EFFICACY OF TOPOISOMERASE I SUMO-INHIBITING COMPOUNDS IN SENSITIZING CELLS TO CAMPTOTHECIN

To determine the translational potential of novel small molecules in combination with the DNA Topoisomerase I (TOP1) poison, camptothecin (CPT), the crystal violet method was employed to quantify cell proliferation rates in treated cultures of the 293T cell line. 293T cells, derived from the human embryonic kidney, were treated with different concentrations of the cyroprotectant, dimethylsulfoxide (DMSO), CPT, and novel small molecules. Each compound was surveyed for 48 and 72-hour periods. TOP1 is the only currently known target of CPT; CPT has been developed as a chemotherapeutic drug due to its ability to enhance covalent trapping of TOP1 onto DNA by preventing completion of its topoisomerase reaction. The resulting increase in TOP1 trapped on the DNA subsequently sensitizes human cells to the effects of TOP1 poisons. Although efficacious in killing various types of cancers, employed dosages of TOP1 poisons also produce potentially lethal side effects. However, recent studies have discovered that TOP1 is catalytically suppressed specifically at the highly transcribed regions by SUMO modifications at its K391 and K436 residues. Here we show a preliminary screening of novel small molecules that have been developed to block K391/K436 SUMOylation, which we hypothesize will hypersensitize cells to TOP1 poisons. In doing so, we have also identified a candidate compound to be further tested as a cancer chemotherapeutic agent in combinational therapy.