OBJECTIVE: The aim of this study is to investigate the inhibitory effect of camptothecin derivative 3j on Non-Small Cell Lung Cancer (NSCLCs) cells and the potential anti-tumor mechanisms. BACKGROUND: Camptothecin compounds are considered as the third largest natural drugs which are widely investigated in the world and they suffered restriction because of serious toxicity, such as hemorrhagic cystitis and bone marrow suppression. METHODS: Using cell proliferation assay and S180 tumor mice model, a series of 20(S)-O-substituted benzoyl 7- ethylcamptothecin compounds were screened and evaluated the antitumor activities in vitro and in vivo. Camptothecin derivative 3j was selected for further study using flow cytometry in NSCLCs cells. Cell cycle related protein cyclin A2, CDK2, cyclin D and cyclin E were detected by Western Blot. Then, computer molecular docking was used to confirm the interaction between 3j and Topo I. Also, DNA relaxation assay and alkaline comet assay were used to investigate the mechanism of 3j on DNA damage. RESULTS: Our results demonstrated that camptothecin derivative 3j showed a greater antitumor effect in eleven 20(S)-O-substituted benzoyl 7-ethylcamptothecin compounds in vitro and in vivo. The IC50 of 3j was 1.54+/- 0.41 microM lower than irinotecan with an IC50 of 13.86+/-0.80 microM in NCI-H460 cell, which was reduced by 8 fold. In NCI-H1975 cell, the IC50 of 3j was 1.87+/-0.23 microM lower than irinotecan (IC50+/-SD, 5.35+/-0.38 microM), dropped by 1.8 fold. Flow cytometry analysis revealed that 3j induced significant accumulation in a dose-dependent manner. After 24h of 3j (10 microM) treatment, the percentage of NCI-H460 cell in S-phase significantly increased (to 93.54 +/- 4.4%) compared with control cells (31.67 +/- 3.4%). Similarly, the percentage of NCI-H1975 cell in Sphase significantly increased (to 83.99 +/- 2.4%) compared with control cells (34.45 +/- 3.9%) after treatment with 10microM of 3j. Moreover, increased levels of cyclin A2, CDK2, and decreased levels of cyclin D, cyclin E further confirmed that cell cycle arrest was induced by 3j. Furthermore, molecular docking studies suggested that 3j interacted with Topo I-DNA and DNA-relaxation assay simultaneously confirmed that 3j suppressed the activity of Topo I. Research on the mechanism showed that 3j exhibited anti-tumour activity via activating the DNA damage response pathway and suppressing the repair pathway in NSCLC cells. CONCLUSION: Novel camptothecin derivative 3j has been demonstrated as a promising antitumor agent and remains to be assessed in further studies. CI - Copyright(c) Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.