IC50 was not reached in LR5 cells. MM cell lines.(PDF) pone.0050005.s003.pdf (14K) GUID:?EB09D843-51F5-4AF9-B915-FA22CF004561 Abstract The PI3K/Akt/mTOR signal transduction pathway plays a central role in multiple myeloma (MM) disease progression and development of therapeutic resistance. mTORC1 inhibitors have shown limited efficacy in the clinic, largely attributed to the reactivation of Akt due to rapamycin induced mTORC2 activity. Here, we present promising anti-myeloma activity of MK-2206, a novel allosteric pan-Akt inhibitor, in MM cell lines and patient cells. MK-2206 was able to induce cytotoxicity and inhibit proliferation in all MM cell lines tested, albeit with significant heterogeneity Rabbit Polyclonal to APLF that was highly dependent on basal pAkt levels. MK-2206 was able to inhibit proliferation of MM cells even when cultured with marrow stromal cells or tumor promoting cytokines. The induction of cytotoxicity was due to apoptosis, which at least partially was mediated by caspases. MK-2206 inhibited pAkt and its down-stream targets and up-regulated pErk in MM cells. Using MK-2206 in combination with rapamycin (mTORC1 inhibitor), LY294002 (PI3K Gentamycin sulfate (Gentacycol) inhibitor), or U0126 (MEK1/2 inhibitor), we show that Erk- mediated downstream activation of PI3K/Akt pathway results in resistance to Akt inhibition. These provide the basis Gentamycin sulfate (Gentacycol) for clinical evaluation of MK-2206 alone or in combination in MM and potential use of baseline pAkt and pErk as biomarkers Gentamycin sulfate (Gentacycol) for patient selection. Introduction Multiple myeloma (MM) is an incurable plasma cell neoplasm that has seen considerable improvement in patient survival in the last decade due to the introduction of several effective therapies [1]. However, the responders eventually relapse and become refractory to current therapies [1]. Novel drugs based on better understanding of the disease biology are urgently required to overcome resistance and improve patient outcomes in MM [2]. Phosphotidylinositol-3-kinase (PI3K) represents a family of serine threonine kinases that initiate a complex signaling cascade in response to the binding of extracellular cytokines to their receptors expressed on cellular membranes [3]. When activated, the PI3Ks phosphorylate phosphotidylinositol-4,5-bisphosphate (PIP2) to PIP3. Gentamycin sulfate (Gentacycol) PIP3 binds to the PH domain name of Akt, which causes a conformational change in Akt exposing amino acids (Thr308 and Ser473) that are then phosphorylated and activated [4], [5]. Akt then phosphorylates and modulates multiple proteins leading to increased cell growth and survival, decreased apoptosis and drug resistance [6], [7], [8], [9], [10], [11], [12], [13]. A critical down-stream member of the PI3K/Akt pathway is the mammalian target of rapamycin complex I (mTORC1) which is usually activated by Akt either directly by relieving the PRAS40 mediated inhibition of mTORC1 or indirectly through the inhibition of TSC2 [14], [15]. Once activated, mTORC1 regulates cell growth, metabolism, translation and autophagy [16], [17]. In MM, activating mutations of PI3K/Akt/mTOR pathway members or inactivating mutations of the tumor suppressor PTEN are uncommon events [18], [19]. However, the pathway is usually up regulated in a significant proportion of MM patients due to the Gentamycin sulfate (Gentacycol) conversation of MM cells with non-malignant cells in the microenvironment, increased levels of tumor promoting cytokines and activating mutations or aberrant expression levels of other signaling pathways that feed into the PI3K/Akt pathway [20], [21], [22], [23], [24]. Activated PI3K/Akt pathway inactivates caspase-9 and offers resistance against Dexamethasone induced apoptosis [20]. IL6 stimulated PI3K/Akt signaling has also been found to phosphorylate and inactivate forkhead transcriptional factor (FKHR) resulting in G1/S phase transition, whereas PI3K inhibitors such as LY294002 block this signaling, resulting in up regulation of p27 (KIP1) and G1 growth arrest [20]. Prevention of IL6 induced mTOR activity by rapamycin and CCI779 results in inhibition of.