Abstract A178: Developing chemotherapeutics which selectively disable the actin cytoskeleton of tumor cells.

Background: The actin cytoskeleton is an important regulator of a variety of cellular functions including cell motility, adhesion, and proliferation, making it an ideal chemotherapeutic target. Despite this promise there are still no anti-actin compounds used in current chemotherapy, primarily due to the inability of existing anti-actin agents to discriminate between the actin cytoskeleton of tumor cells and the actin filaments of the muscle sarcomere. We have previously shown that tropomyosin, an integral component of the actin cytoskeleton, defines functionally distinct populations of actin filaments. We have identified a specific tropomyosin isoform common to all tumor cells tested to date which regulates cell proliferation and have designed a new class of compounds to target this filament population. Summary of Results: Anti-tropomyosin (Tm) compounds were selected based their ability to target the actin cytoskeleton and their efficacy against a panel of neuroblastoma and melanoma cell lines. The lead compound, TR100, was shown to be effective against a panel of tumor cell lines with an average EC 50 of 3μM. When tested in 3D melanoma spheroid models, which more accurately mimic the tumor microenvironment, TR100 inhibited melanoma cell growth and motility. This effect translated to a reduction in tumor cell growth in vivo in both neuroblastoma and melanoma xenograft models. In vitro data using isolated rat cardiomyocytes demonstrated that TR100 had minimal impact on contractile function. In vivo data from the drug treated animals also showed no evidence of cardiac damage as measured by blood Troponin I levels and no changes in the intraventricular septum thickness of isolated hearts. These results demonstrate that it is possible to target distinct actin filament populations based on the tropomyosin composition. Next generation anti-Tm compounds with improved efficacy and specificity have now been developed. Preliminary data demonstrate that these compounds exhibit increased selectivity for transformed cells. Conclusions: Taken together, our findings suggest that the anti-Tm compounds show a significant improvement in the therapeutic window compared to existing anti-actin agents. This novel approach and the development of the new class of anti-Tm compounds may be the key for disabling a long sought after target, the actin cytoskeleton, and may lead to a new class of chemotherapeutics active against a broad range of cancer types. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A178.