Vascular normalization as an emerging strategy to enhance cancer immunotherapy

Inverse association between programmed death ligand 1 and genes in the VEGF pathway in primary clear cell renal cell carcinoma

Increased angiogenesis and tumor-induced immune evasion are two mechanisms by which clear cell renal cell carcinoma (ccRCC) proliferate and metastasize; however, the relationship between these pathways in human ccRCC is poorly understood. We conducted a nested case-control study using 98 archived tumor samples from patients diagnosed with primary ccRCC between 1990 and 2006, half of which were identified by immunohistochemistry (IHC) as either programmed death ligand 1 (PDL-1)-positive or PDL-1-negative. RNAs were extracted from the formalin-fixed paraffin-embedded tumor slides and the expression of the VEGFA, VEGFR1, VEGFR2, and PDL-1 genes was quantified. We assessed the presence of tumor-infiltrating lymphocytes (TIL) by IHC for CD3, and then analyzed the relationship among VEGFA, VEGFR1, VEGFR2, CD3, and PDL-1. When analyzed as a continuous variable, PDL-1 protein expression by IHC inversely correlates with the expression of the three VEGF-related genes: VEGFA (r = -0.23; P = 0.01), VEGFR1 (r = -0.34; P < 0.001), and VEGFR2 (r = -0.23; P = 0.01). When dichotomized, the PDL-1-positive cohort trended toward a lower expression of VEGFA (fold change = 0.72; P = 0.056) and VEGFR1 (fold change = 0.69; P = 0.057). In addition, there was a significant and positive relationship between the presence of TIL as assessed by IHC for CD3 and PDL-1 by IHC (r = 0.25; P = 0.015), and there was a trend toward an inverse relationship between TIL and VEGFA gene expression (r = -0.18; P = 0.089). In conclusion, this is the first demonstration of an inverse association between the angiogenesis and PDL-1 pathways in tumor samples from primary ccRCC, and this relationship may be related to the immunosuppressive effects of VEGF signaling.

Vascular permeability and drug delivery in cancers

The endothelial barrier strictly maintains vascular and tissue homeostasis, and therefore modulates many physiological processes such as angiogenesis, immune responses, and dynamic exchanges throughout organs. Consequently, alteration of this finely tuned function may have devastating consequences for the organism. This is particularly obvious in cancers, where a disorganized and leaky blood vessel network irrigates solid tumors. In this context, vascular permeability drives tumor-induced angiogenesis, blood flow disturbances, inflammatory cell infiltration, and tumor cell extravasation. This can directly restrain the efficacy of conventional therapies by limiting intravenous drug delivery. Indeed, for more effective anti-angiogenic therapies, it is now accepted that not only should excessive angiogenesis be alleviated, but also that the tumor vasculature needs to be normalized. Recovery of normal state vasculature requires diminishing hyperpermeability, increasing pericyte coverage, and restoring the basement membrane, to subsequently reduce hypoxia, and interstitial fluid pressure. In this review, we will introduce how vascular permeability accompanies tumor progression and, as a collateral damage, impacts on efficient drug delivery. The molecular mechanisms involved in tumor-driven vascular permeability will next be detailed, with a particular focus on the main factors produced by tumor cells, especially the emblematic vascular endothelial growth factor. Finally, new perspectives in cancer therapy will be presented, centered on the use of anti-permeability factors and normalization agents.