Metallointercalator [Ru(dppz)₂(PIP)]²⁺ Renders BRCA Wild-Type Triple-Negative Breast Cancer Cells Hypersensitive to PARP Inhibition

Abstract

There is a need to improve and extend the use of clinically-approved poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi), including for BRCA wild-type triple-negative breast cancer (TNBC). The demonstration that ruthenium(II) polypyridyl complex (RPC) metallointercalators can rapidly stall DNA replication fork progression provides the rationale for their combination alongside DNA damage response (DDR) inhibitors to achieve synergism in cancer cells. The aim of the present study was to evaluate use of the multi-intercalator [Ru(dppz)2(PIP)] 2+ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine, PIP = (2-(phenyl)imidazo[4,5f][1,10]phenanthroline, Ru-PIP) alongside the PARP inhibitors (PARPi) olaparib and NU1025. Cell proliferation and clonogenic survival assays indicated a synergistic relationship between Ru-PIP and olaparib in MDA-MB-231 TNBC and MCF7 human breast cancer cells. Strikingly, low dose Ru-PIP renders both cell lines hypersensitive to olaparib, with a 300-fold increase in olaparib potency in TNBC; the largest non-genetic PARPi enhancement effect described to date. Negligible impact on the viability of normal human fibroblasts was observed for any combination tested. Increased levels of DNA double-strand break (DSB) damage and olaparib abrogation of Ru-PIP activated pChk1 signalling is consistent with PARPi-facilitated collapse of Ru-PIP-associated stalled replication forks. This results in enhanced G2/M cell-cycle arrest, apoptosis and decreased cell motility for the combination treatment compared to single-agent conditions. This work establishes that an RPC metallo-intercalator can be combined with PARPi for potent synergy in BRCAproficient breast cancer cells, including TNBC.

<p>Ruthenium Complexes as Anticancer Agents: A Brief History and Perspectives</p>

“…An interesting approach to overcome the uptake, efficacy and biocompatibility issues related to Ru complexes will be a nanomaterial-conjugated PDT. 142 Another idea worthy of consideration would be a drug combination to synergize the efficacy without increasing the toxicity and drug resistance 143 such as a combination with poly(ADP-ribose)polymerase (PARP) inhibitors 144 to treat BRCA wild-type triple-negative breast cancer (TNBC). Recent studies are shedding new light on the anticancer potential of Ru complexes.…”

Combining PARP Inhibition with Platinum, Ruthenium or Gold Complexes for Cancer Therapy

“…Recently, we demonstrated that the combination of the multi-intercalator [Ru(dppz) 2 (PIP)] 2 + (or Ru-PIP, Figure 9a) where dppz = dipyrido[3,2-a:2',3'-c]phenazine and PIP = 2-(phenyl)-imidazo [4,5-f] [1,10]phenanthroline with either NU1025, a second-generation PARPi, or olaparib showed synergy in BRCA wild-type TNBC breast cancer cells (Figure 9b). [134] As the predominantly cytostatic Ru-PIP acts to stalls replication fork progression without triggering a DSB damage response, [133] PARPi-mediated replication fork collapse results in a significant increase in DSBs damage, accompanied by G2/M cell cycle arrest and cell death via apoptosis. This combination led to a dramatic increase in the potency of olaparib, where 300-fold greater activity due to the addition of Ru-PIP was observed by clonogenic survival assay (Figure 9c).…”

“…This finding provides justification for the assessment of this class of complexes alongside PARPi. Recently, we demonstrated that the combination of the multi‐intercalator [Ru(dppz) 2 (PIP)] 2+ (or Ru‐PIP, Figure 9a) where dppz=dipyrido[3,2‐ a :2′,3′‐ c ]phenazine and PIP=2‐(phenyl)‐imidazo[4,5‐ f ][1,10]phenanthroline with either NU1025, a second‐generation PARPi, or olaparib showed synergy in BRCA wild‐type TNBC breast cancer cells (Figure 9b) [134] . As the predominantly cytostatic Ru‐PIP acts to stalls replication fork progression without triggering a DSB damage response, [133] PARPi‐mediated replication fork collapse results in a significant increase in DSBs damage, accompanied by G2/M cell cycle arrest and cell death via apoptosis.…”

Small-Molecule Drug Discovery in Triple Negative Breast Cancer: Current Situation and Future Directions

“…194 In BRCA mutant TNBC cells, the ruthenium(II) polypyridyl complex (RPC) metal intercalation agent Ru-PIP combined with the PARP inhibitor 15 can enhance G2/M cell cycle arrest and apoptosis and decrease cell viability, without damaging DNA doublestrand break (DSB) compared with PARP inhibitor monotherapy, and is not easy to cause a large number of cytotoxic and potential genotoxic DSB damage. 195 Dinaciclib, a CDK 1/2/5/9 inhibitor, has a strong inhibitory effect on the transcription regulator CDK12 of HR. In BRCA mutant TNBC cells and PDXs, dinacilib can ablate the restored HR and reversed resistance to 16, a PARP inhibitor, enhances the response of the sensitive model of the PARP inhibitor, and transformed tumor growth inhibition into persistent degeneration.…”

“…In Myc-driven TNBC cells, Myc blockade combined with PARP inhibition produced synthetic lethality . In BRCA mutant TNBC cells, the ruthenium­(II) polypyridyl complex (RPC) metal intercalation agent Ru-PIP combined with the PARP inhibitor 15 can enhance G2/M cell cycle arrest and apoptosis and decrease cell viability, without damaging DNA double-strand break (DSB) compared with PARP inhibitor monotherapy, and is not easy to cause a large number of cytotoxic and potential genotoxic DSB damage …”