Chiang Li

Abstract 4777: Cancer stemness and resistance: Napabucasin (BBI-608) sensitizes stemness-high cancer cells to Paclitaxel by inhibiting the STAT3-MUC1 pathway

Stemness-high cancer cells, or cancer stem cells (CSC) represent a subpopulation of cancer cells with enhanced tumorigenic capacity, metastasis-forming potential, and resistance to conventional chemotherapy and radiation. One such key CSC pathway is regulated by STAT3, a transcription factor that is downstream of several cytokines and growth factor receptors which controls the expression of a broad range of target genes and plays essential roles in CSC biology in many tumor types. Cancer stemness inhibitor Napabucasin (BBI-608), a small molecule that inhibits gene transcription driven by STAT3, can inhibit stemness gene expression, block spherogenesis, and kill CSCs. In vivo, BBI-608 effectively blocks cancer relapse and metastasis in xenograft models while sparing normal hematopoietic stem cells, suggesting that targeting stemness-high cancer cells is a feasible approach for developing next-generation cancer therapeutics to combat cancer recurrence. SOX2 (sex-determining region Y-box protein 2), a transcription factor that is essential for self-renewal and pluripotency, is amplified in various cancer types and has been shown to be required for CSC self-renewal and maintenance. Mucin 1 (MUC1), a glycoprotein normally expressed at the apical surface of epithelial cells, is overexpressed in most human epithelial cancers. MUC1 has been implicated in regulating tumor proliferation, metabolism, invasion, angiogenesis, chemoresistance, and inflammation. Here, we generated a stemness-high culture system based on the reporter activity of a SOX2-regulatory region construct in MKN28 gastric cancer cells (MKN28 SOX2-reporter GFP+ cells). BBI-608 treatment inhibited the STAT3-MUC1 pathway in stemness-high cells. High MUC1 status in stemness-high cells was associated with Paclitaxel resistance. Down-regulation of MUC1 sensitized stemness-high cells to Paclitaxel. Moreover, BBI-608 synergized with Paclitaxel in inhibiting spherogenesis of stemness-high cells. This study provides a new mechanism for the association of cancer stemness with drug resistance. Our findings support this combination therapy, which pairs a conventional chemotherapy (Paclitaxel) with a cancer stemness inhibitor (BBI-608), as a promising strategy to combat cancer. Citation Format: Harry A. Rogoff, Juying Li, Chiang Li. Cancer stemness and resistance: Napabucasin (BBI-608) sensitizes stemness-high cancer cells to Paclitaxel by inhibiting the STAT3-MUC1 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4777. doi:10.1158/1538-7445.AM2017-4777

Abstract 2222: Dual inhibition of cancer stemness and immune checkpoint genes by targeting Stat3

Highly malignant stemness-high cancer cells, also termed cancer stem cells, have been found to hijack stemness genes important for embryonic stem cells to acquire a state of high-stemness. Cancer stemness has been associated with enhanced tumorigenicity and resistance to chemotherapies. Moreover, stemness-high cancer cells have been isolated from a variety of human cancer types. Therefore, targeting cancer stemness holds significant promise for advancing cancer treatment. Recent clinical success with antibodies targeting PD1 and PDL1 has validated that cancer cells can hijack immune checkpoint genes to subvert endogenous anticancer surveillance by the immune system. It is, therefore, highly desirable to develop therapeutics that simultaneously target both cancer cell stemness and immune checkpoints. The transcription factor Signal Transducer and Activator of Transcription 3 (Stat3) is activated by a multitude of upstream oncogenic pathways and cytokine receptors. Aberrant and constitutive activation of Stat3 has been found in a wide variety of human cancers, and has also been implicated in cancer cell proliferation, survival, and immune evasion. By using aiRNA (asymmetric RNA duplexes) we have achieved potent Stat3 silencing with precision in stemness-high cancer cells. We observed that Stat3 silencing leads to simultaneous down regulation of cancer cell stemness and immune checkpoint gene expression. Treatment of stemness-high cancer cells with BB608, a small molecule inhibitor of Stat3, led to simultaneous inhibition of stemness-high cancer cell survival and self-renewal, as well as downregulation of immune checkpoint genes, including IDO1 in vitro and in vivo. Furthermore, while expression of stemness genes and immune checkpoint genes in tumor tissues are known to predict poor patient survival, patients with higher expression levels of stemness genes and immune checkpoint genes showed prolonged overall survival after treatment with BB608 in clinical trials. Targeting Stat3 is, therefore, a promising strategy to achieve dual inhibition of cancer cell stemness and immune evasion. Citation Format: Yuan Gao, Sarah Keates, Eric Hsu, Janet Huang, Emily Brooks, Matt Hitron, Youzhi Li, Harry A. Rogoff, Chiang Li. Dual inhibition of cancer stemness and immune checkpoint genes by targeting Stat3. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2222.

Abstract LB-47: Specific and potent silencing of K-Ras by asymmetric RNA technology reveals addiction of gastric cancer stem cells

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA The protein K-Ras is a molecular switch that under normal conditions regulates cell growth and cell division. Mutations in this protein lead to the formation of tumors through continuous cell growth. About 30% of human cancers have a mutated Ras protein that is constitutively bound to GTP due to decreased GTPase activity and insensitivity to GAP action. Ras is also an important factor in many cancers in which it is not mutated but rather functionally activated through inappropriate activity of other signal transduction elements. Mutated K-Ras proteins are found in a large proportion of all tumour cells. K-Ras protein occupies a central position of interest. The identification of oncogenically mutated K-Ras in many human cancers led to major efforts to target this constitutively activated protein as a rational and selective treatment. Despite decades of active agent research, significant challenges still remain to develop therapeutic inhibitors of K-Ras. To elucidate the function of K-Ras in the cancer development and maintenance, we developed asymmetric interfering RNAs (aiRNAs) which are able to silence target genes with high potency leading to long-lasting knockdown, and reducing off-target effects, and investigated the dependency of K-ras on cell survival in several types of human cancer cell lines. Much to our surprise, we found K-Ras plays a more significant role for gastric cancer maintenance compared to other types of cancer. Here we report aiRNA-induced silencing of K-Ras inhibited the cell proliferation of gastric cancer cells and the ability of gastric cancer cells to form colonies compared to other cancer types. Accumulating evidence has revealed that cancer stem cells (CSCs) are highly associated with prognosis, metastasis, and recurrence. To investigate the effect of K-Ras on CSCs, we tested the K-Ras gene silencing effects on an in vitro CSC culturing system. As a result, K-Ras inhibition decreased the colonies derived from gastric CSCs and altered the gene expression patterns of several genes involved in “stemness” compared to other cancer types. The results of these studies suggest that gastric cancer and gastric CSCs are affected by the K-Ras oncogene and that Kras aiRNAs are promising therapeutic candidates for the treatment of gastric cancer. Citation Format: Xiangao Sun, Youzhi Li, Hiroki Umehara, Jun Oishi, Nithya Jesuraj, Jelena Barbulovic, Xiaoshu Dai, Keyur Gada, Chiang Li. Specific and potent silencing of K-Ras by asymmetric RNA technology reveals addiction of gastric cancer stem cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-47. doi:10.1158/1538-7445.AM2014-LB-47