Cancer cells acquire characteristics that promote growth, survival and dissemination, including dysregulation of cell cycle control, failure to respond to cell death signals, elicitation of angiogenesis and invasiveness. The most invasive cancer cells have invadopodia: actin-rich membrane protrusions that control pericellular proteolysis. Invadopodia are related to podosomes, which are elaborated in migratory differentiated cells such as phagocytes, vascular smooth muscle and endothelial cells. Although invadopodia are not required for cancer cell growth on tissue culture plastic, they facilitate growth in 3-dimensional collagen matrices. Furthermore, loss of invadopodia correlates with decreased tumorigenicity and dissemination in vivo. We hypothesized that key regulators of invadopodia were yet to be discovered. We set out to isolate these regulators, which may represent novel therapeutic targets. Many important oncology targets are kinases. Indeed, several kinase inhibitors are approved chemotherapeutic agents, and many others are in clinical testing. Most were selected on the basis of inhibition of cell cycle progression, cell survival or angiogenesis. Few studies have focused on kinases that regulate invasive cell behavior. Furthermore, there are few publications on most members of the human kinome, suggesting that this is an untapped resource for target identification. We therefore focused our search on kinases. We established a high content screening assay to quantify invadopodia in high throughput. We screened for invadopodia inhibitors in an siRNA library specific for the kinome, and identified 14 strong hits. To date we have focused on three of these hits. In preliminary studies we found that each is involved in invadopodia formation, and overexpressed in human cancer cells. Other kinases are at an earlier stage of validation. Thus we have developed a prioritized list of kinases with invadopodia functions, which may play roles in human tumor growth and progression. Our high content screening assay has provided us with a rich pipeline of kinase regulators, and we hypothesize that some of these kinases are novel therapeutic targets. We propose to further evaluate the therapeutic potential of our top hits, as well as extend our validation efforts to other kinases in the pipeline. The overarching significance of this research is the extraordinary opportunity to develop new therapeutic approaches to the treatment of disseminated cancers. The near term impact lies in the ability of this research to identify new molecular targets with novel mechanisms of action.
The growth of disseminated cancers leads to morbidity and mortality, and there is an urgent unmet need for new therapeutic targets. This research seeks to identify kinases that mediate invasive behavior of cancer cells, and thus is of relevance to the public health problem of metastatic cancer.
