Developing Pharmacological tGLI1 Inhibitors

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Project Summary Patients with breast cancer brain metastasis (BCBM) survive only 6-18 months following diagnosis. It remains a significant challenge in managing BCBM patients. The goal of this project is thus to meet the need of identifying novel actionable targets and developing treatments against these targets for BCBM. Building on our preliminary results summarized below, we will focus the project on truncated glioma-associated oncogene homolog 1 (tGLI1), which was discovered in Sponsor’s/Mentor’s Lab as a tumor-specific gain-of-function GLI1 zinc-finger transcription factor that promotes breast cancer preferential metastasis to the brain, breast cancer stem cells (BrCSCs), and metastasis-supporting astrocytes in the brain metastatic niche. In the preliminary studies, we screened 1,520 compounds and identified ketoconazole (KCZ), an FDA-approved azole antifungal, selectively killed tGLI1-expressing breast cancer cells and BCBM cells with heightened efficacy against BrCSCs in vitro. Two intracardiac implantation mouse studies showed systemic KCZ administration selectively prevented circulating tGLI1-positive breast cancer cells from developing into brain metastases and suppressed the progression of existing brain metastases. We further showed KCZ reduced tGLI1-mediated expression of circulating exosomal microRNAs, miR-1246 and miR-1290, in vivo, and KCZ effectively penetrated the blood- brain barrier (BBB) without acute toxicity to liver tissues. While the mechanisms of action for KCZ inhibition of tGLI1 are still unclear, our pilot data suggest that KCZ can inhibit tGLI1 transcriptional activity and disrupt tGLI1 interactions with cellular proteins. These important novel findings have led to an FDA-approved Phase 0 clinical trial at Wake Forest Comprehensive Cancer Center that determines the effects of KCZ on tGLI1 target gene expression and KCZ penetration of the BBB in BCBM patients. Based on these observations, we hypothesized that KCZ elicits clinical activity in suppressing tGLI1 target genes in BCBM and that novel tGLI1 inhibitors can be developed through either modification of KCZ side groups or SAR analysis of fragmented hit compounds. To test this innovative hypothesis, we will test KCZ derivatives against tGLI1-positive BCBM to determine if they present with increased efficacy and retain tGLI1-targeting specificity using cell line- and PDX-derived BCBM mouse models, and elucidate the mechanisms that underlie their activity (Aim 1), and test the de novo tGLI1 inhibitors WF-217A and WF-229A synthesized via structure-activity relationship (SAR) analysis of KCZ fragments (Aim 2). This F31 predoctoral fellowship is tailored to facilitate the applicant’s development into an independent investigator who conducts translational cancer research. This goal will be achieved through relevant course work, weekly seminars and journal club presentations, presentation at national conferences, grant- and manuscript-writing workshops, regular meetings with the primary mentor and the mentoring team (4 mentors with relevant expertise), and research training that tests an innovative hypothesis using preclinical models.