Poster Presentation 32nd Lorne Cancer 2020

Enhancing the efficacy of microtubule targeting agents through cytoskeletal crosstalk (#189)

Sharissa L Latham 1 2 3 , Theresia Reindl 3 , Nicole Bryce 4 , Manuel H Taft 3 , Monica Phimmachanh 1 , Yolande O'Donnell 1 , Max Nobis 1 2 , David Herrmann 1 2 , Astrid Magenau 1 2 , Paul Timpson 1 2 , Edna Hardeman 4 , John Lock 4 , Peter W Gunning 4 , Thomas R Cox 1 2 , Dietmar J Manstein 3 , David R Croucher 1 2
  1. Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
  2. St Vincent's Clinical School, UNSW, Darlinghurst, NSW, Australia
  3. Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany
  4. School of Medical Sciences, UNSW, Kensington, NSW, Australia

Current standard-of-care for the aggressive, triple negative breast cancer (TNBC) subtype involves preoperative drug regimens incorporating microtubule targeting agents (MTAs), a compound class that aims to inhibit cell proliferation and invasion by disrupting microtubule dynamics. However, these frontline agents ignore the finely-tuned balance that exists between the actin and microtubule cytoskeletons. Compensatory effects mediated by the actin cytoskeleton in response to MTAs have been shown to drive metastasis and drug-resistance, factors that ultimately limit the response to MTAs and likely underlie poor patient outcomes. Here, we assess whether TNBC cells can be sensitized to clinically-approved MTAs by co-targeting and disrupting actin-microtubule crosstalk.

Actomyosin complexes comprising nonmuscle myosin-2 (NM-2) motors generate the contractile forces essential for cell adhesion, migration and division, and represent an established point of crosstalk between the two cytoskeletal networks. However, the few NM-2 destabilizing compounds identified to date have shown limited anti-tumorigenic potential. Using biochemical approaches, we have now identified and characterized a commercially available small molecule that instead directly binds and activates NM-2 motors, which we refer to as Myosin-2 Motor Activator (M-2MA). Within tumour cells, M-2MA stabilizes a contractile phenotype and reduces both proliferation and invasion in a 3D setting. As a combination therapy, M-2MA exhibits strong synergistic effects with a subset of MTAs, enhancing their ability to induce apoptosis throughout the entire cell cycle.

Using M-2MA as a first-in-class molecule, we have exploited a large-scale, chemically diverse screen (Bryce et al., 2019, Cell Systems) to identify further compounds that induce similar F-actin phenotypes. Of the 39 compounds identified, 33 enhance the efficacy of clinically-approved MTAs, 10 display MTA synergy profiles consistent with M-2MA and 3 are effective at nanomolar doses. Together, these data demonstrate that disrupting cytoskeletal crosstalk may represent a powerful and viable therapeutic approach to enhance the sensitivity of tumour cells to standard-of-care treatment.