In Vitro Long-Term Proliferation Assays to Study Antiproliferative Effects of PARP Inhibitors on Cancer Cells

: Cell proliferation assays are an important component of small molecule inhibitor screens for cancer therapies. An important but often overlooked variable involves the timing and timeframe of inhibitor treatment. Whereas many traditional chemotherapeutics kill or inhibit proliferation on the timeframe of hours or in a few days of treatment, more targeted therapies that affect other cancer-relevant pathways, including differentiation or cell stress responses, can take longer, often several days to weeks to impact cellular growth and survival. Many poly(ADP-ribose) polymerases (PARPs) are involved in cellular stress pathways; therefore, phenotypic effects of PARP inhibition are often only observed with long-term inhibitor treatment. Here we summarize several assays for analyzing long-term proliferation of both adherent and suspension cells, relying either on growth in two-dimensional tissue culture or on systems than enable growth in 3D.