Antitumor Activity and Induction of TP53-Dependent Apoptosis toward Ovarian Clear Cell Adenocarcinoma by the Dual PI3K/mTOR Inhibitor DS-7423

<div><p>DS-7423, a novel, small-molecule dual inhibitor of phosphatidylinositol-3-kinase (PI3K) and mammalian target of rapamycin (mTOR), is currently in phase I clinical trials for solid tumors. Although DS-7423 potently inhibits PI3Kα (IC₅₀ = 15.6 nM) and mTOR (IC₅₀ = 34.9 nM), it also inhibits other isoforms of class I PI3K (IC₅₀ values: PI3Kβ = 1,143 nM; PI3Kγ = 249 nM; PI3Kδ = 262 nM). The PI3K/mTOR pathway is frequently activated in ovarian clear cell adenocarcinomas (OCCA) through various mutations that activate PI3K-AKT signaling. Here, we describe the anti-tumor effect of DS-7423 on a panel of nine OCCA cell lines. IC₅₀ values for DS-7423 were <75 nM in all the lines, regardless of the mutational status of <i>PIK3CA</i>. In mouse xenograft models, DS-7423 suppressed the tumor growth of OCCA in a dose-dependent manner. Flow cytometry analysis revealed a decrease in S-phase cell populations in all the cell lines and an increase in sub-G1 cell populations following treatment with DS-7423 in six of the nine OCCA cell lines tested. DS-7423-mediated apoptosis was induced more effectively in the six cell lines without <i>TP53</i> mutations than in the three cell lines with <i>TP53</i> mutations. Concomitantly with the decreased phosphorylation level of MDM2 (mouse double minute 2 homolog), the level of phosphorylation of TP53 at Ser46 was increased by DS-7423 in the six cell lines with wild-type <i>TP53</i>, with induction of genes that mediate TP53-dependent apoptosis, including <i>p53AIP1</i> and <i>PUMA</i> at 39 nM or higher doses. Our data suggest that the dual PI3K/mTOR inhibitor DS-7423 may constitute a promising molecular targeted therapy for OCCA, and that its antitumor effect might be partly obtained by induction of TP53-dependent apoptosis in <i>TP53</i> wild-type OCCAs.</p></div

Inhibition of cell proliferation by DS-7423 and rapamycin.

<p>(A) Cell viability for each cell line was analyzed using the methyl thiazolyl tetrazolium (MTT) assay 72 h after treatment with DS-7423 or rapamycin at the doses indicated. The data were normalized relative to the value of the control cells. In all nine cell lines, DS-7423 suppressed cell proliferation more robustly than rapamycin when both were used at higher doses. (B) IC₅₀ values for DS-7423 in seven ovarian serous adenocarcinoma (OSA) cell lines (left) were compared with those of nine OCCA cells (right). Four of seven OSA cells had IC₅₀ values >100 nM, which is higher than that of any OCCA cells.</p

Inhibition of PI3K/mTOR signaling by DS-7423 and rapamycin in ovarian clear cell adenocarcinoma cell lines.

<p>(A) Immunoblotting of total protein extracts from OCCA cells (OVISE and OVMANA) treated with DS-7423 at concentrations ranging from 0 to 2,500 nM. (B) Immunoblotting of total protein extracts from OVISE cells treated with rapamycin at concentrations ranging from 0 to 2,500 nM.</p