Isovalerylspiramycin I suppresses small cell lung cancer proliferation via ATR/CHK1 mediated DNA damage response and PERK/eIF2α/ATF4/CHOP mediated ER stress.

Small cell lung cancer (SCLC) urgently needs new therapeutic approaches. We found that the antibiotic-derived compound Isovalerylspiramycin I (ISP-I) has potent anti-tumor activity against SCLC cell lines H1048 and DMS53 both in vitro and in vivo. ISP-I induced apoptosis, G2/M phase cell cycle arrest, and mitochondrial respiratory chain dysfunction in both cell lines. Comprehensive RNA sequencing revealed that the anti-SCLC effects of ISP-I were primarily attributed to ATR/CHK1-mediated DNA damage response and PERK/eIF2α/ATF4/CHOP-mediated ER stress. Importantly, the induction of DNA damage, ER stress, and apoptosis by ISP-I was mitigated by the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine (NAC), underscoring the critical role of ROS in the anti-SCLC mechanism of ISP-I. Moreover, ISP-I treatment induced immunogenic cell death (ICD) in SCLC cells, as evidenced by increased adenosine triphosphate (ATP) secretion, elevated release of high-mobility group box 1 (HMGB1), and enhanced exposure of calreticulin (CRT) on the cell surface. Additionally, network pharmacology analysis, combined with cellular thermal shift assay (CETSA) and cycloheximide (CHX) chase experiments, demonstrated that ISP-I acted as a ligand for apurinic/apyrimidinic endonuclease 1 (APEX1) and promoted its degradation, leading to the accumulation of ROS. In conclusion, our findings elucidate the multifaceted mechanisms underlying the anti-cancer effects of ISP-I, highlighting its potential as a promising therapeutic candidate for SCLC treatment.