Cellular Target of a Rhodium Metalloinsertor is the DNA Base Pair Mismatch

Abstract

Defects in DNA mismatchrepair (MMR) are commonly found in various cancers, especially in colorectal cancers. Despite the high prevalence of MMR-deficient cancers, mismatch-targeted therapeuticsa re limited and diagnostic tools are indirect. Here, we examine the cytotoxic properties of ar hodiummetalloinsertor, [Rh(phen)(chrysi)(PPO)] 2 + (RhPPO)i n2 7d iversec olorectal cancer cell lines. Despite the low frequency of genomic mismatches and the non-covalentn ature of the RhPPO-DNA lesion, RhPPO is on average five times more potent than cisplatin. Importantly,t he biological target and profile for RhPPO differs from that of cisplatin. Af luorescent metalloinsertor, RhCy3,w as used to demonstrate that the cellulart arget of RhPPO is the DNA mismatch. RhCy3 representsadirect probe for MMR-deficiency and correlates directlyw ith the cytotoxicity of RhPPO across different cell lines. Overall, our studies clearly indicate that RhPPO and RhCy3 are promising anticancer and diagnostic probes for MMR-deficient cancers, respectively.

In vivo anticancer activity of a rhodium metalloinsertor in the HCT116 xenograft tumor model

“…Furthermore, a study assessing the cytotoxicity of Rh-PPO in 27 CRC cell lines spanning the four subtypes of CRC, as well as both MMR-deficient and MMR-proficient phenotypes, provided additional support to the hypothesis that the targets of Rh-PPO are DNA base-pair mismatches (23,24). Rh-PPO was found to be on average five times more potent than the Food and Drug Administration (FDA)-approved chemotherapeutic cisplatin with mean IC 50 values (50% inhibitory concentration) of 2.9 μM and 13.2 μM, respectively, across CRC cell lines.…”

An 111In-labelled bis-ruthenium(ii) dipyridophenazine theranostic complex: mismatch DNA binding and selective radiotoxicity towards MMR-deficient cancer cells

“…In the area of designing small molecules to bind non-canonical DNA structures, DNA mismatch-interactive compounds have shown encouraging preferential activity towards MMR-decient colorectal cancers. 44 While denitive data on the lifetime of mismatches themselves (as opposed to their mutation signatures) in human cells is currently lacking, a genome-wide study in yeast indicated repair of TT mismatches to be one of the least efficient of all mismatch base pairings. 12 Preferential stabilisation of a TT mismatch is a relatively rare nding for mismatchinteractive compounds described to date.…”

Cell-Selective Cytotoxicity of a Fluorescent Rhodium Metalloinsertor Conjugate Results from Irreversible DNA Damage at Base Pair Mismatches

“…The preferential cytotoxicity of RhPPO-Cy3 for MMRdeficient cells was also observed against other CRC cell lines (Supplemental Information, Figure S10). 24 In co-staining experiments with phospho-H2AX, the nuclear RhPPO-Cy3 foci exhibited partial overlap with phospho-H2AX foci (20 + 4%) ( Figure 3B), suggesting that the DNA lesions formed by RhPPO-Cy3 binding occur at or near sites of DNA mismatches.…”

“…Phospho-H2AX, as a component of chromatin, spans megabases of DNA surrounding a DNA break. 32 To explore further the potential colocalization of RhPPO-Cy3 with DNA damage foci, we compared RhPPO-Cy3 nuclear localization to that of intensity that correlated with the presence of DNA mismatches and with RhPPO cytotoxicity 24 . In the current study, we directly labeled RhPPO with a fluorescent…”

“…These results support the hypothesis that the DNA lesions induced by RhPPO-Cy3 binding to DNA mismatches are not able to be repaired in the presence of the compound and also prevent cross-talk between DNA checkpoint proteins and p53, the key mediator of the apoptotic pathway.DISCUSSIONDNA mismatches present in MMR-deficient cancer cells present an opportunity for selective therapeutic targeting. The rhodium metalloinsertor RhPPO is characterized by high cellular potency across MMR-deficient cell lines,22,24 and we have proposed that its buckled orientation in the DNA minor groove leads to a pronounced extrusion of the mismatched base pair from the DNA helix that activates DNA-binding proteins to generate DNA lesions 22,23. Crystallography efforts are ongoing to address the molecular structure of RhPPO bound to the DNA mismatch.…”