Combined targeting of MEK and the glucocorticoid receptor for the treatment of RAS-mutant multiple myeloma

Abstract

Background: Multiple myeloma (MM) remains incurable despite recent therapeutic advances. RAS mutations are frequently associated with relapsed/refractory disease. Efforts to target the mitogen-activated protein kinase (MAPK) pathway with the MEK inhibitor, trametinib (Tra) have been limited by toxicities and the development of resistance. Dexamethasone (Dex) is a corticosteroid commonly used in clinical practice, to enhance efficacy of anti-myeloma therapy. Therefore, we hypothesised that the combination of Tra and Dex would yield synergistic activity in RASmutant MM. Methods: The response of human MM cell lines to drug treatment was analysed using cell proliferation assays, Western blotting, Annexin V and propidium iodide staining by flow cytometry and reverse phase protein arrays. The efficacy of trametinib and dexamethasone treatment in the MM.1S xenograft model was assessed by measuring tumor volume over time. Results:The Tra/Dex combination demonstrated synergistic cytotoxicity in KRAS G12A mutant lines MM.1S and RPMI-8226. The induction of apoptosis was associated with decreased MCL-1 expression and increased BIM expression. Reverse phase proteomic arrays revealed suppression of FAK, PYK2, FLT3, NDRG1 and 4EBP1 phosphorylation with the Tra/Dex combination. Notably, NDRG1 expression was associated with the synergistic response to Tra/Dex. MM cells were sensitive to PDK1 inhibition and IGF1-induced signalling partially protected from Tra/Dex treatment, highlighting the importance of this pathway. In the MM.1S tumor xenograft model, only the combination of Tra/Dex resulted in a significant inhibition of tumor growth.Conclusions: Overall Tra/Dex demonstrates antiproliferative activity in RAS-mutant MM cell lines associated with suppression of pro-survival PDK1 signalling and engagement of apoptotic pathways. Our data support further investigation of this combination in RAS-mutant MM.The combination of the MEK inhibitor trametinib and dexamethasone exhibits antiproliferative activity in models of RAS-mutant multiple myeloma. Suppression of PDK1 signalling is identified as a potential biomarker of response.

In Vivo Modeling of Patient Genetic Heterogeneity Identifies New Ways to Target Cholangiocarcinoma

“…The target proteins analysed by RPPA are listed in Supplementary Materials Table 4. Reverse Phase Protein Array (RPPA) analysis was carried out using established protocols for nitrocellulose-based arrays (17). Slide images were acquired using an InnoScan 710-IR scanner (Innopsys) with laser power and gain settings optimised for highest readout without saturation of the fluorescence signal.…”

Ponatinib sensitizes myeloma cells to MEK inhibition in the high-risk VQ model

“…To further explore the efficacy of Pon and the synergy between Tra and Pon in vitro, we extended the drug treatment to several human myeloma cell lines (HMCLs), including OPM2 with t(4;14) translocation, MM.1S with oncogenic KRAS mutation, H929 with t(4;14) translocation and oncogenic NRAS mutation, and Delta47 without either event [21][22][23] . Interestingly, regardless of t(4;14) status, OPM2 and MM.1S were more responsive to Pon with an IC 50 at ~ 1.4-2 µM (Fig.…”

Epidemiology, genetics and treatment of multiple myeloma and precursor diseases

“…108 The discovery of such somatic mutations has informed the development of targeted therapies such as MEK inhibitors and BRAF inhibitors. 124,125 Such targeted approaches are relatively new to MM, but based on experience in other cancers, will likely be challenged by multiple resistance mechanisms as well as clonal heterogeneity. 112,126 As well as genetic changes, alteration of gene expression through epigenetic dysregulation, for example, the abnormal histone methylation pattern observed with MMSET overexpression in t(4;14), 127 contributes to the pathogenesis MM.…”

“…Pathways annotated by somatic genetic abnormalities include the RAS/MAPK signaling, DNA damage response and the NF‐κB pathway (Figure S3). 108 The discovery of such somatic mutations has informed the development of targeted therapies such as MEK inhibitors and BRAF inhibitors 124,125 . Such targeted approaches are relatively new to MM, but based on experience in other cancers, will likely be challenged by multiple resistance mechanisms as well as clonal heterogeneity 112,126 …”