Research Spotlight: New Imaging Method Could Improve Patient Selection for Cancer Immunotherapy

Rahul Pal, PhD, an investigator at Mass Eye and Ear and an instructor of otolaryngology at Harvard Medical School, is the lead author of a recent study in Cancer Research, Fluorescence Lifetime Imaging Enables In Vivo Quantification of PD-L1 Expression and Interturmoral Heterogeneity.

Anand Kumar, PhD, director of the Mike Toth Head and Neck Cancer Research Center at Mass Eye and Ear and an associate professor of otolaryngology at Harvard Medical School, is co-corresponding author along with Dan G. Duda, PhD, Director of Translational Research in Gastrointestinal Radiation Oncology at Massachusetts General Hospital.

Q: What question were you investigating with this study?

Patient selection for cancer immunotherapy requires precise, quantitative readouts of biomarker expression in intact tumors that can be reliably compared across multiple subjects over time.

The current clinical standard biomarker for assessing immunotherapy response in cancer patients is PD-L1expression, typically quantified using immunohistochemistry in microscopic regions of ex vivo specimens. However, this method only provides snapshots of PD-L1 expression, which can change in response to tumor progression or after treatment.

Although various targeted probes have been investigated for in vivo imaging of PD-L1 over time, nonspecific probe accumulation within the tumor microenvironment has hindered accurate quantification, limiting the utility for preclinical and clinical studies.

We wanted to develop a new, more accurate method for measuring PD-L1 expression in tumors.

Q: What was unique about your approach?

To overcome the limitations of conventional molecular imaging techniques, we employed fluorescence lifetime (FLT) detection of anti-PD-L1 antibodies.

Q: What did you find?

We demonstrated that our imaging technique can yield quantitative estimates of baseline tumor PD-L1 heterogeneity in mice. This approach can also measure variations in PD-L1 expression in mice undergoing anti-cancer treatment, including with anti-PD-1 antibodies.

Q: What are the clinical implications?

Our results highlight the distinct advantages of preclinical FLT imaging for quantifying PD-L1 expression and potentially other disease biomarkers that are heterogeneously expressed in a tumor population.

Due to the noninvasive nature of the imaging method and the use of non-radioactive probes, longitudinal imaging of biomarkers can be realized in the future, which may alter the current preclinical testing approaches of novel diagnostic and therapeutic agents.

In addition to preclinical testing, FLT imaging can be extended to a wide range of targeted dyes (e.g., pH sensing, enzyme activated, metabolic cofactors, etc.) that have already crossed the safety and efficacy barriers for human use and facilitate their clinical translation.

Paper Cited: Pal, R., Krishnamoorthy, M., Matsui, A., Kang, H., Morita, S., Taniguchi, H., Kobayashi, T., Morita, A., Choi, H. S., Duda, D. G., & Kumar, A. T. N. (2024). Fluorescence Lifetime Imaging Enables In vivo Quantification of PD-L1 Expression and Inter-tumoral Heterogeneity. Cancer research, 10.1158/0008-5472.CAN-24-0880. Advance online publication. https://doi.org/10.1158/0008-5472.CAN-24-0880

Funding and Acknowledgements: This work was supported by the NIH grants R01-CA211084, R01-CA260857, and MGH-Executive Committee on Research Interim Support Fund. D.G. Duda’s research is funded through NIH (grant nos. R01CA260872 and R01CA247441) and by Department of Defense PRCRP (grant no. W81XWH-21–1-0738). R. Pal’s research was partly funded by the Jeane B. Kempner postdoctoral fellowship (UTMB Health). We acknowledge the Harvard Medical School (Boston, MA) MicRoN for access to the Leica Stellaris 8 used in this work and for the extensive assistance in imaging.

Disclosures: D.G. Duda reports grants from Bayer, Surface Oncology, Exelixis, and Bristol Myers and Squibb and personal fees from Innocoll outside the submitted work. A.T.N. Kumar reports grants from NIH during the conduct of the study. No disclosures were reported by the other authors.