Promising Immunotherapy for Prostate Cancers

A new drug, a monoclonal antibody known as enoblituzumab, is safe in men with aggressive prostate cancer and may induce clinical activity against cancer throughout the body, according to a phase 2 study led by investigators at the Johns Hopkins Kimmel Cancer Center and its Bloomberg~Kimmel Institute for Cancer Immunotherapy. 

If confirmed in additional studies, enoblituzumab could become the first promising antibody-based immunotherapy agent against prostate cancer.

In a clinical trial, 32 men with high-risk or very high-risk prostate cancers who were scheduled for prostate cancer surgery were treated with six weekly infusions of enoblituzumab prior to surgery, and were followed for an average of 30 months thereafter. 

Twenty-one patients, or 66%, had an undetectable prostate-specific antigen (PSA) level 12 months following surgery, suggesting that there was no sign of residual disease. Additionally, the drug was well-tolerated overall; no patients had any surgical delays or medical complications during or after the operation.

Enoblituzumab works by binding to a protein called B7-H3 that is overexpressed on prostate cancer cells and believed to impede the immune system’s ability to attack cancer cells. 

The new therapy could pack a one-two punch against cancer, Shenderov says, by blocking B7-H3’s inhibition of the immune system’s recognition and elimination of cancer cells, and also triggering a process called antibody-dependent cellular cytoxicity (ADCC), which leads to tumor cell destruction by activating additional immune cells such as macrophages and natural killer cells.

The median age of study participants was 64 (age range 48-74). About half (47%) had a PSA greater than 10 ng/mL at diagnosis, which is abnormally high, and 50% had Gleason grade group 5 at biopsy, meaning they had highly aggressive disease. Patients were enrolled from February 2017 through June 2019. 

Enoblituzumab was confirmed to penetrate into prostate tumors and to bind to B7-H3 in the vast majority of participants, according to prostate samples studied after surgery.

Side effects of enoblituzumab were generally mild and included fatigue, neurological symptoms such as headache or dizziness, and flu-like or cold symptoms. 

One patient developed inflammation of the heart (myocarditis), which fully resolved with steroid treatment, and is a known side effect of other immune checkpoint drugs.

Beyond safety and anti-tumor activity based on PSA dropping to undetectable levels, investigators also looked for changes in the tumor microenvironment before and after enoblituzumab treatment. 

They found increased markers of cytotoxicity after treatment, consistent with the concept that the immune system was activated against tumor cells. The tumors showed increased infiltration with granulocytes, leukocytes and effector T-cells, and there was roughly a doubling of the density of cytotoxic T cells after treatment.

“The findings are exciting but exploratory, and need to be confirmed in larger study cohorts,” cautions senior study author Emmanuel S. Antonarakis, M.D., the Clark Endowed Professor of Medicine and director of GU Oncology for the University of Minnesota Masonic Cancer Center. 

“However, these results in high-risk prostate cancer patients, and the broader need for immunotherapeutic strategies with efficacy in prostate cancers, provide justification to further develop multipronged approaches that include targeting B7-H3 to optimize antitumor activity in prostate cancers and other solid malignancies,” he says.

Sources:

Eugene Shenderov, Angelo M. De Marzo, Tamara L. Lotan, Hao Wang, Sin Chan, Su Jin Lim, Hongkai Ji, Mohamad E. Allaf, Carolyn Chapman, Paul A. Moore, Francine Chen, Kristina Sorg, Andrew M. White, Sarah E. Church, Briana Hudson, Paul A. Fields, Shaohui Hu, Samuel R. Denmeade, Kenneth J. Pienta, Christian P. Pavlovich, Ashley E. Ross, Charles G. Drake, Drew M. Pardoll, Emmanuel S. Antonarakis. Neoadjuvant enoblituzumab in localized prostate cancer: a single-arm, phase 2 trial. Nature Medicine, 2023; DOI: 10.1038/s41591-023-02284-w
Johns Hopkins Medicine. (2023, April 10). Novel immunotherapy agent safe, shows promise against high-risk prostate cancers. ScienceDaily. Retrieved April 10, 2023 from www.sciencedaily.com/releases/2023/04/230410123651.htm