Cancer stem cells (CSCs) are responsible for chemoresistance, tumor recurrence and metastasis. Reportedly, aminopeptidase N (APN, also known as CD13) is a marker for semi-quiescent CSCs and a therapeutic target in human liver CSCs. In the present study, the effect of BC-02, a compound obtained by conjugating a CD13 inhibitor bestatin and fluorouracil (5-FU), was investigated toward liver CSCs. Tumor spheres formed in serum-free culture conditions have been successfully used to enrich CSCs. In this study, the sphere cells were shown to have several characteristics of CSCs, including drug resistance, high tumorigenicity, epithelial-mesenchymal transition (EMT) phenotype, lower reactive oxygen species (ROS) levels, greater colony-forming efficiency and increased proliferation capacity in vitro. Furthermore, BC-02 effectively suppressed self-renewal and malignant proliferation of CSCs compared with 5-FU, bestatin, and even the combination of 5-FU and bestatin. In addition, cell proliferation was effectively suppressed when exposed to 5-FU plus CD13-neutralizing antibody (CD13 Ab) compared with 5-FU alone. BC-02 can effectively inhibit the activity of CD13. Results demonstrated that CD13 inhibitor BC-02 impaired the properties of liver CSCs by targeting CD13 and upregulating the intracellular ROS and ROS-induced DNA damage. BC-02 might be a potential therapeutic agent for eradicating the liver CSCs and overcoming chemoresistance in liver cancer.
Multidrug resistance (MDR) of hepatocellular carcinoma is a serious problem. Although CD13 is a biomarker in human liver cancer stem cells, the relationship between CD13 and MDR remains uncertain. This study uses liver cancer cell model to understand the role of CD13 in enhancing the cytotoxic effect of chemotherapy agents. Cytotoxic agents can induce CD13 expression. CD13 inhibitor, bestatin, enhances the antitumor effect of cytotoxic agents. Meanwhile, CD13-targeting siRNA and neutralizing antibody can enhance the cytotoxic effect of 5-fluorouracil (5FU). CD13 overexpression increases cell survival upon cytotoxic agents treatment, while the knockdown of CD13 causes hypersensitivity of cells to cytotoxic agents treatment. Mechanistically, the inhibition of CD13 leads to the increase of cellular reactive oxygen species (ROS). BC-02 is a novel mutual prodrug (hybrid drug) of bestatin and 5FU. Notably, BC-02 can inhibit cellular activity in both parental and drug-resistant cells, accompanied with significantly increased ROS level. Moreover, the survival time of Kunming mice bearing H22 cells under BC-02 treatment is comparable to the capecitabine treatment at maximum dosage. These data implicate a therapeutic method to reverse MDR by targeting CD13, and indicate that BC-02 is a potent antitumor compound.
The chemoresistance of hepatocellular carcinoma (HCC) is a serious problem that directly hinders the effect of chemotherapeutic agents. We previously reported that Aminopeptidase N (CD13) inhibition can enhance the cytotoxic efficacy of chemotherapy agents. In the present study, we use liver cancer cells to explore the molecular mechanism accounting for the relationship between CD13 and chemoresistance. We demonstrate that CD13 overexpression activates the P38/heat shock protein 27/ cAMP response element-binding protein (CREB) signaling pathway to limit the efficacy of cytotoxic agents. Moreover, blockade of P38 or CREB sensitizes HCC cells to 5-fluorouracil. Then we reveal that CREB binds to the autophagy related 7 (ATG7) promoter to induce autophagy and promote HCC cell chemoresistance. CD13 inhibition also downregulates the expression of ATG7, autophagy, and tumor cell growth in vivo. Overall, the combination a CD13 inhibitor and chemotherapeutic agents may be a potential strategy for overcoming drug resistance in HCC.
SIGNIFICANCE STATEMENTOur study demonstrates that Aminopeptidase N (CD13) promotes hepatocellular carcinoma (HCC) cell chemoresistance via the P38/heat shock protein 27/cAMP response element-binding protein (CREB) pathway. CREB regulates autophagy related 7 transcription and expression to induce autophagy. Our results collectively suggest that CD13 may serve as a potential target for overcoming HCC resistance.
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