Abstract B121: PROTAC-mediated degradation of TACC3 enhances the efficacy of anti-mitotic drugs in cancer

Abstract Although multiple solid and hematological cancers often respond to anti-mitotic drugs such as taxanes, vinca alkaloids, maytansinoid and dolastatin analogs and other compounds, the efficacy of the treatment is limited by persistent residual cancer cells. To identify the mediators of cancer cell persistence to anti-mitotic agents we performed a genome-wide CRISPR editing screen in cancer cells treated with taxanes. The most essential gene for survival under taxane treatment in our screen was Transforming Acidic Coiled-Coil containing protein 3 (TACC3), which encodes a protein localized in the centrosomes and involved in the stabilization of the gamma-tubulin ring complex at the Microtubule-Organizing Center, a structure where microtubules are nucleated and anchored on their minus end during spindle formation. Follow-up validation experiments in several breast, lung and leukemia cancer cell lines using CRISPR-mediated single-gene knock-out (KO) confirmed that ablation of TACC3 increased taxane-induced G2/M arrested cell fraction, and sensitized tumor cells to anti-tubulin drug classes, including taxanes, vinca alkaloids, maytansinoid and dolastatin analogs, but also to inhibitors of microtubule associated proteins such as KIF18A. Notably, the cancer cell lines with centrosome amplification (CA, a cancer hallmark present in many aggressive tumors and typically absent in normal cells) were strongly sensitized to anti-mitotic drugs after TACC3 KO. Cancer cells with TACC3 gene KO readily engrafted in immunocompromised mice, but the TACC3-KO xenografts were significantly more sensitive to taxane treatment compared to control, confirming the in vivo relevance of our in vitro observations. Given that existing TACC3 small molecule ligands did not phenocopy the anti-mitotic drug sensitization induced by TACC3 gene KO, we reasoned that i) TACC3-targeting PROTAC (Proteolysis Targeting Chimeras) molecules can be designed by combining TACC3 ligands with ligands of E3 ubiquitin ligases (e.g. CRBN, VHL or XIAP), and ii) such PROTAC molecules would deplete TACC3 in cancer cells and phenocopy the synergistic effect of anti-mitotic drugs with TACC3 gene KO. We synthesized and evaluated more than 100 distinct PROTAC molecules against TACC3 and identified several degraders that sensitize cancer cells to anti-mitotic drugs. One PROTAC (KHS-C4) degraded TACC3 at low nanomolar concentrations, strongly synergized with anti-mitotic drugs and eliminated residual cancer cells in vitro, had acceptable in vitro liver microsome stability, excellent predicted pharmacokinetic properties, no in vivo toxicity and was selected for further in vivo efficacy evaluation in combination with anti-mitotic drugs. Our data suggests that combining anti-mitotic drugs targeting the microtubule plus end with degraders against TACC3 can induce potent synergistic anti-tumor effect. Citation Format: Slawomir Andrzejewski, Keita Nakane, Olusiji Akinrinmade, Leandro Encarnacao. Garcia, Marie Winter, Seiya Kitamura, Eugen Dhimolea. PROTAC-mediated degradation of TACC3 enhances the efficacy of anti-mitotic drugs in cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr B121.