A CD13 inhibitor, ubenimex, synergistically enhances the effects of anticancer drugs in hepatocellular carcinoma

Abstract

Cancer stem cells (CSCs) were reported to be involved in resistance to chemo/radiation therapy. We previously reported that CD13 was both a marker of CSCs and a candidate therapeutic target in HCC. In the present study, we explored the antitumor effect of a combined therapy, where ubenimex, a CD13 inhibitor, was combined with conventional anticancer drugs, fluorouracil (5-FU), cisplatin (CDDP), doxorubicin (DXR) and sorafenib (SOR), and we elucidated the mechanism of these combination therapies. We evaluated changes in the expression of CD13 before and after treatment with anticancer drugs and with or without ubenimex in the human HCC cell lines HuH7 and PLC/PRF/5. The interactions between the anticancer drugs and ubenimex were determined with isobologram analyses. We analyzed cell cycle, apoptosis, and intracellular reactive oxygen species (ROS) levels to explore the mechanisms of the combination therapies. In both cell lines, the expression of CD13 increased after a 72-h exposure to each anticancer drug alone (P<0.05), and the expression of CD13 decreased with ubenimex administration (P<0.05). Isobologram analyses indicated that ubenimex had synergistic effects with 5-FU, CDDP and DXR, and an additive effect with SOR. Cell cycle analyses showed that ubenimex decreased the proportion of cells in G0/G1. Ubenimex enhanced the effects of 5-FU, CDDP and DXR by increasing apoptosis and intracellular ROS levels. In combination therapies, ubenimex synergistically enhanced the antitumor effects of 5-FU, CDDP and DXR on cell cycle regulation and apoptosis induction in HCC cell lines. The effects of ubenimex were due to increased intracellular ROS levels.

The miR‐200b–ZEB1 circuit regulates diverse stemness of human hepatocellular carcinoma

“…Since CD13 regulates the stemness‐mediated dormancy of cancer cells and CD24 upregulates NANOG expression by increasing STAT3 phosphorylation, we investigated whether CD13 and CD24 are functionally involved in HCC stemness. We examined their roles in tumor initiation by silencing their expression in HCC cells.…”

“…Past and present findings indicate that CD24 is a potential surface target for anti‐HCC therapies. In contrast, CD13, which overexpresses in 15.8% of HCCs, protects cells from DNA damage by regulating the level of reactive oxygen species, and CD13 inhibitors such as ubenimex have been shown to synergistically enhance the anti‐HCC efficacy of several anti‐cancer drugs …”

“…We failed to clone the EpCAM promoter region because of its high GC content. We then used chromatin immunoprecipitation assays and verified that ZEB1 binds 3.7 | CD13 and CD24 are functional stemness markers in HCC Since CD13 regulates the stemness-mediated dormancy of cancer cells 6,13,43 and CD24 upregulates NANOG expression by increasing STAT3 phosphorylation, 7 we investigated whether CD13 and CD24 are functionally involved in HCC stemness. We examined their roles in tumor initiation by silencing their expression in HCC cells.…”

“…Many of these surface markers are also functionally implicated in tumor development and progression. CD13 helps HCC cells escape chemotherapy by inducing cells into dormancy and reducing accumulation of reactive oxygen species, DNA damage, and cell death . CD24 facilitates activation of STAT3‐mediated signaling, which subsequently induces expression of NANOG, a pivotal stemness transcription factor, thereby endowing tumor cells with stemness traits .…”

“…CD13 helps HCC cells escape chemotherapy by inducing cells into dormancy and reducing accumulation of reactive oxygen species, DNA damage, and cell death. 6,13 CD24 facilitates activation of STAT3-mediated signaling, which subsequently induces expression of NANOG, a pivotal stemness transcription factor, thereby endowing tumor cells with stemness traits. 7 EpCAM, a cell adhesion molecule that connects to the actin cytoskeleton via β-actinin, is involved in the regulation of cell proliferation.…”