Fig. 5. Predictive biomarkers for PARPi-mediated cytotoxicity in SCLC.

(A) Extent of DNA damage in a panel of SCLC cells treated with talazoparib. Cells were treated with talazoparib (1 μM for 48 hours), and cell lysates were subjected to immunoblot analysis. Red: Sensitive SCLC cells; blue: resistant SCLC cells. (B) Levels of ASCL1 and cleaved PARP1 in ASCL1^high SCLC cells treated with talazoparib. ASCL1^high SCLC cells were treated with talazoparib [1 (+) and 10 (++) μM for 48 hours]. Cell lysates were subjected to immunoblot analysis. Red: Sensitive ASCL1^high SCLC cells; blue: resistant ASCL1^high SCLC cells. (C) Levels of HUWE1 in ASCL1^high SCLC cells. Values were presented as means ± SD from (n = 3 to 7). Red: Sensitive ASCL1^high SCLC cells; blue: resistant ASCL1^high SCLC cells. S.E., short exposure; L.E., long exposure. (D) Relative levels of HUWE1 in ASCL1^high SCLC cells from TMT-based proteomic datasets. The values of HUWE1 from the DMSO-treated samples in PARPi-sensitive and PARPi-resistant ASCL1^high SCLC cells used in this study were collected, normalized, and presented as means ± SD. (E) HUWE1-mediated ASCL1 degradation in PARPi-resistant ASCL1^high SCLC cells. H1436 and H889 cells expressing Flag-HUWE1 were treated with talazoparib (1 μM for 48 hours), and cell lysates were subjected to immunoblot analysis. Values were presented as means ± SD (n = 3). (F) HUWE1-mediated cell death in PARPi-resistant ASCL1^high SCLC cells. H1436 and H889 cells expressing Flag-HUWE1 were treated with talazoparib (1 μM for 48 hours). Viability was measured and values were presented as means ± SEM (n = 4). (G) Boxplots showing the sensitivity of a panel of ASCL1^high SCLC cells to PARPi. ASCL1^high SCLC cells were grouped by the relative levels of HUWE1 expression, and the sensitivity was determined by the analysis of the GDSC database measuring IC₅₀ against talazoparib treatment. Values were presented as means ± SD.