Melanoma differentiation associated gene-7/interleukin-24 (MDA-7/IL-24), a secreted protein of the IL-10 family, was first identified more than two decades ago as a novel gene differentially expressed in terminally differentiating human metastatic melanoma cells. MDA-7/IL-24 functions as a potent tumor suppressor exerting a diverse array of functions including the inhibition of tumor growth, invasion, angiogenesis, and metastasis, and induction of potent “bystander” antitumor activity and synergy with conventional cancer therapeutics. MDA-7/IL-24 induces cancer-specific cell death through apoptosis or toxic autophagy, which was initially established in vitro and in preclinical animal models in vivo and later in a Phase I clinical trial in patients with advanced cancers. This review summarizes the history and our current understanding of the molecular/biological mechanisms of MDA-7/IL-24 action rendering it a potent cancer suppressor.

Metastasis poses significant obstacles to effective therapy and drug development. Melanoma differentiation-associated gene-9/Syntenin-1/Syndecan Binding Protein (MDA-9) is a pro-metastatic gene robustly and differentially expressed in cancer cells in comparison with corresponding adjacent normal/primary cells and represents an attractive therapeutic target to inhibit cancer cell dissemination and tumor growth. MDA-9 contains two tandem PDZ domains that provide a nexus for interactions with multiple proteins that can initiate the transcription of metastasis-associated genes. The goal of this project was to evaluate the efficiency of a unique first-in-class, second-generation MDA-9 dual-PDZ targeted pharmacological inhibitor generated using a combination of a PDZ1 small molecule and a PDZ2 selective peptide. Fragment-based drug discovery and NMR identified PDZ1i, an inhibitor of the PDZ1 domain, that effectively blocks cancer invasion in vitro and in vivo in multiple experimental animal models. To maximize the disruption of MDA-9 signaling an inhibitor has now been developed that simultaneously binds and blocks the activity of both PDZ domains. PDZ1i was joined to the second PDZ binding peptide (TNYYFV) with a PEG linker, resulting in IVMT-Rx-3 that simultaneously engages both PDZ domains of MDA-9. Mechanistic studies involved a combination of molecular and cell biology approaches and included both established and early passaged patient-derived melanoma cell lines. To test the efficacy of potential combinatorial effects in vivo we used a murine syngeneic model and B16F10, an immunotherapy-resistant murine cell line. After confirming synthesis using multiple analytical methods, e.g., HPLC, LC/MS, and NMR, the dissociation constant (determined by microscale thermophoresis (MST) analysis, of the IVMT-Rx-3 recombinant MDA-9 complex was 63 +/- 11 μM. This compound is not toxic to normal melanocytes or melanoma cells, but significantly inhibits invasion in vitro in a wide range of melanomas. IVMT-Rx-3 interrupts c-Src binding to MDA-9 and downregulates NF-kB activation. Inactivation of this transcription factor causes suppression of MMP2/MMP9 and inhibits the secretion of cytokines/growth factors. These molecular changes block cellular invasiveness and facilitate immune cytotoxicity by converting an unfavorable into a favorable tumor microenvironment culminating in the repression of melanoma metastasis. In addition, the in vivo anti-metastatic properties of IVMT-Rx-3 are enhanced when combined with an immune-checkpoint inhibitor. IVMT-Rx-3 is a unique MDA-9 antagonist in terms of composition that effectively inhibits melanoma metastasis as does our small molecule PDZ1i and holds potential for developing novel therapeutic strategies effectively targeting melanoma and in principle, a broad spectrum of human cancers that also overexpress MDA-9. Citation Format: Anjan K. Pradhan, Jinkal Modi, Santanu Maji, Amit Kumar, Praveen Bhoopathi, Padmanabhan Mannangatti, Chunqing Guo, Daniel K. Afosah, Mark Mochel, Nitai D. Mukhopadhyay, John M. Kirkwood, Xiang-Yang Wang, Umesh R. Desai, Devanand Sarkar, Luni Emdad, Swadesh K. Das, Paul B. Fisher. Simultaneous targeting of the PDZ1 and PDZ2 domains of MDA-9 inhibits melanoma metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3394.