Abstract 2378: Methylmalonic acid is elevated in non-small cell lung cancer and promotes drug resistance
Authors: Parang Bobak , Li Zhongchi , Low Vivien , Endress Jennifer , Malbari Murtaza , Saxena Ashish , Altorki Nasser , Blenis John 
Published: June 2022

Lung cancer is the leading cause of cancer-related deaths in the United States. Identifying new factors that promote drug resistance is critical to restoring drug sensitivity and improving patient outcomes. Methylmalonic acid (MMA) is a dicarboxylic acid by-product of propionate metabolism. MMA levels rise in the serum with age and are associated with cancer-related mortality (the higher the MMA, the worse the mortality). We recently asked whether this metabolite had a functional impact and showed that treating non-small cell lung cancer (NSCLC) cells with MMA in vitro promotes drug resistance through triggering epithelial-to-mesenchymal transition (EMT). However, whether MMA is elevated in lung cancer is not known, and how MMA levels are regulated is poorly understood.

To determine if MMA is elevated in NSCLC, we performed targeted metabolomics on 20 resected lung adenocarcinomas and squamous cell carcinomas with matched normal lung tissue. We found that MMA was 2.5 fold elevated in tumors compared to controls (p&lt;0.001, paired t-test). To our knowledge, this is the first report of MMA being elevated in any cancer. MMAB is one of the key MMA regulatory genes. When MMAB is inactivated or underexpressed, MMA cannot be metabolized and its intracellular levels increase. We hypothesized that loss of MMAB expression may explain elevated MMA levels in lung cancer. To test this, we analyzed publicly available mRNA expression data sets and found that MMAB is underexpressed in NSCLC (suggesting high levels of MMA). Moreover, MMAB expression correlates with survival. The lower the MMAB expression (suggesting higher MMA), the worse the survival (Hazard Ratio 0.36, p&lt;0.001). We thus asked if suppressing MMAB expression had a functional impact on cell lines. Using shRNA constructs, we knocked down MMAB in the A549 and H1975 NSCLC cell lines. Targeted metabolomics confirmed that knockdown of MMAB increased MMA levels. Moreover, knockdown of MMAB decreased cellular proliferation and increased resistance to carboplatin, pemetrexed, and osimertinib. RNA-seq analysis showed that suppressing MMAB induced EMT and senescence expression signatures. Furthermore, we found that hypoxia and nutrient stress downregulate MMAB expression at the mRNA and protein level. Collectively, our data suggest that loss of MMAB expression through hypoxia or nutrient stress can increase MMA levels, triggering EMT and resistance to chemotherapy and targeted therapy in NSCLC. Our results indicate that dysregulation of MMA plays an important role in lung cancer.

Citation Format: Bobak Parang, Zhongchi Li, Vivien Low, Jennifer Endress, Murtaza Malbari, Ashish Saxena, Nasser Altorki, John Blenis. Methylmalonic acid is elevated in non-small cell lung cancer and promotes drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2378.