Biochemical and Proteomic Analysis of a Potential Anticancer Agent: Palladium(II) Saccharinate Complex of Terpyridine Acting through Double Strand Break Formation

Metal
based chemotherapeutic drugs are widely used as an effective
method to defeat various cancers. In this study, the mechanism of
action of a novel therapeutic agent, [Pd­(sac)­(terpy)]­(sac)·4H2O (sac = saccharinate, and terpy = 2,2′:6′,2″-terpyridine)
was studied. To better understand the proteomic changes in response
to this agent, we performed nano LC-MS/MS analyses in human breast
cancer cells (MDA-MB-231). Thirty proteins were identified to be differentially expressed more
than 40% after drug treatment. Many cellular pathways were affected,
including proteins involved in DNA repair, apoptosis, energy metabolism,
protein folding, cytoskeleton, pre-mRNA maturation, or protein translation.
The changes in protein expression were further verified for XRCC5,
which plays a role in double strand break (DSB) repair, and ubiquitin,
which is involved in protein degradation and apoptosis. The elevated
XRCC5 levels were suggestive of increased DSBs. The presence of DSBs
was confirmed by smearing of plasmid DNA in vitro and induction of
γH2AX foci in vivo. There was also increased intracellular reactive
oxygen species (ROS) formation, as detected by 2′,7′-dichlorofluorescein
diacetate (DCFDA) staining. Scavenging ROS by N-acetylcysteine
rescued cell death in response to Pd­(II) treatment, potentially explaining
how the Pd­(II) complex damaged the DNA. The details of this analysis
and the significance will be discussed during the scope of this work.