Using Fluorescence Lifetime Imaging Microscopy to Probe the Metabolic Peritumor Microenvironment and Beyond

Abstract

Fluorescence lifetime imaging microscopy (FLIM) is an advanced microscopy technique that enables label-free, non-destructive optical metabolic imaging (OMI) of biological materials at spatiotemporal resolution. Accordingly, FLIM has emerged as a widely used platform for multi-scale characterization of the tumor microenvironment (TME), providing valuable fundamental insights into cancer biology and demonstrating great promise for clinical utility. The surrounding host tissue, or peritumor microenvironment (pTME), has received considerably less attention in this area, however, despite being recognized as a molecularly distinct tissue region compared to both malignant and normal tissue. In this Review, we describe the application of FLIM for monitoring the metabolic TME and its relatively minimal use in probing the pTME. Notably, within the context of the TME, the ability of FLIM to exploit metabolic heterogeneity has been extensively leveraged to characterize diverse tumor-associated and malignant cell populations and states, perform drug screening and monitoring in vitro and in vivo , and non-invasively distinguish tumor from tumor-adjacent tissue regions. By comparison, only a handful of studies have utilized FLIM (mostly at the in vitro scale) to explore and analyze the pTME, with these studies suggesting that tumor-peritumor cross-talk promotes metabolic changes in peritumoral cell types. Furthermore, the biological significance of the peritumor is frequently overlooked in most diagnostic studies, as it is frequently classified as normal rather than treated as a distinct, potentially tumor-supportive compartment. Thus, evaluating the contribution and clinical relevancy of the pTME to tumor progression and treatment response represents an exciting, yet not fully realized, opportunity for FLIM. Owing to its successful and extensive application in interrogating the TME, we propose that the demonstrated capabilities of FLIM can and should be readily extended to the pTME. Doing so has the potential to advance the field, both in our fundamental understanding of cancer progression and our efforts to improve patient outcomes.