Background: Autophagy, a catabolic cell survival process, is upregulated when cancer cells undergo MEK inhibition (MEKi) in preclinical models of pancreas adenocarcinoma (PDAC), and may function as a pathway of resistance. Simultaneous inhibition of the MEK and autophagy pathway in preclinical PDAC models has demonstrated anti-tumor and immune modulating effects. MEKiAUTO evaluated the tolerability and safety of combination cobimetinib, HCQ, and atezolizumab at three dose levels (DL), in advanced KRAS-mutated malignancies. Methods: This multicenter phase I study used the time-to-event continual reassessment method (TITE-CRM) with the primary objective of estimating the maximum tolerated dose (MTD) of the combination of cobimetinib (DL1 and DL2: 40mg; DL3: 60mg PO daily; on days 1-21); HCQ (DL1-DL3: 600mg PO BID), without (DL1) or with (DL2 and DL3) atezolizumab (840mg IV on days 1 and 15) every 28 days, in patients with advanced KRAS-mutated malignancies who had received at least one prior line of therapy (N=18). The secondary objective was to evaluate safety. Exploratory analysis included interrogating the MEK, autophagy, and key molecular pathways. Results: A total of 14 patients with PDAC were enrolled at Columbia University and Brown University between 02/24/20 through 03/15/22. The median age was 58, 57% were female. Of the 10 evaluable patients for dose limiting toxicity ((DLT); >80% drug adherence and ≥4 week of follow-up), 4 experienced a DLT (3 out of 8 at DL1 and 1 out of 2 at DL2). The estimated MTD is dose level 1 with an estimated probability of DLT 0.37. Grade 3 or higher treatment-related adverse events occurred in 7 of 14 (50%) patients with elevation in AST and ALT (14%), acute kidney injury, hypokalemia, anemia, rash, and CPK increase (7% each). One grade 5 multi-organ failure and acute kidney injury occurred at DL1 possibly related to cobimetinib. Clinical benefit was observed in 5 of 14 (36%) patients, all of whom experienced stable disease as best response. The median PFS and OS for overall population was 7.7 weeks (95%CI: 6-NA) and 20.7 weeks (95%CI: 15.6-46.1). Patients with KRAS^G12R (N=7) had a trend toward longer OS (mOS: 20.9 vs 16.4 weeks) than patients with KRAS^non-G12R mutations (N=7). Correlative analysis on paired tumor specimens using single nucleus RNAseq, multiplex immunofluorescence, and pathway analysis will discuss putative mechanisms of resistance. Conclusions: Combination cobimetinib, HCQ and atezolizumab had limited tolerability and efficacy in advanced KRAS-mutated PDAC. Patients with KRAS^G12R had a trend towards improved OS versus KRAS^non-G12R mutations. Correlative analysis for pharmacodynamic and resistance mechanisms will be discussed. Funding: Roche-Genentech. Clinical trial information: NCT04214418.