Bayer, Kairos Pharma Collaborate to Boost Xofigo Effectiveness in Metastatic Prostate Cancer

Editor’s Note: New drug combinations can be a way for standard-of-care treatments not to lose their effectiveness over time.

Bayer and Kairos Pharma are collaborating to study Kairos’ lead antibody, ENV-105 (carotuximab), in combination with Bayer’s Xofigo (radium-223 dichloride).

ENV-105 is a first-in-class CD105/BMP signaling inhibitor—CD105, a protein driving resistance and relapse in response to standard cancer therapy. The two companies want to evaluate it, along with Xofigo, in metastatic castration-resistant prostate cancer (mCRPC) involving bone.

Kairos and Bayer Synergy

In previously published work, ENV-105 has proven effective in radiation sensitization in prostate cancer preclinical models. Targeting CD105 with ENV-105, then, may re-sensitize resistant tumors, extending duration and depth of response to Xofigo.

“Drug resistance remains one of the greatest challenges in advanced prostate cancer,” Kairos Pharma CEO John Yu, MD, said. “Xofigo, like many standard-of-care therapies, can lose efficacy over time.”

To date, Kairos’ ENV-105 programs include a Phase II trial for CRPC that in 2025 showed positive interim efficacy data. Currently, ENV-105 is also in a Phase I trial in epidermal growth factor receptor (EGFR)-driven non-small cell lung cancer.

“ENV-105 has already demonstrated the ability to re-sensitize tumors to existing treatments with a strong safety profile,” Yu said. “This collaboration with Bayer represents a major milestone in our mission to deliver more durable and more effective treatment regimens.”

Xofigo Continues Evaluations

Concurrently, Xofigo—the first and only FDA-approved alpha-emitting radiopharmaceutical for mCRPC with symptomatic bone metastases—is in additional combination studies. These include a Phase III trial that showed a 24% reduction in mortality risk when combined with enzalutamide.

Neil Bhowmick, PhD, Kairos Pharma Chief Scientific Officer and Principal Investigator, said the time is right to target CD105.

“CD105’s role as a central resistance mechanism validated now across multiple drug classes makes this collaboration scientifically compelling,” Bhowmick said.