Shinichi Saito

Folate‐appended cyclodextrin carrier targets ovarian cancer cells expressing the proton‐coupled folate transporter

AbstractFolate receptor alpha (FRα) is overexpressed in >80% of epithelial ovarian cancer (EOC). Accordingly, folate is attracting attention as a targeting ligand for EOC. For EOC patients, paclitaxel (PTX) is generally used as a first‐line chemotherapeutic agent in combination with platinum‐based drugs. Cyclodextrin (CyD) is a potential new formulation vehicle for PTX that could replace Cremophor‐EL, a traditional formulation vehicle that causes significant side effects, including neutropenia. Several years ago, folate‐appended β‐CyD (Fol‐c1‐β‐CyD) was developed as an FRα‐targeting drug carrier, but its efficacy as a treatment for EOC remains to be determined. In this study, we assessed the antitumor activity of PTX in Fol‐c1‐β‐CyD (PTX/Fol‐c1‐β‐CyD) in EOC‐derived cell lines. We found that PTX/Fol‐c1‐β‐CyD killed not only FRα‐expressing cells but also FRα‐negative cells. In the FRα‐negative A2780 cells, knockdown of proton‐coupled folate transporter (PCFT) significantly decreased the cytotoxicity of PTX/Fol‐c1‐β‐CyD, whereas knockdown of FRα did not. By contrast, knockdown of either FRα or proton‐coupled folate transporter (PCFT) decreased the cytotoxicity of PTX/Fol‐c1‐β‐CyD in FRα‐expressing SK‐OV‐3 cells. Furthermore, the cytotoxicity of PTX/Fol‐c1‐β‐CyD in A2780 cells was increased at acidic pH, and this increase was suppressed by PCFT inhibitor. In mice intraperitoneally inoculated with FRα‐expressing or PCFT‐expressing EOC cells, intraperitoneal administration of PTX/Fol‐c1‐β‐CyD significantly suppressed the growth of both types of EOC cells relative to PTX alone, without inducing a significant change in the neutrophil/white blood cell ratio. Our data suggest that Fol‐c1‐β‐CyD targets not only FRα but also PCFT, and can efficiently deliver anticancer drugs to EOC cells in the peritoneal cavity.

Indoxyl Sulfate Promotes Metastatic Characteristics of Ovarian Cancer Cells via Aryl Hydrocarbon Receptor–Mediated Downregulation of the Mas Receptor

Although platinum-combination chemotherapy shows a high response rate at the primary site, epithelial ovarian cancer (EOC) treatment remains challenging because of tumor recurrence and metastasis. Recent studies have revealed that chemotherapy paradoxically promotes cancer cell survival, proliferation, and metastasis, although the reason for this remains unclear. The underlying molecular mechanisms that contribute to chemotherapy-induced metastasis need to be elucidated to establish effective therapeutic strategies. Acute kidney injury is a known side effect of cisplatin treatment, and kidney dysfunction results in the accumulation of uremic toxins in the serum. The present study aimed to investigate whether indoxyl sulfate (IS), a representative uremic toxin, affects the pathophysiology of EOC. In this study, IS reduced the expression of Mas receptor (MasR) in cultured human EOC cells. Both knockdown of the aryl hydrocarbon receptor (AhR), which is an intracellular IS receptor, and inhibition of AhR function suppressed IS-mediated downregulation of MasR in SK-OV-3 cells. IS induced the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in an AhR-dependent manner. Inhibition of the STAT3 pathway or reactive oxygen species production suppressed the IS-mediated reduction of MasR. IS stimulated cell migration and invasion of SK-OV-3 cells in an AhR-dependent manner. Cisplatin-nephropathy model mice exhibited elevated levels of serum IS accompanied by elevated levels of blood urea nitrogen and serum creatinine. Furthermore, intraperitoneal administration of IS in mice promoted tumor growth and metastasis. Finally, we found that the MasR agonist Ang-(1-7) suppressed the IS-mediated effects on cell proliferation, migration, and invasion of SK-OV-3 cells. However, the knockdown of MasR expression by specific small interfering RNA in the absence of IS resulted in only minimal promotion of cell migration and invasion. These findings demonstrate that IS promotes malignancy in ovarian cancer via AhR-mediated downregulation of MasR function, whereas Ang-(1-7) attenuates this effect, thereby suggesting that Ang-(1-7) could provide a future treatment strategy for this cancer type.