Kairos Pharma has announced a strategic collaboration with Bayer to evaluate a new combination treatment approach for metastatic castration-resistant prostate cancer (mCRPC) that has spread to the bones, a setting where treatment resistance remains a major challenge.
The collaboration will assess Kairos Pharma’s investigational antibody ENV-105 (carotuximab) in combination with Bayer’s XOFIGO (radium-223 dichloride), the first and only FDA-approved alpha-emitting radiopharmaceutical for patients with symptomatic bone metastases from mCRPC.
Under the agreement, the companies will explore whether ENV-105 can improve the effectiveness and durability of XOFIGO by targeting biological pathways associated with treatment resistance.
Metastatic castration-resistant prostate cancer is an advanced form of prostate cancer that continues to progress despite therapies that lower testosterone levels. Bone metastases are common in this disease and can cause severe pain, fractures, and other complications that significantly affect quality of life.
Kairos Pharma is developing ENV-105 as a first-in-class inhibitor of CD105 and bone morphogenetic protein (BMP) signaling, pathways that have been linked to tumor survival and resistance to cancer therapies.
The company is currently studying the antibody in multiple clinical programs, including a Phase 1 trial in EGFR-driven non-small cell lung cancer and a Phase 2 trial in castration-resistant prostate cancer.
According to Kairos, interim data from the Phase 2 prostate cancer study showed a median progression-free survival of more than 13 months, which the company described as a meaningful improvement compared with current standard treatments. The results were presented at the 2025 ESMO Congress in Berlin.
XOFIGO, meanwhile, is already established as a treatment for patients with mCRPC and symptomatic bone metastases. The radiopharmaceutical delivers targeted alpha radiation directly to areas of bone affected by cancer while limiting exposure to surrounding healthy tissue.
Bayer is also investigating XOFIGO in additional combination regimens. Recent results from the Phase III PEACE-3 trial showed that combining XOFIGO with enzalutamide reduced the risk of death by 24%, further increasing interest in strategies that could enhance the drug’s clinical benefit.
John Yu, M.D., Chief Executive Officer of Kairos Pharma, said resistance to therapy remains one of the biggest unmet needs in advanced prostate cancer.
“Drug resistance remains one of the greatest challenges in advanced prostate cancer, and XOFIGO, like many standard-of-care therapies, can lose efficacy over time,” Yu said. “ENV-105 has already demonstrated the ability to re-sensitize tumors to existing treatments while maintaining a favorable safety profile. This collaboration with Bayer represents an important milestone in our effort to develop more durable and effective treatment regimens for patients with metastatic prostate cancer.”
The scientific rationale for the collaboration is supported by previous preclinical research showing that ENV-105 can enhance the effects of radiation therapy in prostate cancer models.
Researchers have found that CD105 expression increases in response to androgen receptor inhibitors and ionizing radiation, activating BMP-SMAD signaling pathways that help cancer cells survive treatment. By blocking CD105, ENV-105 may restore sensitivity in resistant tumors and potentially extend the depth and duration of response to XOFIGO’s targeted alpha therapy.
Neil Bhowmick, Ph.D., Chief Scientific Officer of Kairos Pharma and principal investigator for the program, said the growing evidence supporting CD105 as a resistance mechanism makes the collaboration particularly compelling.
“CD105 has now been implicated as a central resistance mechanism across multiple classes of cancer therapies,” Bhowmick said. “That makes this collaboration both scientifically compelling and clinically timely, especially given the recent positive Phase III momentum for XOFIGO.”
The companies have not yet disclosed the specific design or timeline of the planned combination study.
If the approach proves successful, it could offer a new strategy for overcoming resistance in advanced prostate cancer and help extend the benefits of radiopharmaceutical therapy for patients with bone metastatic disease, an area where treatment options remain limited and outcomes are often poor.