Poly ADP-ribose Polymerase Research Articles

Estimation of the Serum Level of Poly Adenosine Diphosphate Ribose Polymerase-1 in Psoriasis and its Correlation with Disease Severity

Estimation of the Serum Level of Poly Adenosine Diphosphate Ribose Polymerase-1 in Psoriasis and its Correlation with Disease Severity

NMNAT1 Is Essential for Human iPS Cell Differentiation to the Retinal Lineage.

The gene encoding nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1), a nicotinamide adenine dinucleotide synthetase localized in the cell nucleus, is a causative factor in Leber's congenital amaurosis, which is the earliest onset type of inherited retinal degeneration. We sought to investigate the roles of NMNAT1 in early retinal development. We used human induced pluripotent stem cells (hiPSCs) and established NMNAT1-knockout (KO) hiPSCs using CRISPR/cas9 technology to reveal the roles of NMNAT1 in human retinal development. NMNAT1 was not essential for the survival and proliferation of immature hiPSCs; therefore, we subjected NMNAT1-KO hiPSCs to retinal organoid (RO) differentiation culture. The expression levels of immature hiPSC-specific genes decreased in a similar manner after organoid culture initiation up to 2 weeks in the control and NMNAT1-KO. Neuroectoderm-specific genes were induced in the control and NMNAT1-KO organoids within a few days after starting the organoid culture; PAX6 and TUBB3 were higher in NMNAT1-KO organoids up to 7days than in the control organoids. However, the induction of genes involving retinal early development, such as RAX, which was induced at around day 10 in this culture, was considerably reduced in NMNAT1-KO organoids. Morphological examination also showed failure of retinal primordial structure formation, which became visible at around 2 weeks of the control culture, in the NMNAT1-KO organoids. Decreased intracellular NAD levels and poly(ADP-ribosyl)ation were observed in NMNAT1-KO organoids at 7 to 10days of the culture. Mass spectrometry analysis of inhibited proteins in the poly(ADP-ribosyl)ation pathway identified poly(ADP-ribosyl)ation of poly(ADP-ribose) polymerase 1 (PARP1) as a major protein. These results indicate that NMNAT1 was dispensable for neural lineage differentiation but essential for the commitment of retinal fate differentiation in hiPSCs. The NMNAT1-NAD-PARP1 axis may play a critical role in the appropriate development of human retinal lineage differentiation.

Inactive Parp2 causes Tp53-dependent lethal anemia by blocking replication-associated nick ligation in erythroblasts

Poly (ADP-ribose) polymerase (PARP) 1 and 2 enzymatic inhibitors (PARPi) are promising cancer treatments. But recently, their use has been hindered by unexplained severe anemia and treatment-related leukemia. Inaddition to enzymatic inhibition, PARPi also trap PARP1 and 2 at DNA lesions. Here we report that, unlike Parp2-/- mice, which develop normally, mice expressing catalytically inactive Parp2 (E534A and Parp2EA/EA) succumb to Tp53- and Chk2-dependent erythropoietic failure in utero, mirroring Lig1-/- mice. While DNA damage mainly activates PARP1, we demonstrate that DNA replication activates PARP2 robustly. PARP2 is selectively recruited and activated by 5'-phosphorylated nicks (5'p-nicks), including those between Okazaki fragments, resolved by ligase 1 (Lig1) and Lig3. Inactive PARP2, but not its active form or absence, impedes Lig1- and Lig3-mediated ligation, causing dose-dependent replication fork collapse, which is detrimental to erythroblasts with ultra-fast forks. This PARylation-dependent structural function of PARP2 at 5'p-nicks explains the detrimental effects of PARP2 inactivation on erythropoiesis, shedding light on PARPi-induced anemia and the selection for TP53/CHK2 loss.

Pharmacodynamic Activity of [18F]-Fluorthanatrace Poly(ADP-ribose) Polymerase Positron Emission Tomography in Patients With BRCA1/2-Mutated Breast Cancer Receiving Talazoparib.

We tested the ability of [18F] fluorthanatrace (FTT), a radiolabeled analog of poly(ADP-ribose) polymerase (PARP)-1 inhibitors, to demonstrate target engagement on positron emission tomography (PET) scans from patients with newly diagnosed primary breast cancer receiving the PARP inhibitor (PARPi) talazoparib. Seven patients with germline BRCA1/2 pathogenic variants underwent [18F]FTT PET-computed tomography scanning at baseline, and five underwent repeat scanning 14 days after talazoparib initiation. Maximum uptake on PET was quantified in the primary tumor, involved nodes, contralateral pectoralis muscle, and lumbar vertebra body level 3, and compared between the two time points. Blocking of [18F]FTT was observed on the second scan. Potentially strong but nonsignificant correlations were found between changes in tumor volume (on ultrasound at 1 month v baseline) and percentage changes in tumor-to-muscle uptake ratio at 14 days from baseline (Spearman rank correlation coefficient r = 1; P = .083); and between the highest-grade hematologic toxicity and baseline bone marrow-to-muscle (B/M) uptake ratio (r = 0.72; P = .068) and percentage change in B/M ratio at 14 days from baseline (r = 0.87; P = .058). We conclude that [18F]FTT can image target engagement by PARPi, but larger studies are needed to determine whether [18F]FTT uptake can predict response to PARPi and whether uptake of [18F]FTT in bone marrow may be an early predictor of hematologic toxicity.

337 (PB325): Poly(ADP-Ribose) Polymerase (PARP) inhibition in metastatic breast cancer: comparison of therapeutic outcomes between patients with BRCA1/2 mutations and other alterations

337 (PB325): Poly(ADP-Ribose) Polymerase (PARP) inhibition in metastatic breast cancer: comparison of therapeutic outcomes between patients with BRCA1/2 mutations and other alterations

Niraparib, an FDA-Approved Poly-(ADP-Ribose) Polymerase (PARP) Inhibitor Is Renoprotective against Cisplatin Nephrotoxicity in Ovarian Tumor-Bearing Mice

Niraparib, an FDA-Approved Poly-(ADP-Ribose) Polymerase (PARP) Inhibitor Is Renoprotective against Cisplatin Nephrotoxicity in Ovarian Tumor-Bearing Mice

Poly (ADP-ribose) Polymerase Inhibitor Resistance Driven by Emergence of Polyclonal Mutations With Convergent Evolution: A Molecular Tumor Board Discussion.

Polyclonal convergent evolution to PARPi resistance in a patient with metastatic breast cancer with gPALB2.

Carvedilol through ß1-Adrenoceptor blockade ameliorates glomerulonephritis via inhibition of oxidative stress, apoptosis, autophagy, ferroptosis, endoplasmic reticulum stress and inflammation

Glomerulonephritis (GN) is one of the main causes of end stage renal disease and requires an effective treatment for inhibiting GN. Renal nerves through efferent (RENA) and afferent (RANA) innervation to glomeruli regulate the glomerular function. We delineated the role of RENA and RANA on anti-Thy1.1-induced GN. Female Wistar rats were divided into Control, Thy1.1 plus anti-Thy1.1, bilaterally renal nerve denervation (DNX) plus anti-Thy1.1, and topical capsaicin to bilateral renal nerves for selective ablation of RANA (DNAX) plus anti-Thy1.1. We examined RANA and RENA response to anti-Thy1.1 and compared the effect of DNX or DNAX on urinary oxidative stress, renal gp91, tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP), apoptosis, autophagy, ferroptosis, antioxidant enzymes, endoplasmic reticulum (ER) stress and inflammation by western blot. Anti-Thy1.1 significantly enhanced RENA, but did not affect RANA. DNX significantly decreased TH and CGRP expression, whereas DNAX only reduced CGRP expression. Anti-Thy1.1 significantly increased glomerulosclerosis injury, urinary protein, electron paramagnetic resonance signals of alpha-(4-pyridyl-N-oxide)-N-tert-butylnitrone adducts, 8-isoprostane and nitrotyrosine levels, NADPH oxidase gp91phox (gp91), macrophage/monocyte (ED-1), GRP-78, Beclin-1/LC3-II, Bax/caspase-3/poly(ADP-ribose) polymerase expression, inflammatory cytokines levels and decreased renal Copper/Zinc superoxide dismutase, Cystine/glutamate transporter (xCT) and Glutathione peroxidase 4 (GPX4) expression vs. Control. The enhanced oxidative parameters or reduced antioxidant defense by anti-Thy1.1 were significantly attenuated by DNX but not DNAX. Additionally, oral ß1-adrenoceptor antagonist-Carvedilol at an early stage reduced anti-Thy1.1 increased proteinuria level and oxidative parameters. Our data suggest that DNX and ß1-adrenoceptor antagonist-Carvedilol efficiently attenuate oxidative stress, inflammation, ER stress, autophagy, ferroptosis and apoptosis in GN

Novel repurposing of sulfasalazine for the treatment of adrenocortical carcinomas, probably through the SLC7A11/xCT-hsa-miR-92a-3p-OIP5-AS1 network pathway

BackgroundRecent multigenomic analysis of adrenocortical carcinomas (ACCs) identified SLC7A11/xCT as a novel biomarker. The Food and Drug Administration–approved anti-inflammatory drug, sulfasalazine (SAS), induces ferroptosis by blocking SLC7A11 expression. We hypothesize that SAS could be repurposed to target ACC cells. MethodsExpression of SLC7A11 and its association with ACC survival was analyzed using Gene Expression Profiling Interactive Analysis (GEPIA). The validated ACC cell lines NCI-H295R, ACC1, and ACC2 were grown in 2D culture. In vitro studies included the CellTiter-Glo assay to calculate viability, Western blot (WB) analysis for apoptosis and other target protein changes, reverse transcriptase polymerase chain reaction for steroidogenic enzyme changes, C11BODIPY for lipid peroxidation, and mass spectrometry for changes in lipids. ResultsThe Cancer Genome Atlas Program database analysis in GEPIA showed that SLC7A11 and linked long noncoding RNA OAP5-AS1 are highly expressed in ACC tumors versus normal adrenals (n = 77 vs 128; P < .05). This was associated with poor overall and disease-free survival with hazard ratios of 4.3 and 5.2 for SLC7A11 and 4.8 and 2.7 for OAP5-AS1, respectively. ACC cell line half-inhibitory maximum concentration values after 72-hour SAS treatment ranged from 412 nM (ACC1) to 799 nM (ACC2), and all showed cleavage of poly (ADP-ribose) polymerase, upregulation of p-Akt and p-ERK, and downregulation of GPX4 and SLC7A11 (P < .05) by WB analysis. Sphere formation, migration, and invasion assay showed inhibition, and lipid peroxidation using C11BODIPY, increase in intracellular iron, induction of oxidative stress, and significant upregulation of oxidized polyunsaturated fatty acid phospholipids (P < .05 each) by mass spectrometry suggests induction of ferroptosis. ConclusionSAS downregulates tSLC7A11 in ACCs, targets the Akt/ERK pathway and lipid metabolism, and induces cell death in vitro, warranting additional translational studies to define its therapeutic potential in ACC.

Comprehensive Genomic Assessment of Advanced-Stage GI Stromal Tumors Using the Japanese National Center for Cancer Genomics and Advanced Therapeutics Database.

Clinical utility of comprehensive genomic profiling (CGP) for precision medicine has become evident. Although there are several reports on the genomic landscape of GI stromal tumors (GISTs), large-scale data specific to GIST are limited, especially in Asia. Additionally, the applicability of molecular-targeted agents identified using CGP has not been extensively examined. We investigated the status of genomic alterations in Japanese patients with advanced GISTs using the National Center for Cancer Genomics and Advanced Therapeutics (C-CAT) database to identify novel treatment strategies and drug development. We retrospectively reviewed the clinical and CGP data of patients with advanced-stage GIST registered in the C-CAT database to assess the genomic landscape and potential actionable alterations. Data from 144 patients were reviewed. Oncogenic alterations were detected frequently in KIT (78%), CDKN2A (37%), CDKN2B (29%), RB1 (11%), STK11 (10%), TP53 (9%), PDGFRA (6%), and SDHB (6%). Loss of CDKN2A/CDKN2B was only observed in KIT/PDGFRA-mutated GISTs, while alterations in SDHA/SDHB were only detected in KIT/PDGFRA wild-type GISTs. Among 119 KIT/PDGFRA-mutated GISTs, 95 (80%) had oncogenic genomic alterations and 29 (24%) had actionable alterations, excluding KIT and PDGFRA. However, among 25 KIT/PDGFRA wild-type GISTs, 22 (88%) had oncogenic alterations and 11 (44%) had actionable alterations. Representative candidate drugs for genome-matched therapies in KIT/PDGFRA-mutated and wild-type GISTs were as follows: pembrolizumab for tumor mutation burden-high in one and two patients, respectively; poly-adenosine diphosphate ribose polymerase inhibitors for alterations related to homologous recombination deficiency in 12 and one patient, respectively; NTRK inhibitor for ETV6-NTRK3 fusion in one with KIT/PDGFRA wild-type GIST; and human epidermal growth factor receptor 2-antibody-drug conjugate in one with KIT/PDGFRA-mutated GIST. This study highlights the genomic landscape of advanced GISTs and the important role of CGP in identifying rational molecular-targeted therapeutic options.

Temporal and Apparent Decrease of Creatinine-Derived eGFR in the Patients with Cancer Treated with Poly ADP-Ribose Polymerase Inhibitors

Temporal and Apparent Decrease of Creatinine-Derived eGFR in the Patients with Cancer Treated with Poly ADP-Ribose Polymerase Inhibitors

TMPRSS2:ERG Gene Fusion Might Predict Resistance to PARP Inhibitors in Metastatic Castration-resistant Prostate Cancer.

The emergence of novel DNA damage repair (DDR) pathways in molecular-target therapy drugs (MTTD) has shown promising outcomes in treating patients with metastatic castration-resistant prostate cancer (mCRPC). About 25% of mCRPC patients have actionable deleterious aberrations in DDR genes, primarily in the homologous recombination (HR) pathway. However, the response rate in patients with BRCA1/2 or mutations in HRR-related genes is only 45%-55%, when exposed to poly ADP ribose polymerase (PARP) inhibitor-based therapy (PARPi). A frequent characteristic feature of prostate cancer (PC) is the occurrence of genomic rearrangement that affects the transmembrane protease serine 2 (TMPRSS2) and E26 transformation-specific (ETS)- transcription factor-related gene (ERG). In this study, a total of 114 patients with mCRPC had their RNA and DNA sequenced using next-generation sequencing. Based on their genetic profile of deleterious gene alterations of BRCA1/2 or ATM, six patients were selected for PARPi. Patients with TMPRSS2:ERG gene fusion and homozygous alteration in ATM or BRCA2 (n=2) or heterozygous alterations (BRCA1 or BRCA2) and lack of TMPRSS2:ERG gene fusion (n=2) did not show clinical benefit from PARPi (treatment duration <16 weeks). In contrast, patients (n=2) without TMPRSS2:ERG gene fusion and homozygous deleterious alterations in ATM or BRCA2 all had clinical benefit from PARPi (treatment duration ≥16 weeks). The TMPRSS2:ERG transcript product might be used as a PARPi resistance biomarker.

Repurposing Valrubicin as a Potent Inhibitor of Ovarian Cancer Cell Growth.

Ovarian cancer (OC) is a leading cause of cancer-related mortality among women, and there remains a significant unmet need for new therapeutic agents to improve patient outcomes. This study aimed to explore drug repositioning by screening a library of Food and Drug Administration (FDA)-approved compounds to identify those with therapeutic potential against OC. We also aimed to elucidate the molecular mechanisms of action of such compounds to better understand how they inhibit cancer cell proliferation. Using the WST-1 assay, a library of 1710 FDA-approved drugs was screened to evaluate their effects on OC cell proliferation. The molecular mechanisms underlying the effects of selected compounds were assessed through terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay and immunoblot analysis. Screening of FDA-approved libraries revealed valrubicin as a potent inhibitor of OVCAR8 cell proliferation and SKOV3 and A2780 cell growth. Furthermore, valrubicin treatment led to increased DNA fragmentation, as evidenced by the TUNEL assay, and activated apoptosis signaling through enhancement of cleaved caspase-3 and poly(ADP-ribose) polymerase levels. Valrubicin, through drug repositioning, can be applied as a new therapeutic agent for OC.

Antitumor Potential of Guttiferone E Combined With Carboplatin Against Osimertinib-resistant H1975 Lung Cancer Through Apoptosis.

Low selectivity and high frequency of side-effects are the major problems of currently used chemotherapeutics. Among natural compounds, the polyprenylated acylphloroglucinol, guttiferone E, isolated from Brazilian red propolis, has attracted attention due to its marked anticancer properties and was evaluated here for its role against osimertinib-resistant H1975 cells (with double mutations of epidermal growth factor receptor: EGFR L858R/T790M). Guttiferone E was obtained from red propolis using established extraction procedures. Guttiferone E was tested using the H1975 cell line in in vitro (2D and 3D) cell cultures and in vivo in BALB/c athymic nude mice. Live/dead assay was also performed to support the results. Tumor tissues obtained from in vivo studies were used for western blotting. Guttiferone E reduced H1975 cell viability in a concentration-dependent manner. The IC50 values in 2D and 3D cell lines were 2.56±0.12 μM and 11.25±0.34 μM. Furthermore, at 10 mg/kg intraperitoneally, guttiferone E significantly reduced the tumor volume in tumor xenografts when used alone and in combination with carboplatin. Guttiferone E and carboplatin displayed synergistic inhibition of H1975 cells and animal tumors. Co-treatment of guttiferone E with carboplatin induced more prominent apoptosis than treatment with either drug alone. Guttiferone E treatment induced cleavage of poly-ADP ribose polymerase and induced apoptosis by significantly reducing levels of mammalian target of rapamycin, sirtuin 1, sirtuin 7, superoxide dismutase, programmed death-ligand 1, and programmed cell death 1 in tumor tissues. Our results show guttiferone E to be a promising, novel and potent antitumor drug candidate for osimertinib-resistant lung cancer with EGFR L858R/T790M mutations.

Identification of BBC3 as a novel indicator for predicting prostate cancer development and olaparib resistance

Prostate cancer (PCa) is a commonly occurring malignancy in elderly men. Olaparib, a poly ADP-ribose polymerase inhibitor, is utilized in PCa treatment. However, patients often develop resistance to olaparib after a period of treatment. Genetic alterations may play a significant role in this resistance, but the specific genes involved remain unclear. This study collected RNA-sequence data from the Gene Expression Omnibus database on both olaparib-sensitive and -resistant PCa cells to identify genes crucial for resistance. Subsequently, the enriched pathways of these genes were analyzed, and a protein–protein interaction (PPI) network was constructed to identify hub genes. The effect of these hub genes on PCa occurrence, progression, and prognosis was assessed using data from The Cancer Genome Atlas and Chinese Prostate Cancer Genome and Epigenome Atlas databases. Finally, this study validated our findings in clinical PCa samples and cells. From the GSE189186 dataset, 50 upregulated genes and 2 downregulated genes were identified in olaparib-resistant C4-2B and LNCaP cells. Utilizing the PPI network, eight upregulated genes (BBC3, TP53I3, FDXR, DDB2, CDKN1A, GADD45A, ZMAT3, and SESN1) were identified as hub genes for olaparib-resistant PCa cells. Furthermore, some of these genes were central to PCa occurrence, with BBC3 also influencing progression and prognosis. Importantly, BBC3 expression was upregulated in clinical PCa samples and affected PCa cells sensitive to olaparib, suggesting its potential as a predictive marker for PCa development and olaparib resistance.

Genetic Implications for Cancer Management: The Changing Landscape of Poly (ADP-ribose) Polymerase Inhibitor Indications in the Treatment of Ovarian Cancer.

Between December 2014 and May 2020, the United States Food and Drug Administration approved 9 indications for poly (ADP-ribose) polymerase (PARP) inhibitor use in ovarian cancer. Between June 2022 and September 2022, all 3 indications for PARP inhibitor treatment of recurrent ovarian cancer were withdrawn. Between November 2022 and September 2023, all 3 indications for PARP inhibitor maintenance therapy in recurrent ovarian cancer were restricted. The 3 indications for PARP inhibitor maintenance therapy in newly diagnosed advanced ovarian cancer are unchanged. This article reviews the timelines and data leading to regulatory changes for PARP inhibitor use in ovarian cancer in the United States.

Analysis of the mechanisms underlying the anticancer and biological activity of retinoic acid and chitosan nanoparticles containing retinoic acid.

Retinoic acid (RA) has been shown in earlier investigations to have anticancer properties in various cancer cells. RA's effect on breast cancer treatment remains uncertain, though. This study investigated whether RA and chitosan nanoparticles (NPs) loaded with RA could be harmful to the MCF-7 cell line. In this study, NPs with RA were used in characterization tests. Using ELISA kits, the amounts of 8-okso-2'-deoksiguanozin (8-oxo-dG), BCL-2, Bcl-2-Associated X-protein (Bax), cleaved Poly (ADP-ribose) polymerases (PARP), total oxidant and antioxidant, and cleaved caspase-3 capacities were determined. The analysis of chitosan NPs showed that their drug-release profile, encapsulation efficiency (EE), and particle size were suitable for cell culture experiment. The EE value of NPs including RA was calculated as 83.32 ± 0.04%. The IC50 value for RA was 2.89 ± 0.03µg/mL, while the IC50 value for RA-loaded NPs was significantly lower at 2.28 ± 0.02µg/mL. In ELISA testing, RA and chitosan NPs containing RA at a concentration of 2µg/mL dramatically increased the concentrations of total oxidant, cleaved caspase-3. Cleaved caspase-3 levels were quantified as 614.90 ± 3.40pg/mg protein in the control group, 826.37 ± 5.82pg/mg protein in RA-treated cells, and 863.52 ± 4.32pg/mg protein in RA-NP-treated cells. Interestingly, no substantial variations were observed in the levels of the anti-apoptotic protein BCL-2. Overall, studies revealed that RA and RA-NPs promoted apoptosis in MCF-7 cells by upregulating the expression of pro-apoptotic proteins Bax, cleaved caspase-3, and cleaved PARP.

Enhancing targeted therapy by combining PI3K and AKT inhibitors with or without cisplatin or vincristine in medulloblastoma cell lines in vitro

AimDespite current intensive therapy, survival rates of medulloblastoma (MB) greatly vary according to molecular subgroup, so new therapies are needed. Recently, we showed that combining phosphoinositide 3-kinase (PI3K), fibroblast growth factor receptor and cyclin-dependent-kinase-4/6 inhibitors (BYL719, JNJ-42756493 and PD-0332991, respectively) or poly (ADP-ribose) polymerase (PARP) and WEE-1 inhibitors (BMN673 and MK1775 respectively) had synergistic effects on MB. Here, in continuation, we investigated the effects of single and combined administrations of PI3K and AKT inhibitors, with/without cisplatin or vincristine on adherent or suspension cultures of different MB subgroups as well as in a spheroid culture of one MB line. Material and methodsMB cell lines DAOY, UW228–3, D425, Med8A, and D283 were treated with single and combined administrations of BYL719, AZD5363, cisplatin or vincristine and followed for viability, cell confluence, cytotoxicity, and cell migration. DAOY was also tested as a spheroid culture. Key findingsSingle BYL719, AZD5363, cisplatin, or vincristine administrations gave dose-dependent responses with regard to inhibition of viability and cell confluence. Combining AZD5363 with BYL719, cisplatin or vincristine resulted in synergistic effects with regard to inhibition of viability in all cell lines, and confluence and migration in all tested cell lines. The administration of single and combined treatments to DAOY spheroids produced largely similar effects. SignificanceThis study provides pre-clinical evidence that AKT inhibitors combined with PI3K inhibitors, cisplatin, or vincristine exhibit additive/synergistic anti-MB activity, and lower doses could be used. The latter also applied to one MB line grown as spheroids, further supporting their future potential use.

Synthetic Lethal Targeting of Cyclin Dependent Kinase-12-Deficient Prostate Cancer with PARP Inhibitors.

CDK12 is a cyclin-dependent kinase (CDK) that is mutated or amplified in multiple cancers. We previously described a subtype of prostate cancer (PC) characterized predominantly by frameshift, loss-of-function mutations in CDK12. This subtype exhibits aggressive clinical features. Using isogenic PC models generated by CRISPR/Cas9-mediated inactivation of CDK12, we conducted a chemical library screen of ~1800 FDA-approved drugs. We inhibited cyclin K and CDK13 and evaluated the effects on poly ADP-ribose polymerase inhibitor (PARPi) sensitivity. CDK12 truncation and kinase domain mutations were expressed in cell lines to determine effects on PARPi sensitivity. Mice bearing control and CDK12 mutant prostate tumors were treated with rucaparib. Finally, we evaluated prostate specific antigen (PSA) responses in patients with CDK12 mutations treated with rucaparib on the TRITON2 trial. Cancer cells lacking CDK12 are more sensitive to PARPi than isogenic wild-type cells, and sensitivity depends on the degree of CDK12 inhibition. Inhibiting cyclin K, but not CDK13, also led to PARPi sensitivity and suppressed homologous recombination. CDK12 truncation mutants remained sensitive to PARPi, whereas kinase domain mutants exhibited intermediate sensitivity. The PARPi rucaparib suppressed tumor growth in mice bearing CDK12-mutated tumors. Finally, 6 of 11 (55%) PC patients with biallelic CDK12 mutations had reductions in serum PSA levels when treated with rucaparib on the TRITON2 clinical trial. In PC, sensitivity to PARPi is dependent on the specific type and zygosity of the CDK12 mutation. PARPi monotherapy may have some activity in PC patients with biallelic inactivating CDK12 alterations.

Molecular mechanism of PARP inhibitor resistance.

Poly (ADP-ribose) polymerases (PARP) inhibitors (PARPi) are the first-approved anticancer drug designed to exploit synthetic lethality. PARPi selectively kill cancer cells with homologous recombination repair deficiency (HRD), as a result, PARPi are widely employed to treated BRCA1/2-mutant ovarian, breast, pancreatic and prostate cancers. Currently, four PARPi including Olaparib, Rucaparib, Niraparib, and Talazoparib have been developed and greatly improved clinical outcomes in cancer patients. However, accumulating evidences suggest that required or de novo resistance emerged. In this review, we discuss the molecular mechanisms leading to PARPi resistances and review the potential strategies to overcome PARPi resistance.