A novel oral camptothecin analog, gimatecan, exhibits superior antitumor efficacy than irinotecan toward esophageal squamous cell carcinoma in vitro and in vivo

Esophageal squamous cell carcinoma (ESCC) is a frequently diagnosed and deadly malignancy with few standard therapeutic options. Camptothecins are considered one of the most promising antitumor drugs. A modified lipophilic analog, gimatecan, was synthesized as a novel oral camptothecin and showed impressive effects in various tumors, but its therapeutic efficacy and mechanisms in ESCC remain unclear. This study investigated the antitumor efficacy and mechanisms of gimatecan in ECSS both in vitro and in vivo. Using ESCC cell lines, cell line-derived xenografts and patient-derived xenografts models, we evaluated gimatecan’s inhibition of tumor growth, and compared its antitumor efficacy with that of irinotecan. Topoisomerase I function and expression were assessed using the DNA relaxation assay and Western blotting, respectively. DNA damage was evaluated by Western blotting. Cell cycle progression and cell apoptosis were assessed using flow cytometry and Western blotting. Gimatecan could significantly suppress tumor growth in vivo and inhibit tumor cell proliferation in vitro, which was superior to irinotecan. Gimatecan suppressed the function and expression of topoisomerase I. It also caused DNA damage and activated the phosphorylation of multiple checkpoint gatekeepers, such as ATM, ATR, BRCA1, H2AX, CHK1, CHK2, and p53. It induced S phase arrest, enhanced the expression of p21(WAF1/CIP), and suppressed the expression of CDK2 and cyclin A. Induction of apoptosis was accompanied by increases in Bax, cleaved-caspase 3 activation, cleaved-caspase 9 induction, and a decrease in Bcl-2. The molecular and phenotypic changes induced by gimatecan were stronger than that of irinotecan. In ESCC, gimatecan suppressed the expression and function of topoisomerase I, induced DNA damage and intra-S phase cell cycle arrest, and resulted in apoptosis. And the results suggest that gimatecan has higher potency in inhibiting ESCC tumor growth than irinotecan, providing a rational novel therapeutic strategy for future clinical evaluation.