Nanoscale Reaction Vessels Designed for Synthesis of Copper-Drug Complexes Suitable for Preclinical Development

Abstract

The development of copper-drug complexes (CDCs) is hindered due to their very poor aqueous solubility. Diethyldithiocarbamate (DDC) is the primary metabolite of disulfiram, an approved drug for alcoholism that is being repurposed for cancer. The anticancer activity of DDC is dependent on complexation with copper to form copper bis-diethyldithiocarbamate (Cu(DDC)2), a highly insoluble complex that has not been possible to develop for indications requiring parenteral administration. We have resolved this issue by synthesizing Cu(DDC)2 inside liposomes. DDC crosses the liposomal lipid bilayer, reacting with the entrapped copper; a reaction that can be observed through a colour change as the solution goes from a light blue to dark brown. This method is successfully applied to other CDCs including the anti-parasitic drug clioquinol, the natural product quercetin and the novel targeted agent CX-5461. Our method provides a simple, transformative solution enabling, for the first time, the development of CDCs as viable candidate anticancer drugs; drugs that would represent a brand new class of therapeutics for cancer patients.

Development and optimization of an injectable formulation of copper diethyldithiocarbamate, an active anticancer agent

“…We have previously described a method that solves the formulation issue: a method wherein the copper-complexation reaction occurs inside copper-containing liposomes. 19 Here we demonstrate, for the first time, the anticancer activity of the resultant Cu(DDC) 2 formulation. This method allows for the development of a parenterally suitable Cu(DDC) 2 formulation and can take advantage of the well-established potential for liposomes to modulate the PK characteristics of an associated drug candidate.…”

“…13,35,36 We, as well as others, have previously shown that the cytotoxicity of DSF and Cu is attributed to the formation of a Cu(DDC) 2 complex. 11,19 Attempts have been made to prepare the complex in vivo by administering DSF and Cu (usually given as Cu-gluconate) separately. However, the PK and distribution behaviors of copper and DSF are remarkably different and this has contributed to the lack of success using this approach.…”

“…19 One of the examples disclosed in this previous publication included the use of DSPC/Chol (55:45) liposomes, prepared in 300 mM copper sulfate, as nano-scale reaction vessels for the synthesis of Cu(DDC) 2 . This process solved solubility issues because the highly insoluble complex was formed when the ligand was added to the outside of copper-containing liposomes.…”

“…This suggests clearly that the copper complex of DDC is the therapeutically active agent. 19,20 Cvek et al have shown that Cu(DDC) 2 acts as a proteosome inhibitor, 21 specifically through binding to the 19S lid of the proteosome rather than the 20S subunit, which is targeted by bortezomib. 22 Before developing any therapeutic application for Cu(DDC) 2 , there are formulation issues that need to be addressed if its use in vivo is to be evaluated.…”

“…22 Before developing any therapeutic application for Cu(DDC) 2 , there are formulation issues that need to be addressed if its use in vivo is to be evaluated. Specifically, the complex is a slightly soluble precipitate (,0.1 mg/mL) 19 and, to date, there has not been any pharmaceutically appropriate formulations of Cu(DDC) 2 suitable for in vivo use. We have previously described a method that solves the formulation issue: a method wherein the copper-complexation reaction occurs inside copper-containing liposomes.…”