PARP Inhibitor Therapy Research Articles

A Gene Expression Signature that Predicts Gastric Cancer Sensitivity to PARP Inhibitor Therapy.

Biomarkers indicating sensitivity to poly ADP-ribose polymerase (PARP) inhibitors have not yet been identified in gastric cancer. PARP inhibitors target homologous recombination deficiency (HRD); however, homologous recombination (HR) induces complex changes in gene expression, which makes it difficult to identify reliable biomarkers. In this study, we identified a multi-gene expression signature as a marker of PARP inhibitor sensitivity in gastric cancer. Seven gastric cancer cell lines were evaluated for susceptibility to PARP inhibitors using a growth inhibition assay. Gene expression profiling (GEP) was used to identify differentially expressed genes between PARP inhibitor-sensitive and -resistant cell lines. The resulting gene set was subjected to cluster analysis using tumor samples from 250 patients who underwent gastrectomy for primary gastroesophageal junction and gastric adenocarcinoma. HRD was defined as a truncating mutation in one or more of 22 HR-related genes and HRD scores were calculated using whole-exome sequencing data. In the growth inhibition assays, the HGC27 and HSC39 cell lines were sensitive to the PARP inhibitors, olaparib, and rucaparib, and were significantly correlated with the GEP results. Seven (2.8%) patients harbored truncating mutations in HR-related genes. A gene expression signature based on the top 100 high and low differentially expressed genes between sensitive and resistant cell lines revealed a patient cluster with a high prevalence of HR-related gene mutations and high HRD scores. The 100-gene expression signature identified in this study may serve as a valuable predictive biomarker for PARP inhibitor sensitivity in gastric cancer.

The effect of antibiotics, proton pump inhibitors, H2-receptor antagonists, and steroids on survival among ovarian cancer patients receiving PARP inhibitor therapy

The effect of antibiotics, proton pump inhibitors, H2-receptor antagonists, and steroids on survival among ovarian cancer patients receiving PARP inhibitor therapy

Clinical Outcomes of Poly(ADP–Ribose) Polymerase Inhibitors as Maintenance Therapy in Patients with Ovarian Cancer in the Southeastern Region of Korea

Purpose: In this study, we aimed to retrospectively investigate the real-world clinical efficacy and adverse events of poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitors in real-world clinical practice among patients with newly diagnosed epithelial ovarian cancer. Methods: We retrospectively reviewed the medical records from hospitals. Patients with epithelial ovarian cancer treated with olaparib or niraparib as frontline maintenance treatment between 1 January 2014 and 31 December 2022 were included. Progression-free survival (PFS) was analyzed using the Kaplan–Meier method, and adverse events associated with PARP inhibitor treatment were investigated. Results: Ninety-six patients treated with PARP inhibitors were identified. The median follow-up period was 21.8 months (95% confidence interval [CI] 19.4–24.0). Twenty (20.1%) patients experienced disease progression, and two patients died. The median PFS was 45.3 months (95% CI 39.4–NA). BRCA1 or BRCA2 gene mutations and primary cytoreductive surgery were associated with better PFS. Adverse events of any grade occurred in 74 (77.1%) patients. Nineteen (19.8%) patients experienced PARP inhibitor therapy interruptions, and 35 (36.5%) patients experienced dose reductions. Only three patients discontinued the drug due to adverse events. Conclusions: In a real-world setting, PARP inhibitors showed efficacy comparable to that reported in published randomized controlled trials and had acceptable safety profiles.

Germline DNA damage repair variants and prognosis of patients with high-risk or metastatic prostate cancer.

Deleterious germline variants in certain DNA repair genes are risk factors for developing aggressive prostate cancer. The objective was to quantify their prognostic impact after prostate cancer diagnosis. Men with prostate cancer, predominantly of European ancestry, were included from four cohorts with long-term follow-up. Pathogenic or likely pathogenic germline variants in 26 DNA repair genes were assessed in relation to metastasis-free survival in high-risk, localized prostate cancer and to overall survival in metastatic castration-sensitive prostate cancer (mCSPC) and metastatic castration-resistant prostate cancer (mCRPC). Among 3,525 patients initially diagnosed with non-metastatic prostate cancer, 2,594 had high-risk localized prostate cancer, 429 mCSPC, and 502 mCRPC at inclusion. BRCA2 variant carriers did not have worse metastasis-free survival in high-risk localized prostate cancer (hazard ratio [HR] 1.01, 95% confidence interval [CI] 0.69, 1.46) or overall survival in mCSPC (HR 0.46, 95% CI 0.14, 1.45) or mCRPC (HR 0.60, 95% CI 0.31, 1.17) compared to non-carriers of DNA repair variants. Among 868 additional patients with de novo metastatic (M1) prostate cancer, BRCA2 variant carriers tended to have worse overall survival (HR 1.59, 95% CI 1.01, 2.51). BRCA2 prognostic associations were not explained by radiation, PARP inhibitor, or platinum therapy. Results for other genes were limited in precision because variants were less common. Among patients with high-risk or metastatic prostate cancer who were initially diagnosed with and treated for non-metastatic tumors, germline DNA repair variants in BRCA2 do not confer a substantially worse prognosis.

Usefulness of Nutritional Assessment Indicators in Predicting Treatment Discontinuation Due to Adverse Events from PARP Inhibitors in Ovarian Cancer Patients.

Nutritional status is an important factor influencing toxicity of treatment. Nutritional assessment indicators such as the Prognostic Nutritional Index (PNI), Controlling Nutritional Status (CONUT) score and modified Glasgow Prognostic Score (mGPS) have been reported to be associated with treatment-related adverse events (AEs) for various malignancies. However, there are no reports investigating the relationship between nutritional status and AEs from poly-(ADP-ribose) polymerase (PARP) inhibitors (PARPi), which are widely used in recent years as maintenance therapy for ovarian cancer. The primary objective was to investigate the usefulness of nutritional assessment indicators in predicting treatment discontinuation due to AEs from PARPi. This multicenter retrospective study included patients diagnosed with ovarian cancer who received maintenance therapy with PARPi from January 2018 to December 2023. PNI, CONUT score, and mGPS were calculated based on hematological parameters measured within 7 days before the start of PARPi therapy. A total of 272 patients received maintenance therapy with PARPi during the period, but due to the absence of the blood collection of albumin levels within one week or other exclusion criteria, 71 patients were finally included in this analysis. AEs were seen in 59 patients (83.1%), including 25 (35.2%) severe events (grade ≥3 in Common Terminology Criteria for Adverse Events v5.0). Eighteen patients (25.4%) discontinued treatment due to PARPi-related AEs. Low PNI (<48.44) and high mGPS (≥1) were predictors of treatment discontinuation in both univariate and multivariate analyses. CONUT was not a significant predictor in this study. Our study suggested that PNI and mGPS can predict the risk of treatment discontinuation due to PARPi-related AEs before starting maintenance therapy. This insight opens avenues for more personalized treatment plans, potentially improving patient outcomes.

Impact of PARP inhibitors on progression-free survival in platinum-sensitive recurrent epithelial ovarian cancer: a retrospective analysis

ObjectivePoly (ADP-ribose) polymerase (PARP) inhibitors such as olaparib and niraparib have shown promise in extending progression-free survival (PFS) in patients with platinum-sensitive recurrent (PSR) epithelial ovarian cancer. In this retrospective study, we aimed to present our own data on the effect of PARP inhibitors on PFS in recurrent epithelial ovarian cancer.Methods82 patients diagnosed with PSR epithelial ovarian, tubal, or primary peritoneal cancer between May 2017 and September 2023 were initially enrolled from our hospital. However, 16 patients had prior exposure to PARP inhibitors during primary treatment, and 11 were lost to follow-up. Consequently, the study focused on 55 eligible patients. PFS was compared between patients receiving PARP inhibitor maintenance therapy and those who did not.ResultsAmong the 55 patients with PSR epithelial ovarian cancer, 18 received olaparib as maintenance therapy, 19 received niraparib, and 18 opted for observation. PARP inhibitor therapy significantly extended PFS (mean 24.0 months) compared to observation (mean 9.0 months, p = 0.0005), regardless of BRCA mutation status (HR = 0.20, 95% CI: 0.08–0.50). Subgroup analysis showed no statistical difference between olaparib and niraparib. Additionally, there was no PFS difference based on BRCA mutation status within both PARP inhibitor groups.ConclusionOur retrospective study demonstrates that PARP inhibitor maintenance therapy, including olaparib and niraparib, significantly prolongs PFS in patients with PSR epithelial ovarian, tubal, or primary peritoneal cancer, These findings support the broad utilization of PARP inhibitors as a standard maintenance therapy for PSR epithelial ovarian cancer irrespective of BRCA mutation status.

Abstract C046: Targeting wild-type IDH1 sensitizes homologous recombination proficient pancreatic cancer to PARP inhibition

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer-related mortality in the United States. While Poly (ADP-ribose) polymerase (PARP) inhibitors show promise for PDAC with Homologous Recombination Deficiency (HRD), this mutation is present in less than 10% of cases. Our research focuses on exploiting a vulnerability in the remaining 90% of HR proficient (HRP) tumors. We identified that wild-type isocitrate dehydrogenase 1 (IDH1) plays a critical role in HR repair. By inhibiting IDH1, we discovered suppression of the homologous recombination (HR) pathway, leading to compromised genomic integrity. This renders cancer cells more susceptible to PARP inhibitor therapy, offering a novel therapeutic approach for HRP PDAC. Methods:We assessed the impact of IDH1 inhibition on HR pathway activity using Western blotting to measure HR repair protein levels and HR reporter assays. The effect of IDH1 inhibition (Ivosidenib) combined with PARP inhibition (Olaparib) on in vitro growth inhibition was assessed through drug combination assays. Additionally, we investigated the molecular mechanisms underlying the synergistic effects of the drug combination. To further evaluate the therapeutic potential of IDH1 inhibition in combination with PARP inhibitors, we examined tumor growth in xenograft models of PDAC in athymic nude mice and survival studies were performed in C57BL/6J mice transplanted with orthotopic murine pancreatic cancer. Results:Wild-type IDH1 blockade induces a BRCA-like phenotype by decreasing α-ketoglutarate (αKG) levels and causing histone hypermethylation. This leads to decreased HR repair efficiency in HRP pancreatic cancer cells (MiaPaCa-2 and Panc-1), resulting in a strong synergistic effect when combined with the DNA-damaging agent Olaparib. The combination treatment significantly reduced cell survival in both short and long-term assays. Furthermore, we discovered that these compounds complemented each other in the DNA damage response, leading to increased γ-H2AX (DNA damage marker) and apoptosis. In vivo studies using murine PDAC models demonstrated that the combination of ivosidenib and olaparib synergistically enhanced anti-tumor activity compared to either single agent alone. Conclusion:These data provide novel insight into the mechanisms underlying in the context of HRP cancer susceptibility to a dual treatment approach involving an IDH1 inhibitor and a PARP inhibitor. This approach holds promise for precision medicine in pancreatic cancer treatment, although further pre- clinical studies are needed for validation and refinement. Citation Format: Mehrdad Zarei, Omid Hajihassani, Hallie J. Graor, Soubhi Tahhan, Alexander W. Loftus, Faith Nakazzi, Semmer A. Ali, Parnian Naji, Luke D. Rothermel, Jonothan R. Brody, Jordan M. Winter. Targeting wild-type IDH1 sensitizes homologous recombination proficient pancreatic cancer to PARP inhibition [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C046.

Characterization of DNA damage repair pathway utilization in high-grade serous ovarian cancers yields rational therapeutic approaches

While poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) have improved the prognosis of ovarian high-grade serous carcinoma (HGSC) tumors that are homologous recombination (HR) deficient (HRD), new therapeutic strategies are needed for tumors that are HR proficient (HRP) because they demonstrate greater resistance to current treatments and thus have poorer clinical outcomes. Additionally, clinical precautionary statements regarding potential risks associated with PARPi, such as myelodysplastic syndrome, highlight the need for combinatorial approaches that can lessen the dose and duration of PARPi treatment to reduce toxicities. Here, we evaluated DNA double-strand damage repair pathways in HRD and HRP ovarian cancer cell lines and found that in HRD cell lines, PARPi therapy reduced non-homologous end joining (NHEJ)-mediated repair, specifically due to decreased theta-mediated end-joining. The combination of PARPi with ATM serine/threonine kinase inhibitor (ATMi) suppressed both NHEJ and HR pathways in HRD and HRP cell lines, with synergistic increases in apoptosis and decreases in cell viability and colony formation. Interestingly, PARPi plus ATMi also decreased NF-κB p65 phosphorylation, which was not observed when PARPi was combined with inhibition of the ATR kinase (ATRi). These findings indicate that PARPi plus ATMi is a promising strategy for HGSC independent of underlying tumor HR status.

Efficacy of PARP inhibitor therapy after targeted BRAF/MEK failure in advanced melanoma

Modern advancements in targeted therapy and immunotherapy have significantly improved survival outcomes for advanced melanoma; however, there remains a need for novel approaches to overcome disease progression and treatment resistance. In recent years, PARPi therapy has shown great promise both as a single regimen and in combination with other therapeutics in melanoma. Here, we describe three unique cases of advanced BRAF V600 mutated melanoma that progressed on targeted BRAF/MEK agents that subsequently exhibited partial to near-complete responses to combinatory PARPi and BRAF/MEK inhibitors. This highlights both a potential synergy underlying this combinatory approach and its efficacy as a treatment option for patients with advanced melanoma refractory to targeted and/or immunotherapies. Prospective clinical trials are needed to explore this synergic effect in larger melanoma cohorts to investigate this combination for treating refractory advanced melanoma.

798TiP Stereotactic radiotherapy alone or followed by niraparib for oligometastases or oligoprogression in ovarian cancer following PARP inhibitor therapy: SOPRANO trial

798TiP Stereotactic radiotherapy alone or followed by niraparib for oligometastases or oligoprogression in ovarian cancer following PARP inhibitor therapy: SOPRANO trial

A randomized phase II study of secondary cytoreductive surgery in patients with relapsed ovarian cancer who have progressed on a PARP inhibitor as first-line maintenance therapy: the SOCCER-P study (KGOG 3067/JGOG 3036/APGOT-OV11)

BackgroundAlthough two recent phase III randomized controlled trials showed survival benefits of undergoing secondary cytoreductive surgery for an initial relapse of ovarian cancer, patients who received a poly-ADP ribose polymerase...

Untapped Potential of Poly(ADP-Ribose) Polymerase Inhibitors: Lessons Learned From the Real-World Clinical Homologous Recombination Repair Mutation Testing.

Testing for homologous recombination deficiency (HRD) mutations is pivotal to assess individual risk, to proact preventive measures in healthy carriers and to tailor treatments for cancer patients. Increasing prominence of poly(ADP-ribose) polymerase (PARP) inhibitors with remarkable impact on molecular-selected patient survival across diverse nosologies, ingrains testing for BRCA genes and beyond in clinical practice. Nevertheless, testing strategies remain a question of debate. While several pathogenic BRCA1/2 gene variants have been described as founder pathogenic mutations frequently found in patients from Russia, other homologous recombination repair (HRR) genes have not been sufficiently explored. In this study, we present real-world data of routine HRR gene testing in Russia. We evaluated clinical and sequencing data from cancer patients who had germline/somatic next-generation sequencing (NGS) HRR gene testing in Russia (BRCA1/2/ATM/CHEK2, or 15 HRR genes). The primary objectives of this study were to evaluate the frequency of BRCA1/2 and non-BRCA gene mutations in real-world unselected patients from Russia, and to determine whether testing beyond BRCA1/2 is feasible. Data of 2,032 patients were collected from February 2021 to February 2023. Most had breast (n = 715, 35.2%), ovarian (n = 259, 12.7%), pancreatic (n = 85, 4.2%), or prostate cancer (n = 58, 2.9%). We observed 586 variants of uncertain significance (VUS) and 372 deleterious variants (DVs) across 487 patients, with 17.6% HRR-mutation positivity. HRR testing identified 120 (11.8%) BRCA1/2-positive, and 172 (16.9%) HRR-positive patients. With 51 DVs identified in 242 formalin-fixed paraffin-embedded (FFPE), testing for variant origin clarification was required in one case (0.4%). Most BRCA1/2 germline variants were DV (121 DVs, 26 VUS); in non-BRCA1/2 genes, VUS were ubiquitous (53 DVs, 132 VUS). In silico prediction identified additional 4.9% HRR and 1.2% BRCA1/2/ATM/CHEK2 mutation patients. Our study represents one of the first reports about the incidence of DV and VUS in HRR genes, including genes beyond BRCA1/2, identified in cancer patients from Russia, assessed by NGS. In silico predictions of the observed HRR gene variants suggest that non-BRCA gene testing is likely to result in higher frequency of patients who are candidates for PARP inhibitor therapy. Continuing sequencing efforts should clarify interpretation of frequently observed non-BRCA VUS.

Gynecologic Cancer InterGroup CA125 response has a high negative predictive value for CHK1 inhibitor RECIST response in recurrent ovarian cancer

We investigated the association of CA125 response with prognosis and RECIST response/progressive disease (PD) criteria in recurrent high grade serous ovarian cancer (HGSOC) patients treated with a cell cycle checkpoint kinase 1 inhibitor (CHK1i), prexasertib. 81 patients had measurable disease per RECISTv1.1, of which 72 and 70 were measurable by Gynecologic Cancer InterGroup (GCIG) CA125 response and PD criteria, respectively. Univariate and multivariate analyses showed that GCIG CA125 response (n = 32) is associated with improved progression-free survival (PFS) and overall survival (OS) compared to no GCIG CA125 response (n = 40) (median PFS 8.0 vs. 3.5 months [HR: 0.30, 95% CI: 0.18–0.51, p < 0.0001]; median OS 19.8 vs. 10.0 months [HR: 0.38, 95% CI: 0.23–0.64, p < 0.001]) independent of BRCA mutation status, platinum-sensitivity, previous PARP inhibitor therapy, ECOG performance status, and FIGO stage. Notably, GCIG CA125 response had a high negative predictive value (NPV: 93%, 95% CI: 80–98), but poor positive predictive value (PPV: 53%, 95% CI: 35–71) in predicting RECIST response. CA125 PD criteria also showed poor concordance with RECIST PD (PPV 56%, 95% CI: 40–71; NPV 33%, 95% CI: 17–54). Therefore, serum CA125 may be useful as a highly accessible prognostic and predictive biomarker to CHK1i therapy in recurrent HGSOC.

PARP inhibitor therapy in patients with IDH1 mutated cholangiocarcinoma.

Isocitrate dehydrogenase 1 (IDH1) missense mutations occur at a frequency of 10%-15% in intrahepatic cholangiocarcinoma (iCCA). IDH1 mutations result in accumulation of (R)-2-hydroxyglutarate, an oncometabolite that leads to DNA hypermethylation and impairment of homologous recombination (HR). Impairment of HR results in a "BRCAness" phenotype which may confer sensitivity to poly(ADP ribose) polymerase (PARP) inhibition. We conducted a retrospective cohort review to identify patients with advanced, IDH1 mutated iCCA treated with a PARP inhibitor (PARPi) at the University of Michigan between 2018 and 2023. Patients are described with respect to prior lines of therapy, response to platinum-based chemotherapy, and progression-free survival (PFS) and overall survival (OS) from the time of PARPi initiation. Between 2018 and 2023 we identified 40 patients with IDH1 mutated iCCA of which 6 patients were treated with a PARPi as monotherapy or in combination with an ATR inhibitor or anti-PD-1 immune checkpoint inhibitor. Majority of patients (n = 5) carried an IDH1 R132C mutation per tissue-based next generation sequencing. All patients had previously received at least one line of cisplatin-based systemic therapy for advanced disease prior to treatment with PARPi. PFS and OS from time of PARPi initiation ranged from 1.4 to 18.5 months and 2.8 to 42.4 months, respectively. Best response on PARPi therapy included 2 partial responses. This is the first case series to describe PARPi treatment in IDH1 mutated iCCA. Results underscore the limitation of PARPi monotherapy, potentially support combined PARPi therapies, and highlight a need for effective treatment options for patients with IDH1 mutated iCCA.

BRCAness, DNA gaps, and gain and loss of PARP inhibitor-induced synthetic lethality.

Mutations in the tumor-suppressor genes BRCA1 and BRCA2 resulting in BRCA1/2 deficiency are frequently identified in breast, ovarian, prostate, pancreatic, and other cancers. Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPis) selectively kill BRCA1/2-deficient cancer cells by inducing synthetic lethality, providing an effective biomarker-guided strategy for targeted cancer therapy. However, a substantial fraction of cancer patients carrying BRCA1/2 mutations do not respond to PARPis, and most patients develop resistance to PARPis over time, highlighting a major obstacle to PARPi therapy in the clinic. Recent studies have revealed that changes of specific functional defects of BRCA1/2-deficient cells, particularly their defects in suppressing and protecting single-stranded DNA gaps, contribute to the gain or loss of PARPi-induced synthetic lethality. These findings not only shed light on the mechanism of action of PARPis, but also lead to revised models that explain how PARPis selectively kill BRCA-deficient cancer cells. Furthermore, new mechanistic principles of PARPi sensitivity and resistance have emerged from these studies, generating potentially useful guidelines for predicting the PARPi response and design therapies for overcoming PARPi resistance. In this Review, we will discuss these recent studies and put them in context with the classic views of PARPi-induced synthetic lethality, aiming to stimulate the development of new therapeutic strategies to overcome PARPi resistance and improve PARPi therapy.

Susceptibility gene mutations in germline and tumors of patients with HER2-negative advanced breast cancer

Germline mutations in BRCA1 and BRCA2 (gBRCA1/2) are required for a PARP inhibitor therapy in patients with HER2-negative (HER2−) advanced breast cancer (aBC). However, little is known about the prognostic impact of gBRCA1/2 mutations in aBC patients treated with chemotherapy. This study aimed to investigate the frequencies and prognosis of germline and somatic BRCA1/2 mutations in HER2- aBC patients receiving the first chemotherapy in the advanced setting. Patients receiving their first chemotherapy for HER2- aBC were retrospectively selected from the prospective PRAEGNANT registry (NCT02338167). Genotyping of 26 cancer predisposition genes was performed with germline DNA of 471 patients and somatic tumor DNA of 94 patients. Mutation frequencies, progression-free and overall survival (PFS, OS) according to germline mutation status were assessed. gBRCA1/2 mutations were present in 23 patients (4.9%), and 33 patients (7.0%) had mutations in other cancer risk genes. Patients with a gBRCA1/2 mutation had a better OS compared to non-mutation carriers (HR: 0.38; 95%CI: 0.17–0.86). PFS comparison was not statistically significant. Mutations in other risk genes did not affect prognosis. Two somatic BRCA2 mutations were found in 94 patients without gBRCA1/2 mutations. Most frequently somatic mutated genes were TP53 (44.7%), CDH1 (10.6%) and PTEN (6.4%). In conclusion, aBC patients with gBRCA1/2 mutations had a more favorable prognosis under chemotherapy compared to non-mutation carriers. The mutation frequency of ~5% with gBRCA1/2 mutations together with improved outcome indicates that germline genotyping of all metastatic patients for whom a PARP inhibitor therapy is indicated should be considered.

18F]F-Poly(ADP-Ribose) Polymerase Inhibitor Radiotracers for Imaging PARP Expression and Their Potential Clinical Applications in Oncology.

Including poly(ADP-ribose) polymerase (PARP) inhibitors in managing patients with inoperable tumors has significantly improved outcomes. The PARP inhibitors hamper single-strand deoxyribonucleic acid (DNA) repair by trapping poly(ADP-ribose)polymerase (PARP) at sites of DNA damage, forming a non-functional "PARP enzyme-inhibitor complex" leading to cell cytotoxicity. The effect is more pronounced in the presence of PARP upregulation and homologous recombination (HR) deficiencies such as breast cancer-associated gene (BRCA1/2). Hence, identifying HR-deficiencies by genomic analysis-for instance, BRCA1/2 used in triple-negative breast cancer-should be a part of the selection process for PARP inhibitor therapy. Published data suggest BRCA1/2 germline mutations do not consistently predict favorable responses to PARP inhibitors, suggesting that other factors beyond tumor mutation status may be at play. A variety of factors, including tumor heterogeneity in PARP expression and intrinsic and/or acquired resistance to PARP inhibitors, may be contributing factors. This justifies the use of an additional tool for appropriate patient selection, which is noninvasive, and capable of assessing whole-body in vivo PARP expression and evaluating PARP inhibitor pharmacokinetics as complementary to the currently available BRCA1/2 analysis. In this review, we discuss [18F]Fluorine PARP inhibitor radiotracers and their potential in the imaging of PARP expression and PARP inhibitor pharmacokinetics. To provide context we also briefly discuss possible causes of PARP inhibitor resistance or ineffectiveness. The discussion focuses on TNBC, which is a tumor type where PARP inhibitors are used as part of the standard-of-care treatment strategy.

Identification of CXCL13 as a Promising Biomarker for Immune Checkpoint Blockade Therapy and PARP Inhibitor Therapy in Ovarian Cancer

Identification of CXCL13 as a Promising Biomarker for Immune Checkpoint Blockade Therapy and PARP Inhibitor Therapy in Ovarian Cancer

The genomic landscape of breast and non-breast cancers from individuals with germline CHEK2 deficiency.

CHEK2 is considered to be involved in homologous recombination repair (HRR). Individuals who have germline pathogenic variants (gPVs) in CHEK2 are at increased risk to develop breast cancer and likely other primary cancers. PARP inhibitors (PARPi) have been shown to be effective in the treatment of cancers that present with HRR deficiency-for example, caused by inactivation of BRCA1/2. However, clinical trials have shown little to no efficacy of PARPi in patients with CHEK2 gPVs. Here, we show that both breast and non-breast cancers from individuals who have biallelic gPVs in CHEK2 (germline CHEK2 deficiency) do not present with molecular profiles that fit with HRR deficiency. This finding provides a likely explanation why PARPi therapy is not successful in the treatment of CHEK2-deficient cancers.

Epigenetic and Genomic Hallmarks of PARP-Inhibitor Resistance in Ovarian Cancer Patients.

Patients with advanced-stage epithelial ovarian cancer (EOC) receive treatment with a poly-ADP ribose-polymerase (PARP) inhibitor (PARPi) as maintenance therapy after surgery and chemotherapy. Unfortunately, many patients experience disease progression because of acquired therapy resistance. This study aims to characterize epigenetic and genomic changes in cell-free DNA (cfDNA) associated with PARPi resistance. Blood was taken from 31 EOC patients receiving PARPi therapy before treatment and at disease progression during/after treatment. Resistance was defined as disease progression within 6 months after starting PARPi and was seen in fifteen patients, while sixteen patients responded for 6 to 42 months. Blood cfDNA was evaluated via Modified Fast Aneuploidy Screening Test-Sequencing System (mFast-SeqS to detect aneuploidy, via Methylated DNA Sequencing (MeD-seq) to find differentially methylated regions (DMRs), and via shallow whole-genome and -exome sequencing (shWGS, exome-seq) to define tumor fractions and mutational signatures. Aneuploid cfDNA was undetectable pre-treatment but observed in six patients post-treatment, in five resistant and one responding patient. Post-treatment ichorCNA analyses demonstrated in shWGS and exome-seq higher median tumor fractions in resistant (7% and 9%) than in sensitive patients (7% and 5%). SigMiner analyses detected predominantly mutational signatures linked to mismatch repair and chemotherapy. DeSeq2 analyses of MeD-seq data revealed three methylation signatures and more tumor-specific DMRs in resistant than in responding patients in both pre- and post-treatment samples (274 vs. 30 DMRs, 190 vs. 57 DMRs, Χ2-test p < 0.001). Our genome-wide Next-Generation Sequencing (NGS) analyses in PARPi-resistant patients identified epigenetic differences in blood before treatment, whereas genomic alterations were more frequently observed after progression. The epigenetic differences at baseline are especially interesting for further exploration as putative predictive biomarkers for PARPi resistance.