded the dose-escalation portion of the first-in-human Phase I clinical trial of INBRX-105 plus Keytruda in patients with locally advanced or metastatic solid tumours. 

A new targeted 4-1BB agonist, INBRX-105 is a multi-specific therapeutic candidate based on the company’s single domain antibody (sdAb) platform.

Keytruda is a programmed death receptor-1 checkpoint inhibitor.

The open-label, multicentre, non-randomised four-part trial is designed to analyse the safety profile and detect the maximum tolerated dose and the recommended Phase II dose of INBRX-105 given along with Keytruda. 

The concluded part 3 of the trial was dose escalation of INBRX-105 in combination with Keytruda and enrolled 30 patients.

According to the findings, INBRX-105 plus Keytruda was found to be reasonably well-tolerated and durable responses in checkpoint-naïve and relapsed refractory patients were reported. 

These data informed the optimal dose level for INBRX-105 plus Keytruda in part 4. Furthermore, single-agent responses were reported at this same dose level in checkpoint-naïve as well as relapsed/refractory patients.

The company commenced subject enrolment in the part 4 dose expansion cohorts of INBRX-105 plus Keytruda in May this year. 

This portion will have nearly 90 patients in five separate cohorts with preliminary findings anticipated in the first half of next year.

Meanwhile, Inhibrx has obtained an additional $60m from Oxford Finance under a Loan and Security Agreement taking its cash balance to nearly $176m.

Inhibrx CEO Mark Lappe said: “We are very encouraged by the results observed in Part 3 and believe the Part 4 expansion cohorts have been designed to demonstrate the potential of INBRX-105. 

“The additional debt provided by Oxford provides non-dilutive financing and, we believe, the time needed to mature our programs ahead of various potential strategic options.”

In March this year, the US Food and Drug Administration (FDA) granted orphan drug designation to Inhibrx’s INBRX-101 for the treatment of alpha-1 antitrypsin deficiency.