Approximately one-third of endocrine-treated women with estrogen receptor alpha–positive (ER+) breast cancers are at risk of recurrence due to intrinsic or acquired resistance. Thus, it is vital to understand the mechanisms underlying endocrine therapy resistance in ER+ breast cancer to improve patient treatment. Mitochondrial fatty acid β-oxidation (FAO) has been shown to be a major metabolic pathway in triple-negative breast cancer (TNBC) that can activate Src signaling. Here, we found metabolic reprogramming that increases FAO in ER+ breast cancer as a mechanism of resistance to endocrine therapy. A metabolically relevant, integrated gene signature was derived from transcriptomic, metabolomic, and lipidomic analyses in TNBC cells following inhibition of the FAO rate-limiting enzyme carnitine palmitoyl transferase 1 (CPT1), and this TNBC-derived signature was significantly associated with endocrine resistance in patients with ER+ breast cancer. Molecular, genetic, and metabolomic experiments identified activation of AMPK-FAO-oxidative phosphorylation (OXPHOS) signaling in endocrine-resistant ER+ breast cancer. CPT1 knockdown or treatment with FAO inhibitors in vitro and in vivo significantly enhanced the response of ER+ breast cancer cells to endocrine therapy. Consistent with the previous findings in TNBC, endocrine therapy–induced FAO activated the Src pathway in ER+ breast cancer. Src inhibitors suppressed the growth of endocrine-resistant tumors, and the efficacy could be further enhanced by metabolic priming with CPT1 inhibition. Collectively, this study developed and applied a TNBC-derived signature to reveal that metabolic reprogramming to FAO activates the Src pathway to drive endocrine resistance in ER+ breast cancer. Significance: Increased fatty acid oxidation induced by endocrine therapy activates Src signaling to promote endocrine resistance in breast cancer, which can be overcome using clinically approved therapies targeting FAO and Src.

Background: Metabolic disorders and chronic liver disease (CLD) play crucial roles in the development and progression of liver cancer (LC). Since the ethnic minority population increasingly suffers from CLD and LC, it is vital to understand the biosocial factors contributing to CLD and LC. The ’All of Us’ database, with significant participation from minority populations, provides a valuable tool for studies in different racial/ethnic groups. Using different databases, including the ‘All of Us’ and ‘The Cancer Genome Atlas’, this study aimed to understand the biosocial factors contributing to CLD and LC. Methods: Using ‘All of Us’ data, confounding factors like the lack of immunization, comorbidities, and socioeconomic status (SES) barriers were analyzed in a cohort of 33767 CLD [non-alcoholic fatty liver disease, alcoholic liver disease, and Hepatitis B and C] patients. Among the 556 LC patients in the ‘All of Us’ database, 92% had CLD. Since hypoxanthine is known to be increased in the urine of LC patients, purine metabolic pathway genes were analyzed using different databases and validated using publicly available RNASeq data. Results: We identified several confounding factors associated with CLD in Hispanic (HA) and African American (AA) populations compared to the non-Hispanic White (NHW) populations. HA and AA CLD patients suffer from high SES barriers. While most of the genes related to the purine metabolic pathway were upregulated in LC, xanthine dehydrogenase (XDH), which converts hypoxanthine to uric acid, showed a downregulation in the tumor compared to the normal tissues. The TCGA data among different racial/ethnic groups showed that only in Asian (AN) LC tumors the XDH expression was significantly lower compared to the NHW. The decreased XDH mRNA expression in AN LC compared to benign tissues was further validated using publicly available RNAseq datasets. Survival analysis confirmed poor overall survival among the AN LC patients with lower XDH expression in their tumors. Conclusions: Our study identified several confounding factors contributing to the minority CLD population. This study also identified decreased XDH expression as a critical metabolic alteration that has clinical significance in AN LC patients.

Approximately one-third of endocrine-treated women with estrogen receptor alpha–positive (ER+) breast cancers are at risk of recurrence due to intrinsic or acquired resistance. Thus, it is vital to understand the mechanisms underlying endocrine therapy resistance in ER+ breast cancer to improve patient treatment. Mitochondrial fatty acid β-oxidation (FAO) has been shown to be a major metabolic pathway in triple-negative breast cancer (TNBC) that can activate Src signaling. Here, we found metabolic reprogramming that increases FAO in ER+ breast cancer as a mechanism of resistance to endocrine therapy. A metabolically relevant, integrated gene signature was derived from transcriptomic, metabolomic, and lipidomic analyses in TNBC cells following inhibition of the FAO rate-limiting enzyme carnitine palmitoyl transferase 1 (CPT1), and this TNBC-derived signature was significantly associated with endocrine resistance in patients with ER+ breast cancer. Molecular, genetic, and metabolomic experiments identified activation of AMPK-FAO-oxidative phosphorylation (OXPHOS) signaling in endocrine-resistant ER+ breast cancer. CPT1 knockdown or treatment with FAO inhibitors in vitro and in vivo significantly enhanced the response of ER+ breast cancer cells to endocrine therapy. Consistent with the previous findings in TNBC, endocrine therapy–induced FAO activated the Src pathway in ER+ breast cancer. Src inhibitors suppressed the growth of endocrine-resistant tumors, and the efficacy could be further enhanced by metabolic priming with CPT1 inhibition. Collectively, this study developed and applied a TNBC-derived signature to reveal that metabolic reprogramming to FAO activates the Src pathway to drive endocrine resistance in ER+ breast cancer.Significance:Increased fatty acid oxidation induced by endocrine therapy activates Src signaling to promote endocrine resistance in breast cancer, which can be overcome using clinically approved therapies targeting FAO and Src.

Supplementary Material and Methods