Tumor Endothelial Cells as a Targetable Gateway That Modulates Access of Drugs to Cancer Cells
INTRODUCTION
The human endothelial cell (EC) lining of the vasculature is preserved in primary xenografts of surgical remnants of human prostate cancer (CaP). Testosterone deprivation (T-D) induced apoptotic loss of 40-60% of ECs in CaP xenografts. This study investigated the consequences of targeted perturbation of the CaP EC compartment on access of chemotherapeutic agents to the CaP cells. Cisplatin (Pt), which targets slowly/non-proliferating cancer cells (CaP), was investigated because it is excluded by the membrane pumps/transporters of an intact EC barrier.
METHODS
nu/nu mice were castrated and implanted with a device for sustained delivery of T at human levels. Fresh human CaP or benign prostate tissue were transplanted and allowed to engraft for 30 days. The T delivery device was removed and mice were treated with Pt at different times after T-D. Xenografts were harvested, enzymatically disaggregated, and EC and CaP cells isolated using cell type-specific antibody-conjugated magnetic beads. Transcriptomes of EC and epithelial/CaP cells were obtained using RNASeq, and compared for cells recovered from fresh tissue, xenografts, and xenografts after T-D. Integrity of the EC barrier was evaluated using MRI; immunohistochemistry (IHC); and Photo-Acoustic Imaging. Pt-induced DNA adduct load was analyzed using Pt-adduct specific antibodies and Cytof.
RESULTS
The human EC barrier was disrupted transiently by T-D, and was restored by re-endothelialization, in spite of the absence of T. Transcriptomes of fresh tissue and xenografts validated that all cell types in xenografts were consistent with fresh tissue. Transcriptomes of EC and endothelial/CaP cells revealed a highly dynamic microenvironment in prostate tissue in response to T-D, including drug-related trans-membrane pumps/transporters. Increased CaP cell exposure to Pt was demonstrated by greater levels of Pt-DNA adducts in xenografts treated during the peak of EC apoptotic death induced by T-D.
CONCLUSION
Transient destruction of the EC barrier by T-D provides a therapeutically important "window" during which chemotherapeutic agents that are effectively excluded by an intact prostate EC barrier can flood the CaP tissue microenvironment, allowing therapeutically significant levels at reduced systemic dosages. The tissue xenograft model provides a unique tool for analysis of the role of targeted microvascular damage in development of organ-specific therapies, and the role of a reconstituted human EC compartment in "acquired resistance".
Funding: NIH grant: 1R01CA193829-01A1.