Deoxycytidine kinase (dCK) inhibition is synthetic lethal with BRCA2 deficiency

Poly (ADP-ribose) polymerase inhibitors in cancer therapy

ABSTRACT

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPis) have emerged as critical agents for cancer therapy. By inhibiting the catalytic activity of PARP enzymes and trapping them in the DNA, PARPis disrupt DNA repair, ultimately leading to cell death, particularly in cancer cells with homologous recombination repair deficiencies, such as those harboring BRCA mutations. This review delves into the mechanisms of action of PARPis in anticancer treatments, including the inhibition of DNA repair, synthetic lethality, and replication stress. Furthermore, the clinical applications of PARPis in various cancers and their adverse effects as well as their combinations with other therapies and the mechanisms underlying resistance are summarized. This review provides comprehensive insights into the role and mechanisms of PARP and PARPis in DNA repair, with a particular focus on the potential of PARPi-based therapies in precision medicine for cancer treatment.

Blocking Deoxycytidine Kinase in Activated Lymphocytes Depletes Deoxycytidine Triphosphate Pools and Alters Cell Cycle Kinetics to Yield Less Disease in a Mouse Multiple Sclerosis Model

Autoreactive, aberrantly activated lymphocytes that target myelin antigens in the central nervous system (CNS) are primary drivers of the autoimmune disease multiple sclerosis (MS). Proliferating cells including activated lymphocytes require deoxyribonucleoside triphosphates (dNTPs) for DNA replication. dNTPs can be synthesised via the de novo pathway from precursors such as glucose and amino acids or the deoxyribonucleoside salvage pathway from extracellular deoxyribonucleosides. Deoxycytidine kinase (dCK) is the rate-limiting enzyme in the salvage pathway. In prior work, we showed that targeting dCK with the small molecule inhibitor TRE-515 limits clinical symptoms in two myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) mouse models of MS and decreases the levels of activated CD4 T and B lymphocytes in vivo. However, whether targeting dCK limits disease in additional EAE models and how targeting dCK directly impacts activated and proliferating CD4 T and B cells has yet to be determined. Here, we show that dCK is activated in the lymph nodes and spleen in an EAE model induced by amino acids 139-151 of the proteolipid protein (PLP139-151) that is driven by CD4 T and B cells and is characterised by acute disease followed by disease remission. Treating this model with TRE-515 limits clinical symptoms and decreases the levels of activated CD4 T and B cells. In culture, CD4 T and B cells induce deoxyribonucleoside salvage following activation, and TRE-515 directly blocks CD4 T and B cell activation-induced proliferation and activation marker expression. TRE-515 decreases deoxycytidine triphosphate (dCTP) and deoxythymidine triphosphate (dTTP) pools and increases the length of time cells spend in S phase of the cell cycle without inducing a replication stress response in B cells. Our results suggest that dCK activity is required to supply needed dNTPs and to enable rapid cell division following lymphocyte activation against autoantigens in EAE mouse models.

Development of Uniform Ribosome Display Technology Enabling Easy and Efficient Identification of Full-Length Proteins that Interact with Bioactive Small and Large Molecules

Identifying target proteins that interact with bioactive molecules is indispensable for understanding their mechanisms of action. In this study, we developed a uniform ribosome display technology using equal-length DNAs and mRNAs to improve molecular display principle for target identification. The equal-length DNAs were designed to contain various coding sequences for full-length proteins with molecular weights of up to 130 kDa and were used to synthesize equal-length mRNAs, which allowed the formation of full-length protein-ribosome-equal-length mRNA complexes. Uniform ribosome display selections of dihydrofolate reductase and haloalkane dehalogenase mutant were performed against methotrexate and chlorohexane, respectively. Quantitative changes of proteins after each selection indicated that the target protein-displaying ribosomal complexes were specifically selected through non-covalent or covalent interactions with the corresponding bioactive molecules. Furthermore, selection of full-length proteins interacting with methotrexate or anti-DDX46 antibody from protein pools showed that only the target proteins could be precisely identified even though the molar amounts of equal-length mRNAs encoding them were adjusted to 1/20,000 of the total equal-length mRNAs. Thus, the uniform ribosome display technology enabled efficient identification of target proteins that interact with bioactive small and large molecules through simplified operations without deep sequencing.

Dynamic immunoediting by macrophages in homologous recombination deficiency-stratified pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease, notably resistant to existing therapies. Current research indicates that PDAC patients deficient in homologous recombination (HR) benefit from platinum-based treatments and poly-ADP-ribose polymerase inhibitors (PARPi). However, the effectiveness of PARPi in HR-deficient (HRD) PDAC is suboptimal, and significant challenges remain in fully understanding the distinct characteristics and implications of HRD-associated PDAC. We analyzed 16 PDAC patient-derived tissues, categorized by their homologous recombination deficiency (HRD) scores, and performed high-plex immunofluorescence analysis to define 20 cell phenotypes, thereby generating an in-situ PDAC tumor-immune landscape. Spatial phenotypic-transcriptomic profiling guided by regions-of-interest (ROIs) identified a crucial regulatory mechanism through localized tumor-adjacent macrophages, potentially in an HRD-dependent manner. Cellular neighborhood (CN) analysis further demonstrated the existence of macrophage-associated high-ordered cellular functional units in spatial contexts. Using our multi-omics spatial profiling strategy, we uncovered a dynamic macrophage-mediated regulatory axis linking HRD status with SIGLEC10 and CD52. These findings demonstrate the potential of targeting CD52 in combination with PARPi as a therapeutic intervention for PDAC.

Butterfly Effect in Cytarabine: Combined NMR-NQR Experiment, Solid-State Computational Modeling, Quantitative Structure-Property Relationships and Molecular Docking Study

Cytarabine (Ara-C) is a synthetic isomer of cytidine that differs from cytidine and deoxycytidine only in the sugar. The use of arabinose instead of deoxyribose hinders the formation of phosphodiester linkages between pentoses, preventing the DNA chain from elongation and interrupting the DNA synthesis. The minor structural alteration (the inversion of hydroxyl at the 2' positions of the sugar) leads to change of the biological activity from anti-depressant and DNA/RNA block builder to powerful anti-cancer. Our study aimed to determine the molecular nature of this phenomenon. Three 1H-14N NMR-NQR experimental techniques, followed by solid-state computational modelling (Quantum Theory of Atoms in Molecules, Reduced Density Gradient and 3D Hirshfeld surfaces), Quantitative Structure-Property Relationships, Spackman's Hirshfeld surfaces and Molecular Docking were used. Multifaceted analysis-combining experiments, computational modeling and molecular docking-provides deep insight into three-dimensional packing at the atomic and molecular levels, but is challenging. A spectrum with nine lines indicating the existence of three chemically inequivalent nitrogen sites in the Ara-C molecule was recorded, and the lines were assigned to them. The influence of the structural alteration on the NQR parameters was modeled in the solid (GGA/RPBE). For the comprehensive description of the nature of these interactions several factors were considered, including relative reactivity and the involvement of heavy atoms in various non-covalent interactions. The binding modes in the solid state and complex with dCK were investigated using the novel approaches: radial plots, heatmaps and root-mean-square deviation of the binding mode. We identified the intramolecular OH···O hydrogen bond as the key factor responsible for forcing the glycone conformation and strengthening NH···O bonds with Gln97, Asp133 and Ara128, and stacking with Phe137. The titular butterfly effect is associated with both the inversion and the presence of this intramolecular hydrogen bond. Our study elucidates the differences in the binding modes of Ara-C and cytidine, which should guide the design of more potent anti-cancer and anti-viral analogues.

Overexpression of ABCC1 and ABCG2 confers resistance to talazoparib, a poly (ADP-Ribose) polymerase inhibitor

AIMS

The overexpression of ABC transporters on cancer cell membranes is one of the most common causes of multidrug resistance (MDR). This study investigates the impact of ABCC1 and ABCG2 on the resistance to talazoparib (BMN-673), a potent poly (ADP-ribose) polymerase (PARP) inhibitor, in ovarian cancer treatment.

METHODS

The cell viability test was used to indicate the effect of talazoparib in different cell lines. Computational molecular docking analysis was conducted to simulate the interaction between talazoparib and ABCC1 or ABCG2. The mechanism of talazoparib resistance was investigated by constructing talazoparib-resistant subline A2780/T4 from A2780 through drug selection with gradually increasing talazoparib concentration.

RESULTS

Talazoparib cytotoxicity decreased in drug-selected or gene-transfected cell lines overexpressing ABCC1 or ABCG2 but can be restored by ABCC1 or ABCG2 inhibitors. Talazoparib competitively inhibited substrate drug efflux activity of ABCC1 or ABCG2. Upregulated ABCC1 and ABCG2 protein expression on the plasma membrane of A2780/T4 cells enhances resistance to other substrate drugs, which could be overcome by the knockout of either gene. In vivo experiments confirmed the retention of drug-resistant characteristics in tumor xenograft mouse models.

CONCLUSIONS

The therapeutic efficacy of talazoparib in cancer may be compromised by its susceptibility to MDR, which is attributed to its interactions with the ABCC1 or ABCG2 transporters. The overexpression of these transporters can potentially diminish the therapeutic impact of talazoparib in cancer treatment.