Ways to Strengthen Immunity against Skin Cancer Identified

A new way to keep the immune system engaged in its fight against skin cancer has been identified by recent research. The research team is planning to test the approach in phase 1 clinical trial. Skin cancer reprograms immune cells to ignore cancerous cells
"Understanding how cancers suppress the immune system is the key to identifying more effective immuno-therapies," said Brent Hanks, M.D., Ph.D., at Duke and senior author of the study. "Our research is an important step in that direction. We've identified a new mechanism of immunotherapy resistance that appears to be reversible, potentially enhancing the effects of the therapies we now have."

Hanks and colleagues, studying genetic mouse models of melanoma and verifying the findings in human specimens, focused on immune system messengers called dendritic cells. These cells are on high alert for pathogens such as viruses, bacteria and even tumor cells, signaling the body's T-cell immune fighters into action when sensing harmful invaders.

Somehow, melanomas reprogram dendritic cells so they ignore the cancerous cells, but this process has not been well understood. In the current study, Hanks and colleagues identified a signaling pathway within the tumor micro-environment that melanomas manipulate to silence dendritic cells.

Fighting skin cancer in its pathway
The pathway relies on a regulatory enzyme called IDO, which plays an important role in immune suppression and is controlled by fatty acid metabolism. Hanks's team found that this metabolic pathway is what melanomas compromise, setting in motion a cascade of events that ultimately leads to the immune system tolerating the tumor cells.

Once they identified this pathway, Hanks and colleagues conducted laboratory tests of a molecule that blocks melanoma cells from going stealth, enabling the immune system to mount a direct attack while also enhancing the function of current immunotherapies such as pembrolizumab and nivolumab.

"The IDO enzyme has been a focus of research in recent years, and there are several drugs that are being investigated to target it," Hanks said. "Our research looked at how we might influence the immune suppression function of IDO by targeting it upstream, along the metabolic pathway that controls it.

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"We found that this pathway regulates not only IDO but also other important components of the immune system, suggesting that blocking this pathway may be superior to targeting IDO only," Hanks said.

Hanks said a phase 1 clinical study using an existing molecule that targets this newly identified pathway is in the planning stages. It would likely explore whether the investigational drug might boost the success of current immunotherapies.

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"While there is understandable excitement around new therapies that enlist the immune system to fight cancer, we are still in a situation where greater than half of patients don't respond in melanoma and the response rate is even worse in other cancer types," Hanks said. "We need to figure out why that is, and figure out how to reverse it. We're hoping this research is a good step in that direction."

References:

1. Fei Zhao, Christine Xiao et al. Paracrine Wnt5a-beta-Catenin Signaling Triggers a Metabolic Program that Drives Dendritic Cell Tolerization, Immunity http://dx.doi.org/10.1016/j.immuni.2017.12.004

Source-Eurekalert