The aim of this project is to investigate the molecular-mechanical regulation of the actomyosin cortex of melanoma cells and the solid tumor microenvironment for deciphering self-organization in cancer biology.

Metastatic melanoma is the deadliest form of skin cancer, expected to kill ~7,230 people in the United States in 2019 alone (estimated by cancer.org). Different cells and mediators in the tumor microenvironment play important roles in the progression of cancer. To successfully metastasize to a distal site, melanoma cells use a variety of migration modalities that critically depend on spatial tumor microenvironment changes and changes in actomyosin cytoskeleton organization. Thus, the ability of tumor cells to adapt is a critical driver of the upregulated cancer cell motility and invasiveness which leads to tumor progression and metastasis. This cell adaption process has been shown to be highly mechanosensitive, thus mechanical properties may play an important role in fine regulating tumor progression and aggression.

We have recently developed multiple advanced atomic force microscopy (AFM) methodologies to determine the nanoscale and global mechanical properties of cells^1,2. AFM is a versatile biomedical technique in which a sample is probed with a microcantilever with or without an indenter to non-invasively measure the physical material properties of complex biological systems in a physiologically relevant environment. A major advantage of this experimental approach is that it does not require any chemical manipulation (neither labeling or fixation).

First, we used a recently developed quasi-static AFM force spectroscopy method that employs tipless cantilevers to determine global physical relevant mechanical properties including actomyosin tension, elastic Young’s modulus, viscosity, and intracellular pressure². We sought to investigate the contribution of formin activity in actomyosin cortex self-organization and mechanical regulation in melanoma cells.

Second, we implemented high spatial and temporal resolution PeakForce Tapping AFM and JPK QI modalities to map the nanoscale mechanical properties of the microenvironment of melanoma solid tumors. This enabled us to examine the changes in the mechanical properties' heterogeneity and structural self-organization that resulted in metastatic progression.

¹Efremov, Y. M.*, Cartagena-Rivera, A. X.*, Athamneh, A. I. M., Suter, D. M. & Raman, A. Mapping heterogeneity of cellular mechanics by multi-harmonic atomic force microscopy. Nat. Proct. 13, 2200-2216 (2018) *Equal contribution

²Cartagena-Rivera, A. X., Logue, J. S., Waterman, C. M. & Chadwick, R. S. Actomyosin cortical mechanical properties in nonadherent cells determined by atomic force microscopy. Biophys. J. 110, 2528-2539 (2016)

The goal of this project is to determine the anisotropic mechanical properties of developmental and mature inner ear sensory and non-sensory epithelial tissues using a novel noncontact AFM approach.

It is estimated that more than 38 million people in the United States suffer some form of hearing trouble. Additionally, in the U.S., for every 1,000 newborns, two to three are born with detectable levels of hearing loss³. Hearing loss often results from dysfunction of sensory and non-sensory epithelia in the cochlea. Sound stimuli deflect stereociliary bundles that project from the apical surface of inner and outer hair cells and open mechanotransduction channels. The apical surface of interconnected cells (hair cells and supporting cells) in the sensory epithelia need to be in mechanical equilibrium for normal hearing. Perturbations to this equilibrium cause modification to the force transmission causing a defect in sound detection and transmission. Therefore, the molecular-mechanical regulation of forces within sensory and non-sensory epithelia needs to be carefully investigated.

Formerly, we developed a noninvasive AFM method that uses acoustic frequency modulation curves acquired using cantilevers with an attached microsphere to determine the supracellular apical surface tension, effective viscosity, and intercellular adhesive forces in polarized epitheliums^4,5. More recently, we developed an advanced AFM methodology that builds upon our previously described noncontact frequency modulation AFM capable of measuring the strong anisotropy of the mechanical properties in tissues. We are currently using this new method to explore the anisotropic mechanical properties of developmental and mature inner ear sensory and non-sensory epithelia.

³NIDCD Health statistics web page 

⁴Cartagena-Rivera, A. X., Van Itallie, C. M., Anderson, J. M. & Chadwick, R. S. Apical surface supracellular mechanical properties in polarized epithelium using noninvasive acoustic force spectroscopy. Nat. Commun. 8, 1030 (2017)

⁵Cartagena-Rivera, A. X.*, Le Gal, S., Richards, K., Verpy, E. & Chadwick, R. S.* Cochlear outer hair cell horizontal top connectors mediate mature stereocilia bundle mechanics. Sci. Adv. 5, eaat9934 (2019) *Co-corresponding authors