A novel hypoxia-selective epigenetic agent RRx-001 triggers apoptosis and overcomes drug resistance in multiple myeloma cells

Abstract

The hypoxic bone-marrow (BM) microenvironment confers growth/survival and drug-resistance in multiple myeloma (MM) cells. Novel therapies targeting the MM cell in its hypoxic-BM milieu may overcome drug resistance. Recent studies led to the development of a novel molecule RRx-001 with hypoxia-selective epigenetic and Nitric Oxide-donating properties. Here we demonstrate that RRx-001 decreases the viability of MM cell lines and primary patient cells, as well as overcomes drug-resistance. RRx-001 inhibits MM cell growth in the presence of BM stromal cells. RRx-001 induced apoptosis is associated with: 1) activation of caspases; 2) release of ROS and nitrogen-species; 3) induction of DNA damage via ATM/γ-H2AX; and 4) decrease in DNA methytransferase (DNMT) and global methylation. RNA interference study shows a predominant role of DNMT1 in MM cell survival versus DNMT3a or DNMT3b. Deubiquitylating enzyme USP7 stimulates DNMT1 activity; and conversely, USP7-siRNA reduced DNMT1 activity and decreased MM cell viability. RRx-001 plus USP7 inhibitor P5091 triggered synergistic anti-MM activity. MM xenograft studies show that RRx-001 is well tolerated, inhibits tumor growth, and enhances survival. Combining RRx-001 with pomalidomide, bortezomib or SAHA induces synergistic anti-MM activity. Our results provide the rationale for translation of RRx-001, either alone or in combination, to clinical evaluation in MM.

RRx-001: a systemically non-toxic M2-to-M1 macrophage stimulating and prosensitizing agent in Phase II clinical trials

“…SCCVII and MM.1S tumor cells treated with RRx-001 exhibit genome wide re-expression of genes such as the tumor suppressor, p53 [22]; in this way, RRx-001 may 're-program' the genome and increase the efficacy of co-therapies such as radiation and conventional chemotherapy.…”

“…Supporting experimental evidence for selective tumor nitro-oxidation includes stimulation of inducible nitric oxide in vivo [22], as well as oxidation of tumor thiols detected by enhanced MRI [23]. These data suggest that through the intermediary of the TAM RRx-001 modifies the intracellular tumor environment to a more pro-oxidant phenotype, and any subsequent processes such as epigenetic enzymes, for example, DNA methyltransferases and histone deacetylases (HDACs) that are redox-sensitive may be altered, attenuated, or inhibited.…”

Shikonin induces mitochondria-mediated apoptosis and enhances chemotherapeutic sensitivity of gastric cancer through reactive oxygen species

“…Both pathways induce cell death by activating caspase cascade28. Many chemotherapy drugs achieve anti-tumour effects by inducing apoptosis but drug resistance often occurs by caspase escape29. Recently, researchers discovered that cells can die and display apoptosis morphology without caspase activation via the translocation of apoptosis inducing factor (AIF) and Endonuclease G (Endo G) from the mitochondria to nucleus3031.…”

Dual-utility NLS drives RNF169-dependent DNA damage responses

“…As a DNA damage-regulated deubiquitylating (DUB) activity (24), USP7 is reported to confer cell resistance to genotoxic stress by targeting a panel of DDR proteins, including Rad18 (25), RNF168 (26), and Claspin (27). Moreover, in line with antiapoptotic functions, USP7 is overexpressed in breast and prostate cancers (28,29), and genetic ablation or chemical inhibition of USP7 DUB activity induced cell killing in vitro and tumor regression in vivo (30)(31)(32)(33)(34), underscoring the potential development of USP7 inhibitors as anticancer therapeutics.…”