Combating resistance to DNA damaging agents

Overcoming Cancer Multi-drug Resistance (MDR): Reasons, mechanisms, nanotherapeutic solutions, and challenges

Multi-drug resistance (MDR) in cancer cells, either intrinsic or acquired through various mechanisms, significantly hinders the therapeutic efficacy of drugs. Typically, the reduced therapeutic performance of various drugs is predominantly due to the inherent over expression of ATP-binding cassette (ABC) transporter proteins on the cell membrane, resulting in the deprived uptake of drugs, augmenting drug detoxification, and DNA repair. In addition to various physiological abnormalities and extensive blood flow, MDR cancer phenotypes exhibit improved apoptotic threshold and drug efflux efficiency. These severe consequences have substantially directed researchers in the fabrication of various advanced therapeutic strategies, such as co-delivery of drugs along with various generations of MDR inhibitors, augmented dosage regimens and frequency of administration, as well as combinatorial treatment options, among others. In this review, we emphasize different reasons and mechanisms responsible for MDR in cancer, including but not limited to the known drug efflux mechanisms mediated by permeability glycoprotein (P-gp) and other pumps, reduced drug uptake, altered DNA repair, and drug targets, among others. Further, an emphasis on specific cancers that share pathogenesis in executing MDR and effluxed drugs in common is provided. Then, the aspects related to various nanomaterials-based supramolecular programmable designs (organic- and inorganic-based materials), as well as physical approaches (light- and ultrasound-based therapies), are discussed, highlighting the unsolved issues and future advancements. Finally, we summarize the review with interesting perspectives and future trends, exploring further opportunities to overcome MDR.

Genotoxicity of Novel Pyrazolo[4,3-e]tetrazolo[1,5-b][1,2,4]triazine Sulfonamides in Normal and Cancer Cells In Vitro

Pyrazolo[4,3-e]tetrazolo[1,5-b][1,2,4]triazine sulfonamides constitute a novel group of heterocyclic compounds with broad biological activities including anticancer properties. The compounds investigated in this study (MM134, -6, -7, and 9) were found to have antiproliferative activity against BxPC-3 and PC-3 cancer cell lines in micromolar concentrations (IC₅₀ 0.11-0.33 µM). Here, we studied the genotoxic potential of the tested compounds with alkaline and neutral comet assays, accompanied by immunocytochemical detection of phosphorylated γH2AX. We found that pyrazolo[4,3-e]tetrazolo[1,5-b][1,2,4]triazine sulfonamides induce significant levels of DNA damage in BxPC-3 and PC-3 cells without causing genotoxic effects in normal human lung fibroblasts (WI-38) when used in their respective IC₅₀ concentrations (except for MM134) and showed a dose-dependent increase in DNA damage following 24 h incubation of tested cancer cells with these agents. Furthermore, the influence of MM compounds on DNA damage response (DDR) factors was assessed using molecular docking and molecular dynamics simulation.

Cholinergic drugs bind at the minor groove and reverse induced oxidative stress of calf thymus DNA: a new perspective towards an unexplored therapeutic efficacy

Four FDA approved cholinesterase inhibitors reverse the hydrogen peroxide induced oxidative damage of ct-DNA.

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

Platinum drugs are heavily used first-line chemotherapeutic agents for many solid tumours and have stimulated substantial interest in the biological activity of DNA-binding metal complexes. These complexes generate DNA lesions which trigger the activation of DNA damage response (DDR) pathways that are essential to maintain genomic integrity. Cancer cells exploit this intrinsic DNA repair network to counteract many types of chemotherapies. Now, advances in the molecular biology of cancer has paved the way for the combination of DDR inhibitors such as poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) and agents that induce high levels of DNA replication stress or single-strand break damage for synergistic cancer cell killing. In this review, we summarise early-stage, preclinical and clinical findings exploring platinum and emerging ruthenium anti-cancer complexes alongside PARPi in combination therapy for cancer and also describe emerging work on the ability of ruthenium and gold complexes to directly inhibit PARP activity.

HAUSP stabilizes Cdc25A and protects cervical cancer cells from DNA damage response

Resistance to DNA-damaging agents is one of the main reasons for the low survival of cervical cancer patients. Previous reports have suggested that the Cdc25A oncoprotein significantly affects the level of susceptibility to DNA-damaging agents, but the molecular mechanism remains unclear. In this study, we used Western blot and flow cytometry analyses to demonstrate that the deubiquitinating enzyme HAUSP stabilizes Cdc25A protein level. Furthermore, in a co-immunoprecipitation assay, we found that HAUSP interacts with and deubiquitinates Cdc25A both exogenously and endogenously. HAUSP extends the half-life of the Cdc25A protein by circumventing turnover. HAUSP knockout in HeLa cells using the CRISPR/Cas9 system caused a significant delay in Cdc25A-mediated cell cycle progression, cell migration, and colony formation and attenuated tumor progression in a mouse xenograft model. Furthermore, HAUSP-mediated stabilization of the Cdc25A protein produced enhanced resistance to DNA-damaging agents. Overall, our study suggests that targeting Cdc25A and HAUSP could be a promising combinatorial approach to halt progression and minimize antineoplastic resistance in cervical cancer.

DNA polymerase δ proofreads errors made by DNA polymerase ε

Polδ and Polε are the two major replicative polymerases in eukaryotes, but their precise roles at the replication fork remain a subject of debate. A bulk of data supports a model where Polε and Polδ synthesize leading and lagging DNA strands, respectively. However, this model has been difficult to reconcile with the fact that mutations in Polδ have much stronger consequences for genome stability than equivalent mutations in Polε. We provide direct evidence for a long-entertained idea that Polδ can proofread errors made by Polε in addition to its own errors, thus, making a more prominent contribution to mutation avoidance. This paper provides an essential advance in the understanding of the mechanism of eukaryotic DNA replication.

During eukaryotic replication, DNA polymerases ε (Polε) and δ (Polδ) synthesize the leading and lagging strands, respectively. In a long-known contradiction to this model, defects in the fidelity of Polε have a much weaker impact on mutagenesis than analogous Polδ defects. It has been previously proposed that Polδ contributes more to mutation avoidance because it proofreads mismatches created by Polε in addition to its own errors. However, direct evidence for this model was missing. We show that, in yeast, the mutation rate increases synergistically when a Polε nucleotide selectivity defect is combined with a Polδ proofreading defect, demonstrating extrinsic proofreading of Polε errors by Polδ. In contrast, combining Polδ nucleotide selectivity and Polε proofreading defects produces no synergy, indicating that Polε cannot correct errors made by Polδ. We further show that Polδ can remove errors made by exonuclease-deficient Polε in vitro. These findings illustrate the complexity of the one-strand–one-polymerase model where synthesis appears to be largely divided, but Polδ proofreading operates on both strands.

DNA Damage Stress: Cui Prodest?

DNA is an entity shielded by mechanisms that maintain genomic stability and are essential for living cells; however, DNA is constantly subject to assaults from the environment throughout the cellular life span, making the genome susceptible to mutation and irreparable damage. Cells are prepared to mend such events through cell death as an extrema ratio to solve those threats from a multicellular perspective. However, in cells under various stress conditions, checkpoint mechanisms are activated to allow cells to have enough time to repair the damaged DNA. In yeast, entry into the cell cycle when damage is not completely repaired represents an adaptive mechanism to cope with stressful conditions. In multicellular organisms, entry into cell cycle with damaged DNA is strictly forbidden. However, in cancer development, individual cells undergo checkpoint adaptation, in which most cells die, but some survive acquiring advantageous mutations and selfishly evolve a conflictual behavior. In this review, we focus on how, in cancer development, cells rely on checkpoint adaptation to escape DNA stress and ultimately to cell death.