MYCi361 is a MYC inhibitor that engages MYC inside cells, disrupts MYC/MAX dimers, and impairs MYC-driven gene expression. MYCi361 binds to MYC with Kd of 3.2 μM. MYCi361 suppresses in vivo tumor growth, increases tumor immune cell infiltration, upregulates PD-L1 on tumors, and sensitizes tumors to anti-PD1 immunotherapy.