Background: Although most cancers are initially susceptible to existing anticancer therapies, over time cancer cells develop resistance. BOLD-100 is a first-in-class therapy that targets the GRP78 pathway, a major regulator of cellular stress and resistance. This therapy suppresses drug resistance, survival and proliferation by restraining stress-induced upregulation of GRP78 in tumor cells, leading to inhibition of the cell survival response. BOLD-100 successfully completed a Phase 1 monotherapy trial, with a manageable safety profile; it has demonstrated synergy in established preclinical models in combination with a wide variety of anticancer therapies and shown to restore sensitivity of drug-resistant cell lines. Methods: BOLD-100-001 is a multicenter, prospective, two-stage, non-randomized Phase 1b dose escalation and expansion study of BOLD-100 in combination with FOLFOX chemotherapy for selected advanced solid gastrointestinal (GI) tumors: colorectal (CRC), pancreatic (PANC), gastric (GC) and bile duct cancers (BDC). Each patient will receive BOLD-100 along with FOLFOX chemotherapy on Day 1 of each 14-day cycle. In the dose-escalation phase (Part A), patients will be enrolled to determine the combination recommended dose using a standard 3+3 design. In the dose-expansion phase (Part B), up to 80 patients with selected GI tumors will be enrolled in 5 cohorts (comprising the 4 GI cancers referred) and treated with BOLD-100 at the recommended dose and FOLFOX, until progressive disease or unacceptable toxicity. In Part A dose-escalation, the primary objective is to assess the safety, tolerability and maximum tolerated dose. The Part B dose-expansion will assess the efficacy (progression free survival, overall survival and response rate), of FOLFOX chemotherapy plus BOLD-100. Secondary objectives in Part A and B include the assessment of pharmacokinetic and pharmacodynamic parameters and potential biomarkers predictive of efficacy. Eligible patients will have previously treated histologically/cytologically confirmed metastatic/unresectable GI tumor (CRC, PANC, GC or BDC), measurable disease per RECIST criteria, an ECOG performance score of 0 or 1, and adequate organ function. In Part A, no formal statistical hypotheses will be tested; analysis of the data will focus on comparisons of safety and dose-limiting toxicities between cohorts and only descriptive methods will be used. In Part B, Bayesian modelling will be used to continually reassess the efficacy endpoints: progression free survival, overall survival and objective response rates. The study was opened for enrollment in August 2020; approximately 25-30 patients will be screened to achieve up to 20 patients in Part A and up to 80 patients will be enrolled in Part B with a maximum of 25 patients per arm. Clinical trial information: NCT04421820