An FDA-Approved Antifungal, Ketoconazole, and Its Novel Derivative Suppress tGLI1-Mediated Breast Cancer Brain Metastasis by Inhibiting the DNA-Binding Activity of Brain Metastasis-Promoting Transcription Factor tGLI1

Abstract

The goal of this study is to identify pharmacological inhibitors that target a recently identified novel mediator of breast cancer brain metastasis (BCBM), truncated glioma-associated oncogene homolog 1 (tGLI1). Inhibitors of tGLI1 are not yet available. To identify compounds that selectively kill tGLI1-expressing breast cancer, we screened 1527 compounds using two sets of isogenic breast cancer and brain-tropic breast cancer cell lines engineered to stably express the control, GLI1, or tGLI1 vector, and identified the FDA-approved antifungal ketoconazole (KCZ) to selectively target tGLI1-positive breast cancer cells and breast cancer stem cells, but not tGLI1-negative breast cancer and normal cells. KCZ’s effects are dependent on tGLI1. Two experimental mouse metastasis studies have demonstrated that systemic KCZ administration prevented the preferential brain metastasis of tGLI1-positive breast cancer and suppressed the progression of established tGLI1-positive BCBM without liver toxicities. We further developed six KCZ derivatives, two of which (KCZ-5 and KCZ-7) retained tGLI1-selectivity in vitro. KCZ-7 exhibited higher blood–brain barrier penetration than KCZ/KCZ-5 and more effectively reduced the BCBM frequency. In contrast, itraconazole, another FDA-approved antifungal, failed to suppress BCBM. The mechanistic studies suggest that KCZ and KCZ-7 inhibit tGLI1’s ability to bind to DNA, activate its target stemness genes Nanog and OCT4, and promote tumor proliferation and angiogenesis. Our study establishes the rationale for using KCZ and KCZ-7 for treating and preventing BCBM and identifies their mechanism of action.

Ketoconazole-loading strategy to improve antifungal activity and overcome cytotoxicity on human renal proximal tubular epithelial cells

“…Ketoconazole is a broad-spectrum synthetic imidazole antifungal approved by the FDA [55] for the treatment of systemic fungal infections [56]. Its aqueous solubility is not sufficient (0.087 mg l −1 at 25 °C) [57] to dissolve the entire dose in gastrointestinal fluids under normal conditions and is not absorbed systemically after topical application.…”

Hedgehog pathway and cancer: A new area (Review)

“…tGLI1 increases the degree of cancer cell stemness by upregulating genes such as Nanog and by activating astrocytes to achieve metastasis ( 219 ). In summary, it is hypothesized that tGLI1 is more likely to be a marker for the diagnosis and prognosis of cancer metastasis, and thus may become a new therapeutic target ( 222 ).…”

Metastatic Breast Cancer: Review of Emerging Nanotherapeutics

“…Ketoconazole is being used for treating patients with recurrent glioma or BC brain metastasis [83]. The antifungal drug ketoconazole blocks the effect of tGLI1, a protein involved in upregulation of the cancer stem-cell subpopulation and in the activation of astrocytes in glioblastomas [91].…”