Dual-mTOR Inhibitor Rapalink-1 Reduces Prostate Cancer Patient-Derived Xenograft Growth and Alters Tumor Heterogeneity

Federico La Manna; Marta De Menna; Nikhil Patel; Sofia Karkampouna; Maria Rosaria De Filippo; Irena Klima; Peter Kloen; Lijkele Beimers; George N Thalmann; Rob C M Pelger; Estela Jacinto; Marianna Kruithof-de Julio

doi:10.3389/fonc.2020.01012

Dual-mTOR Inhibitor Rapalink-1 Reduces Prostate Cancer Patient-Derived Xenograft Growth and Alters Tumor Heterogeneity

Front Oncol. 2020 Jun 23:10:1012. doi: 10.3389/fonc.2020.01012. eCollection 2020.

Authors

Affiliations

¹ Department for BioMedical Research, Urology Research Laboratory, University of Bern, Bern, Switzerland.
² Department of Urology, Leiden University Medical Center, Leiden, Netherlands.
³ Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, United States.
⁴ Institute of Pathology and Medical Genetics, University Hospital Basel, University of Basel, Basel, Switzerland.
⁵ Department of Orthopedic Trauma Surgery, Academic Medical Center, Amsterdam, Netherlands.
⁶ Department of Orthopedic Surgery, MC Slotervaart, Amsterdam, Netherlands.
⁷ Department of Urology, Inselspital, Bern University Hospital, Bern, Switzerland.

Abstract

Bone metastasis is the leading cause of prostate cancer (PCa) mortality, frequently marking the progression to castration-resistant PCa. Dysregulation of the androgen receptor pathway is a common feature of castration-resistant PCa, frequently appearing in association with mTOR pathway deregulations. Advanced PCa is also characterized by increased tumor heterogeneity and cancer stem cell (CSC) frequency. CSC-targeted therapy is currently being explored in advanced PCa, with the aim of reducing cancer clonal divergence and preventing disease progression. In this study, we compared the molecular pathways enriched in a set of bone metastasis from breast and prostate cancer from snap-frozen tissue. To further model PCa drug resistance mechanisms, we used two patient-derived xenografts (PDX) models of bone-metastatic PCa, BM18, and LAPC9. We developed in vitro organoids assay and ex vivo tumor slice drug assays to investigate the effects of mTOR- and CSC-targeting compounds. We found that both PDXs could be effectively targeted by treatment with the bivalent mTORC1/2 inhibitor Rapalink-1. Exposure of LAPC9 to Rapalink-1 but not to the CSC-targeting drug disulfiram blocked mTORC1/2 signaling, diminished expression of metabolic enzymes involved in glutamine and lipid metabolism and reduced the fraction of CD44⁺ and ALDEFluor^high cells, in vitro. Mice treated with Rapalink-1 showed a significantly delayed tumor growth compared to control and cells recovered from the tumors of treated animals showed a marked decrease of CD44 expression. Taken together these results highlight the increased dependence of advanced PCa on the mTOR pathway, supporting the development of a targeted approach for advanced, bone metastatic PCa.

Keywords: ALDH; PDX; bone metastasis; disulfiram; mTOR; prostate cancer.