Mutated RAS and constitutively activated Akt delineate distinct oncogenic pathways, which independently contribute to multiple myeloma cell survival

Abstract

We have recently shown that approximately half of primary multiple myeloma (MM) samples display constitutive Akt activity, which disposes them for sensitivity to Akt inhibition. The Akt pathway counts among the signaling conduits for oncogenic RAS and activating mutations of K-and N-RAS frequently occur in MM. We therefore analyzed the relation between RAS mutation and Akt dependency in biopsies and CD138-purified cells from MM patients (n ‫؍‬ 65) and the function of oncogenic RAS for MM cell survival in a range of MM cell lines with differing RAS status. Whereas RAS mutations do not predict Akt dependency, oncogenic RAS retains an important role for MM cell survival. Knockdown of either K-or N-RAS strongly decreased the viability of MM cells that harbored the respective oncogenic isoform, whereas ablation of wild-type RAS isoforms had little or no effect. Silencing of oncogenic RAS did not affect the Akt pathway, again indicating lack of a direct link. Combined inhibition of RAS and Akt strongly enhanced MM cell death. These data suggest that oncogenic RAS and Akt may independently contribute to MM cell survival. Tar IntroductionMultiple myeloma (MM) is an incurable neoplasia of the terminally differentiated plasma cell and accounts for approximately 10% of all hematologic cancers. 1 Intrinsic genetic lesions as well as the bone marrow microenvironment contribute to the activation of proliferation and survival pathways, impairment of cell death mechanisms, and drug resistance. [2][3][4][5] Two pathways commonly dysregulated in MM involve activation of the serine/threonine kinase Akt (Akt pathway) and of the guanine nucleotide exchange factor RAS (RAS/MAPK pathway). The Akt pathway has repeatedly been found to be important for MM cell survival, 6,7 and we have recently shown that approximately 50% of primary MM samples display an Akt-dependent, phospho-Akt-positive phenotype. 7 Little is known about the mechanisms that lead to constitutive Akt activation in MM, but suitable genetic lesions, such as deletion of PTEN 8,9 or activating mutations of PIK3CA, 10,11 appear to be relatively rare in this disease. Conversely, the reported prevalence of activating mutations of K-and N-RAS in MM ranges from approximately 30% to 50% of patient samples. [12][13][14][15][16][17] The occurrence of RAS mutation appears independent of clinical stage, 13,17 but oncogenic RAS is associated with disease progression, aggressive phenotype, and shorter survival. 12,[17][18][19] It is also implied in the transition to MM because RAS mutations are rarely found in monoclonal gammopathy of undetermined significance. 13,16 However, analyses of the functional role of oncogenic RAS in MM are rare, mainly because of the entire lack of specific inhibitors. Prenylation blockers, such as farnesyltransferase inhibitors, had initially been developed to curb RAS signaling. Encouraging preclinical data, however, did not translate into clinical efficiency, and it has subsequently been shown that the observed effects were largely independent of oncoge...

The novel AKT inhibitor afuresertib shows favorable safety, pharmacokinetics, and clinical activity in multiple myeloma

“…9,10 The PI3K/AKT pathway activation in MM is mostly related to signaling from major growth factor receptors such as insulin-like growth factor-1 or interleukin-6. [11][12][13] This dependence on the PI3K/AKT pathway is suggested by the observation that inhibition of the pathway with PI3K inhibitors and/or mTOR inhibitors has been shown to induce apoptosis in myeloma cell lines and in tumor cells derived from patients. 11,14 Afuresertib is a reversible, ATP-competitive, oral, low-nanomolar, pan-AKT kinase inhibitor.…”

RSK2Ser227 at N-Terminal Kinase Domain Is a Potential Therapeutic Target for Multiple Myeloma

“…Everolimus exerts its cytotoxic effect by inhibiting the pathway, so that coadministration of everolimus and BI-D1870 can be expected to exert powerful antiproliferative effects on myeloma cells through simultaneous inhibition of both the RAS/ERK1/2 and PI3K/AKT signaling pathways (17). HDACi has shown its antimyeloma effects both in vitro and in vivo, whereas p21 WAF1/CIP1 induction by HDACi has been shown to be one of the mechanisms for HDACi resistance (43)(44)(45).…”

“…As for myeloma, previous studies have suggested the importance of RSK2 signaling associated with fibroblast growth factor receptor 3 (FGFR3) activation by t(4;14) (13,14). Considering that the activation of RAS/ERK1/2 cascades may occur through various cell-intrinsic molecular abnormalities and extracellular microenvironmental signals regardless of t(4;14) status (15)(16)(17), we hypothesized that RSK2 could be a possible general therapeutic target for multiple myeloma therapy. In this study, we investigated the activation of RSK2, especially of RSK2 Ser227 at NTKD, in myeloma-derived cell lines and patient-derived primary myeloma cells with various cytogenetic abnormalities, and assessed the importance of RSK2 as a potential therapeutic target for multiple myeloma.…”

PI3KCA plays a major role in multiple myeloma and its inhibition with BYL719 decreases proliferation, synergizes with other therapies and overcomes stroma-induced resistance

“…The modelling of the time-dependent changes in the fluxes of the constituent pathway was performed utilizing modified ordinary differential equation (ODE) and mass action kinetics of proliferation (CDK4-CCND1, CDK2-CCNA, CDK2-CCNE, Creation of cell line models. To create simulation model characterized equivalents of cell lines, the mutation information was derived from resources such as Sanger and other literature research and functionally introduced (Finelli et al, 1999;Ikediobi et al, 2006;Cassinelli et al, 2009;Steinbrunn et al, 2011). The created simulation cell lines models were validated against a set of experimental studies to confirm the definition accuracy (see Table I).…”