PROJECT SUMMARY/ABSTRACT Patients diagnosed with advanced cancers typically required systemic therapies, which include chemotherapy, targeted therapy, and immunotherapy. This proposal will address major issues affecting clinical outcomes; the question of which patient will respond to which therapy, and the question of what factors are associated with intrinsic or acquired resistance. Although intrinsic resistance can sometimes be clearly assigned to tumor-specific factors, such as specific somatic mutations, in many cases the underlying basis for resistance is obscure. This proposal will address the novel hypothesis that use of cannabidiol (CBD) provides an under-appreciated source of variation in response to clinically important cancer therapies. A growing number of individuals use CBD during cancer treatment to alleviate cancer pain, or even because of perceived benefits for treating their cancers. In the past, there has been relatively limited study of CBD and other cannabis-derived phytochemicals due to issues of social stigma and legal restrictions; however, a growing number of studies have generated convincing evidence that CBD affects the growth of some types of tumors and interacts with cytotoxic chemotherapies to modulate their activity. Some studies have demonstrated interaction between CBD cellular receptors and signaling by EGFR, SRC, and other signaling proteins that are important therapeutic targets, implying CBD might affect response to drugs targeting those proteins. However, no published studies in any cancer type have systematically probed the interaction of CBD with the signaling pathways commonly targeted in cancer therapy. In pilot studies, we have been investigating the interaction of CBD with 175 kinase-targeted inhibitors and additional control compounds in restricting the growth of cancer cells. This has identified several specific CBD- inhibitor interactions, which differed between two cell models tested, but were more notable in an EGFR- dependent cell model. Given multiple connections identified between CBD and EGFR signaling detected, the objective of this proposal is to evaluate the degree to which CBD influences the activity of pathway-targeted inhibitors in two EGFR-dependent tumor types (head and neck squamous cell carcinoma (HNSCC), and colorectal cancer (CRC)), and to characterize the underlying mechanisms of CBD-inhibitor interaction. In Aim 1, we will screen the targeted inhibitor library in additional HNSCC and CRC cell models to establish consistent patterns of interaction, using CellTiterBlue and nuclear count as initial screening assays. Positive hits will be further explored using clonogenic and 3D spheroid growth analysis, and dose range of interaction defined. Reverse-phase protein array (RPPA) analysis will be used to establish signaling pathways specifically affected by CBD-inhibitor interaction. In Aim 2, for selected specific protein-targeted inhibitors of interest, we will define the CBD-inhibitor ...