CDK inhibition results in pharmacologic BRCAness increasing sensitivity to olaparib in BRCA1-WT and olaparib resistant in Triple Negative Breast Cancer

One in three Triple Negative Breast Cancer (TNBC) is Homologous Recombination Deficient (HRD) and susceptible to respond to PARP inhibitor (PARPi), however, resistance resulting from functional HR restoration is frequent. Thus, pharmacologic approaches that induce HRD are of interest. We investigated the effectiveness of CDK-inhibition to induce HRD and increase PARPi sensitivity of TNBC cell lines and PDX models. Two CDK-inhibitors (CDKi), the broad range dinaciclib and the CDK12-specific SR-4835, strongly reduced the expression of key HR genes and impaired HR functionality, as illustrated by BRCA1 and RAD51 nuclear foci obliteration. Consequently, both CDKis showed synergism with olaparib, as well as with cisplatin and gemcitabine, in a range of TNBC cell lines and particularly in olaparib-resistant models. In vivo assays on PDX validated the efficacy of dinaciclib which increased the sensitivity to olaparib of 5/6 models, including two olaparib-resistant and one BRCA1-WT model. However, no olaparib response improvement was observed in vivo with SR-4835. These data support that the implementation of CDK-inhibitors could be effective to sensitize TNBC to olaparib as well as possibly to cisplatin or gemcitabine.

Highlighting recent progress in the treatment of men with advanced prostate cancer

PURPOSE OF REVIEW

This review is designed to highlight recent research efforts to optimize treatment strategies in men with advanced prostate cancer.

RECENT FINDINGS

Recent research analyses have suggested an overall survival advantage to treating some men with newly identified metastatic prostate cancer with a "triplet" of androgen deprivation therapy, docetaxel, and an androgen receptor axis-targeted agent (ARAT), but further work remains to refine which men need this aggressive of a treatment approach. Randomized trials have led to the approval of poly(ADP-ribose) polymerase inhibitor/ARAT agent combinations for some men with metastatic castration resistant prostate cancer, but the applicability of this approach to the growing number of men receiving combinations of systemic therapy in the castration-sensitive setting is unclear. Trials to refine use of prostate-specific membrane antigen (PSMA)-directed radiopharmaceuticals are ongoing, while novel treatment approaches targeting mechanisms driving advanced prostate cancer continue to be explored.

SUMMARY

Ongoing research focuses on refining the best combination and sequence of treatments for men with advanced prostate cancer. Future questions remain about use of existing therapies, and novel treatment approaches need to be developed.

CRABP2 reduces the sensitivity of Olaparib in ovarian cancer by downregulating Caspase-8 and decreasing the production of reactive oxygen species

Poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors, such as Olaparib, have been pivotal in treating BRCA-deficient ovarian cancer. However, their efficacy is limited in over 40% of BRCA-deficient patients, with acquired resistance posing new clinical challenges. To address this, we employed bioinformatics methods to identify key genes impacting Olaparib sensitivity in ovarian cancer. Through comprehensive analysis of public databases including GEO, CPTAC, Kaplan Meier Plotter, and CCLE, we identified CRABP2 as significantly upregulated at both mRNA and protein levels in ovarian cancer, correlating with poor prognosis and decreased Olaparib sensitivity. Using colony formation and CCK-8 assays, we confirmed that CRABP2 knockdown in OVCAR3 and TOV112D cells enhanced sensitivity to Olaparib. Additionally, 4D label-free quantitative proteomics analysis, GSEA, and GO/KEGG analysis revealed CRABP2's involvement in regulating oxidation signals. Flow cytometry, colony formation assays, and western blotting demonstrated that CRABP2 knockdown promoted ROS production by activating Caspase-8, thereby augmenting Olaparib sensitivity and inhibiting ovarian cancer cell proliferation. Moreover, in xenograft models, CRABP2 knockdown significantly suppressed tumorigenesis and enhanced Olaparib sensitivity, with the effect being reversed upon Caspase-8 knockdown. These findings suggest that CRABP2 may modulate Olaparib sensitivity in ovarian cancer through the Caspase-8/ROS axis, highlighting its potential as a target for Olaparib sensitization.

Long-Acting Poly(ADP-ribose) Polymerase Inhibitor Prodrug for Humans

Poly(ADP-ribose) polymerase inhibitors (PARPi) have been approved for once or twice daily oral use in the treatment of cancers with BRCA defects. However, for some patients, oral administration of PARPi may be impractical or intolerable, and a long-acting injectable formulation is desirable. We recently developed a long-acting PEGylated PARPi prodrug, PEG∼talazoparib (TLZ), which suppressed the growth of PARPi-sensitive tumors in mice for very long periods. However, the release rate of TLZ from the conjugate was too fast to be optimal in humans. We prepared several new PEG∼TLZ prodrugs having longer half-lives of drug release and accurately measured their pharmacokinetics in the rat. Using the rates of release of TLZ from these prodrugs and the known pharmacokinetics of free TLZ in humans, we simulated the pharmacokinetics of the macromolecular prodrugs and released TLZ in humans. From several possibilities, we chose two conjugates that could be administered intravenously every 2 weeks and maintain TLZ within its known therapeutic window. We describe situations where the PEG∼TLZ conjugates would find utility in humans and suggest how the intravenously administered long-acting prodrugs could in fact be more effective than daily oral administration of free TLZ.

Formononetin alleviates cerebral ischemia-reperfusion injury in rats by targeting the PARP-1/PARG/Iduna signaling pathway

Formononetin has been demonstrated to protect against cerebral ischemia-reperfusion injury, however its mechanism has to be further researched. This study examined the effect of formononetin on cerebral ischemia-reperfusion injury in rats using the PARP-1/PARG/Iduna signaling pathway. In male SD rats, a model of cerebral ischemia-reperfusion injury was developed. Animals were randomly assigned to one of eight groups: Sham operation, Sham operation + formononetin, MCAO, MCAO + formononetin, PARP inhibitor (PJ34) + MCAO, formononetin + PJ34 + MCAO, PARG inhibitor (Ethacridine lactate) + MCAO, and ethacridine lactate + formononetin. The neurological deficit test, TTC staining, HE staining, Nissl staining, TUNEL staining, and western blotting were utilized to assess formononetin's protective effects in MCAO rats. The data show that formononetin can effectively alleviate neurological dysfunction and pathological changes in brain tissue in rats with cerebral ischemia-reperfusion injury, reduce the area of cerebral infarction and neuronal apoptosis, decrease the protein levels of PARP-1, PARG, Caspase-3, P53, and AIF in brain tissue, and increase the protein levels of Iduna and p-AKT. As a result, we concluded that formononetin improves brain ischemia-reperfusion injury in rats by modulating the PARP-1/PARG/Iduna signaling pathway.

Germline Mutations of Holliday Junction Resolvase Genes in Multiple Primary Malignancies Involving Lung Cancer Lead to PARP Inhibitor Sensitization

PURPOSE

The incidence of multiple primary malignancies (MPM) involving lung cancer has increased in recent decades. There is an urgent need to clarify the genetic profile of such patients and explore more efficacious therapy for them.

EXPERIMENTAL DESIGN

Peripheral blood samples from MPM involving patients with lung cancer were assessed by whole-exome sequencing (WES), and the identified variants were referenced for pathogenicity using the public available database. Pathway enrichment analysis of mutated genes was performed to identify the most relevant pathway. Next, the effects of mutations in relevant pathway on function and response to targeted drugs were verified by in vitro and in vivo experiments.

RESULTS

Germline exomes of 71 patients diagnosed with MPM involving lung cancer were sequenced. Pathway enrichment analysis shows that the homologous recombination repair (HRR) pathway has the strongest correlation. Moreover, HRR genes, especially key Holliday junction resolvases (HJR) genes (GEN1, BLM, SXL4, and RMI1), were most frequently mutated, unlike the status in the samples from patients with lung cancer only. Next, we identified a total of seven mutations in HJR genes led to homologous recombination DNA repair deficiency and rendered lung cancer cells sensitive to PARP inhibitor treatment, both in vitro and in vivo.

CONCLUSIONS

This is the first study to map the profile of germline mutations in patients with MPM involving lung cancer. This study may shed light on early prevention and novel targeted therapies for MPM involving patients with lung cancer with HJR mutations.

Poor Concordance Between Cancer Antigen-125 and RECIST Assessment for Progression in Patients With Platinum-Sensitive Relapsed Ovarian Cancer on Maintenance Therapy With a Poly(ADP-ribose) Polymerase Inhibitor

PURPOSE

Cancer antigen-125 (CA-125) is recommended by treatment guidelines and widely used to diagnose ovarian cancer recurrence. The value of CA-125 as a surrogate for disease progression (PD) and its concordance with radiologic progression are unclear, particularly for women with platinum-sensitive relapsed ovarian cancer (PSROC) who have responded to chemotherapy and treated with maintenance poly(ADP-ribose) polymerase inhibitor (PARPi).

METHODS

In this pooled analysis of four randomized trials of maintenance PARPi or placebo (Study 19, SOLO2, ARIEL3, and NOVA), we extracted data on CA-125 PD as defined by Gynecologic Cancer InterGroup criteria and RECIST v1.1. We evaluated the concordance between CA-125 and RECIST PD and reported on the negative predictive value (NPV) and positive predictive value (PPV).

RESULTS

Of 1,262 participants (n = 818 PARPi, n = 444 placebo), 403 (32%) had CA-125 PD, and of these, 366 had concordant RECIST PD (PPV, 91% [95% CI, 88 to 93]). However, of 859 (68%) without CA-125 PD, 382 also did not have RECIST PD (NPV, 44% [95% CI, 41 to 48]). Within the treatment arms, PPV remained high (PARPi, 91% [95% CI, 86 to 94]; placebo, 91% [95% CI, 86 to 95]) but NPV was lower on placebo (PARPi, 53% [95% CI, 49 to 57]; placebo, 25% [95% CI, 20 to 31]). Of 477 with RECIST-only PD, most (95%) had a normal CA-125 at the start of maintenance therapy and the majority (n = 304, 64%) had CA-125 that remained within normal range. Solid organ recurrence without peritoneal disease was more common in those with RECIST-only PD than in those with CA-125 and RECIST PD (36% v 24%; P < .001).

CONCLUSION

In patients with PSROC treated with maintenance PARPi, almost half with RECIST PD did not have CA-125 PD, challenging current guidelines. Periodic computed tomography imaging should be considered as part of surveillance, particularly in those with a normal CA-125 at the start of maintenance therapy and on treatment.

Evaluating homologous recombination activity in tissues to predict the risk of hereditary breast and ovarian cancer and olaparib sensitivity

Homologous recombination (HR) repairs DNA damage including DNA double-stranded breaks and alterations in HR-related genes results in HR deficiency. Germline alteration of HR-related genes, such as BRCA1 and BRCA2, causes hereditary breast and ovarian cancer (HBOC). Cancer cells with HR deficiency are sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors and DNA-damaging agents. Thus, accurately evaluating HR activity is useful for diagnosing HBOC and predicting the therapeutic effects of anti-cancer agents. Previously, we developed an assay for site-specific HR activity (ASHRA) that can quantitatively evaluate HR activity and detect moderate HR deficiency. HR activity in cells measured by ASHRA correlates with sensitivity to the PARP inhibitor, olaparib. In this study, we applied ASHRA to lymphoblastoid cells and xenograft tumor tissues, which simulate peripheral blood lymphocytes and tumor tissues, respectively, as clinically available samples. We showed that ASHRA could be used to detect HR deficiency in lymphoblastoid cells derived from a BRCA1 pathogenic variant carrier. Furthermore, ASHRA could quantitatively measure the HR activity in xenograft tumor tissues with HR activity that was gradually suppressed by inducible BRCA1 knockdown. The HR activity of xenograft tumor tissues quantitatively correlated with the effect of olaparib. Our data suggest that ASHRA could be a useful assay for diagnosing HBOC and predicting the efficacy of PARP inhibitors.

Prevalence of germline BRCA1/2 pathogenic variants in Japanese patients treated with castration-resistant prostate cancer and efficacy of CRPC treatment in real-world clinical practice

OBJECTIVE

The companion diagnosis for olaparib, a poly (ADP-ribose) polymerase inhibitor for prostate cancer, aims to detect BRCA1/2 gene variants. In clinical practice, the frequency of germline BRCA1/2 variants in patients receiving castration-resistant prostate cancer treatment is unknown. We aimed to evaluate the prevalence of germline BRCA1/2 variants and their relationship to prognosis and treatment efficacy in castration-resistant prostate cancer.

METHODS

Between June 2021 and 2023, 92 patients receiving castration-resistant prostate cancer treatment were examined for germline BRCA1/2 variants using BRACAnalysis CDx®. Furthermore, the associations between BRCA1/2 pathogenic variants and clinical outcomes were assessed.

RESULTS

Of the 92 patients referred for genetic testing, 6 (6.5%) carried germline pathogenic variants in BRCA1/2. The BRCA2 variant was the most frequent (n = 5), followed by BRCA1 variant (n = 1). Among the five variants in BRCA2, the p.Asp427Thrfs*3 variant was identified for the first time in prostate cancer. Overall survival from castration-resistant prostate cancer for patients with BRCA1/2 variants was significantly shorter than for patients without BRCA1/2 variants (P = 0.043). Progression-free survival of androgen receptor signaling inhibitors for patients with BRCA1/2 variants was significantly shorter than for those without (P = 0.003). Progression-free survival of taxane chemotherapy was significantly shorter in patients with BRCA1/2 variants than in those without (P = 0.0149).

CONCLUSIONS

In clinical practice, 6.5% of patients treated with castration-resistant prostate cancer carried germline BRCA1/2 pathogenic variants. Japanese castration-resistant prostate cancer patients with germline BRCA1/2 mutants have a poor prognosis and may be less responsive to treatment with androgen receptor signaling inhibitors and taxane-based chemotherapy for castration-resistant prostate cancer.

Targeting PARG induces tumor cell growth inhibition and antitumor immune response by reducing phosphorylated STAT3 in ovarian cancer

BACKGROUND

Ovarian cancer is the most lethal gynecological malignancy, with limited treatment options after failure of standard therapies. Despite the potential of poly(ADP-ribose) polymerase inhibitors in treating DNA damage response (DDR)-deficient ovarian cancer, the development of resistance and immunosuppression limit their efficacy, necessitating alternative therapeutic strategies. Inhibitors of poly(ADP-ribose) glycohydrolase (PARG) represent a novel class of inhibitors that are currently being assessed in preclinical and clinical studies for cancer treatment.

METHODS

By using a PARG small-molecule inhibitor, COH34, and a cell-penetrating antibody targeting the PARG's catalytic domain, we investigated the effects of PARG inhibition on signal transducer and activator of transcription 3 (STAT3) in OVCAR8, PEO1, and Brca1-null ID8 ovarian cancer cell lines, as well as in immune cells. We examined PARG inhibition-induced effects on STAT3 phosphorylation, nuclear localization, target gene expression, and antitumor immune responses in vitro, in patient-derived tumor organoids, and in an immunocompetent Brca1-null ID8 ovarian mouse tumor model that mirrors DDR-deficient human high-grade serous ovarian cancer. We also tested the effects of overexpressing a constitutively activated STAT3 mutant on COH34-induced tumor cell growth inhibition.

RESULTS

Our findings show that PARG inhibition downregulates STAT3 activity through dephosphorylation in ovarian cancer cells. Importantly, overexpression of a constitutively activated STAT3 mutant in tumor cells attenuates PARG inhibitor-induced growth inhibition. Additionally, PARG inhibition reduces STAT3 phosphorylation in immune cells, leading to the activation of antitumor immune responses, shown in immune cells cocultured with ovarian cancer patient tumor-derived organoids and in immune-competent mice-bearing mouse ovarian tumors.

CONCLUSIONS

We have identified a novel antitumor mechanism underlying PARG inhibition beyond its primary antitumor effects through blocking DDR in ovarian cancer. Furthermore, targeting PARG activates antitumor immune responses, thereby potentially increasing response rates to immunotherapy in patients with ovarian cancer.

PARP inhibitor plus radiotherapy reshape the immune suppressive microenvironment and potentiate the efficacy of immune checkpoint inhibitors in tumors with IDH1 mutation

Isocitrate dehydrogenase 1 mutant (IDH1mut) tumors respond poorly to immunotherapy, but are more sensitive to chemoradiotherapy and poly (ADP-ribose) polymerase inhibition (PARPi). Accordingly, some efforts have aimed to capitalize on the IDH1 mutation rather than reverse it. Moreover, radiotherapy (RT) and PARPi can stimulate antitumor immunity, raising the possibility of reversing the immunosuppression caused by IDH1 mutation while killing the tumor. To assess this possibility, we treated IDH1mut tumors and cells with RT + PARPi. RT + PARPi showed enhanced efficacy over either modality alone both in vitro and in vivo. RT + PARPi induced more DNA damage and activated the cGAS-STING pathway more. IFNβ, CXCL10, and CCL5 were also more highly expressed at both the mRNA and protein levels. In two different tumor models, RT + PARPi increased infiltration and cytolytic function of CD8+ T cells, with one model also showing increased CD8+T cell proliferation. RT+PARPi also increased PD-L1 expression and enhanced checkpoint inhibition. Knocking out cGAS reversed the increased CD8+ T cell infiltration and the antitumor effect of RT+PARPi. We conclude that RT + PARPi reshapes the IDH1mut tumor immunosuppressive microenvironment, thereby augmenting checkpoint inhibition.

Preclinical Characterization of AZD9574, a Blood-Brain Barrier Penetrant Inhibitor of PARP1

PURPOSE

We evaluated the properties and activity of AZD9574, a blood-brain barrier (BBB) penetrant selective inhibitor of PARP1, and assessed its efficacy and safety alone and in combination with temozolomide (TMZ) in preclinical models.

EXPERIMENTAL DESIGN

AZD9574 was interrogated in vitro for selectivity, PARylation inhibition, PARP-DNA trapping, the ability to cross the BBB, and the potential to inhibit cancer cell proliferation. In vivo efficacy was determined using subcutaneous as well as intracranial mouse xenograft models. Mouse, rat, and monkey were used to assess AZD9574 BBB penetration and rat models were used to evaluate potential hematotoxicity for AZD9574 monotherapy and the TMZ combination.

RESULTS

AZD9574 demonstrated PARP1-selectivity in fluorescence anisotropy, PARylation, and PARP-DNA trapping assays and in vivo experiments demonstrated BBB penetration. AZD9574 showed potent single agent efficacy in preclinical models with homologous recombination repair deficiency in vitro and in vivo. In an O6-methylguanine-DNA methyltransferase (MGMT)-methylated orthotopic glioma model, AZD9574 in combination with TMZ was superior in extending the survival of tumor-bearing mice compared with TMZ alone.

CONCLUSIONS

The combination of three key features-PARP1 selectivity, PARP1 trapping profile, and high central nervous system penetration in a single molecule-supports the development of AZD9574 as the best-in-class PARP inhibitor for the treatment of primary and secondary brain tumors. As documented by in vitro and in vivo studies, AZD9574 shows robust anticancer efficacy as a single agent as well as in combination with TMZ. AZD9574 is currently in a phase I trial (NCT05417594). See related commentary by Lynce and Lin, p. 1217.

Subsequent management and outcomes after first-line PARP inhibitors progression in ovarian cancer patients

OBJECTIVES

This retrospective study aims to evaluating the subsequent management and outcomes after first-line PARPi progression in Chinese ovarian cancer population.

METHODS

Clinical and pathologic variables, treatment modalities, and outcomes were assessed. We investigated the subsequent management and outcomes after first-line PARPi progression. The objective response rate (ORR) and disease control rate (DCR) parameters were evaluated to determine the response to subsequent chemotherapy. For the survival analyses, progression-free survival 1 (PFS1), PFS2, overall survival (OS) and PFS2 - PFS1 were analysed.

RESULTS

A total of 124 patients received PARPi maintenance treatment after first-line chemotherapy during the study period in our center. 44 of them (35.5%) experienced a recurrence. The median duration of PARPi in these patients was 11.1 months (range: 1.2-75.1 months). A total of 40 patients (40/44, 90.9%) received subsequent chemotherapy with 35 (35/44, 79.5%) and 5 (5/44, 11.4%) patients received platinum-based and non-platinum-based chemotherapy in our center. 2 patients (4.5%) received target therapy and other 2 patients (4.5%) received best supportive care. 27.3% (12/44) patients received secondary cytoreduction surgery (SCS). After subsequent chemotherapy, 14 patients received PARPi retreatment as maintenance therapy. In patients who received platinum-based regimens (n = 35), 23 of 35 patients (65.7%) had complete/partial response (CR/PR), 8 of 35 (22.9%) had stable disease (SD), and 4 of 35 (12.1%) had progressive disease (PD). The ORR and DCR of patients who received subsequent chemotherapy was 65.7% and 88.6%, respectively. 15 patients (57.7%, 15/26) were reported to be platinum resistant with a platinum-free interval (PFI)  of < 6 months in patients whose platinum sensitivity of the second line platinum-based regimens was evaluable. Patients who received SCS after PARPi resistant associated with a borderline better PFS2 (median PFS2: 41.9 vs. 29.2 months, P = 0.051) and a non-significantly increased PFS2-PFS1 (median PFS2-PFS1: 12.2 vs. 9.8 months, P = 0.551). Patients with a PFI ≥ 12 months had a significantly better PFS2 (median PFS2: 37.0 vs. 25.3 months, P < 0.001) and a tendency towards a better PFS2-PFS1 than those with a PFI < 12 months (median PFS2-PFS1: 11.2 vs. 8.5 months, P = 0.334). A better PFS2 was observed in patients who received second PARPi maintenance therapy (median PFS2 of 35.4 vs. 28.8 months); however, the difference was not statistically significant (P = 0.200). A better PFS2-PFS1 was observed in patients who received second PARPi maintenance therapy (median PFS2-PFS1: 13.6 vs. 8.9 months, P = 0.002) than those without.

CONCLUSIONS

In summary, some degree of resistance to standard subsequent platinum and non-platinum chemotherapy is noted in the entire cohort. A trend towards higher benefit from subsequent chemotherapy after first-line PARP inhibitors progression was observed in the PFI ≥ 12 months subgroup than those with PFI < 12 months. PARPi retreatment as maintenance therapy and SCS can be offered to some patients with PARPi resistance.

Cost-Effectiveness Analysis of HRD Testing for Previously Treated Patients with Advanced Ovarian Cancer in Italy

INTRODUCTION

Ovarian cancer (OC) is the eighth most common cancer among women, and homologous recombination deficiency (HRD) is present in approximately 50% of these patients. For this group, poly(ADP-ribose) polymerase (PARP) inhibitors are more likely to be effective. The aim of the study was to investigate the cost-effectiveness of HRD testing versus BRCA testing (which identifies mutations present only in 25% of patients) in Italy to optimize the treatment management, possibly with PARP inhibitors.

METHODS

A cost-effectiveness partition survival model was developed to estimate the expected costs and outcomes (life years, LYs; quality-adjusted life years, QALYs) with lifetime horizon of HRD testing versus BRCA testing alone in women with high-grade serous or endometrioid advanced ovarian cancer. The option to perform the tests in sequence, that is, the BRCA test followed by the HRD test, in patients with BRCA-negative test was also considered, and the model accounted for the National Healthcare Service (NHS) perspective in Italy. The treatments represented the best available options according to the initial test results and according to PARP inhibitors available in Italy. A 3% discount rate was applied. Both deterministic and probabilistic sensitivity analyses were performed to test the robustness of the model results.

RESULTS

HRD testing was shown to be a cost-effective strategy compared to BRCA testing (incremental cost-utility ratio 22,610€/QALY) and a cost-saving strategy compared to the sequence of tests. The probabilistic sensitivity analysis showed that the HRD test is cost-effective compared to BRCA testing in 98.5% of model simulations considering a willingness-to-pay threshold of 50,000€/QALY.

CONCLUSION

The identification of genetic anomalies in patients with advanced OC is a costly process. Regardless, HRD upfront testing compared to BRCA testing had a cost-effective profile, allowing the efficient use of healthcare resources and better life expectancy and quality of life for patients.

Repeat Next-Generation Sequencing Testing on Progression in Men With Metastatic Prostate Cancer Can Identify New Actionable Alterations

PURPOSE

There are limited data available on the real-world patterns of molecular testing in men with advanced prostate cancer. We thus sought to evaluate next-generation sequencing (NGS) testing in the United States, focused on single versus serial NGS testing, the different disease states of testing (hormone-sensitive v castration-resistant, metastatic vs nonmetastatic), tissue versus plasma circulating tumor DNA (ctDNA) assays, and how often actionable data were found on each NGS test.

METHODS

The Prostate Cancer Precision Medicine Multi-Institutional Collaborative Effort clinical-genomic database was used for this retrospective analysis, including 1,597 patients across 15 institutions. Actionable NGS data were defined as including somatic alterations in homologous recombination repair genes, mismatch repair deficiency, microsatellite instability (MSI-high), or a high tumor mutational burden ≥10 mut/MB.

RESULTS

Serial NGS testing (two or more NGS tests with specimens collected more than 60 days apart) was performed in 9% (n = 144) of patients with a median of 182 days in between test results. For the second NGS test and beyond, 82.1% (225 of 274) of tests were from ctDNA assays and 76.1% (217 of 285) were collected in the metastatic castration-resistant setting. New actionable data were found on 11.1% (16 of 144) of second NGS tests, with 3.5% (5 of 144) of tests detecting a new BRCA2 alteration or MSI-high. A targeted therapy (poly (ADP-ribose) polymerase inhibitor or immunotherapy) was given after an actionable result on the second NGS test in 31.3% (5 of 16) of patients.

CONCLUSION

Repeat somatic NGS testing in men with prostate cancer is infrequently performed in practice and can identify new actionable alterations not present with initial testing, suggesting the utility of repeat molecular profiling with tissue or blood of men with metastatic castration-resistant prostate cancer to guide therapy choices.

Real-world data of poly (ADP-ribose) polymerase inhibitor response in Japanese patients with ovarian cancer

BACKGROUND

Poly (ADP-ribose) polymerase (PARP) inhibitors have been increasingly used in the treatment of ovarian cancer, with BRCA positivity and homologous recombination deficiency (HRD) being common biomarkers used for predicting their efficacy. However, given the limitations of these biomarkers, new ones need to be explored.

METHODS

This retrospective study included 181 ovarian cancer patients who received olaparib or niraparib at two independent hospitals in Japan between May 2018 and December 2022. Clinical information and blood sampling data were collected. Patient characteristics, treatment history, and predictability of treatment duration based on blood data before treatment initiation were examined.

RESULTS

High-grade serous carcinoma, BRCA positivity, HRD, and maintenance therapy after recurrence treatment were observed more frequently in the olaparib group than in the niraparib group. The most common reasons for treatment interruption were anemia, fatigue, and nausea in the olaparib group and thrombocytopenia in the niraparib group. Regarding response to olaparib treatment, complete response to the most recent treatment, maintenance therapy after the first chemotherapy, high-grade serous carcinoma, and germline BRCA positivity were observed significantly more frequently among responders than among non-responders. Furthermore, neutrophil counts were significantly higher among responders than among non-responders.

CONCLUSIONS

Inflammation-related blood data, such as neutrophil count, obtained at the initial pre-treatment visit might serve as potential predictors for prolonged olaparib treatment. While this study offers valuable insights into potential indicators for prolonged olaparib treatment, it underscores the need for more expansive research to strengthen our understanding of PARP inhibitors and optimize treatment strategies in ovarian cancer.

Combining PARP Inhibitors and Androgen Receptor Signalling Inhibitors in Metastatic Prostate Cancer: A Quantitative Synthesis and Meta-analysis

CONTEXT

PARP inhibitors (PARPi) are established treatments for metastatic castration-resistant prostate cancer (mCRPC) with homologous recombination repair (HRR) deficiency after androgen receptor signalling inhibitor (ARSI) failure. New PARPi + ARSI combinations have been tested in all comers, although their clinical relevance in HRR-proficient tumours remains uncertain.

OBJECTIVE

To quantitatively synthesise evidence from randomised trials assessing the efficacy and safety of PARPi + ARSI combinations for first-line treatment of mCRPC.

EVIDENCE ACQUISITION

We searched the PubMed, EMBASE, SCOPUS, and Cochrane Library databases up to February 28, 2023. Randomised controlled trials (RCTs) comparing PARPi + ARSI versus placebo + ARSI for first-line treatment of mCRPC were eligible. Two reviewers independently performed screening and data extraction and assessed the risk of bias, while a third reviewer evaluated the eligibility criteria.

EVIDENCE SYNTHESIS

Overall, three phase 3 RCTs were included in the systematic review: PROPEL, MAGNITUDE, and TALAPRO-2. A total of 2601 patients with mCRPC were enrolled. Two of these trials (PROPEL and TALAPRO-2) assessed the radiographic progression-free survival benefit of PARPi + ARSI for first-line treatment of mCRPC, independent of HRR status. The pooled hazard ratio was 0.62 (95% confidence interval 0.53-0.72). The pooled hazard ratio for overall survival was 0.84 (95% confidence interval 0.72-0.98), indicating a 16% reduction in the risk of death among patients who received the combination.

CONCLUSIONS

Results from this meta-analysis support the use of ARSI + PARPi combinations in biomarker-unselected mCRPC. However, such combinations might be less clinically relevant in HRR-proficient cancers, especially considering the change in treatment landscape for mCRPC.

PATIENT SUMMARY

We looked at outcomes from trials testing combinations of two classes of drugs (PARP inhibitors and ARSI) in advanced prostate cancer. We found that these combinations seem to work regardless of gene mutations identified as biomarkers of response to PARP inhibitors when used on their own.

Longitudinal profiling identifies co-occurring BRCA1/2 reversions, TP53BP1, RIF1 and PAXIP1 mutations in PARP inhibitor-resistant advanced breast cancer

BACKGROUND

Resistance to therapies that target homologous recombination deficiency (HRD) in breast cancer limits their overall effectiveness. Multiple, preclinically validated, mechanisms of resistance have been proposed, but their existence and relative frequency in clinical disease are unclear, as is how to target resistance.

PATIENTS AND METHODS

Longitudinal mutation and methylation profiling of circulating tumour (ct)DNA was carried out in 47 patients with metastatic BRCA1-, BRCA2- or PALB2-mutant breast cancer treated with HRD-targeted therapy who developed progressive disease-18 patients had primary resistance and 29 exhibited response followed by resistance. ctDNA isolated at multiple time points in the patient treatment course (before, on-treatment and at progression) was sequenced using a novel >750-gene intron/exon targeted sequencing panel. Where available, matched tumour biopsies were whole exome and RNA sequenced and also used to assess nuclear RAD51.

RESULTS

BRCA1/2 reversion mutations were present in 60% of patients and were the most prevalent form of resistance. In 10 cases, reversions were detected in ctDNA before clinical progression. Two new reversion-based mechanisms were identified: (i) intragenic BRCA1/2 deletions with intronic breakpoints; and (ii) intragenic BRCA1/2 secondary mutations that formed novel splice acceptor sites, the latter being confirmed by in vitro minigene reporter assays. When seen before commencing subsequent treatment, reversions were associated with significantly shorter time to progression. Tumours with reversions retained HRD mutational signatures but had functional homologous recombination based on RAD51 status. Although less frequent than reversions, nonreversion mechanisms [loss-of-function (LoF) mutations in TP53BP1, RIF1 or PAXIP1] were evident in patients with acquired resistance and occasionally coexisted with reversions, challenging the notion that singular resistance mechanisms emerge in each patient.

CONCLUSIONS

These observations map the prevalence of candidate drivers of resistance across time in a clinical setting, information with implications for clinical management and trial design in HRD breast cancers.

FSP1 inhibition enhances olaparib sensitivity in BRCA-proficient ovarian cancer patients via a nonferroptosis mechanism

Poly ADP-ribose polymerase inhibitors (PARPis) exhibit promising efficacy in patients with BRCA mutations or homologous repair deficiency (HRD) in ovarian cancer (OC). However, less than 40% of patients have HRD, it is vital to expand the indications for PARPis in BRCA-proficient patients. Ferroptosis suppressor protein 1 (FSP1) is a key protein in a newly identified ferroptosis-protective mechanism that occurs in parallel with the GPX4-mediated pathway and is associated with chemoresistance in several cancers. Herein, FSP1 is reported to be negatively correlated with the prognosis in OC patients. Combination therapy comprising olaparib and iFSP1 (a FSP1 inhibitor) strongly inhibited tumour proliferation in BRCA-proficient OC cell lines, patient-derived organoids (PDOs) and xenograft mouse models. Surprisingly, the synergistic killing effect could not be reversed by ferroptosis inhibitors, indicating that mechanisms other than ferroptosis were responsible for the synergistic lethality. In addition, cotreatment was shown to induce increased γH2A.X foci and to impair nonhomologous end joining (NHEJ) activity to a greater extent than did any single drug. Mass spectrometry and immunoprecipitation analyses revealed that FSP1 interacted with Ku70, a classical component recruited to and occupying the end of double-strand breaks (DSBs) in the NHEJ process. FSP1 inhibition decreased Ku70 PARylation, impaired subsequent DNA-PKcs recruitment to the Ku complex at DSB sites and was rescued by restoring PARylation. These findings unprecedentedly reveal a novel role of FSP1 in DNA damage repair and provide new insights into how to sensitize OC patients to PARPi treatment.

Free drug and ROS-responsive nanoparticle delivery of synergistic doxorubicin and olaparib combinations to triple negative breast cancer models

Combinations of the topoisomerase II inhibitor doxorubicin and the poly (ADP-ribose) polymerase inhibitor olaparib offer potential drug-drug synergy for the treatment of triple negative breast cancers (TNBC). In this study we performed in vitro screening of combinations of these drugs, administered directly or encapsulated within polymer nanoparticles, in both 2D and in 3D spheroid models of breast cancer. A variety of assays were used to evaluate drug potency, and calculations of combination index (CI) values indicated that synergistic effects of drug combinations occurred in a molar-ratio dependent manner. It is suggested that the mechanisms of synergy were related to enhancement of DNA damage as shown by the level of double-strand DNA breaks, and mechanisms of antagonism associated with mitochondrial mediated cell survival, as indicated by reactive oxygen species (ROS) generation. Enhanced drug delivery and potency was observed with nanoparticle formulations, with a greater extent of doxorubicin localised to cell nuclei as evidenced by microscopy, and higher cytotoxicity at the same time points compared to free drugs. Together, the work presented identifies specific combinations of doxorubicin and olaparib which were most effective in a panel of TNBC cell lines, explores the mechanisms by which these combined agents might act, and shows that formulation of these drug combinations into polymeric nanoparticles at specific ratios conserves synergistic action and enhanced potency in vitro compared to the free drugs.

A synergistic two-drug therapy specifically targets a DNA repair dysregulation that occurs in p53-deficient colorectal and pancreatic cancers

The tumor-suppressor p53 is commonly inactivated in colorectal cancer and pancreatic ductal adenocarcinoma, but existing treatment options for p53-mutant (p53Mut) cancer are largely ineffective. Here, we report a therapeutic strategy for p53Mut tumors based on abnormalities in the DNA repair response. Investigation of DNA repair upon challenge with thymidine analogs reveals a dysregulation in DNA repair response in p53Mut cells that leads to accumulation of DNA breaks. Thymidine analogs do not interrupt DNA synthesis but induce DNA repair that involves a p53-dependent checkpoint. Inhibitors of poly(ADP-ribose) polymerase (PARPis) markedly enhance DNA double-strand breaks and cell death induced by thymidine analogs in p53Mut cells, whereas p53 wild-type cells respond with p53-dependent inhibition of the cell cycle. Combinations of trifluorothymidine and PARPi agents demonstrate superior anti-neoplastic activity in p53Mut cancer models. These findings support a two-drug combination strategy to improve outcomes for patients with p53Mut cancer.

Top advances of the year: Ovarian cancer

Although cure rates remain low and effective screening strategies are elusive, the recent advances in systemic therapies over the past year highlighted in this review have prolonged survival for women with ovarian cancer. In 2022, the first antibody-drug conjugate for platinum-resistant ovarian cancer received accelerated US Food and Drug Administration (FDA) approval. Confirmatory studies examining the efficacy of mirvetuximab and other antibody-drug conjugates are underway. In the upfront setting, the first data establishing an overall survival benefit from poly(ADP-ribose) polymerase inhibitor maintenance was demonstrated after a 7-year follow-up period. In contrast, long-term updates from poly(ADP-ribose) polymerase inhibitor trials in the noncurative setting reported survival detriments, and the FDA withdrew the respective indications. Several trials attempted to improve upon the standard of care for platinum-sensitive ovarian carcinoma and those with rare ovarian cancer histologies (carcinosarcoma, clear cell carcinoma) but failed to demonstrate a clinically or statistically meaningful benefit. This leaves the open question of how to further optimize systemic therapy for advanced ovarian carcinoma to improve long-term survival and cure rates.

PARP-1 inhibitor alleviates cerebral ischemia/reperfusion injury by reducing PARylation of HK-1 and LDH in mice

Poly (ADP-ribose) polymerase-1 (PARP-1) activity significantly increases during cerebral ischemia/reperfusion. PARP-1 is an NAD+-consumption enzyme. PARP-1 hyperactivity causes intracellular NAD+ deficiency and bioenergetic collapse, contributing to neuronal death. Besides, the powerful trigger of PARP-1 causes the catalyzation of poly (ADP-ribosyl)ation (PARylation), a posttranslational modification of proteins. Here, we found that PARP-1 was activated in the ischemic brain tissue during middle-cerebral-artery occlusion and reperfusion (MCAO/R) for 24 h, and PAR accumulated in the neurons in mice. Using immunoprecipitation, Western blotting, liquid chromatography-mass spectrometry, and 3D-modeling analysis, we revealed that the activation of PARP-1 caused PARylation of hexokinase-1 and lactate dehydrogenase-B, which, therefore, caused the inhibition of these enzyme activities and the resulting cell energy metabolism collapse. PARP-1 inhibition significantly reversed the activity of hexokinase and lactate dehydrogenase, decreased infarct volume, and improved neuronal deficiency. PARP-1 inhibitor combined with pyruvate further alleviated MCAO/R-induced ischemic brain injury in mice. As such, we conclude that PARP-1 inhibitor alleviates neuronal death partly by inhibiting the PARylation of metabolic-related enzymes and reversing metabolism reprogramming during cerebral ischemia/reperfusion injury in mice. PARP-1 inhibitor combined with pyruvate might be a promising therapeutic approach against brain ischemia/reperfusion injury.

Discovery and Proof of Concept of Potent Dual Polθ/PARP Inhibitors for Efficient Treatment of Homologous Recombination-Deficient Tumors

DNA polymerase theta (Polθ) has recently emerged as a new attractive synthetic lethal target involved in DNA damage repair. Inactivating Polθ alone or in combination with PARP inhibitors has demonstrated substantial therapeutic potential against tumors with homologous recombination (HR) defects such as alternation of BRCA genes. Herein, we report the design and proof of concept of a highly potent dual Polθ/PARP inhibitor 25d, which exhibited low nanomolar inhibitory activities against both Polθ and PARP1. Compared to combination treatment, 25d demonstrated superior antitumor efficacy in both MDA-MB-436 cells and xenografts by inducing more DNA damage and apoptosis. Importantly, 25d retained sensitivity in PARP inhibitor-resistant MDA-MB-436 cells with 53BP1 defect. Altogether, these findings illustrate the potential advantages of 25d, a first-in-class dual Polθ/PARP inhibitor, over monotherapy in treating HR-deficient tumors, including those with acquired PARP inhibitor resistance.

A real-world study of treatment patterns following disease progression in epithelial ovarian cancer patients undergoing poly-ADP-ribose polymerase inhibitor maintenance therapy

BACKGROUND

The efficacy of subsequent therapy after poly-ADP-ribose polymerase (PARP) inhibitor maintenance treatment has raised concerns. Retrospective studies show worse outcomes for platinum-based chemotherapy after progression of PARP inhibitor-maintenance therapy, especially in BRCA-mutant patients. We aimed to describe subsequent therapy in ovarian cancer patients after PARP inhibitor-maintenance therapy and evaluate their response to treatment. We focused on chemotherapy for patients with a progression-free interval (PFI) of ≥ 6 months after prior platinum treatment, based on BRCA status.

METHODS

We analyzed real-world data from Peking University Cancer Hospital, subsequent therapy after progression to PARP inhibitor-maintenance therapy for epithelial ovarian cancer between January 2016 and December 2022. Clinicopathological characteristics and treatment outcomes were extracted from medical records. The last follow-up was in May 2023.

RESULTS

A total of 102 patients were included, of which 29 (28.4%) had a germline BRCA1/2 mutation and 73 (71.6%) exhibited BRCA1/2 wild-type mutations. The PARP inhibitors used were Olaparib (n = 62, 60.8%), Niraparib (n = 35, 34.3%), and others (n = 5, 4.9%). The overall response rate (ORR) was 41.2%, and the median time to second progression (mTTSP) was 8.1 months (95%CI 5.8-10.2). Of 91 platinum-sensitive patients (PFI ≥ 6 months) after progression to PARP inhibitor-maintenance therapy, 65 patients subsequently received platinum regimens. Among them, 30 had received one line of chemotherapy before PARP inhibitor-maintenance therapy. Analysis of these 30 patients by BRCA status showed an ORR of 16.7% versus 33.3% and mTTSP of 7.1 (95% CI 4.9-9.1) versus 6.2 months (95% CI 3.7-8.3, P = 0.550), for BRCA-mutant and wild-type patients, respectively. For the remaining 35 patients who had received two or more lines of chemotherapy before PARP inhibitor-maintenance therapy, ORR was 57.1% versus 42.9%, and mTTSP was 18.0 (95% CI 5.0-31.0) versus 8.0 months (95% CI 4.9-11.1, P = 0.199), for BRCA-mutant and wild-type patients, respectively.

CONCLUSION

No differences in survival outcomes were observed among patients with different BRCA statuses. Furthermore, for patients who had undergone two or more lines of chemotherapy before PARP inhibitor maintenance therapy, no negative effects of PARP inhibitors on subsequent treatment were found, regardless of BRCA status.

Abrogation of KLF5 sensitizes BRCA1-proficient pancreatic cancer to PARP inhibition

Poly ADP-ribose polymerase (PARP) inhibitor monotherapies are selectively effective in patients with pancreatic, breast, prostate, and ovarian cancers with BRCA1 mutations. Cancer patients with more frequent wild-type BRCA show poor responses to PARP inhibitors. Moreover, patients who are initially sensitive to these inhibitors eventually respond poorly to drugs. In the present study, we discover that abrogation of Kruppel-like factor 5 (KLF5) significantly inhibits homologous recombination, which is the main mechanism for DNA double-stranded repair. Furthermore, the downregulation of KLF5 expression promotes the DNA damage induced by olaparib and significantly reduces the IC 50 of the RARP inhibitor in pancreatic cancer cells. Overexpression of BRCA1 reverses the above effects caused by silencing of KLF5. Olaparib combined with a KLF5 inhibitor has an enhanced cytotoxic effect. Mechanistically, we identify BRCA1 as a KLF5 target gene. BRCA1 is positively correlated with KLF5 in PDAC tissue. Our results indicate that inhibition of KLF5 may induce BRCAness in a larger pancreatic cancer subset with proficient BRCA. The combination of KLF5 inhibitors and PARP inhibitors provides a novel treatment strategy to enhance the sensitivity of BRCA1-proficient pancreatic cancer to PARP inhibitors.

DNA Damage Response and Mismatch Repair Gene Defects in Advanced and Metastatic Prostate Cancer

Alterations in DNA damage response (DDR) and related genes are present in up to 25% of advanced prostate cancers (PCa). Most frequently altered genes are involved in the homologous recombination repair, the Fanconi anemia, and the mismatch repair pathways, and their deficiencies lead to a highly heterogeneous spectrum of DDR-deficient phenotypes. More than half of these alterations concern non- BRCA DDR genes. From a therapeutic perspective, poly-ADP-ribose polymerase inhibitors have demonstrated robust clinical efficacy in tumors with BRCA2 and BRCA1 alterations. Mismatch repair-deficient PCa, and a subset of CDK12-deficient PCa, are vulnerable to immune checkpoint inhibitors. Emerging data point to the efficacy of ATR inhibitors in PCa with ATM deficiencies. Still, therapeutic implications are insufficiently clarified for most of the non- BRCA DDR alterations, and no successful targeted treatment options have been established.

Identification of indole-based natural compounds as inhibitors of PARP-1 against triple-negative breast cancer: a computational study

Triple-negative breast cancer (TNBC) is the most aggressive kind of breast cancer known to mankind. It is a heterogeneous disease that is formed due to the missing estrogen, progesterone and human epidermal growth factor 2 receptors. Poly(ADP-ribose) polymerase-1 (PARP-1) protein helps in the development of TNBC by repairing the cancer cells, which proliferate and spread metastatically. To determine the potential PARP-1 inhibitors (PARPi), 0.2 million natural products from Universal Natural Product Database were screened using molecular docking and six hit compounds were selected based on their binding affinity towards PARP-1. The bio-availability and drug-like properties of these natural products were evaluated using ADMET analysis. Molecular dynamics simulations were conducted for these complexes for 200 ns to examine their structural stability and dynamic behaviour and further compared with the complex of talazoparib (TALA), an FDA-approved PARPi. Using MM/PBSA calculations, we conclude that the complexes HIT-3 and HIT-5 (-25.64 and -23.14 kcal/mol, respectively) show stronger binding energies with PARP-1 than TALA with PARP-1 (-10.74 kcal/mol). Strong interactions were observed between the compounds and hotspot residues, Asp770, Ala880, Tyr889, Tyr896, Ala898, Asp899 and Tyr907, of PARP-1 due to the existence of various types of non-covalent interactions between the compounds and PARP-1. This research offers critical information about PARPi, which could potentially be incorporated into the treatment of TNBC. Moreover, these findings were validated by comparing them with an FDA-approved PARPi.

Targeting BRCA and PALB2 in Pancreatic Cancer

OPINION STATEMENT

An important subgroup of pancreatic ductal adenocarcinomas (PDACs) harbor pathogenic variants in BRCA1, BRCA2, or PALB2. These tumors are exquisitely sensitive to platinum-based chemotherapy and patients may experience deep and durable responses to this treatment. PARP inhibitors offer potential respite from the cumulative toxicities of chemotherapy as they significantly extend progression-free survival compared to a chemotherapy holiday. Given the lack of proven survival benefit, the decision to use a maintenance PARP inhibitor rather than continue chemotherapy should be individualized. Interestingly, in both published clinical trials of maintenance PARP inhibitors, there is a striking range of interpatient benefit: Even in the platinum-sensitive setting, roughly 25% of tumors appear to be PARP inhibitor refractory (progressive disease within 2 months of starting treatment), 50% sustain moderate benefit (up to 2 years), and 25% are hyper-responsive (more than 2 years of benefit). This finding highlights the need to refine our understanding of which patients will respond to maintenance PARP inhibitors, both by being able to identify biallelic loss and by deepening our knowledge of resistance mechanisms and who develops them. Recent data supports that reversion mutations are common in PARP inhibitor refractory patients, but we have little understanding of the mechanisms that drive delayed resistance and long-term responses. Identifying which patients are more prone to certain mechanisms of resistance and tackling them with specific treatment strategies are areas of active investigation. Additionally, given that PARP inhibitors have limited overall efficacy for most patients, upfront combination strategies are an important future strategy.

High expression of BCAT1 sensitizes AML cells to PARP inhibitor by suppressing DNA damage response

Previous evidence has confirmed that branched-chain aminotransferase-1 (BCAT1), a key enzyme governing branched-chain amino acid (BCAA) metabolism, has a role in cancer aggression partly by restricting αKG levels and inhibiting the activities of the αKG-dependent enzyme family. The oncogenic role of BCAT1, however, was not fully elucidated in acute myeloid leukemia (AML). In this study, we investigated the clinical significance and biological insight of BCAT1 in AML. Using q-PCR, we analyzed BCAT1 mRNAs in bone marrow samples from 332 patients with newly diagnosed AML. High BCAT1 expression independently predicts poor prognosis in patients with AML. We also established BCAT1 knockout (KO)/over-expressing (OE) AML cell lines to explore the underlying mechanisms. We found that BCAT1 affects cell proliferation and modulates cell cycle, cell apoptosis, and DNA damage/repair process. Additionally, we demonstrated that BCAT1 regulates histone methylation by reducing intracellular αKG levels in AML cells. Moreover, high expression of BCAT1 enhances the sensitivity of AML cells to the Poly (ADP-ribose) polymerase (PARP) inhibitor both in vivo and in vitro. Our study has demonstrated that BCAT1 expression can serve as a reliable predictor for AML patients, and PARP inhibitor BMN673 can be used as an effective treatment strategy for patients with high BCAT1 expression. KEY MESSAGES: High expression of BCAT1 is an independent risk factor for poor prognosis in patients with CN-AML. High BCAT1 expression in AML limits intracellular αKG levels, impairs αKG-dependent histone demethylase activity, and upregulates H3K9me3 levels. H3K9me3 inhibits ATM expression and blocks cellular DNA damage repair process. Increased sensitivity of BCAT1 high expression AML to PARP inhibitors may be used as an effective treatment strategy in AML patients.

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.

[Current post-surgical treatment strategies in first-line ovarian cancer]

Although the management of epithelial ovarian cancer has evolved significantly over the past few years, it remains a public health issue, as most patients are diagnosed at an advanced stage and relapse after first line treatment. Chemotherapy remains the standard adjuvant treatment for International Federation of Gynecology and Obstetrics (FIGO) stage I and II tumors, with some exceptions. For FIGO stage III/IV tumors, carboplatin- and paclitaxel-based chemotherapy are the standard of care, in combination with targeted therapies, especially bevacizumab and/or poly-(ADP-ribose) polymerase inhibitors, that have become a key milestone of first-line treatment. Our decision making for the maintenance therapy is based on the FIGO stage, tumor histology, timing of surgery (i.e. primary or interval debulking surgery), residual tumor, response to chemotherapy, BRCA mutation and homologous recombination (HR) status.

Does the choice of platinum doublet matter? A study to evaluate the impact of platinum doublet choice for treatment of platinum-sensitive ovarian cancer recurrence on the development of future PARP inhibitor and platinum resistance

OBJECTIVES

The use of a platinum doublet for the treatment of platinum-sensitive epithelial ovarian cancer (EOC) recurrence is well established. The impact of the non‑platinum chemotherapy used as part of a platinum doublet on PARP inhibitor (PARPi) and platinum sensitivity it not known. We aimed to describe oncologic outcomes in cases of recurrent EOC receiving PARPi as maintenance therapy based on preceding platinum doublet.

METHODS

Retrospective study of patients with platinum-sensitive recurrent ovarian, fallopian tube or primary peritoneal cancer treated with platinum doublet followed by maintenance PARPi from 1/1/2015 and 1/1/2022. Comparisons were made between patients receiving carboplatin + pegylated liposomal doxorubicin (CD) versus other platinum doublets (OPDs). Descriptive statistics, Kaplan-Meier and univariate survival analyses were performed.

RESULTS

100 patients received PARPi maintenance following a platinum doublet chemotherapy regimen for platinum-sensitive recurrence. 25/100 (25%) received CD and 75/100 (75%) received OPDs. Comparing CD and OPDs, median progression-free survival was 8 versus 7 months (p = 0.26), median time to platinum resistance was 15 versus 13 months (p = 0.54), median OS was 64 versus 90 months (p = 0.28), and median OS from starting PARPi was 25 versus 26 months (p = 0.90), respectively.

CONCLUSIONS

Using pegylated liposomal doxorubicin as part of a platinum doublet preceding maintenance PARPi for platinum-sensitive recurrence does not seem to hasten PARPi resistance or platinum resistance compared to OPDs. Although there was a non-significant trend towards increased OS among patients who received a platinum doublet other than CD prior to PARPi, the OS from PARPi start was similar between groups. Given the retrospective nature of this study and small study population, further research is needed to evaluate if the choice of platinum doublet preceding PARPi maintenance impacts PARPi resistance, platinum resistance and survival.

Patient-derived tumor organoids with p53 mutations, and not wild-type p53, are sensitive to synergistic combination PARP inhibitor treatment

Poly (ADP-ribose) polymerase inhibitors (PARPi) are used for patients with BRCA1/2 mutations, but patients with other mutations may benefit from PARPi treatment. Another mutation that is present in more cancers than BRCA1/2 is mutation to the TP53 gene. In 2D breast cancer cell lines, mutant p53 (mtp53) proteins tightly associate with replicating DNA and Poly (ADP-ribose) polymerase (PARP) protein. Combination drug treatment with the alkylating agent temozolomide and the PARPi talazoparib kills mtp53 expressing 2D grown breast cancer cell lines. We evaluated the sensitivity to the combination of temozolomide plus PARPi talazoparib treatment to breast and lung cancer patient-derived tumor organoids (PDTOs). The combination of the two drugs was synergistic for a cytotoxic response in PDTOs with mtp53 but not for PDTOs with wtp53. The combination of talazoparib and temozolomide induced more DNA double-strand breaks in mtp53 expressing organoids than in wild-type p53 expressing organoids as shown by increased γ-H2AX protein expression. Moreover, breast cancer tissue microarrays (TMAs) showed a positive correlation between stable p53 and high PARP1 expression in sub-groups of breast cancers, which may indicate sub-classes of breast cancers sensitive to PARPi therapy. These results suggest that mtp53 could be a biomarker to predict response to the combination of PARPi talazoparib-temozolomide treatment.

Natural pentacyclic triterpenoid from Pristimerin sensitizes p53-deficient tumor to PARP inhibitor by ubiquitination of Chk1

Inhibition of checkpoint kinase 1 (Chk1) has shown to overcome resistance to poly (ADP-ribose) polymerase (PARP) inhibitors and expand the clinical utility of PARP inhibitors in a broad range of human cancers. Pristimerin, a naturally occurring pentacyclic triterpenoid, has been the focus of intensive studies for its anticancer potential. However, it is not yet known whether low dose of pristimerin can be combined with PARP inhibitors by targeting Chk1 signaling pathway. In this study, we investigated the efficacy, safety and molecular mechanisms of the synergistic effect produced by the combination olaparib and pristimerin in TP53-deficient and BRCA-proficient cell models. As a result, an increased expression of Chk1 was correlated with TP53 mutation, and pristimerin preferentially sensitized p53-defective cells to olaparib. The combination of olaparib and pristimerin resulted in a more pronounced abrogation of DNA synthesis and induction of DNA double-strand breaks (DSBs). Moreover, pristimerin disrupted the constitutional levels of Chk1 and DSB repair activities. Mechanistically, pristimerin promoted K48-linked polyubiquitination and proteasomal degradation of Chk1 while not affecting its kinase domain and activity. Importantly, combinatorial therapy led to a higher rate of tumor growth inhibition without apparent hematological toxicities. In addition, pristimerin suppressed olaparib-induced upregulation of Chk1 and enhanced olaparib-induced DSB marker γΗ2ΑΧ in vivo. Taken together, inhibition of Chk1 by pristimerin has been observed to induce DNA repair deficiency, which may expand the application of olaparib in BRCA-proficient cancers harboring TP53 mutations. Thus, pristimerin can be combined for PARP inhibitor-based therapy.

Major clinical research advances in gynecologic cancer in 2023: a tumultuous year for endometrial cancer

In the 2023 series, we summarized the major clinical research advances in gynecologic oncology based on communications at the conference of Asian Society of Gynecologic Oncology Review Course. The review consisted of 1) Endometrial cancer: immune checkpoint inhibitor, antibody drug conjugates (ADCs), selective inhibitor of nuclear export, CDK4/6 inhibitors WEE1 inhibitor, poly (ADP-ribose) polymerase (PARP) inhibitors. 2) Cervical cancer: surgery in low-risk early-stage cervical cancer, therapy for locally advanced stage and advanced, metastatic, or recurrent setting; and 3) Ovarian cancer: immunotherapy, triplet therapies using immune checkpoint inhibitors along with antiangiogenic agents and PARP inhibitors, and ADCs. In 2023, the field of endometrial cancer treatment witnessed a landmark year, marked by several practice-changing outcomes with immune checkpoint inhibitors and the reliable efficacy of PARP inhibitors and ADCs.

Somatic mutations in four novel genes contribute to homologous recombination deficiency in breast cancer: a real-world clinical tumor sequencing study

Breast cancers involving mutations in homologous recombination (HR) genes, most commonly BRCA1 and BRCA2 (BRCA1/2), respond well to PARP inhibitors and platinum-based chemotherapy. However, except for these specific HR genes, it is not clear which other mutations contribute to homologous recombination defects (HRD). Here, we performed next-generation sequencing of tumor tissues and matched blood samples from 119 breast cancer patients using the OncoScreen Plus panel. Genomic mutation characteristics and HRD scores were analyzed. In the HR genes, we found that BRCA1/2 and PLAB2 mutations were related to HRD. HRD was also detected in a subset of patients without germline or somatic mutations in BRCA1/2, PLAB2, or other HR-related genes. Notably, LRP1B, NOTCH3, GATA2, and CARD11 (abbreviated as LNGC) mutations were associated with high HRD scores in breast cancer patients. Furthermore, functional experiments demonstrated that silencing CARD11 and GATA2 impairs HR repair efficiency and enhances the sensitivity of tumor cells to olaparib treatment. In summary, in the absence of mutations in the HR genes, the sensitivity of tumor cells to PARP inhibitors and platinum-based chemotherapy may be enhanced in a subset of breast cancer patients with LNGC somatic mutations.

Combination therapy application of Abemaciclib with Doxorubicin in triple negative breast cancer cell line MDA-MB-231

Due to lack of clinical biomarkers, Triple Negative Breast Cancer (TNBC) is more likely to have spread to other tissues at time of diagnosis and therapy planning generally involves use of cytotoxic chemotherapy agents, such as Doxorubicin. We aimed to investigate possible advantages of using combination strategy using Doxorubicin alongside Abemaciclib. After determining the IC50 values for Doxorubicin (DOX) and Abemaciclib (ABE); CompuSyn and ComBenefit software were used to reveal the effect resulting from the combination of two drugs. Following the determined effect, cell death was revealed by fluorescence microscopy and a colony forming assay was performed to see the potential of even a single cancer cell with adhesive character to survive over time and form a clone of itself. Detection of changing antioxidant activity following DOX, ABE and DOX+ABE combination therapy in MDAMB231 cells was determined by measuring MDA, SOD and GSH activities. The expression of Cleaved Caspase 3, PARP, Cleaved PARP, Cdk2 and Bax, which changed as a result of DOX, ABE and DOX+ABE application, was shown by Western Blotting.Cyclin-dependent kinase inhibitors appear as promising agents in therapy planning for breast cancer due to their prominent role in cell cycle regulation, where the number of studies interrogating its efficiency in the treatment of cancer such as TNBC is limited. For this reason, in this study, we aimed to determine the impact of the combined use of the CDK4/6 inhibitors ABE and DOX on the cytotoxicity, apoptotic homeostasis, alterations in antioxidative mechanisms, and the molecular pathways that they utilize. Our results showed that when used in combination, Doxorubicin and Abemaciclib showed a synergistic effect on TNBC cell line MDA-MB-231.

PARP inhibitor era in ovarian cancer treatment: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Ovarian cancer is the eighth leading cause of cancer-related death among women, characterized by late diagnosis and a high relapse rate. In randomized controlled trials, we aimed to evaluate the efficacy and safety of PARP inhibitors (PARPi) in treating advanced ovarian cancer.

METHODS

This review was registered on PROSPERO (CRD42021283150), included all phase II and phase III randomized controlled trials (RCTs) assessing the effect of PARPi on ovarian cancer until the 13th of April, 2022. The main outcomes were progression- free survival (PFS), overall survival (OS), and adverse events (AEs). Pooled hazard ratios (HRs), and risk ratios (RRs) were calculated with 95% confidence intervals (95% CI). The random-effects model was applied in all analyses.

RESULTS

In the meta-analysis, 16 eligible RCTs were included, with a total of 5,815 patients. In recurrent ovarian cancer, PARPi maintenance therapy showed a significant PFS benefit over placebo in the total population (HR 0.34, CI 0.29-0.40), BRCA mutant (HR 0.24, CI 0.18-0.31), germline BRCA mutant (HR 0.23, CI 0.18-0.30), and BRCA wild-type cases (HR 0.50, CI 0.39-0.65). PARPi monotherapy also improved PFS (HR 0.62, CI 0.51-0.76) compared with chemotherapy in BRCAm patients with recurrent ovarian cancer. The use of PARPi maintenance therapy resulted in an improvement in PFS over placebo in newly-diagnosed cancers in the overall population (HR 0.46, CI 0.30-0.71) and the BRCAm population (HR 0.36, CI 0.29-0.44). Although the risk of severe AEs was increased by PARPi therapy compared to placebo in most settings investigated, these side effects were controllable with dose modification, and treatment discontinuation was required in the minority of cases.

CONCLUSIONS

PARPis are an effective therapeutic option for newly-diagnosed and recurrent ovarian cancer. Despite a minor increase in the frequency of serious adverse effects, they are generally well tolerated.

Contemporary Systemic Therapy Intensification for Prostate Cancer: A Review for General Practitioners in Oncology

Prostate cancer accounts for a significant proportion of cancer diagnoses in Canadian men. Over the past decade, the therapeutic landscape for the management of metastatic prostate cancer has undergone rapid changes. Novel strategies use hormonal agents, chemotherapy, homologous recombination repair inhibitors, and radioligand therapy or combination strategies in addition to androgen deprivation therapy. In this review, we summarize the available data addressing key therapeutic areas along the disease continuum and focus on practical aspects for general practitioners in oncology managing patients with metastatic prostate cancer.

R-Loop Accumulation in Spliceosome Mutant Leukemias Confers Sensitivity to PARP1 Inhibition by Triggering Transcription-Replication Conflicts

RNA splicing factor (SF) gene mutations are commonly observed in patients with myeloid malignancies. Here we showed that SRSF2- and U2AF1-mutant leukemias are preferentially sensitive to PARP inhibitors (PARPi), despite being proficient in homologous recombination repair. Instead, SF-mutant leukemias exhibited R-loop accumulation that elicited an R-loop-associated PARP1 response, rendering cells dependent on PARP1 activity for survival. Consequently, PARPi induced DNA damage and cell death in SF-mutant leukemias in an R-loop-dependent manner. PARPi further increased aberrant R-loop levels, causing higher transcription-replication collisions and triggering ATR activation in SF-mutant leukemias. Ultimately, PARPi-induced DNA damage and cell death in SF-mutant leukemias could be enhanced by ATR inhibition. Finally, the level of PARP1 activity at R-loops correlated with PARPi sensitivity, suggesting that R-loop-associated PARP1 activity could be predictive of PARPi sensitivity in patients harboring SF gene mutations. This study highlights the potential of targeting different R-loop response pathways caused by spliceosome gene mutations as a therapeutic strategy for treating cancer.

SIGNIFICANCE

Spliceosome-mutant leukemias accumulate R-loops and require PARP1 to resolve transcription-replication conflicts and genomic instability, providing rationale to repurpose FDA-approved PARP inhibitors for patients carrying spliceosome gene mutations.

Precision Medicine in Castration-Resistant Prostate Cancer: Advances, Challenges, and the Landscape of PARPi Therapy-A Narrative Review

After recent approvals, poly-adenosine diphosphate [ADP]-ribose polymerase inhibitors (PARPis) have emerged as a frontline treatment for metastatic castration-resistant prostate cancer (mCRPC). Unlike their restricted use in breast or ovarian cancers, where approval is limited to those with BRCA1/2 alterations, PARPis in mCRPC are applied across a broader spectrum of genetic aberrations. Key findings from the phase III PROPEL trial suggest that PARPis' accessibility may broaden, even without mandatory testing. An increasing body of evidence underscores the importance of distinct alterations in homologous recombination repair (HRR) genes, revealing unique sensitivities to PARPis. Nonetheless, despite the initial effectiveness of PARPis in treating BRCA-mutated tumors, resistance to therapy is frequently encountered. This review aims to discuss patient stratification based on biomarkers and genetic signatures, offering insights into the nuances of first-line PARPis' efficacy in the intricate landscape of mCRPC.

Genetic Basis of Breast and Ovarian Cancer: Approaches and Lessons Learnt from Three Decades of Inherited Predisposition Testing

Germline variants occurring in BRCA1 and BRCA2 give rise to hereditary breast and ovarian cancer (HBOC) syndrome, predisposing to breast, ovarian, fallopian tube, and peritoneal cancers marked by elevated incidences of genomic aberrations that correspond to poor prognoses. These genes are in fact involved in genetic integrity, particularly in the process of homologous recombination (HR) DNA repair, a high-fidelity repair system for mending DNA double-strand breaks. In addition to its implication in HBOC pathogenesis, the impairment of HR has become a prime target for therapeutic intervention utilizing poly (ADP-ribose) polymerase (PARP) inhibitors. In the present review, we introduce the molecular roles of HR orchestrated by BRCA1 and BRCA2 within the framework of sensitivity to PARP inhibitors. We examine the genetic architecture underneath breast and ovarian cancer ranging from high- and mid- to low-penetrant predisposing genes and taking into account both germline and somatic variations. Finally, we consider higher levels of complexity of the genomic landscape such as polygenic risk scores and other approaches aiming to optimize therapeutic and preventive strategies for breast and ovarian cancer.

Homologous Recombination Deficiency Unrelated to Platinum and PARP Inhibitor Response in Cell Line Libraries

While large publicly available cancer cell line databases are invaluable for preclinical drug discovery and biomarker development, the association between homologous recombination deficiency (HRD) and drug sensitivity in these resources remains unclear. In this study, we comprehensively analyzed molecular profiles and drug screening data from the Cancer Cell Line Encyclopedia. Unexpectedly, gene alterations in BRCA1/2 or homologous recombination-related genes, HRD scores, or mutational signature 3 were not positively correlated with sensitivity to platinum agents or PARP inhibitors. Rather, higher HRD scores and mutational signature 3 were significantly associated with resistance to these agents in multiple assays. These findings were consistent when analyzing exclusively breast and ovarian cancer cell lines and when using data from the COSMIC Cell Line Project. Collectively, the existing data from established cancer cell lines do not reflect the expected association between HRD status and drug response to platinum agents and PARP inhibitors in clinical tumors. This discrepancy may extend to other tumor characteristics, highlighting the importance of recognizing potential limitations in cell line data for researchers.

Dual target PARP1/EZH2 inhibitors inducing excessive autophagy and producing synthetic lethality for triple-negative breast cancer therapy

Currently available PARP inhibitors are mainly used for the treatment of BRCA-mutated triple-negative breast cancer (TNBC), with a narrow application range of approximately 15% of patients. Recent studies have shown that EZH2 inhibitors have an obvious effect on breast cancer xenograft models and can promote the sensitivity of ovarian cancer cells to PARP inhibitors. Here, a series of new dual-target PARP1/EZH2 inhibitors for wild-BRCA type TNBC were designed and synthesized. SAR studies helped us identify compound 12e, encoded KWLX-12e, with good inhibitory activity against PARP1 (IC50 = 6.89 nM) and EZH2 (IC50 = 27.34 nM). Meanwhile, KWLX-12e showed an optimal cytotoxicity against MDA-MB-231 cells (IC50 = 2.84 μM) and BT-549 cells (IC50 = 0.91 μM), with no toxicity on normal breast cell lines. KWLX-12e also exhibited good antitumor activity with the TGI value of 75.94%, more effective than Niraparib plus GSK126 (TGI = 57.24%). Mechanistic studies showed that KWLX-12e achieved synthetic lethality indirectly by inhibiting EZH2 to increase the sensitivity to PARP1, and induced cell death by regulating excessive autophagy. KWLX-12e is expected to be a potential candidate for the treatment of TNBC.

PARP Inhibitors in Breast Cancer: a Short Communication

PURPOSE OF REVIEW

In the last decade, poly (ADP-ribose) polymerase (PARP) inhibitors have been approved in the treatment of several cancers, such as breast and ovarian cancer. This article aims to discuss the current uses, limitations, and future directions for PARP inhibitors (PARPis) in the treatment of breast cancer.

RECENT FINDINGS

Following the results of the OlympiAD and EMBRACA trials, PARPis were approved in HER2-negative breast cancer with a germline BRCA mutation. We reviewed this class of drugs' mechanism of action, efficacy, and limitations, as well as further studies that discussed resistance, impaired homologous recombination repair (HRR), and the combination of PARPis with other drugs. Improving understanding of HRR, increasing the ability to target resistance, and combining PARPis with other novel agents are continuing to increase the clinical utility of PARPis.

PARP inhibitors in ovarian cancer

Poly-ADP-ribose polymerase inhibitors (PARPis) were first approved for the treatment of epithelial ovarian cancer (EOC), where as a maintenance therapy they transformed clinical management of this disease in both patients with and without homologous recombination deficiency. In this review, we provide a historical overview of PARPi use in EOC and discuss recent updates on overall survival data, highlighting their impact on regulatory approvals. We explore their potential as combination regimens with antiangiogenic and cell-cycle checkpoint inhibitors, as well as other small molecule inhibitors, to overcome resistance mechanisms and enhance therapeutic efficacy, providing a future perspective on the use of PARPis in EOC treatment.

Osteoclast Cancer Cell Metabolic Cross-talk Confers PARP Inhibitor Resistance in Bone Metastatic Breast Cancer

The majority of patients with late-stage breast cancer develop distal bone metastases. The bone microenvironment can affect response to therapy, and uncovering the underlying mechanisms could help identify improved strategies for treating bone metastatic breast cancer. Here, we observed that osteoclasts reduced the sensitivity of breast cancer cells to DNA damaging agents, including cisplatin and the PARP inhibitor (PARPi) olaparib. Metabolic profiling identified elevated glutamine production by osteoclasts. Glutamine supplementation enhanced the survival of breast cancer cells treated with DNA damaging agents, while blocking glutamine uptake increased sensitivity and suppressed bone metastasis. GPX4, the critical enzyme responsible for glutathione oxidation, was upregulated in cancer cells following PARPi treatment through stress-induced ATF4-dependent transcriptional programming. Increased glutamine uptake and GPX4 upregulation concertedly enhanced glutathione metabolism in cancer cells to help neutralize oxidative stress and generate PARPi resistance. Analysis of paired patient samples of primary breast tumors and bone metastases revealed significant induction of GPX4 in bone metastases. Combination therapy utilizing PARPi and zoledronate, which blocks osteoclast activity and thereby reduces the microenvironmental glutamine supply, generated a synergistic effect in reducing bone metastasis. These results identify a role for glutamine production by bone-resident cells in supporting metastatic cancer cells to overcome oxidative stress and develop resistance to DNA-damaging therapies.

SIGNIFICANCE

Metabolic interaction between osteoclasts and tumor cells contributes to resistance to DNA-damaging agents, which can be blocked by combination treatment with PARP and osteoclast inhibitors to reduce bone metastatic burden.

Maintenance therapy for newly and recurrent epithelial ovarian cancer: current therapies and future perspectives

PURPOSE OF REVIEW

Epithelial ovarian cancer (EOC) is the fifth cause of cancer death among women, and 70-80% of patients relapse within 2 years from the last cycle of first-line chemotherapy despite a complete response to chemotherapy and optimal debulking surgery. In this context, the goal of the maintenance treatment strategy is to prolong the time to recurrence. The recent development of targeted molecular therapies resulted in a broader spectrum of maintenance therapeutic options with consequent higher clinical benefit but less toxicity. This review summarizes the currently available maintenance strategies for newly and recurrent EOC, focusing on the decision-making process to personalize treatment and future perspectives.

RECENT FINDINGS

Over the past 10 years, several studies have demonstrated the clear benefit in terms of survival with the addition of a maintenance treatment strategy over the 'watchful waiting' approach both in the first line and recurrent setting. Since December 2016, the United States Food and Drug Administration and European Medicines Agency have approved four drugs for ovarian cancer maintenance based on the results of several clinical trials demonstrating efficacy and tolerability. These include the antiangiogenic drug Bevacizumab and three polyadenosine diphosphate-ribose polymerase (PARP) inhibitors: olaparib, niraparib, and rucaparib.

SUMMARY

These data led American and European Treatment guidelines to include bevacizumab, olaparib, niraparib, rucaparib, and combination bevacizumab-olaparib as maintenance treatment options in first-line and recurrent ovarian cancer therapy. However, with the availability of different maintenance options, identifying the best treatment choice for each patient can be challenging, and several clinical and molecular aspects have to be taken into account in the decision-making process.