Background: Patients (pts) with advanced biliary tract cancers (BTC) have poor prognosis despite systemic chemotherapy. Gemcitabine and cisplatin is a standard first-line systemic therapy with an overall response rate (ORR) of 26% and a median overall survival of 11.7 months. This investigator-initiated, multi-institutional phase 1b/2 trial is designed to investigate the role of gemcitabine, cisplatin and CPI-613 in pts with advanced BTC. CPI-613 is a stable intermediate of a lipoate analog that inhibits pyruvate dehydrogenase and a-ketoglutarate dehydrogenase enzymes of the tricarboxylic (TCA) cycle preferentially within the mitochondria of cancer cells. Methods: Key eligibility criteria include histologically confirmed, metastatic or unresectable BTC (intra- or extra-hepatic and gallbladder) without prior systemic treatment, measurable disease per RECIST v1.1, and ECOG PS 0-1. Primary objective of the phase 1b portion (n = 20 pts; TiTE-CRM methodology) is to determine the recommended phase 2 dose of the combination, and for the phase 2 portion, ORR (n = 48-58 pts; 2:1 randomization). Assuming a null hypothesis ORR of 25% and an alternative hypothesis of 43%, this ongoing trial has at least 80% power with a one-sided alpha of 0.05 to identify treatment efficacy of the study arm. Secondary objectives include evaluation of progression-free survival, overall survival, and safety in this patient population. Exploratory objectives include identification of molecular markers of response and resistance in tumor samples and serially collected blood (pre-, on-, and post-therapy), including whole exome/transcriptomic analysis, and immunohistochemical staining (PDK, PDH, KGDH, SOD2 and CD79a). Gemcitabine 1000 mg/m², cisplatin 25 mg/m² with or without CPI-613 (dose levels: 500 mg/m², 1000 mg/m², 1500 mg/m², and 2000 mg/m²) will be given IV on days 1 and 8 every 21 days. In the absence of disease progression, pts may continue therapy for up to 2 years. Total accrual goal is 68-78 evaluable pts. To date, 5 of planned 20 pts enrolled on the phase 1b portion are without dose limiting toxicity. Clinical trial information: NCT04203160