Abstract 190: Tumor endothelial cells as a targetable gateway that modulates access of drugs to cancer cells

Introduction: Based upon our demonstration that the human endothelial cell (EC) lining of the tumor vasculature of human prostate adenocarcinoma is preserved in primary xenografts of intact surgical remnant tissue, this study sought to determine the consequences of targeted perturbation of this key component of the tumor microenvironment on access of chemotherapeutic agents to prostate cancer cells (CaP). Methods: Primary xenografts of intact CaP tissue were employed to investigate multiple aspects of the response of the human ECs to iatrogenic modulation, including changes in gene expression, changes in cell-cell interaction, and in the function of human tissue/tumor microvascular EC-mediated, blood–tissue barrier. SCID mice were castrated and implanted with a device for sustained delivery of testosterone (T) to establish “humanized” mice. Freshly procured surgical specimens of human CaP or benign human prostate were transplanted onto the “humanized” mice within 3-7 days. Xenografts were allowed 30 days to engraft before the integrity of the human microvascular EC barrier was perturbed by removal of the T delivery device, T-deprivation (T-D). T-D induced apoptosis of the AR-expressing human ECs was maximal on Day 3, resulting in loss of 40-60% of human ECs. Significantly, the microvascular compartment re-endothelialized by Day 15 after T-D, in spite of the absence of T, providing a unique model for analysis of the role of the repaired human EC compartment in “acquired resistance.” After various times/treatments, xenografts were harvested, enzymatically disaggregated, and EC and CaP cells isolated using cell type-specific surface marker antibody-conjugated magnetic beads. Results: Enhanced access to the xenograft tissue of imaging markers in circulation during the interval of the compromised EC barrier, and after re-endothelialization, was demonstrated by: MRI (contrast dyes), MS (nanoparticles), immunohistochemistry (IHC) (lectins), and photo-acoustic imaging (hemoglobin). RNA-Seq of EC and epithelial/CaP populations characterized similarities/differences in gene expression profiles between cells recovered from fresh tissue versus established xenografts, and the effects of T-D in xenografts. Of ~2000 genes identified in the literature as AR-regulated/interacting, few were affected in either ECs or epithelial cells by T-D, with the notable exception of KLK2, KLK3, KLK4, MSMB, and ORM2. Expression profiles of membrane transporters and pumps for cellular uptake and efflux of chemotherapeutic agents were different between fresh tissue and established xenograft. Cisplatin (Cis-Pt) was investigated because it is excluded effectively by the membrane pumps/transporters in human prostate ECs, and it effectively kills slowly/nonproliferating cancer cells. IHC analysis using an antibody specific for Cis-Pt-induced DNA dimers demonstrated significantly greater levels of Pt-DNA adducts in xenografts treated during the T-D induced “window.” Quantitative analysis by Cytof technology of adduction in ECs and CaP cells isolated from xenografts is under way. Conclusions: Transient destruction of the EC barrier by T-D provides a therapeutically important “window” during which chemotherapeutic agents that are effectively excluded by the intact prostate EC barrier flood the CaP tissue microenvironment, providing therapeutically significant levels at reduced systemic dosages. Current analyses are focused on characterization of genes that respond to T-D, particularly differential characterization of gene expression profiles in the tumor ECs that re-endothelialize CaP xenografts after T-D. This model provides a unique tool for analysis of the roles of targeted microvascular damage in development of organ-specific therapies, and of the evolution of the EC compartment in response to iatrogenic intervention in “acquired resistance.” Citation Format: Michael J. Greene, Gary J. Smith, Yue Wu. Tumor endothelial cells as a targetable gateway that modulates access of drugs to cancer cells [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr B41.