mk-2206 and Bone-Neoplasms

Nutlin-3a is a small molecule MDM2 antagonist and potent activator of wild-type p53. Nutlin-3a disrupts MDM2 binding to p53, thus increasing p53 levels and allowing p53 to inhibit proliferation or induce cell death. Factors that control sensitivity to Nutlin-3a-induced apoptosis are incompletely understood. In this study we isolated cisplatin-resistant clones from MHM cells, an MDM2-amplified and p53 wild-type osteosarcoma cell line. Cisplatin resistance in these clones resulted in part from heightened activation of the IGF-1R/AKT pathway. Interestingly, these cisplatin resistant clones showed hyper-sensitivity to Nutlin-3a induced apoptosis. Increased Nutlin-3a sensitivity was associated with reduced authophagy flux and a greater increase in p53 levels in response to Nutlin-3a treatment. IGF-1R and AKT inhibitors further increased apoptosis by Nutlin-3a in parental MHM cells and the cisplatin-resistant clones, confirming IGF-1R/AKT signaling promotes apoptosis resistance. However, IGF-1R and AKT inhibitors also reduced p53 accumulation in Nutlin-3a treated cells and increased autophagy flux, which we showed can promote apoptosis resistance. We conclude the IGF-1R/AKT pathway has opposing effects on Nutlin-3a-induced apoptosis. First, it can inhibit apoptosis, consistent with its well-established role as a survival-signaling pathway. Second, it can enhance Nutlin-3a induced apoptosis through a combination of maintaining p53 levels and inhibiting pro-survival autophagy.

Topics: Antineoplastic Agents; Apoptosis; Bone Neoplasms; Cell Line, Tumor; Cisplatin; Drug Resistance, Neoplasm; Drug Synergism; Heterocyclic Compounds, 3-Ring; Humans; Imidazoles; Osteosarcoma; Piperazines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-akt; Pyrazines; Receptor, IGF Type 1; Receptors, Somatomedin

P-glycoprotein (P-gp) overexpression is associated with poor prognosis and drug-resistance in osteosarcoma (OS), but the underlying mechanisms remain incompletely understood. Here, we examined the regulation of P-gp, GRP78, and phospho-Akt in doxorubicin (DOX)-treated OS cells. DOX induced P-gp expression, which was associated with increased GRP78 levels and Akt activation in vitro and in vivo. Functional analysis showed that Akt induces P-gp and GRP78 expression, which contributes to the DOX-induced Akt activation. Examination of the relationship between Akt and GRP78 demonstrated that GRP78 suppression attenuates the Akt activity in OS parental sensitive and resistant cells, indicating that GRP78 is required for full Akt activity. Inhibition of Akt activity using MK2206 decreased GRP78 expression in OS cells, which enhanced the inhibitory effect of MK2206 on P-gp expression. GRP78 knockdown combined with MK2206 suppressed the development of DOX resistance in OS cells and inhibited the in vivo tumor growth in the presence of DOX. These results support the development of novel therapeutic strategies that target GRP78 and Akt to sensitize OS cells for chemotherapy.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; ATP Binding Cassette Transporter, Subfamily B; Bone Neoplasms; Cell Line, Tumor; Doxorubicin; Drug Resistance, Neoplasm; Endoplasmic Reticulum Chaperone BiP; Female; Heat-Shock Proteins; Heterocyclic Compounds, 3-Ring; Humans; Mice; Mice, Inbred BALB C; Mice, Nude; Osteosarcoma; Phosphorylation; Proto-Oncogene Proteins c-akt; RNA Interference; RNA, Small Interfering; Up-Regulation; Xenograft Model Antitumor Assays