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

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 ALDEFluorhigh 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.

Rapalink-1 Increased Infarct Size in Early Cerebral Ischemia–Reperfusion With Increased Blood–Brain Barrier Disruption

“…However, Rapalink-1 is a bivalent compound that combines the durable effects of rapamycin and dual inhibition of mTORC1/mTORC2. It blocks the phosphorylation of mTORC1 targets including p-4EBPI and inhibits mTORC2 signaling (Rodrik-Outmezguine et al, 2016 ; Fan et al, 2018 ; La Manna et al, 2020 ). It also crosses the BBB (Fan et al, 2018 ; Morisot et al, 2018 ).…”

“…Rapalink-1 is a third-generation mTOR inhibitor comprising rapamycin and a second-generation ATP-competitive mTOR kinase inhibitor (TORKI). It ablates the activity of both multiproteins mTORC1 and mTORC2, but it has a more durable effect than conventional TORKI (Rodrik-Outmezguine et al, 2016 ; La Manna et al, 2020 ).…”

The Role of mTOR Signaling as a Therapeutic Target in Cancer

“…The exposure of LAPC9 to Rapalink-1 was found to block mTORC1/2 signaling and reduce the fraction of CD44+ in vitro. Mice treated with Rapalink-1 showed a significantly delayed tumor growth, and cells recovered from the tumors of treated animals showed a marked decrease of CD44 expression [ 177 ]. The in vitro and in vivo therapeutic efficacy of Rapalink-1 against renal cell carcinoma (RCC) was evaluated and compared to temsirolimus.…”

Combining mTOR Inhibitors and T Cell-Based Immunotherapies in Cancer Treatment

“…In addition, RapaLink-1 targets glioblastoma stem cells and potentiates the anti-cancer efficacy of temozolomide, further supporting a therapeutic potential of RapaLink-1 in glioblastoma patients [ 52 ]. The anticancer benefit of RapaLink-1 is, however, not restricted to glioblastoma, as it also reduces the growth of sunitinib-resistant renal cell carcinoma tumor xenograft and prostate cancer patient-derived tumor xenograft [ 53 , 54 ].…”