Endothelin Inhibition Potentiates Cancer Immunotherapy Revealing Mechanical Biomarkers Predictive of Response

Abstract

Immunotherapy efficacy depends on T cell trafficking to tumors and migrating to malignant cells to kill them. One barrier to T cell homing is the tumor blood vessel wall, which inhibits T cell attachment and transmigration through the endothelin B receptor, but antagonizing this receptor has not led to a clinically approved drug. One reason may be tumor hypo‐perfusion, which limits the area of perfused vessels for T cell attachment. If collapsed vessels can be decompressed and re‐perfused by alleviating tumor stiffness, then endothelin B receptor antagonism can improve immunotherapy. Here, it is tested whether the nonselective endothelin receptor blocker, bosentan, by simultaneously interfering with endothelin A receptor induced fibrosis, can normalize the tumor microenvironment thereby acting as a “mechanotherapeutic.” Tumor stiffness is monitored with ultrasound elastography and nanomechanical properties with atomic force microscopy to find an optimal dose, which reprograms cancer‐associated fibroblasts resulting in reduced collagen thereby decompressing vessels. Through this mechanism, T cell association with tumor vessels increases and immunosuppressive hypoxia is reduced. Additionally, bosentan increases the CD8+ T cells proliferating fraction. Ultrasound stiffness measurements correlate well with response to immunotherapy, suggesting the potential role of ultrasound elastography as a predictive biomarker of response to immune checkpoint inhibitors.

Normalizing tumor microenvironment with nanomedicine and metronomic therapy to improve immunotherapy

“…S2 and S3A–E). Reduction in tumor stiffness is due to the ability of Doxil to reduce extracellular matrix levels [ 37 , 38 ], while improvement in perfusion is associated with alleviation of intratumoral mechanical forces that decompresses tumor vessels but also due to improved pericyte coverage that induces vascular normalization by decreasing vessel leakinees (i.e., permeability) [ 37 , 38 , 51 , 63 , [68] , [69] , [70] , [71] ]. Indeed, Doxil treatment was able to significantly reduce growth-induced residual stresses, as indicated by the reduction in the tumor opening (Supplementary Fig.…”

“…Ultrasound Shear Wave Elastography (SWE). SWE was employed on a Philips EPIQ Elite ultrasound system using a linear array transducer (eL18-4), according to previous research [ 51 ]. The method generates shear wave velocity via an acoustic push pulse, creating a color mapped elastogram where red indicates hard and blue soft tissue.…”

“…To this end, we employed three different dose schedules providing the same amount of Doxil on a weekly basis: every day, every other day and every 6 days. During Doxil treatment we monitored changes in tumor stiffness and perfusion using ultrasound shear wave elastography (SWE) and dynamic contrast enhanced ultrasound (DCEUS), respectively [ 51 ]. We found that low doses of Doxil every day or every second day can effectively reduce tumor stiffness and improve perfusion thus, inducing normalization of the tumor microenvironment.…”

Towards Immunotherapy-Induced Normalization of the Tumor Microenvironment

“…Simultaneously, newly formed immature blood vessels cannot traffic and distribute infiltrating immune cells efficiently ( Slaney et al, 2014 ), whereas excessive fibrosis poses a physical barrier to immune cell migration into the tumor ( Salmon et al, 2012 ). Accordingly, hypoxia is associated with poor survival across tumor types ( Martin et al, 2019b ) and alleviating hypoxia through ‘normalization’ of the TME increases the efficacy of immunotherapies in preclinical cancer models ( Huang et al, 2012 ; Chauhan et al, 2019 ; Chen et al, 2019 ; Shigeta et al, 2019 ; Panagi et al, 2020 ; Shigeta et al, 2020 ; Mpekris et al, 2021 ; Voutouri et al, 2021 ; Mpekris et al, 2022 ). Circulating, tissue and imaging biomarker studies in patients with glioblastoma ( Sorensen et al, 2009 ) and breast cancer ( Tolaney et al, 2015 ; Boucher et al, 2021 ) support the notion that normalizing blood vessels with antiangiogenic therapies (AATs) correlates with increased antitumor immune cell infiltration and better treatment outcomes.…”

“…CAF reprogramming also appears to be combinable with ICI ( Chauhan et al, 2019 ; Elahi-Gedwillo et al, 2019 ; Chen et al, 2019 ; Panagi et al, 2020 ; Mpekris et al, 2021 ; Voutouri et al, 2021 ). For instance, angiotensin system inhibitors prolonged survival of patients with certain tumor types undergoing ICI in a retrospective analysis ( Drobni et al, 2022 ).…”