In Vitro Assays for Screening Small Molecules

Traditionally anti-cancer therapeutics have been designed to target rapidly proliferating cells causing DNA damage and inducing apoptosis. However, with the development of the cancer stem cell (CSC) hypothesis, it has been postulated that a rare, slow dividing tumor cell population is able to escape therapy and contribute to tumor relapse and metastasis. The advances in characterization of CSCs across multiple cancer subtypes have allowed for development of targeted therapies using small molecule inhibitors. In this chapter, we describe two in vitro assays measuring proliferation and secondary sphere formation, which have become gold-standard assays to evaluate the effects of targeted therapies against CSCs. Together these assays constitute a rapid, inexpensive, and highly reproducible pipeline for testing small molecule inhibitors prior to more resource demanding in vivo studies.