mda-7/IL24 kills pancreatic cancer cells by inhibition of the Wnt/PI3K signaling pathways: Identification of IL-20 receptor-mediated bystander activity against pancreatic cancer

Abstract

The melanoma differentiation-associated gene (mda-7; approved gene symbol IL24) is a tumor suppressor gene whose protein expression in normal cells is restricted to the immune system and to melanocytes. Recent studies have shown that mda-7 gene transfer inhibits cell growth and induces apoptosis in melanoma, lung cancer, breast cancer, and other tumor types through activation of various intracellular signaling pathways. In the current study, we demonstrate that Ad-mda7 transduction of human pancreatic cancer cells results in G2/M cell cycle arrest and cell killing. Cytotoxicity is mediated via apoptosis in a time- and dose-dependent manner. Tumor cell killing correlates with regulation of proteins involved in the Wnt and PI3K pathways: beta-catenin, APC, GSK-3, JNK, and PTEN. Additionally, we identify bystander cell killing activated by exposure of pancreatic tumor cells to secreted human MDA-7 protein. In pancreatic tumor cells, exogenous MDA-7 protein activates STAT3 and kills cells via engagement of IL-20 receptors. The specificity of bystander killing is demonstrated using neutralizing anti-MDA-7 antibodies and anti-receptor antibodies, which inhibit the apoptotic effects. In sum, we show that Ad-mda7 is able to induce growth inhibition and apoptosis in pancreatic cancer cells via inhibition of the Wnt/PI3K pathways and identify a novel bystander mechanism of MDA-7 killing in pancreatic cancer that functions via IL-20 receptors.

Unique aspects of mda-7/IL-24 antitumor bystander activity: establishing a role for secretion of MDA-7/IL-24 protein by normal cells

“…In contrast, a complete set of IL-20/ IL-22 receptor mRNAs was not present in A549 cells (Figure 7a). This finding, relative to A549 not containing a full complement of IL-20/IL-22 receptors, is in agreement with a recent report by Chada et al (2005).…”

Combinatorial synergy induced by adenoviral-mediated mda-7 and Herceptin in Her-2+ breast cancer cells

“…Differences in tumor size were analyzed for significance by the Student's t-test. Enhanced in vitro growth inhibitory and cytotoxic activity of Ad-mda7 and Herceptin in Her-2 þ breast cancer cells The antiproliferative effects of Ad-mda7 in various cancer cell types have been demonstrated in previous studies; [16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33][34]36 and the relevance of these findings to the clinical setting is supported by in vivo lung and breast xenograft models. 17,21 To corroborate that the Her-2 receptors expressed by the breast cancer cells are functional, we evaluated cell death in MDA-MB-453 and MCF-7 lines treated with increasing amounts of Herceptin (0-100 mg/ ml).…”

“…25,28,31 Furthermore, the results of a Phase I dose-escalation clinical trial using intratumoral delivery of MDA-7 (INGN 241) in patients with advanced cancers, including breast cancer, has shown apoptotic effects in a large volume of tumor and immunoactivating events that are consistent with the pre-clinical tumor suppressor activities of MDA-7/IL-24. 32 We hypothesized that the combination of Ad-mda7 and Herceptin would result in enhanced antitumor activity and thus evaluated the combination of Herceptin with the Ad-mda7 gene drug. In this study, we demonstrate that expression of MDA-7 induces dramatic enhancement of the apoptotic and tumor-suppressing capacities of Herceptin, compared to its use as a single agent.…”

Novel Therapeutic Approach for Breast Cancer

“…While our studies identified pancreatic cancer cells to be resistant to Ad.mda-7, another report showed that Ad.mda-7 infection could elicit apoptosis in these cells [101]. This difference may reflect variations in the viral titers and/or vector constructs employed by the two groups.…”