Abstract PO3-06-13: A novel stable 6-aryl-2-benzoyl-pyridine colchicine-binding site inhibitor targeting microtubules (60c) is effective against taxane-resistant, metastatic breast cancer
Authors: Oluwalana Damilola , Hartman Kelli , Krutilina Raisa , Chen Hao , Playa Hilaire , Deng Shanshan , Parke Deanna , Miller Duane , Seagroves Tiffany , Li Wei 
Published: May 2024

Abstract
Background: Improving survival for patients diagnosed with metastatic disease and treating spontaneous chemoresistance remain major clinical challenges in treating breast cancer. Triple negative breast cancer (TNBC), characterized by a lack of therapeutically targetable receptors (ER/PR/HER2), is an aggressive subtype of breast cancer. TNBC therapy relies on a combination of systemically administered chemotherapies, including microtubule-targeting agents (MTAs) like paclitaxel (taxane class) or eribulin (vinca class); however, there are currently no FDA approved MTAs that bind to the colchicine-binding site. Approximately 70% of patients who initially respond to paclitaxel, a first-line MTA, will develop taxane resistance (TxR) within 6 months. We have previously reported that an orally bioavailable colchicine-binding site inhibitor (CBSI), sabizabulin (formerly known as Veru-111), not only inhibits TNBC tumor progression but also treats pre-established metastatic disease in a taxane-refractory PDX model, HCI-10-Luc2. Sabizabulin is currently in phase II/III trials for advanced prostate cancer. To further improve potency and metabolic stability, we created next-generation derivatives of the sabizabulin scaffold, including 60c. Results: 60c shows improved potency compared to sabizabulin against taxane-sensitive and TxR TNBC models, inhibiting proliferation and clonogenicity at low nanomolar concentrations, and inducing apoptosis in a dose-dependent manner. In vivo, 60c therapy significantly suppressed primary tumor growth and lung metastasis in an orthotopic MDA-MB-231-TxR xenograft model without gross toxicity, and with equivalent efficacy to combrestatin A4 phosphate (CA-4P), another CBSI in clinical trials. In the taxane-refractory HCI-10-Luc2 PDX model, 60c significantly suppressed both the growth of the primary tumor (by ~3.5 fold) and the expansion of pre-established axillary metastases (by ~26 fold) whereas paclitaxel had no effect. Analysis of total photon flux of organs excised at study endpoint showed that 60c had distinct anti-metastatic tropism as compared to sabizabulin. Whereas 60c completely suppressed metastases to the spleen (0/9 mice had signal), and significantly reduced metastatic burden in the leg bones (only 3/9 mice had signal) and in the kidney (only 2/9 mice had signal), 60c had no statistically significant effect on liver metastases. In contrast, we had previously reported that sabizabulin strongly repressed liver metastases in the same PDX model (0 mice with detectable liver metastases), with less potent effects on bone. Unlike 60c, sabizabulin showed no improvement relative to the vehicle control for spleen and kidney metastases. Together, our data positions 60c as a promising candidate for TNBC therapy, particularly for patients with TxR disease. Our results also suggest that different CBSI scaffolds may preferentially inhibit metastasis to specific organs, which requires further investigation.
Citation Format: Damilola Oluwalana, Kelli Hartman, Raisa Krutilina, Hao Chen, Hilaire Playa, Shanshan Deng, Deanna Parke, Duane Miller, Tiffany Seagroves, Wei Li. A novel stable 6-aryl-2-benzoyl-pyridine colchicine-binding site inhibitor targeting microtubules (60c) is effective against taxane-resistant, metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-06-13.