Anticancer activity of a Gold(I) phosphine thioredoxin reductase inhibitor in multiple myeloma

Abstract

Multiple myeloma (MM), the second most common haematological malignancy, is a clonal plasma B-cell neoplasm that forms within the bone marrow. Despite recent advancements in treatment, MM remains an incurable disease. Auranofin, a linear gold(I) phosphine compound, has previously been shown to exert a significant anti-myeloma activity by inhibiting thioredoxin reductase (TrxR) activity. A bis-chelated tetrahedral gold(I) phosphine complex [Au(d2pype)2]Cl (where d2pype is 1,2-bis(di-2-pyridylphosphino)ethane) was previously designed to improve the gold(I) compound selectivity towards selenol- and thiol-containing proteins, such as TrxR. In this study, we show that [Au(d2pype)2]Cl significantly inhibited TrxR activity in both bortezomib-sensitive and resistant myeloma cells, which led to a significant reduction in cell proliferation and induction of apoptosis, both of which were dependent on ROS. In clonogenic assays, treatment with [Au(d2pype)2]Cl completely abrogated the tumourigenic capacity of MM cells, whereas auranofin was less effective. We also show that [Au(d2pype)2]Cl exerted a significant anti-myeloma activity in vivo in human RPMI8226 xenograft model in immunocompromised NOD/SCID mice. The MYC oncogene, known to drive myeloma progression, was downregulated in both in vitro and in vivo models when treated with [Au(d2pype)2]Cl. This study highlights the “proof of concept” that improved gold(I)-based compounds could potentially be used to not only treat MM but as an alternative tool to understand the role of the Trx system in the pathogenesis of this blood disease.

Cross-talk between Bcr-abl and the Thioredoxin System in Chronic Myeloid Leukaemia: Implications for CML Treatment

“…Both compounds were also observed to elicit significantly increased levels of caspase-3 activity, with visible PARP-1 degradation, which suggests that the cells are dying via apoptosis. Similar results were observed with auranofin [16,48] and [Au(d2pype) 2 ]Cl [13,30] in other cancer cells. TrxR activity was measured upon treatment of auranofin and [Au(d2pype) 2 ]Cl and it was found that both compounds significantly decreased TrxR activity.…”

“…This study aimed to examine the effectiveness of two TrxR1 inhibitors, auranofin and [Au(d2pype) 2 ]Cl, on overcoming intrinsic imatinib resistance in CML and to investigate the possible links between the CML causing protein, bcr-abl, and the Trx system. It has previously been shown that neither of these compounds elicited significant cell death in healthy peripheral non-cancerous blood mononuclear cells (PBMCs) [13], indicating the suitability of TrxR inhibitors for treating patients.…”

“…TrxR activity assays were performed as described previously [13,19,42]. Briefly, 1.5 × 10 6 cells were treated with auranofin or [Au(d2pype) 2 ]Cl for 24 h. Following this, cells were lysed in cell lysis buffer (150 mM NaCl, 50 mM Tris-Cl, pH 8; 0.5% Nonidet P-40, 0.5 mM EDTA, 2 mM PMSF, 1 µL/mL protease inhibitor cocktail VI and 1× PBS) as described by Sze et al [13]. TrxR activity was then measured by adding 15 µL of whole cell lysate to 25 µL of sample buffer (0.1 M KPi; 20 mM EDTA; 0.1 mg/mL BSA) and 200 µL of assay buffer (0.5 M KPi, pH 7.5; 200 mM EDTA; 20 mM NADPH; 125 mM DTNB).…”

“…The thioredoxin (Trx) system is currently being studied as a novel target in overcoming drug resistance in other cancers, such as multiple myeloma and breast cancer [13][14][15][16][17][18][19]. The Trx system is an antioxidant system that is involved in maintaining low levels of reactive oxygen species (ROS), as well as activating various cell survival pathways, such as the NF-κB and the hypoxia inducible factor 1 (HIF1) pathways.…”

“…However, more specific TrxR inhibitors are also in development; a notable example is [Au(d2pype) 2 ]Cl [30], which will also be used in this study. This TrxR inhibitor has been shown to be effective in inducing cell death in breast cancer [30] and multiple myeloma [13] cells. This study aims to investigate TrxR as a possible therapeutic target by assessing the effectiveness of TrxR inhibitors on CML cells and on overcoming TKI resistance, as well as studying a potential cross talk between bcr-abl and the Trx system.…”