Immunotherapy has revolutionized cancer treatment. Immunotherapy drugs work with the immune system, which normally fights intruders such as viruses, to kill cancer cells. One approach involves taking down defenses set up by cancer cells to escape immune cells. Some tumors, such as kidney cancer, melanoma, and lung cancer, display on their surface a protein (PD-L1) that shuts off approaching killer immune cells. Drugs have been developed that mask PD-L1 allowing killer cells to dispose of cancer cells. Discoveries underlying these developments were recognized with a Nobel Prize in 2018.
However, not all tumors use the same defense mechanism. Here, we propose a novel strategy to identify patients most likely to benefit from drugs masking PD-L1. Up until now, most approaches have focused on evaluating PD-L1 on tumor biopsy samples. However, only one cancer site is sampled, few cells are evaluated, and the results are often unreliable.
We have developed a strategy adapting a radiology test, positron emission tomography (PET), and a PD-L1 masking drug, that allows us to evaluate PD-L1 across all tumor sites. In preliminary experiments, we show that we can label a PD-L1 masking drug so that it can be detected by PET. We then show, using patient tumors transplanted into mice, that we can identify tumors with high PD-L1.
Our goal is to evaluate immuno-PET (iPET) in patients in a clinical trial. If successful, iPET will better match patients to their immunotherapy drug, and identify patients unlikely to benefit and for whom other strategies should be developed.