Establishing the homologous recombination score threshold in metastatic prostate cancer patients to predict the efficacy of PARP inhibitors

Background:The homologous recombination deficiency(HRD)score serves as a promising biomarker to iden-tify patients who are eligible for treatment with PARP inhibitors(PARPi).Previous studies have suggested a 3-biomarker Genomic Instability Score(GIS)threshold of≥42 as a valid biomarker to predict response to PARPi in patients with ovarian cancer and breast cancer.However,the GIS threshold for prostate cancer(PCa)is still lacking.Here,we conducted an exploratory analysis to investigate an appropriate HRD score threshold and to evaluate its ability to predict response to PARPi in PCa patients.Methods:A total of 181 patients with metastatic castration-resistant PCa were included in this study.Tumor tissue specimens were collected for targeted next-generation sequencing for homologous recombination repair(HRR)genes and copy number variation(CNV)analysis.The HRD score was calculated based on over 50,000 single-nucleotide polymorphisms(SNP)distributed across the human genome,incorporating three SNP-based as-says:loss of heterozygosity,telomeric allelic imbalance,and large-scale state transition.The HRD score threshold was set at the last 5th percentile of the HRD scores in our cohort of known HRR-deficient tumors.The relation-ship between the HRD score and the efficacy in 16 patients of our cohort who received PARPi treatment were retrospectively analyzed.Results:Genomic testing was succeeded in 162 patients.In our cohort,61 patients(37.7%)had HRR mutations(HRRm).BRCA mutations occurred in 15 patients(9.3%).The median HRD score was 4(ranged from 0 to 57)in the total cohort,which is much lower than that in breast and ovarian cancers.Patients who harbored HRRm and BRCA or TP53 mutations had higher HRD scores.CNV occured more frequently in patients with HRRm.The last 5th percentile of HRD scores was 43 in the HRR-mutant cohort and consequently HRD high was defined as HRD scores≥43.In the 16 patients who received PARPi in our cohort,4 patients with a high HRD score achieved an objective response rate(ORR)of 100%while 12 patients with a low HRD score achieved an ORR of 8.3%.Progression-free survival(PFS)in HRD high patients was longer compared to HRD low patients,regardless of HRRm.Conclusions:A HRD score threshold of 43 was established and preliminarily validated to predict the efficacy of PARPi in this study.Future studies are needed to further verify this threshold.

Recent advancements in PARP inhibitors-based targeted cancer therapy

Poly(ADP-ribose)polymerase inhibitors(PARPi)are a new class of agents with unparalleled clinical achievement for driving synthetic lethality in BRCA-deficient cancers.Recent FDA approval of PARPi has motivated clinical trials centered around the optimization of PARPi-associated therapies in a variety of BRCA-deficient cancers.This review highlights recent advancements in understanding the molecular mechanisms of PARP‘trapping’and synthetic lethality.Particular attention is placed on the potential extension of PARPi therapies from BRCA-deficient patients to populations with other homologous recombination-deficient backgrounds,and common characteristics of PARPi and non-homologous end-joining have been elucidated.The synergistic antitumor effect of combining PARPi with various immune checkpoint blockades has been explored to evaluate the potential of combination therapy in attaining greater therapeutic outcome.This has shed light onto the differing classifications of PARPi as well as the factors that result in altered PARPi activity.Lastly,acquired chemoresistance is a crucial issue for clinical application of PARPi.The molecularmechanisms underlying PARPi resistance and potential overcoming strategies are discussed.

Cervical cancer:a tale from HPV infection to PARP inhibitors

Globally,cervical cancer(CxCa)ranks 4th common cancer among females and led to 569,847 incidences and 311,365 deaths in 2018.80%of CxCa cases occur due to persistent infection with a high-risk subtype of human papillomavirus(HPV-16 and 18).Smoking,high par-ity,and co-infection with type 2 herpes simplex or HIV are other known risk factors for CxCa.Major histological subtypes are squamous(70%)and adenocarcinoma(25%).Presently,concur-rent radiation plus cisplatin(CDDP)-based chemotherapy is the standard treatment for CxCa patients.However,CDDP resistance and toxic side effects limit its efficacy,leading to a poorer response rate and an expected overall survival ranging from 10 to 17.5 months.Reduced drug uptake,increased DNA damage repair,increased CDDP inactivation,and overexpressed Bcl-2 or caspase inhibition,are primarily accountable mechanisms for CDDP resistance and improving CDDP’s efficacy remains the major challenge.Poly(ADP-ribosyl)polymerase-1,an effective mediator of nucleotide excision repair pathway,is involved in DNA repair as well as maintaining genomic stability and is significantly expressed in malignant lymphomas,hepa-tocellular-,cervical-and colorectal carcinoma,which has been approved effective in mainte-nance therapy and may serve as an effective target to enhance CDDP sensitivity in CxCa.Here,we summarize the etiology and epidemiology of and treatment for CxCa,the mechanism responsible for chemotherapy resistance,PARP inhibitor as a possible therapy for CxCa,and other possible chemotherapeutic options for CxCa treatment.

Ovarian cancer recurrence:“is the definition of platinum resistance modified by PARP inhibitors and other intervening treatments?”

PolyADP ribose polymerase inhibitors(PARPi)have transformed the treatment of ovarian cancer.Particularly in high-grade serous ovarian cancer(HGSOC),a disease characterized by homologous recombination deficiency(HRD),PARPi have had a rapid and profound impact on the disease course,as well as biologic and biomarker definitions of HGSOC,thereby creating a paradigm shift in the approach to treatment.In this review,we discuss the role of PARPi in the maintenance treatment of HGSOC,its effect on platinum sensitivity,and cross-resistance between platinum and PARP inhibitors.

The cancer-testis gene,MEIOB,sensitizes triple-negative breast cancer to PARP1 inhibitors by inducing homologous recombination deficiency

Objective:The newly defined cancer-testis(CT)gene,MEIOB,was previously found to play key roles in DNA double-strand break(DSB)repair.In this study,we aimed to investigate the effects and mechanisms of MEIOB in the carcinogenesis of triple-negative breast cancers(TNBCs).Methods:The Cancer Genome Atlas database was used to quantify the expression of MEIOB.Cox regression analysis was used to evaluate the association between MEIOB expression and the prognosis of human TNBC.The effects of MEIOB on cell proliferation and migration in TNBCs were also assessed in vitro.Patient-derived xenograft(PDX)models were used to assess the sensitivity of breast cancers with active MEIOB to PARP1 inhibitors.Results:We confirmed MEIOB as a CT gene whose expression was restricted to the testes and breast tumors,especially TNBCs.Its activation was significantly associated with poor survival in breast cancer patients[overall,hazard ratio(HR)=1.90(1.16–2.06);TNBCs:HR=7.05(1.16–41.80)].In addition,we found that MEIOB was oncogenic and significantly promoted the proliferation of TNBC cells.Further analysis showed that MEIOB participated in DSB repair in TNBCs.However,in contrast to its function in meiosis,it mediated homologous recombination deficiency(HRD)through the activation of poly ADP-ribose polymerase(PARP)1 by interacting with YBX1.Furthermore,activated MEIOB was shown to confer sensitivity to PARP inhibitors,which was confirmed in PDX models.Conclusions:MEIOB played an oncogenic role in TNBC through its involvement in HRD.In addition,dysregulation of MEIOB sensitized TNBC cells to PARP inhibitors,so MEIOB may be a therapeutic target of PARP1 inhibitors in TNBC.

mTORC2 promotes pancreatic cancer progression and parp inhibitor resistance

Pancreatic cancer is one of the most aggressive cancers with a median survival time of less than 5 months,and conventional chemotherapeutics are the main treatment strategy.Poly(ADP-ribose)polymerase(PARP)inhibitors have been recently approved for BRCA1/2-mutant pancreatic cancer,opening a new era for targeted therapy for this disease.However,most pancreatic cancer patients carry wild-type BRCA1/2 with resistance to PARP inhibitors.Here,we reported that mammalian target of rapamycin complex 2(mTORC2)kinase is overexpressed in pancreatic cancer tissues and promotes pancreatic cancer cell growth and invasion.Moreover,we found that knockdown of the mTORC2 obligate subunit Rictor sensitized pancreatic cancer cells to the PARP inhibitor olaparib.Mechanistically,we showed that mTORC2 positively regulates homologous recombination(HR)repair by modulating BRCA1 recruitment to DNA double-strand breaks(DSBs).In addition,we confirmed that combination treatment with the mTORC2 inhibitor PP242 and the PARP inhibitor olaparib synergistically inhibited pancreatic cancer growth in vivo.Thus,this study provides a novel target and strategy for optimizing PARP inhibitor efficiency in pancreatic cancers.

Targeting DNA repair for cancer treatment: Lessons from PARP inhibitor trials

Ionizing radiation is frequently used to treat solid tumors,as it causes DNA damage and kill cancer cells.However,damaged DNA is repaired involving poly-(ADP-ribose)polymerase-1(PARP-1)causing resistance to radiation therapy.Thus,PARP-1 represents an important target in multiple cancer types,including prostate cancer.PARP is a nuclear enzyme essential for single-strand DNA breaks repair.Inhibiting PARP-1 is lethal in a wide range of cancer cells that lack the homologous recombination repair(HR)pathway.This article provides a concise and simplified overview of the development of PARP inhibitors in the laboratory and their clinical applications.We focused on the use of PARP inhibitors in various cancers,including prostate cancer.We also discussed some of the underlying principles and challenges that may affect the clinical efficacy of PARP inhibitors.

PhaseⅠdose-escalation and expansion study of PARP inhibitor,fluzoparib(SHR3162),in patients with advanced solid tumors

Objective:Fluzoparib(SHR3162)is a novel,potent poly(ADP-ribose)polymerases(PARP)1,2 inhibitor that showed anti-tumor activity in xenograft models.We conducted a phaseⅠ,first-in-human,dose-escalation and expansion(D-Esc and D-Ex)trial in patients with advanced solid cancer.Methods:This was a 3+3 phaseⅠD-Esc trial with a 3-level D-Ex at 5 hospitals in China.Eligible patients for DEsc had advanced solid tumors refractory to standard therapies,and D-Ex enrolled patients with ovarian cancer(OC).Fluzoparib was administered orally once or twice daily(bid)at 11 dose levels from 10 to 400 mg/d.Endpoints included dose-finding,safety,pharmacokinetics,and antitumor activity.Results:Seventy-nine patients were enrolled from March,2015 to January,2018[OC(47,59.5%);breast cancer(BC)(16,20.3%);colorectal cancer(8,10.1%),other tumors(8,10.1%)];48 patients were treated in the D-Esc arm and 31 in the D-Ex arm.The maximum tolerated dose(MTD)was 150 mg bid,with a half-life of 9.14 h.Grade 3/4 adverse events included anemia(7.6%)and neutropenia(5.1%).The objective response rate(ORR)was 30%(3/10)in patients with platinum-sensitive OC and 7.7%(1/13)in patients with BC.Among patients treated with fluzoparib≥120 mg/d,median progression-free survival(m PFS)was 7.2[95%confidence interval(95%CI),1.8-9.3]months in OC,9.3(95%CI,7.2-9.3)months in platinum-sensitive OC,and 3.5(range,2.0-28.0)months in BC.In patients with germline BC susceptibility gene mutation(g BRCAMut)(11/43 OC;2/16 BC),m PFS was 8.9 months for OC(range,1.0-23.2;95%CI,1.0-16.8)and 14 and 28 months for BC(those two patients both also had somatic BRCAMut).Conclusions:The MTD of fluzoparib was 150 mg bid in advanced solid malignancies.Fluzoparib demonstrated single-agent antitumor activity in BC and OC,particularly in BRCAMut and platinum-sensitive OC.

PARP inhibitor reduces proliferation and increases apoptosis in breast cancer cells

Objective： Apoptosis is a reliable marker of chemotherapeutic efficacy. Olaparib and paclitaxel inhibit proliferation and induce apoptosis in a variety of cancers. We investigated the effects of paclitaxel combined with olaparib on apoptosis in breast cancer Bcap37 cells. Methods： Proliferation and apoptosis were detected by MTT assay and PI staining. Degradation of procaspase-3 and poly（ADP-ribose） polymerase （PARP） was analyzed by Western blotting. Results： Compared with paclitaxel alone, paclitaxel combined with 100 mg olaparib significantly reduced survival in Bcap37 cells at all tested treatment durations （P〈0.05）; inhibition increased with increasing olaparib dose and treatment time （P〈0.01）. Combined treatment yielded significantly higher rates of apoptosis （P〈0.05）, which also increased with time （P〈0.01）. Fluorescence micrographs showed that early and late apoptotic cells increased with treatment time. Pro-caspase-3 and PARP degradation was induced by paclitaxel and enhanced by olaparib in a dose-dependent manner. Thus, combined treatment was substantially more effective than treatment with paclitaxel alone. Conclusions： Our findings suggest that paclitaxel and olaparib inhibit breast cancer Bcap37 cell proliferation and induce apoptosis. Combined treatment further reduced cell growth and enhanced apoptosis, suggesting that this combination therapy may be a promising treaunent for breast cancer.

Deciphering resistancemechanisms and novel strategies to overcome drug resistance in ovarian cancer:a comprehensive review

Ovarian cancer is among the most lethal gynecological cancers,primarily due to the lack of specific symptoms leading to an advanced-stage diagnosis and resistance to chemotherapy.Drug resistance(DR)poses the most significant challenge in treating patients with existing drugs.The Food and Drug Administration(FDA)has recently approved three new therapeutic drugs,including two poly(ADP-ribose)polymerase(PARP)inhibitors(olaparib and niraparib)and one vascular endothelial growth factor(VEGF)inhibitor(bevacizumab)for maintenance therapy.However,resistance to these new drugs has emerged.Therefore,understanding the mechanisms of DR and exploring new approaches to overcome them is crucial for effective management.In this review,we summarize the major molecular mechanisms of DR and discuss novel strategies to combat DR.

Poly （ADP-ribose） polymerase inhibitor： an evolving paradigm in the treatment of prostate cancer

Recent phase I studies have reported single-agent activities of poly （ADP-ribose） polymerase （PARP） inhibitor in sporadic and in BRCA-mutant prostate cancers. Two of the most common genetic alterations in prostate cancer, ETS gene rearrangement and loss of PTEN, have been linked to increased sensitivity to PARP inhibitor in preclinical models. Emerging evidence also suggests that PARP1 plays an important role in mediating the transcriptional activities of androgen receptor （AR） and ETS gene rearrangement. In this article, the preclinical work and early-phase clinical trials in developing PARP inhibitor-based therapy as a new treatment paradigm for metastatic prostate cancer are reviewed.

Recent advances in targeted therapy for ovarian cancer

The global burden of ovarian cancer is gradually increasing while patients still suffer from relatively limited treatment options.With recent advances in the decoding of the molecular landscape of ovarian cancer,more options in targeted strategy were offered and can therefore be tailored in different clinical settings for individual patient.Targeting of the abnormal angiogenesis process is the first significant clinical breakthrough which revolutionized the treatment of advanced ovarian cancer,followed by the advent of poly-(ADP)-ribose polymerase(PARP)inhibitors.These two strategies represented by bevacizumab and olaparib respectively underwent tests of numerous clinical trials.In recent years,immune checkpoint inhibitors(ICIs)have been incorporated into the blueprint of ovarian cancer treatment though the effectiveness still left much to be desired.Herein,we systematically outlined recent advances in targeted therapy for ovarian cancer and summarized the landmark clinical trials for each targeted therapy including angiogenesis inhibitors,PARP inhibitors and ICIs.

Searching for Better Outcomes among Patients with Metastatic Triple- Negative Breast Cancer – Do We Have Novel Options on the Treatment Landscape?

Triple-negative breast cancer(TNBC),which accounts for approximately 15%of breast cancers(BCs)is characterized by a lack of expression of the hormone receptors(HRs)(estrogen receptor(ER)and progesterone receptor(PR)),and human epidermal growth factor receptor 2(HER2).TNBC reveals very aggressive behavior and often leads to poor prognosis.Unfortunately,standard chemotherapy(CHT)is related to low response rates and short progression-free survival(PFS)in patients with metastatic TNBC,creating an unmet need.However,recent recognition of different molecular subtypes and mutations within TNBC has allowed exploring some innovative targeted therapies,bringing new hope for women suffering from TNBC.Currently,some promising systemic treatment options in this area have been developed,including targeted therapies,such as poly(ADP-ribose)polymerase(PARP)inhibitors,immune checkpoint inhibitors,antibody-drug conjugates,and AKT inhibitors.The aim of this mini-review is to address these novel treatment modalities and highlight the main directions for further research and clinical practice in the advanced or metastatic forms of TNBC.This article presents poly(ADP-ribose)polymerase(PARP)inhibitors(e.g.,olaparib,talazoparib,and valaparib for treatment of BRCA-mutated,HER2-negative metastatic BC),immune checkpoint inhibitors(atezolizumab and pembrolizumab),an antibody-drug conjugate(ADC)(sacituzumab govitecan),and AKT inhibitors(ipatasertib and capivasertib).A brief outline of the main clinical trials leading to the approval of these new medications has been provided.Moreover,this overview discusses the efficacy and safety of these innovative treatment options,focusing on women with metastatic TNBC.In addition,this paper comments on some recent considerations,regarding avenues of delivering care and conduct clinical trials in patients with BC,during the COVID-19 pandemic.

Mechanism of PARP inhibitor resistance and potential overcoming strategies

PARP inhibitors(PARPi)are a kind of cancer therapy that targets poly(ADP-ribose)polymerase.PARPi is the first clinically approved drug to exert synthetic lethality by obstruct-ing the DNA single-strand break repair process.Despite the significant therapeutic effect in pa-tients with homologous recombination(HR)repair deficiency,innate and acquired resistance to PARPi is a main challenge in the clinic.In this review,we mainly discussed the underlying mechanisms of PARPi resistance and summarized the promising solutions to overcome PARPi resistance,aiming at extending PARPi application and improving patient outcomes.

Ovarian cancer recurrence:is the definition of platinum sensitivity modified by PARPi,bevacizumab or other intervening treatments?:a clinical perspective

In view of the high risk of recurrent disease in stage III and IV ovarian cancer following primary first-line chemotherapy,a variety of maintenance and consolidation treatment strategies have been developed.These have included:radiation,intravenous or intraperitoneal chemotherapy,targeted therapies,and immunotherapy.Popular at this time is the use of Poly-adenosine ribose polymerase(PARP)inhibitors and bevacizumab as maintenance therapy.What effect these maintenance or consolidation therapies have on subsequent response to therapy,specifically platinum-based chemotherapy,is only beginning to be studied.In this manuscript,we review the impact of PARP inhibitors and bevacizumab as well as radiation and maintenance chemotherapy on subsequent response to treatment.Prior use of bevacizumab does not appear to adversely affect subsequent response to platinum-based chemotherapy or platinum-based chemotherapy with bevacizumab.Prior therapy with PARP inhibitors induces platinum resistance to subsequent platinum-based therapy and negates classic predictors of response such as platinum-free interval and breast cancer susceptibility gene(BRCA)mutational status.

Ovarian cancer recurrence:is the definition of platinum resistance modified by PARPi and other intervening treatments?The evolving landscape in the management of platinum-resistant ovarian cancer

Definitions of platinum resistance have been questioned and changed over the last five years,even though no predictive biomarker of resistance exists.These have sculpted how we approach platinum retreatment and,consequently,how we devise new treatment strategies for those patients with tumour progression on platinum therapy.Platinum-non-eligible ovarian cancer is treated with single-agent non-platinum drugs.When bevacizumab can be added to chemotherapy,progression-free survival improves significantly.For patients with a BRCA mutation,PARP inhibitor monotherapy is an option compared to chemotherapy.There is currently no clearly identified role for immune-checkpoint inhibition in this patient population.This review describes some of the challenges in treating patients with platinum resistance and suggests refinements in the selection of patients most likely to benefit from targeting a DNA damage response,angiogenesis or immune modulation.It also describes novel agents of interest and possible mechanisms of the synergy of therapeutic combinations.

The role of PARP1 in the DNA damage response and its application in tumor therapy

Single-strand break repair protein poly(ADP-ribose)polymerase 1(PARP1)catalyzes the poly(ADPribosyl)ation of many key proteins in vivo and thus plays important roles in multiple DNA damage response pathways,rendering it a promising target in cancer therapy.The tumor-suppressor effects of PARP inhibitors have attracted significant interest for development of novel cancer therapies.However,recent evidence indicated that the underlying mechanism of PARP inhibitors in tumor therapy is more complex than previously expected.The present review will focus on recent progress on the role of PARP1 in the DNA damage response and PARP inhibitors in cancer therapy.The emerging resistance of BRCA-deficient tumors to PARP inhibitors is also briefly discussed from the perspective of DNA damage and repair.These recent research advances will inform the selection of patient populations who can benefit from the PARP inhibitor treatment and development of effective drug combination strategies.

Effects of the PARP inhibitor Niraparib on the radiosensitivity of human lung and cervical cancer cells

ObjectiveTo investigate the effect of Niraparib,a clinically approved PARP inhibitor on the radiosensitivity of human lung and cervical cancer cells,and preliminarily explore the underlying mechanism.MethodsThe human lung cancer cell line A549 and human cervical cancer cell line Siha were both treated with Niraparib for 1h,or X-ray irradiation with 4y,or Niraparib for 1h combined with X-ray irradiation with 4Gy.The effect was examined via measurements of cell proliferation by the cell counting kit-8 assay,and cell viability was detected by clone formation assays.Cell apoptosis and cell cycle distribution were investigated by flow cytometry.ResultsIn human lung and cervical cancer cell lines,Niraparib combined with radiation therapy significantly inhibited cell proliferation.The proportion of apoptotic cells in cell lines treated with Niraparib plus radiation(the combination group)was significantly higher compared with control,radiation,and Niraparib groups(P<0.05).Additionally,the proportion of A549 cells in the G_(2)/M phase was significantly increased in the combination group compared with the radiation group(P<0.05).ConclusionPARP inhibitor Niraparib increases the radiosensitivity of tumorcells,promotes their apoptosis,and induces cell cycle redistribution.The possible mechanism is associated with the inhibition of radiation-induced DNA damage repair.

New perspectives on epigenetic modifications and PARP inhibitor resistance in HR-deficient cancers

The clinical treatment of DNA-repair defective tumours has been revolutionised by the use of poly(ADP)ribose polymerase(PARP)inhibitors.However,the efficacy of these compounds is hampered by resistance,which is attributed to numerous mechanisms including rewiring of the DNA damage response to favour pathways that repair PARP inhibitor-mediated damage.Here,we comment on recent findings by our group identifying the lysine methyltransferase SETD1A as a novel factor that conveys PARPi resistance.We discuss the implications,with a particular focus on epigenetic modifications and H3K4 methylation.We also deliberate on the mechanisms responsible,the consequences for the refinement of PARP inhibitor use in the clinic,and future possibilities to circumvent drug resistance in DNA-repair deficient cancers.

A patient with relapsed high-grade serous ovarian carcinoma with somatic RAD51C mutations treated with PARPi monotherapy:a case report

We report our experience in the management of a relapsed ovarian cancer patient with somatic RAD51C mutation,treated with olaparib monotherapy.The patient was diagnosed with stage 4 high-grade serous ovarian carcinoma and was treated with neoadjuvant chemotherapy,cytoreductive surgery,and postoperative chemotherapy.After a second cancer recurrence,she underwent FoundationOne CDx testing following disease progression on multiple lines of chemotherapy.Based on the FoundationOne CDx results,olaparib monotherapy was started.After 13 months of therapy,all lesions responded to the treatment,and she achieved complete response as demonstrated by normalization of the levels of CA125 and positron emission tomography-computed tomography(PET-CT).We plan to continue olaparib monotherapy until disease progression.