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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 p21WAF1/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.

Paclitaxel (PTX) is widely used in the front-line chemotherapy for gastric cancer (GC), but resistance limits its use. Due to the lack of proper models, mechanisms underlying PTX resistance in GC were not well studied. Using established PTX-resistant GC cell sublines HGC-27R, we for the first time integrated biological traits and molecular mechanisms of PTX resistance in GC. Data revealed that PTX-resistant GC cells were characterized by microtubular disorders, an EMT phenotype, reduced responses to antimitotic drugs, and resistance to apoptosis (marked by upregulated β-tubulin III, vimentin, attenuated changes in G2/M molecules or pro-apoptotic factors in response to antimitotic drugs or apoptotic inducers, respectively). Activation of the phosphoinositide 3-kinase, the serine/threonine kinase Akt and mammalian target of rapamycin (PI3K/Akt/mTOR) and mitogen-activated protein kinase (MAPK) pathways were also observed, which might be the reason for above phenotypic alternations. In vitro data suggested that targeting these pathways were sufficient to elicit antitumor responses in PTX-resistant GC, in which the dual PI3K/mTOR inhibitor BEZ235 displayed higher therapeutic efficiency than the mTOR inhibitor everolimus or the MEK inhibitor AZD6244. Antitumor effects of BEZ235 were also confirmed in mice bearing HGC-27R tumors. Thus, these data suggest that PI3K/Akt/mTOR and MAPK pathway inhibition, especially PI3K/mTOR dual blockade, might be a promising therapeutic strategy against PTX-resistant GC.