A modified natural small molecule inhibits triple-negative breast cancer growth by interacting with Tubb3

Triple-negative breast cancer (TNBC) is a malignant tumor without specific therapeutic targets and a poor prognosis. Chemotherapy is currently the first-line therapeutic option for TNBC. However, due to the heterogeneity of TNBC, not all of TNBC patients are responsive to chemotherapeutic agents. Therefore, the demand for new targeted agents is critical. β-tubulin isotype III (Tubb3) is a prognostic factor associated with cancer progression, including breast cancer, and targeting Tubb3 may lead to improve TNBC disease control. Shikonin, the active compound in the roots of Lithospermun erythrorhizon suppresses the growth of various types of tumors, and its efficacy can be improved by altering its chemical structure. In this work, the anti-TNBC effect of a shikonin derivative (PMMB276) was investigated, and its mechanism was also investigated. This study combines flow cytometry, immunofluorescence staining, immunoblotting, immunoprecipitation, siRNA silencing, and the iTRAQ proteomics assay to analyze the inhibition potential of PMMB276 on TNBC. In vivo study was performed, Balb/c female murine models with or without the small molecule treatments. Herein, we screened 300 in-house synthesized analogs of shikonin against TNBC and identified a novel small molecule, PMMB276; it suppressed cell proliferation, induced apoptosis, and arrested the cell cycle at the G2/M phase, suggesting that it could have a tumor suppressive role in TNBC. Tubb3 was identified as the target of PMMB276 using proteomic and biological activity analyses. Meanwhile, PMMB276 regulated microtubule dynamics in vitro by inducing microtubule depolymerization and it could act as a tubulin stabilizer by a different process than that of paclitaxel. Moreover, suppressing or inhibiting Tubb3 with PMMB276 reduced the growth of breast cancer in an experimental mouse model, indicating that Tubb3 plays a significant role in TNBC progression. The findings support the therapeutic potential of PMMB276, a Tubb3 inhibitor, as a treatment for TNBC. Our findings might serve as a foundation for the utilization of shikonin and its derivatives in the development of anti-TNBC.