Loss of LKB1 promotes lactate utiliaztion in KRAS -mutant lung adenocarcinoma

Loss of function of the tumor suppressor LKB1, which is encoded by the gene STK11 , represents about 20% in non-small cell lung cancer (NSCLC). LKB1 is frequently co-mutated with KRAS , and LKB1-deficiency is associated with resistance to anti-PD1 therapy but remain partial response to anti-PD1/CTLA4 dual checkpoint blockade. We previously found that LKB1 loss led to increased lactate levels in the tumor microenvironment and suppressed anti-tumor immunity. However, whether LKB1-deficient tumor cells directly benefit from the lactate rich environment remains unclear. We hypothesized that LKB1 deficiency enhances lactate utilization and promotes a malignant phenotype. We performed metabolic profiling on Kras mutant LKB1-proficient (K) and -deficient (KL) cells treated with lactate. Seahorse assay was performed in K and KL cells to measure lactate utilization in vitro, and isotope tracing was conducted in vitro and in vivo. Single-cell RNAseq (scRNAseq) data from murine syngeneic tumors and clinical samples were used to assess the lactate metabolism score in KRAS mutant tumors with or without LKB1/ STK11 alterations. We treated K and KL cells with lactate as the carbon source and performed metabolic profiling. The data showed that altered metabolites were enriched in several pathways including TCA cycle. We observed that KL cells showed increased oxidative phosphorylation (OXPHOS) and GSH and NADPH levels when cultured with lactate, suggesting that LKB1-deficient cells had an enhanced ability to utilize OXPHOS and maintain redox homeostasis when using lactate as an energy source. Moreover, [U-13C]lactate tracing revealed that isotopologues were significantly enriched in pyruvate and TCA components such as citrate, glutamate and malate in KL cells, indicating the enhanced lactate incorporation into the TCA cycle, which was consistent with the observed elevated OXPHOS. Next, we injected K and KL murine cells into mice to establish syngeneic tumor models. Animals were infused with [U-13C]lactate to detect the isotopologues distribution in vivo. KL tumors showed significantly enhanced lactate incorporation as compared to K tumors. Genetically engineered mouse models of K and KL lung cancer similarly showed that increased amounts of lactate transformed into citrate, succinate and malate. Finally, we analyzed data from clinical samples infused with [U-13C]lactate, although the sample size was limited, patients with KRAS / STK11 co-mutation showed a trend towards increased labeling of TCA cycle metabolites as compared to patients with KRAS or KRAS / TP53 co-mutation. Additionally, scRNAseq data from murine tumors and clinical samples showed significantly elevated lactate metabolic score in KL tumors. Collectively, our data indicates that LKB1-deficient tumors increase lactate incorporation and utilization, suggesting that targeting lactate metabolism as a novel therapeutic approach for this recalcitrant subgroup.