Investigation of the anticancer activity and mechanisms of zinc diethyldithiocarbamate in multiple myeloma

Abstract

Background: Multiple myeloma (MM) is a haematological malignancy of the plasma cells that primarily arises in the bone marrow. Although the advent of multiple treatment options such as immunomodulatory drugs (IMiDs), proteasome inhibitors (PI), CAR-T therapy and antibody-based therapies have improved the prognosis of MM, all patients eventually relapse due to the presence and development of drug resistance. Therefore, the development of new drugs to meet this challenge is of clinical urgency. Due to the time (15 years) and costs (£1.5 billion/drug) for new drug development, repurposing old drugs for new indications is an emerging alternative strategy that is more viable in terms of costs and time. Disulfiram (DS), an anti-alcoholism drug used in the clinic for over 70 years, demonstrates excellent specific anticancer activity with no/low toxicity to normal tissues. DS chelates with transition metals such as copper and zinc to form metal-metabolite complexes (zinc/copper diethyldithiocarbamate), which are the active anticancer compounds. Diethyldithiocarbamate (DDC), a metabolite of DS, has previously been trialled in clinics to treat HIV patients due to its immunomodulatory properties. Zinc diethyldithiocarbamate (ZnDDC) is a promising compound to translate for MM treatment as a multi-target drug due to the established immunomodulatory properties of its structural moieties Zn and DDC. Although the anticancer potential of DS and its metabolites has been known for more than three decades, its translation has been limited by its very short half-life in the bloodstream (< 4 min) and its metabolite DDC is methylated in the liver that results in the loss of anticancer activity. This study focuses on investigating the anticancer and immunomodulatory potential of ZnDDC in MM and developing a novel PEGylated liposome nanoformulation of ZnDDC (PEGLipo-ZnDDC) to overcome the translational limitations of ZnDDC. Results: In this study, ZnDDC showed potent cytotoxicity in MM cell lines and patient-derived MM cells (IC50s: 5-10μM). ZnDDC synergistically enhances the cytotoxicity of IMiDs (lenalidomide, Pomalidomide) and PI (bortezomib) and reverses resistance of MM cells to these drugs. ZnDDC is able to induce apoptosis in MM cells, demonstrated by cleavage of PARP-1. Although ZnDDC has no effect on the mRNA expression of cereblon (CRBN), Ikaros (IKZF1), aiolos (IKZF3) and Interferon regulatory factor-4 (IRF4), a significant downregulation of protein levels was observed after treating the MM cell lines with sub-cytotoxic concentrations of ZnDDC (2-5 μM). After exposure to low concentration of ZnDDC, levels of both IL-2 mRNA and protein were significantly boosted in T lymphocytes. Molecular docking simulation using the AutoDock4 software predicted the potential binding of ZnDDC to the IMiD binding pocket present in CRBN. The study has led to the successful development of a PEGLipo-ZnDDC nano formulation with appreciable drug-loading content and stability. The formulation also retained the potent cytotoxic profile of free ZnDDC. Conclusion: ZnDDC demonstrates excellent cytotoxicity and synergistic effect when used in combination with clinically used IMiDs and BTZ in MM cells. The developed PEGLipo-ZnDDC nano formulation demonstrates desirable drug loading, size, and stability and retains the cytotoxicity.