We have previously demonstrated the in vivo chemopreventive efficacy of flavokawain A (FKA), a novel chalcone from the kava plant, in prostate carcinogenesis models. However, the mechanisms of the anticarcinogenic effects of FKA remain largely unknown. We evaluated the effect of FKA on prostate tumor spheroid formation by prostate cancer stem cells, which were sorted out from CD44+/CD133+ prostate cancer cells 22Rv1 and DU145. FKA treatment significantly decreased both the size and numbers of the tumor spheroids over different generations of spheroid passages. In addition, the dietary feeding of FKA-formulated food to Nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice bearing CD44+/CD133+ 22Rv1 xenograft tumors resulted in a significant reduction of tumor growth compared to those fed with vehicle control food–fed mice. Furthermore, the expression of stem cell markers, such as Nanog, Oct4, and CD44, were markedly downregulated in both tumor spheroids and tumor tissues. We also observed that FKA inhibits Ubc12 neddylation, c-Myc, and keratin-8 expression in both CD44+/CD133+ prostate tumor spheroids and xenograft tumors. Our results suggest that FKA can reduce the tumor-initiating properties and stemness of prostate cancer, which provides a new mechanism for the chemoprevention efficacy of FKA.

S-phase kinase associated protein 2 (Skp2) is a promising drug target as studies have demonstrated that Skp2 is required for spontaneous tumor development that occurs in the retinoblastoma protein (pRb), Pten, or p53 deficient mice. We, therefore, aim to establish CRISPR human Skp2 (hSkp2) knock-in in the prostates of mice to study the molecular profiling features in prostate carcinogenesis. Prostate weights increased in transgenic mice and overexpression of hSkp2 induced prostatic lesions including hyperplasia, mouse prostate intraepithelial neoplasia (mPIN), and carcinoma, which suggested the initial role of hSkp2 in early prostate carcinogenesis. RNAseq results revealed Myl3 and Ctgf as the top down-expressed and up-expressed genes respectively in hSkp2 mice prostates. Gene set enrichment analysis (GSEA) demonstrated the significant upregulations of ribosome and proteasome pathways which had similar alterations in the human prostate cancer dataset with Skp2 overexpression, suggesting the potential role of ribosome biogenesis in prostate tumorigenesis and for drug development. In addition, Skp2 organoids derived from transgenic mice prostates were being developed for convenient and efficient screening of specific Skp2 inhibitors. Flavokawain A (FKA) and Skp2 inhibitor C1 both selectively decreased the viability and altered the morphologies of hSkp2 organoids, meanwhile FKA exhibited less toxicity on wild-type organoids. Citation Format: Liankun Song, Vyvyan Nguyen, Shan Xu, Jana Yamak, Kia Arabzadehkaffash, Ali Fazelpour, Merci Mino, Matthew Tippin, Shuang Meng, Xiaolin Zi. Transcriptional profiling of prostatic Skp2 knock-in mouse model and development of the associated prostate organoids for testing Skp2 targeting agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1.

Prostate cancer stem cells (PCSC) are small tumor subpopulations capable of self-renewal and driving prostate cancer heterogeneity, which is critical for cancer initiation, recurrence, and development of therapeutic resistance. Thus, there’s an urgent need to explore and develop new CSC targeting agents. Flavokawain A (FKA), a novel chalcone from kava plant, can selectively inhibit the growth of pRb deficient cell lines and result in a proteasome-dependent and ubiquitination-mediated Skp2 (S-phase kinase-associated protein 2) degradation, while the potential of FKA to target PCSC is unknown. Therefore, we evaluated the effects of FKA on PCSC self-renewal both in vitro and in vivo. FKA treatment decreased both size and numbers of the tumor spheroids growing from CD44+/CD133+ tumor stem cells, which were sorted out from the prostate tumor cell line DU145 and 22RV1. Expression of the stem cell markers Nanog, Oct4, and Sox2 were all downregulated in the cancer spheroids treated with FKA. Growth of the 22RV1CD44+/CD133+ xenograft tumors was significantly inhibited in FKA diet-fed mice compared to the vehicle control diet-fed mice. Immunohistochemistry analysis revealed less positive Ki67, Nanog, and Oct4 cells in tumor tissues from the FKA dietary group than those from the control dietary group. These results demonstrated that FKA can inhibit prostate cancer stemness and suggested a potential role of FKA for preventing prostate cancer recurrence by targeting PCSC. Citation Format: Liankun Song, Merci Mino, Jana Yamak, Vyvyan Nguyen, Derron Lopez, Victor Pham, Ali Fazelpour, Vinh Le, Dongjun Fu, Matthew Tippin, Xiaolin Zi. Flavokawain A targets cancer stem cells for inhibiting the growth of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2.