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.

New synergistic combination therapy approaches with HDAC inhibitor quisinostat, cisplatin or PARP inhibitor talazoparib for urothelial carcinoma.

Urothelial carcinoma (UC) urgently requires new therapeutic options. Histone deacetylases (HDAC) are frequently dysregulated in UC and constitute interesting targets for the development of alternative therapy options. Thus, we investigated the effect of the second generation HDAC inhibitor (HDACi) quisinostat in five UC cell lines (UCC) and two normal control cell lines in comparison to romidepsin, a well characterized HDACi which was previously shown to induce cell death and cell cycle arrest. In UCC, quisinostat led to cell cycle alterations, cell death induction and DNA damage, but was well tolerated by normal cells. Combinations of quisinostat with cisplatin or the PARP inhibitor talazoparib led to decrease in cell viability and significant synergistic effect in five UCCs and platinum-resistant sublines allowing dose reduction. Further analyses in UM-UC-3 and J82 at low dose ratio revealed that the mechanisms included cell cycle disturbance, apoptosis induction and DNA damage. These combinations appeared to be well tolerated in normal cells. In conclusion, our results suggest new promising combination regimes for treatment of UC, also in the cisplatin-resistant setting.

TALAPRO-3 clinical trial protocol: phase III study of talazoparib plus enzalutamide in metastatic castration-sensitive prostate cancer.

Poly(ADP-ribose) polymerase inhibitors in combination with androgen-receptor signaling inhibitors are a promising therapeutic option for patients with metastatic castration-sensitive prostate cancer (mCSPC) and homologous recombination repair (HRR) gene alterations. Here, we describe the design and rationale of the multinational, phase III, TALAPRO-3 study comparing talazoparib plus enzalutamide versus placebo plus enzalutamide in patients with mCSPC and HRR gene alterations. The primary end point is investigator-assessed radiographic progression-free survival (rPFS) per RECIST 1.1 in soft tissue, or per PCWG3 criteria in bone. The TALAPRO-3 study will demonstrate whether the addition of talazoparib can improve the efficacy of enzalutamide as assessed by rPFS in patients with mCSPC and HRR gene alterations undergoing androgen deprivation therapy. Clinical Trial Registration:NCT04821622 (ClinicalTrials.gov) Registry Name: Study of Talazoparib With Enzalutamide in Men With DDR Gene Mutated mCSPC. Date of Registration: 29 March 2021.

Hereditary breast and ovarian cancer: from genes to molecular targeted therapies.

Hereditary familial tumors constitute 10-15% of all malignancies and present opportunities for the identification of therapeutic approaches against specific germline genetic defects. Hereditary breast and ovarian cancer (HBOC) syndrome, which is linked to the pathogenic mutations of the breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) genes, is an important research model for personalized therapeutic approaches for specific germline mutations. HBOC is characterized by multiple cases of breast and ovarian carcinoma in association with other tumors (prostate, pancreas and stomach carcinoma) within the same family branch, a young age of onset (<36 years), bilaterality and an autosomal dominant pattern of inheritance. Counseling, evaluation of the clinical criteria for the diagnosis of HBOC, and the performance of genetic testing allow for the identification of subjects with BRCA1/2 mutations and provide crucial information for clinical and therapeutic management. The identification of a BRCA gene mutation has therapeutic implications for women with metastatic and non-metastatic breast cancer. In the therapeutic setting of BRCA+ breast cancer, treatment with poly (ADP-ribose) polymerase (PARP) inhibitors, which keep cancer cells from repairing their damaged DNA and cause cell death, is remarkable. This review summarizes the evidence demonstrating the value of BRCA1/2 status as a diagnostic and prognostic tool and as a predictive biomarker in the personalized approach to hereditary BRCA + cancers.

Characteristics, Treatment, and Outcomes of Real-World Talazoparib-Treated Patients With Germline BRCA-Mutated Advanced HER2-Negative Breast Cancer.

BACKGROUND: Talazoparib is a poly (adenosine diphosphate-ribose) polymerase inhibitor approved for the treatment of adult patients with deleterious or suspected deleterious germline BRCA-mutated (gBRCAm), HER2-negative, locally advanced or metastatic breast cancer (LA/mBC), with approval based on the EMBRACA trial. To date, there are no published data on talazoparib use in the real-world United States (USA) setting. PATIENTS AND METHODS: Characteristics, treatment patterns, and clinical outcomes of real-world US patients with gBRCAm HER2-negative LA/mBC treated with talazoparib monotherapy were collected via retrospective chart review and summarized using descriptive statistics. RESULTS: Among 84 eligible patients, 35.7% had hormone receptor-positive tumors and 64.3% had triple-negative LA/mBC (TNBC). At talazoparib initiation, 29.8% had ECOG PS of ≥2 and 19.0% had brain metastasis. Mutations in gBRCA1 or 2 were detected among 64.3% and 35.7% of patients, respectively. Talazoparib was given as 1st-line therapy in 14.3% of patients, 2nd-line in 40.5%, and 3rd- or 4th-line in 45.2%. Median time to talazoparib treatment failure was 8.5 months (95% CI, 8.0-9.7), median progression-free survival was 8.7 months (95% CI, 8.0-9.9), the median time from initiation to chemotherapy was 12.2 months (95% CI, 10.5-20.1), and the overall response rate was 63.1%. No differences in clinical outcomes were observed between patients with HR-positive/HER2-negative LA/mBC and patients with TNBC by using unadjusted statistical comparisons. Brain metastasis and ECOG PS ≥2 at talazoparib initiation were associated with treatment failure and progression or mortality. CONCLUSION: Overall, talazoparib clinical outcomes in this real-world population are consistent with findings from EMBRACA.

Clinical efficacy of PARP inhibitors in breast cancer.

BRCA1 and BRCA2 are key tumor suppressor genes that are essential for the homologous recombination DNA repair pathway. Loss of function mutations in these genes result in hereditary breast and ovarian cancer syndromes, which comprise approximately 5% of cases. BRCA1/2 mutations are associated with younger age of diagnosis and increased risk of recurrences. The concept of synthetic lethality led to the development of PARP inhibitors which cause cell cytotoxicity via the inhibition of PARP1, a key DNA repair protein, in cells with germline BRCA1/2 mutations. Although still poorly understood, the most well-acknowledged proposed mechanisms of action of PARP1 inhibition include the inhibition of single strand break repair, PARP trapping, and the upregulation of non-homologous end joining. Olaparib and talazoparib are PARP inhibitors that have been approved for the management of HER2-negative breast cancer in patients with germline BRCA1/2 mutations. This review article highlights the clinical efficacy of PARP inhibitors in patients with HER2-negative breast cancer in early and advanced settings.

XRCC1 counteracts poly(ADP ribose)polymerase (PARP) poisons, olaparib and talazoparib, and a clinical alkylating agent, temozolomide, by promoting the removal of trapped PARP1 from broken DNA.

Base excision repair (BER) removes damaged bases by generating single-strand breaks (SSBs), gap-filling by DNA polymerase ß (POLß), and resealing SSBs. A base-damaging agent, methyl methanesulfonate (MMS) is widely used to study BER. BER increases cellular tolerance to MMS, anti-cancer base-damaging drugs, temozolomide, carmustine, and lomustine, and to clinical poly(ADP ribose)polymerase (PARP) poisons, olaparib and talazoparib. The poisons stabilize PARP1/SSB complexes, inhibiting access of BER factors to SSBs. PARP1 and XRCC1 collaboratively promote SSB resealing by recruiting POLß to SSBs, but XRCC1-/- cells are much more sensitive to MMS than PARP1-/- cells. We recently report that the PARP1 loss in XRCC1-/- cells restores their MMS tolerance and conclude that XPCC1 facilitates the release of PARP1 from SSBs by maintaining its autoPARylation. We here show that the PARP1 loss in XRCC1-/- cells also restores their tolerance to the three anti-cancer base-damaging drugs, although they and MMS induce different sets of base damage. We reveal the synthetic lethality of the XRCC1-/- mutation, but not POLß-/- , with olaparib and talazoparib, indicating that XRCC1 is a unique BER factor in suppressing toxic PARP1/SSB complex and can suppress even when PARP1 catalysis is inhibited. In conclusion, XRCC1 suppresses the PARP1/SSB complex via PARP1 catalysis-dependent and independent mechanisms.

Pharmacokinetics, safety, and antitumor activity of talazoparib monotherapy in Chinese patients with advanced solid tumors.

Talazoparib, a poly(ADP-ribose) polymerase inhibitor, has demonstrated efficacy in the treatment of advanced breast and prostate cancers in Western populations. This open-label, phase 1 study investigated the pharmacokinetics, safety, and antitumor activity of talazoparib monotherapy in Chinese patients with advanced solid tumors. Molecularly unselected patients (≥18 years) with advanced solid tumors resistant to standard therapy received talazoparib (oral, 1 mg once daily). Primary endpoint was characterization of single-dose and steady-state pharmacokinetics. Secondary endpoints evaluated safety, unconfirmed objective response rate (ORR), and duration of response. The safety population comprised 15 Chinese patients (median [range] age 53.0 [31.0-72.0] years). Single-dose median time to first occurrence of maximum observed concentration was 1.9 h; concentrations then declined with a mean terminal half-life (t1/2) of 67 h. Following multiple dosing, median Tmax was approximately 1.85 h with steady state generally achieved by Day 21. Treatment-related treatment-emergent adverse events (TEAEs) occurred in 86.7% (13/15) of patients (grade 3, 20.0%; grade 4, 13.3%). Two patients (13.3%) experienced serious treatment-related TEAEs. ORR (investigator-assessed) was 6.7% (95% CI: 0.2-31.9); one patient (6.7%) had a partial response. In patients with measurable disease at baseline, the ORR was 9.1% (1/11; 95% CI: 0.2-41.3; duration of response: 114 days); stable disease was achieved by 36.4% (4/11) of patients, and 54.5% (6/11) progressed by data cut-off. In Chinese patients with advanced solid tumors, the pharmacokinetic profile of talazoparib monotherapy (1 mg/day) was consistent with other patient populations. TEAEs were generally manageable with no unexpected safety findings. (ClinicalTrials.gov: NCT04635631 [prospectively registered November 19, 2020]).

Smart and sensitive nanomaterial-based electrochemical sensor for the determination of a poly (ADP-ribose) polymerase (PARP) inhibitor anticancer agent.

In this research, we propose a novel approach for constructing a sensitive and selective electrochemical sensor utilizing high-quality multi-walled carbon nanotubes functionalized with amino groups (MWCNT-NH2) for the detection of Talazoparib (TLZ), a poly (ADP-ribose) polymerase (PARP) enzyme inhibitor, in real samples. The MWCNT-NH2-based sensor exhibited remarkable performance characteristics, including excellent repeatability, reproducibility, and high selectivity against various interferences. Under optimized conditions, the sensor demonstrated a wide linear concentration range of 1.0-5.0 µM, with a low limit of detection (LOD) of 0.201 µM. Substantiated by rigorous analysis of pharmaceutical and biological matrices, our methodology emerges as a paragon of reliability, boasting recovery rates within the satisfactory bracket of 96.38-105.25%. The successful application of the MWCNT-NH2-based sensor in practical sample analysis highlights its potential for implementation in clinical and pharmaceutical settings. This research not only advances the application of MWCNT-NH2 in electrochemical sensing but also opens new avenues for the development and monitoring of innovative anticancer treatments. The insights gained from our study have far-reaching implications, pointing toward a future where precision and innovation converge to improve patient care and treatment outcomes.

Dissecting the molecular determinants of clinical PARP1 inhibitor selectivity for tankyrase1.

Poly-ADP-ribosyltransferases play a critical role in DNA repair and cell death, and poly(ADP-ribosyl) polymerase 1 (PARP1) is a particularly important therapeutic target for the treatment of breast cancer because of its synthetic lethal relationship with breast cancer susceptibility proteins 1 and 2. Numerous PARP1 inhibitors have been developed, and their efficacy in cancer treatment is attributed to both the inhibition of enzymatic activity and their ability to trap PARP1 on to the damaged DNA, which is cytotoxic. Of the clinical PARP inhibitors, talazoparib is the most effective at trapping PARP1 on damaged DNA. Biochemically, talazoparib is also suspected to be a potent inhibitor of PARP5a/b (tankyrase1/2 [TNKS1/2]), which is an important regulator of Wnt/ß-catenin pathway. Here we show using competition experiments in cell lysate that, at a clinically relevant concentration, talazoparib can potentially bind and engage TNKS1. Using surface plasmon resonance, we measured the dissociation constants of talazoparib, olaparib, niraparib, and veliparib for their interaction with PARP1 and TNKS1. The results show that talazoparib has strong affinity for PARP1 as well as uniquely strong affinity for TNKS1. Finally, we used crystallography and hydrogen deuterium exchange mass spectroscopy to dissect the molecular mechanism of differential selectivity of these PARP1 inhibitors. From these data, we conclude that subtle differences between the ligand-binding sites of PARP1 and TNKS1, differences in the electrostatic nature of the ligands, protein dynamics, and ligand conformational energetics contribute to the different pharmacology of these PARP1 inhibitors. These results will help in the design of drugs to treat Wnt/ß-catenin pathway-related cancers, such as colorectal cancers.

Talazoparib, a Poly(ADP-ribose) Polymerase Inhibitor, for Metastatic Castration-resistant Prostate Cancer and DNA Damage Response Alterations: TALAPRO-1 Safety Analyses.

BACKGROUND: The phase II TALAPRO-1 study (NCT03148795) demonstrated durable antitumor activity in men with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC). Here, we detail the safety profile of talazoparib. PATIENTS AND METHODS: Men received talazoparib 1 mg/day (moderate renal impairment 0.75 mg/day) orally until radiographic progression, unacceptable toxicity, investigator decision, consent withdrawal, or death. Adverse events (AEs) were evaluated: incidence, severity, timing, duration, potential overlap of selected AEs, dose modifications/discontinuations due to AEs, and new clinically significant changes in laboratory values and vital signs. RESULTS: In the safety population (N = 127; median age 69.0 years), 95.3% (121/127) experienced all-cause treatment-emergent adverse events (TEAEs). Most common were anemia (48.8% [62/127]), nausea (33.1% [42/127]), decreased appetite (28.3% [36/127]), and asthenia (23.6% [30/127]). Nonhematologic TEAEs were generally grades 1 and 2. No grade 5 TEAEs or deaths were treatment-related. Hematologic TEAEs typically occurred during the first 4-5 months of treatment. The median duration of grade 3-4 anemia, neutropenia, and thrombocytopenia was limited to 7-12 days. No grade 4 events of anemia or neutropenia occurred. Neither BRCA status nor alteration origin significantly impacted the safety profile. The median (range) treatment duration was 6.1 (0.4-24.9) months; treatment duration did not impact the incidence of anemia. Only 3 of the 15 (11.8% [15/127]) permanent treatment discontinuations were due to hematologic TEAEs (thrombocytopenia 1.6% [2/127]; leukopenia 0.8% [1/127]). CONCLUSION: Common TEAEs associated with talazoparib could be managed through dose modifications/supportive care. Demonstrated efficacy and a manageable safety profile support continued evaluation of talazoparib in mCRPC. CLINICALTRIALS.GOV IDENTIFIER: NCT03148795.

Evaluation of pharmacokinetics and safety of talazoparib in patients with advanced cancer and varying degrees of hepatic impairment.

AIM: This phase I study investigated talazoparib pharmacokinetics (PK) and safety in patients with advanced solid tumours and varying degrees of hepatic function. METHODS: Patients with advanced solid tumours and normal hepatic function or varying degrees of hepatic impairment (mild, moderate or severe, based on National Cancer Institute Organ Dysfunction Working Group classification) received talazoparib 0.5 mg once daily for 22 calendar days. Plasma and urine samples after single and multiple doses were collected and analysed for talazoparib using validated assays. Plasma PK data from all patients were analysed using the population PK method. Plasma and urine PK parameters in PK-evaluable patients were calculated using noncompartmental analysis (NCA). Safety was monitored in all enrolled patients. RESULTS: Thirty-eight patients were enrolled; 37 had ≥1 PK concentration, among which 17 were evaluable for NCA. Population PK analysis (n = 37) indicated no significant impact of hepatic function on apparent clearance (CL/F) of talazoparib. Baseline creatinine clearance was the only significant covariate on CL/F (α = 0.05). NCA of data (n = 17) showed no clear trend for increase in exposure on day 22 with worsening hepatic function. Talazoparib protein binding was comparable in patients with varying hepatic function. Talazoparib was generally well tolerated, and the safety profile observed in this study was consistent with the known safety profile of the drug. CONCLUSIONS: Hepatic impairment (mild, moderate or severe) has no impact on the PK of talazoparib. No dose modification is recommended for patients with advanced solid tumours and various degrees of hepatic impairment, and this labelling language has been approved by the US Food and Drug Administration and the European Medicines Agency.

Talazoparib plus enzalutamide in metastatic castration-resistant prostate cancer: TALAPRO-2 phase III study design.

PARP inhibitors in combination with androgen receptor-targeted therapy have demonstrated potential in the treatment of metastatic castration-resistant prostate cancer (mCRPC). Here, we describe the design and rationale of the multinational, phase III, two-part TALAPRO-2 study comparing talazoparib plus enzalutamide versus placebo plus enzalutamide as a first-line treatment for patients with mCRPC with or without DNA damage response (DDR) alterations. This study has two co-primary end points: radiographic progression-free survival (rPFS) by blinded independent clinical review in all-comers (cohort 1) and in patients with DDR alterations (cohort 2). TALAPRO-2 will demonstrate whether talazoparib plus enzalutamide can significantly improve the efficacy of enzalutamide in terms of rPFS in both molecularly unselected and DDR-deficient patients with mCRPC (NCT03395197). Clinical Trial Registration: NCT03395197 (ClinicalTrials.gov).

Plain language summary of the design of the TALAPRO-2 study comparing talazoparib and enzalutamide versus enzalutamide and placebo in men with metastatic castration-resistant prostate cancer.

WHAT IS THIS SUMMARY ABOUT?: This summary describes the design of an ongoing research study (also known as a clinical trial) called TALAPRO-2. The TALAPRO-2 trial is testing the combination of two medicines called talazoparib and enzalutamide as a first treatment in adult men with metastatic castration-resistant prostate cancer. The study began in December 2017 and has enrolled 1037 adult men with metastatic castration-resistant prostate cancer from 26 countries. WHAT IS METASTATIC CASTRATION-RESISTANT PROSTATE CANCER?: Metastatic castration-resistant prostate cancer is a type of cancer that has advanced beyond the prostate and continues to grow even when testosterone levels in the blood are suppressed. WHICH MEDICINES ARE BEING TESTED?: The combination of talazoparib plus enzalutamide will be compared with enzalutamide plus placebo. Enzalutamide is approved to treat men with prostate cancer. Talazoparib is not approved to treat men with prostate cancer. A placebo does not contain any active ingredients and is also known as a sugar pill. WHAT ARE THE AIMS OF THE TALAPRO-2 TRIAL?: The TALAPRO-2 trial will find out if combining talazoparib with enzalutamide increases the length of time the men in the study live without their cancer getting worse compared with enzalutamide plus placebo. The study will also measure how long men in the study live and any side effects the men have while they are taking the study medicines. Researchers are also testing the DNA from the tumor cells of all men in the study to find out if they have faulty DNA repair genes. Clinical Trial Registration: NCT0339519 (ClinicalTrials.gov).

Comparative Analyses of Poly(ADP-Ribose) Polymerase Inhibitors.

Poly(ADP-ribose) polymerase inhibitors (PARPi) are approved as monotherapies in BRCA1/2-mutated (mBRCA1/2) metastatic breast and ovarian cancers, and in advanced pancreatic and metastatic castration-resistant prostate cancers. Differential safety profiles across PARPi necessitate improved mechanistic understanding of inhibitor differences, especially with expansion of PARPi indications and drug combinations. Here, we report in vitro evaluations of PARPi (-/+ PARP trapper temozolomide, TMZ) with reference to total clinical mean concentration average or maximum (tCavg, tCmax), to elucidate contributions of primary pharmacology and structural differences to clinical efficacy and safety. In biochemical assays, rucaparib and niraparib demonstrated off-target secondary pharmacology activities, and in selectivity assays, talazoparib, olaparib, and rucaparib inhibited a broader panel of PARP enzymes. In donor-derived human bone marrow mononuclear cells, only olaparib both increased early apoptosis and decreased the cell viability half inhibitory concentration (IC50) at ≤ tCavg, whereas other PARPi only did so in the presence of TMZ. In cancer cell lines with DNA damage repair mutations, all PARPi decreased cell viability in H1048 but not TK6 cells, and only talazoparib decreased cell growth in DU145 cells at ≤ tCavg concentrations. When combined with low dose TMZ, only talazoparib left-shifted the functional consequences of PARP trapping (S-phase arrest, apoptosis, S-phase double-stranded breaks) and reduced cell viability/growth in TK6 and DU145 cell lines at ≤ tCavg, whereas the other inhibitors required high-dose TMZ. Our study suggests structural differences across PARPi may contribute to differences in PARP selectivity and off-target activities, which along with distinct pharmacokinetic properties, may influence inhibitor-specific toxicities in patients.

Talazoparib Does Not Interact with ABCB1 Transporter or Cytochrome P450s, but Modulates Multidrug Resistance Mediated by ABCC1 and ABCG2: An in Vitro and Ex Vivo Study.

Talazoparib (Talzenna) is a novel poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitor that is clinically used for the therapy of breast cancer. Furthermore, the drug has shown antitumor activity against different cancer types, including non-small cell lung cancer (NSCLC). In this work, we investigated the possible inhibitory interactions of talazoparib toward selected ATP-binding cassette (ABC) drug efflux transporters and cytochrome P450 biotransformation enzymes (CYPs) and evaluated its position in multidrug resistance (MDR). In accumulation studies, talazoparib interacted with the ABCC1 and ABCG2 transporters, but there were no significant effects on ABCB1. Furthermore, incubation assays revealed a negligible capacity of the tested drug to inhibit clinically relevant CYPs. In in vitro drug combination experiments, talazoparib synergistically reversed daunorubicin and mitoxantrone resistance in cells with ABCC1 and ABCG2 expression, respectively. Importantly, the position of an effective MDR modulator was further confirmed in drug combinations performed in ex vivo NSCLC patients-derived explants, whereas the possible victim role was refuted in comparative proliferation experiments. In addition, talazoparib had no significant effects on the mRNA-level expressions of MDR-related ABC transporters in the MCF-7 cellular model. In summary, our study presents a comprehensive overview on the pharmacokinetic drug-drug interactions (DDI) profile of talazoparib. Moreover, we introduced talazoparib as an efficient MDR antagonist.

Safety, pharmacokinetics, and preliminary efficacy of the PARP inhibitor talazoparib in Japanese patients with advanced solid tumors: phase 1 study.

BACKGROUND: Talazoparib is a poly(ADP-ribose) polymerase enzyme inhibitor. This open-label, non-randomized, phase 1 study of talazoparib investigated the safety, pharmacokinetics, and preliminary antitumor activity in Japanese patients with locally advanced or metastatic solid tumors, regardless of mutations in DNA damage repair-related genes, who are resistant to/ineligible for standard therapies. METHODS: Patients received talazoparib dosed orally at 0.75 or 1 mg once daily using a modified 3 + 3 dose-escalation scheme. Primary endpoint was dose-limiting toxicities during the first cycle of talazoparib. RESULTS: Nine patients (median age 62.0 years) were included: 3 and 6 patients at the 0.75 and 1.0 mg once-daily dose levels, respectively. No dose-limiting toxicities were reported. The most commonly reported treatment-emergent adverse events (≥2 patients) were anemia, stomatitis, maculopapular rash, platelet count decreased, neutrophil count decreased, and alanine aminotransferase increased. Three patients had grade ≥ 3 treatment-emergent adverse events (anemia, brain metastases [1 patient each], and neutrophil and white blood cell count decreased [same patient]). Two patients temporarily discontinued treatment due to a treatment-emergent adverse event, and 1 patient required a dose reduction for neutrophil count decreased (all at 1 mg once daily). Talazoparib exposure (Cmax and AUC) after single and multiple dosing was slightly higher proportionally with talazoparib 1 mg than talazoparib 0.75 mg. The overall disease control rate was 44.4%, including 2 patients with stable disease. The recommended phase 2 dose of talazoparib was established as 1 mg once daily. CONCLUSIONS: Single-agent talazoparib was well tolerated and had preliminary antitumor activity in Japanese patients with advanced solid tumors. ClinicalTrials.gov identifier: NCT03343054 (November 17, 2017).

Proteomic analysis of talazoparib resistance in triple-negative breast cancer cells.

Talazoparib (TAL) has been effectively used for the treatment of gBRCA1/2-mutated HER2-negative metastatic breast cancer. However, acquired resistance to TAL remains a major challenge that impedes the clinical success of TAL treatment. Therefore, elucidation of proteins and pathways that contribute to or are affected by the TAL resistance is urgently needed to improve the treatment response and provide novel treatment strategies for advanced metastatic breast cancers. Herein, we aimed to investigate the altered protein signatures in TAL-resistant triple-negative breast cancer (TNBC) cells by comparing with the TNBC parental cell line via proteomic analysis. After validation of TAL-resistance by WST-1 and Annexin V analysis, two-dimensional gel electrophoresis (2DE)-based proteomic analysis coupled to matrix-assisted laser desorption/ionization (MALDI)-time of flight (TOF) mass spectrometry was performed to identify differentially regulated proteins. The findings revealed the identities of 10 differentially regulated proteins in TAL-resistant TNBC cells whose bioinformatic analysis predicted changes in EGF/FGF signaling pathways as well as in the AMPK signaling pathway. In addition, phosphorylation/dephosphorylation dynamics were predicted to be altered in TAL-resistant cells. The proteins identified in this study might be the targets to overcome TAL resistance for the treatment of TNBC.

PARP Inhibitors Display Differential Efficacy in Models of BRCA Mutant High-Grade Serous Ovarian Cancer.

Several poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors are now in clinical use for tumours with defects in BReast CAncer genes BRCA1 or BRCA2 that result in deficient homologous recombination repair (HRR). Use of olaparib, niraparib or rucaparib for the treatment of high-grade serous ovarian cancer, including in the maintenance setting, has extended both progression free and overall survival for women with this malignancy. While different PARP inhibitors (PARPis) are mechanistically similar, differences are apparent in their chemical structures, toxicity profiles, PARP trapping abilities and polypharmacological landscapes. We have treated ovarian cancer cell line models of known BRCA status, including the paired cell lines PEO1 and PEO4, and UWB1.289 and UWB1.289+BRCA1, with five PARPis (olaparib, niraparib, rucaparib, talazoparib and veliparib) and observed differences between PARPis in both cell viability and cell survival. A cell line model of acquired resistance to veliparib showed increased resistance to the other four PARPis tested, suggesting that acquired resistance to one PARPi may not be able to be rescued by another. Lastly, as a proof of principle, HRR proficient ovarian cancer cells were sensitised to PARPis by depletion of BRCA1. In the future, guidelines will need to emerge to assist clinicians in matching specific PARPis to specific patients and tumours.

A novel lncRNA PLK4 up-regulated by talazoparib represses hepatocellular carcinoma progression by promoting YAP-mediated cell senescence.

A growing number of studies recognize that long non-coding RNAs (lncRNAs) are essential to mediate multiple tumorigenic processes, including hepatic tumorigenesis. However, the pathological mechanism of lncRNA-regulated liver cancer cell growth remains poorly understood. In this study, we identified a novel function lncRNA, named polo-like kinase 4 associated lncRNA (lncRNA PLK4, GenBank Accession No. RP11-50D9.3), whose expression was dramatically down-regulated in hepatocellular carcinoma (HCC) tissues and cells. Interestingly, talazoparib, a novel and highly potent poly-ADP-ribose polymerase 1/2 (PARP1/2) inhibitor, could increase lncRNA PLK4 expression in HepG2 cells. Importantly, we showed that talazoparib-induced lncRNA PLK4 could function as a tumour suppressor gene by Yes-associated protein (YAP) inactivation and induction of cellular senescence to inhibit liver cancer cell viability and growth. In summary, our findings reveal the molecular mechanism of talazoparib-induced anti-tumor effect, and suggest a potential clinical use of talazoparib-targeted lncRNA PLK4/YAP-dependent cellular senescence for the treatment of HCC.