In vitro activity: SW044248 is a novel, potent and selective Topoisomerase I inhibitor that was identified through a screen for chemicals selectively toxic for non-small cell lung cancer (NSCLC) cell lines. SW044248 was found to rapidly inhibit macromolecular synthesis in sensitive, but not in insensitive cells. SW044248 killed approximately 15% of a panel of 74 NSCLC cell lines and was nontoxic to immortalized human bronchial cell lines. The acute transcriptional response to SW044248 in sensitive HCC4017 cells correlated significantly with inhibitors of topoisomerases and SW044248 inhibited topoisomerase 1 (Top1) but not topoisomerase 2. SW044248 inhibited Top1 differently from camptothecin and camptothecin did not show the same selective toxicity as SW044248. Elimination of Top1 by siRNA partially protected cells from SW044248, although removing Top1 was itself eventually toxic. Cells resistant to SW044248 responded to the compound by upregulating CDKN1A and siRNA to CDKN1A sensitized those cells to SW044248. Thus, at least part of the differential sensitivity of NSCLC cells to SW044248 is the ability to upregulate CDKN1A.

Cell Assay: SW044248 is selectively toxic in 18/74 NSCLC lines. SW044248 is a non-canonical Top1 inhibitor, and is selectively toxic for certain NSCLC cell lines. SW044248 shows no effect on Top2. SW044248 (2, 5, 10 μM) rapidly inhibits transcription, translation and DNA synthesis in sensitive cells (HCC4017 and H292 cells) but not insensitive cells (HBEC30KT cells and HCC44 cells). SW044248 (10 μM) rapidly activates the integrated stress response through kinases GCN2 and PKR. The inhibition of Top1 in HCC4017 cells is helpful to the toxicity of SW044248. SW044248 (5, 10 μM) shows no effect on HBEC30KT and HCC44 cell lines due to the up-regulation of p21CDKN1A