The Contribution of Oncogenic RAS Mutations in Obesity-Associated Multiple Myeloma
Authors: Diedrich Jonathan D , Musso Samantha A , Pianko Matthew , Bernard Jamie J 
Published: December 2024

Multiple myeloma (MM), a hematologic malignancy of clonal plasma cells, is associated with genomic instability, acquired resistance to therapeutics, and is recognized by the Centers for Disease Control and Prevention as an obesity-associated cancer. Although the mechanisms of accumulated resistance to therapy in MM and transformation from precursor states to symptomatic MM are poorly understood, epidemiological studies have shown that overweight and obese patients have a significantly increased risk of progression. Additionally, those with extreme obesity may experience inferior outcomes (progression-free and overall survival) compared to those with normal body-mass-index (BMI). Nearly 50% of newly diagnosed MM patients have RAS mutations, leading to hyperactivation of the RAS signaling cascade. This suggests that RAS mutations may promote the development of malignant disease. Importantly, up to 80% of patients with refractory disease harbor mutations in RAS, implicating oncogenic RAS signaling as an important contributor to not only progression, but also to the development of resistance to MM therapies. Thus far, obesity has been shown to exacerbate mutant RAS-driven tumor growth in epidemiological studies in pancreatic and lung cancer, but little is known about the effects of obesity on oncogenic RAS prevalence or signaling in MM. Our central hypothesis is that adipocyte-secreted factors activate oncogenic RAS to act as a selective pressure for the clonal expansion of RAS mutant MM cells. To test this hypothesis and establish the clinical and biological significance of RAS mutations in obesity-associated MM, we exposed a panel of wildtype and oncogenic RAS mutant human MM cell lines to bone marrow adipocytes (BMAs) in direct or transwell co-culture or to adipocyte conditioned media in vitro. We demonstrated that all three adipocyte exposure models had elevated phosphorylation of proteins downstream of RAS (ERK, CREB, p70S6K, and Stat3) and enhanced proliferation in response to BMAs, suggesting RAS activation. Interestingly, RAS-pathway activation and elevated proliferation in response to BMA co-culture was not observed in RAS wildtype (WT) MM cell lines. Overexpression of mutant KRAS in WT MM cells promoted baseline growth and further enhanced the proliferative response to adipocyte-secreted factors, when compared to overexpression of WT RAS as the control, suggesting adipocyte-derived factors drive MM cell growth through oncogenic RAS. Additionally, hyperactivation of the RAS signaling pathway by BMAs altered the sensitivity to FDA-approved drugs targeting the RAS signaling cascade (Cobimetinib, Sorafenib, Dabrafenib, and Cabozantinib), further implicating RAS signaling in therapeutic response. Additional interrogation of the adipocyte-conditioned media reveals interleukin-6 (IL-6) impacts ERK activation selectively in MM cells with activating RAS mutations. This study demonstrates a novel interaction between genetic factors (RAS mutations) and the tumor microenvironment (adipocyte secreted factors) to drive MM clonal expansion. Findings from this study will be critical for understanding the role of oncogenic RAS in obesity-associated MM and illuminate novel therapeutic targets or modifiable risk factors to combat disease progression and chemoresistance in MM.