Zoledronic Acid Potentiates mTOR Inhibition and Abolishes the Resistance of Osteosarcoma Cells to RAD001 (Everolimus): Pivotal Role of the Prenylation Process

Abstract

Despite recent improvements in therapeutic management of osteosarcoma, ongoing challenges in improving the response to chemotherapy warrants new strategies still needed to improve overall patient survival. In this study, we investigated vivo the effects of RAD001 (Everolimus®), a new orally available mTOR inhibitor, on the growth of human and mouse osteosarcoma cells either alone and in combination with zoledronate (ZOL), an osteoporesis drug which is used to treat bone metastases. RAD001 inhibited osteosarcoma cell proliferation in a dose- and time-dependent manner with no modification of cell cycle distribution. Combination with ZOL augmented this inhibition of cell proliferation, decreasing PI3K/mTOR signaling compared to single treatments. Notably, in contrast to RAD001, ZOL downregulated isoprenylated membrane-bound Ras concomitantly to an increase of non-isoprenylated cytosolic Ras in sensitive- and resistant-osteosarcoma cell lines to both drugs. Moreover, ZOL and RAD001 synergized to decrease Ras isoprenylation and GTP-bound Ras levels. Further, the drug combination reduced tumor development in two murine models of osteoblastic or osteolytic osteosarcoma. We found that ZOL could reverse RAD001 resistance in osteosarcoma, limiting osteosarcoma cell growth in combination with RAD001. Our findings rationalize further study of the applications of mTOR and mevalonate pathway inhibitors that can limit protein prenylation pathways.

Zoledronic acid reverses cisplatin resistance in nasopharyngeal carcinoma cells by activating the mitochondrial apoptotic pathway

“…Notably, pretreatment with ZOL significantly reversed the CDDP resistance of NPC cells. This chemosensitization effect may have been due to ZOL inducing S phase cell cycle arrest, following a decrease in the percentage of cells in the G0/G1 phase and subsequent promotion of apoptosis, consistent with previous reports (17)(18)(19)25,27). The lower percentage of CDDP-resistant HNE1 cells in the G0/G1 phase may indicate a reduced capacity for DNA damage repair, which is considered a mechanism to overcome drug resistance.…”

“…Among the chemotherapeutic agents, ZOL has exhibited promising sensitizing activity to be used in combination with chemotherapy and radiotherapy for cancer treatment (17)(18)(19). Notably, ZOL exhibited excellent activities against drug-resistant cancer cells (25,26). The present study investigated the effects of a low concentration of ZOL on CDDP-resistant NPC cells; the low dose was selected as the peak plasma levels of ZOL was 1-2 µM (17).…”

Activity of the novel dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235 against osteosarcoma

“…RAD001) only showed cytostatic activity, without inducing osteosarcoma cell death. 31 Indeed, protein synthesis, which is required for cell growth and cell cycle progression, is regulated by mTORC1, while PI3K-Akt as well as mTORC2 activation is also important for cell survival. 32,33 Interestingly, in consistent with recent studies, 34,35 we found that NVP-BEZ235 caused increased phosphorylation of MEK/Erk, although it appeared to be less significant compared with mTOR or PI3K inhibitors.…”

Synergistic inhibitory effect of apomine and lovastatin on osteosarcoma cell growth

“…Four-week-old male C3H/He mice were anesthetized as described previously before they were inoculated subcutaneously with a POS-1 cell suspension containing 2 Â 10 6 cells in the hind footpad. 29 Under these conditions, mice develop a primary tumor at the site of injection in 3 weeks that can be transplanted to mice of the same strain as a small fragment (2 Â 2 Â 2 mm) in close contact with the tibia. For this purpose, the periosteum of the diaphysis was opened and resected along a length of 5 mm, and the underlying bone was kept intact.…”