We have developed a new therapeutic cancer strategy based on targeting a core component of the cancer cell actin cytoskeleton, tropomyosin Tpm3.1^1,2. The first-in-class series of anti-tropomyosin (ATM) compounds prevent the cancer-associated tropomyosin Tpm3.1 from stabilizing actin filaments, leading to the collapse of the actin cytoskeleton in cancer cells¹. Most important, ATM agents strongly synergize with anti-microtubule (anti-MT) chemotherapeutics (e.g. vinca-alkaloids and taxanes) that are among the most widely used front-line treatment strategies for multiple cancer types. Such synergy has been observed in childhood solid tumours (e.g. neuroblastoma) and adult cancers (e.g. cervical, prostate and lung cancer) both in vitro and in vivo.

Specifically, isobologram analysis has been used to quantitatively evaluate the degree of synergy between ATM agent TR100 and anti-MT drug Vincristine in HeLa cells. This drug combination has shown strong or very strong synergistic combinational effect (CI < 0.3 at ED50; CI < 0.02 at ED95) at inhibiting cell proliferation and inducing apoptosis. TR100 alone exhibits no impact on HeLa cell cycle distribution, however it significantly enhances the Vincristine-induced cell cycle arrest of mitosis, particularly at prometaphase and metaphase. 3D-SIM super resolution microscopy imaging and live cell imaging showed that this drug combination impacts the assembly and dynamics of the mitotic spindle in HeLa cells, causing multipolar spindle formation and astral microtubules defects extending to the cell cortex. Moreover, co-immunoprecipitation analysis suggests potential interactions among Tpm3.1, actin filaments, microtubules and their associated proteins. Together, these data indicate that Tpm3.1-containing actin filaments interact with microtubules to orient the mitotic spindle.

The synergy between ATM agents and anti-MT drugs demonstrates a crosstalk between Tpm3.1-containing actin filaments and microtubules, and a potential role for actin in mitotic spindle formation, which can be utilized to develop new cancer therapies. This novel combination therapeutic strategy has the potential both to increase the clinical effectiveness of anti-MT drugs and to reduce their neurotoxicity by dose reduction.