Augmented antitumor activity of 5‐fluorouracil by double knockdown of MDM4 and MDM2 in colon and gastric cancer cells

• Published in: Cancer science 2019-02, Vol.110 (2), p.639-649
• Main Authors: Imanishi, Mamiko, Yamamoto, Yoshiyuki, Wang, Xiaoxuan, Sugaya, Akinori, Hirose, Mitsuaki, Endo, Shinji, Natori, Yukikazu, Yamato, Kenji, Hyodo, Ichinosuke
• Format: Article
• Language: English
• Subjects: 5‐fluorouracil; Animals; Antineoplastic Agents - pharmacology; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation - drug effects; Cell Proliferation - genetics; colon cancer; Colonic Neoplasms - drug therapy; Colonic Neoplasms - genetics; Female; Fluorouracil - pharmacology; G1 Phase - drug effects; G1 Phase - genetics; gastric cancer; Gene Expression Regulation, Neoplastic - drug effects; HCT116 Cells; Humans; MDM4; Mice; Mice, Inbred BALB C; Mice, Nude; Nuclear Proteins - genetics; Original; p53; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins c-mdm2 - genetics; Stomach Neoplasms - drug therapy; Stomach Neoplasms - genetics; Tumor Suppressor Protein p53 - genetics; Up-Regulation - drug effects; Up-Regulation - genetics
• ISSN: 1347-9032; 1349-7006
• DOI: 10.1111/cas.13893

Inactivation of the TP53 tumor suppressor gene is essential during cancer development and progression. Mutations of TP53 are often missense and occur in various human cancers. In some fraction of wild‐type (wt) TP53 tumors, p53 is inactivated by upregulated murine double minute homolog 2 (MDM2) and MDM4. We previously reported that simultaneous knockdown of MDM4 and MDM2 using synthetic DNA‐modified siRNAs revived p53 activity and synergistically inhibited in vitro cell growth in cancer cells with wt TP53 and high MDM4 expression (wtTP53/highMDM4). In the present study, MDM4/MDM2 double knockdown with the siRNAs enhanced 5‐fluorouracil (5‐FU)‐induced p53 activation, arrested the cell cycle at G1 phase, and potentiated the antitumor effect of 5‐FU in wtTP53/highMDM4 human colon (HCT116 and LoVo) and gastric (SNU‐1 and NUGC‐4) cancer cells. Exposure to 5‐FU alone induced MDM2 as well as p21 and PUMA by p53 activation. As p53‐MDM2 forms a negative feedback loop, enhancement of the antitumor effect of 5‐FU by MDM4/MDM2 double knockdown could be attributed to blocking of the feedback mechanism in addition to direct suppression of these p53 antagonists. Intratumor injection of the MDM4/MDM2 siRNAs suppressed in vivo tumor growth and boosted the antitumor effect of 5‐FU in an athymic mouse xenograft model using HCT116 cells. These results suggest that a combination of MDM4/MDM2 knockdown and conventional cytotoxic drugs could be a promising treatment strategy for wtTP53/highMDM4 gastrointestinal cancers. Intratumoral injection of MDM4/MDM2 siRNAs suppressed in vivo tumor growth and boosted the antitumor effect of 5‐fluorouracil in an athymic mouse xenograft model using HCT116 cells.