bmn-673 and Neoplasms

DDR (DNA damage response) defects in cells drive tumor formation by promoting DNA mutations, which also provides cancer-specific vulnerabilities that can be targeted by synthetic lethality-based therapies. Until now, PARP inhibitors like olaparib are the first successful case of utilizing synthetic lethality-based therapy to treat cancers with DNA-repairing deficiency (e.g. BRCA1 or BRCA2 mutation), which has fueled the search for more targetable components in the DDR signaling pathway by exploiting synthetic lethality, including but not limited to DNA-PK, ATR, ATM, CHK1, and WEE1. After years of efforts, numerous DDR kinase inhibitors have been discovered. Some of them are being investigated in clinical trials and have shown promising results for cancer therapy. In this review, we summarize the latest advancement in the development of DDR kinase inhibitors including those in preclinical stages and clinical trials, the crystal structures of DDR enzymes, and binding modes of inhibitors with target proteins. The biological functions involving different genes and proteins (ATR, DNA-PK, ATM, PARP, CHK1, and WEE1) are also elucidated.

Topics: DNA Damage; DNA Repair; Humans; Mutation; Neoplasms; Poly(ADP-ribose) Polymerase Inhibitors; Signal Transduction

We aimed to evaluate comparative safety and tolerability of the approved PARP inhibitors in people with cancer.. Eligible studies included randomized controlled trials comparing an approved PARP inhibitor (fluzoparib, olaparib, rucaparib, niraparib, or talazoparib) with placebo or chemotherapy in cancer patients. Outcomes of interest included: serious adverse event (SAE), discontinuation due to adverse event (AE), interruption of treatment due to AE, dose reduction due to AE, and specific grade 1-5 AEs.. Ten trials including 3763 participants and six treatments (olaparib, rucaparib, niraparib, talazoparib, placebo, and protocol-specified single agent chemotherapy) were identified. SAE and discontinuation of treatment did not differ significantly among the four approved PARP inhibitors. Regarding interruption of treatment and dose reduction due to AE, statistically significant differences and statistically non-significant trend were observed. Talazoparib is associated with a higher risk of interruption of treatment and dose reduction (excluding rucaparib) due to AE as compared with the other drugs. Niraparib showed a trend of lower risk of AE related dose reduction as compared with the other drugs. Furthermore, there were significant differences in specific grade 1-5 AE among the four drugs.. The safety profile of the four approved PARP inhibitors is comparable in terms of SAE and AE-related discontinuation of treatment. Statistically significant differences in the AEs spectrum and AEs related dose interruption and dose reduction demonstrated the prompt identification of AE and dose personalization seem mandatory to obtain maximal benefit from PARP inhibitors.

Topics: Humans; Indazoles; Indoles; Neoplasms; Network Meta-Analysis; Phthalazines; Piperazines; Piperidines; Poly(ADP-ribose) Polymerase Inhibitors; Randomized Controlled Trials as Topic

Poly(ADP-ribose) polymerases(PARP) synthesize the ADP-ribose polymers onto proteins and play a role in DNA repair. PARP inhibitors block the repair of single-strand breaks, which in turn gives rise to double-strand breaks during DNA replication. Thus, PARP inhibitors elicit synthetic lethality in cancer with BRCA1/2 loss-of-function mutations that hamper homologous recombination repair of double-strand breaks. Olaparib, the first-in-class PARP inhibitor, was approved for treatment of BRCA-mutated ovarian cancer in Europe and the United States in 2014. Other PARP inhibitors under clinical trials include rucaparib, niraparib, veliparib, and the "PARP-trapping" BMN-673. BRCA1/2 sequencing is an FDA-approved companion diagnostics, which predicts the cancer vulnerability to PARP inhibition. Together, synthetic lethal PARP inhibition is a novel promising strategy for cancer intervention even in cases without prominent driver oncogenes.

Topics: Antineoplastic Agents; Benzimidazoles; BRCA1 Protein; BRCA2 Protein; DNA Breaks, Double-Stranded; DNA Replication; DNA, Single-Stranded; Enzyme Inhibitors; Humans; Indazoles; Indoles; Molecular Targeted Therapy; Mutation; Neoplasms; Phthalazines; Piperazines; Piperidines; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Recombinational DNA Repair

On the basis of preclinical data, we hypothesized that low doses of chemotherapy (10% of therapeutic doses) with full dose of a PARP inhibitor could have improved efficacy and tolerability.. In this phase I dose-escalation study, patients with BRCA-normal advanced malignancies were assigned to either talazoparib/temozolomide or talazoparib/irinotecan. Talazoparib was dose-escalated from 500 mcg to 1 mg daily before dose escalation of temozolomide/irinotecan. The starting dose of temozolomide was 25 mg/m2/day orally on days 1 to 5 and irinotecan was 25 mg/m2/day intravenously on days 1 and 15. The primary objectives of this trial were safety and tolerability, dose-limiting toxicities (DLT), and maximum tolerated dose (MTD).. Of 40 patients enrolled, 18 (mean: 7 prior therapies) were enrolled in talazoparib + temozolomide and 22 in talazoparib + irinotecan. DLTs were hematologic in both arms, but all hematologic adverse events resolved with either treatment interruption and/or dose reductions of talazoparib. The MTDs were talazoparib 1 mg + temozolomide 37.5 mg/m2 and talazoparib 1 mg + irinotecan 37.5 mg/m2. There were four partial responses in the talazoparib + temozolomide arm and five in the talazoparib + irinotecan arm for a response rate of 23% (9/40). The pharmacokinetic profiles of talazoparib + temozolomide/irinotecan were similar to that of talazoparib monotherapy. Responses were seen independent of homologous recombination (HR) status and HR deficiency score.. These results show that talazoparib with low-dose temozolomide or irinotecan is reasonably well tolerated and demonstrates clinical activity in a wide range of cancers. Randomized trials of talazoparib with or without low-dose chemotherapy are ongoing in small cell lung cancer and ovarian cancer.

Topics: Antineoplastic Combined Chemotherapy Protocols; Female; Humans; Irinotecan; Neoplasms; Temozolomide

Topics: Administration, Oral; Adult; Aged; Antineoplastic Agents; Drug-Related Side Effects and Adverse Reactions; East Asian People; Humans; Male; Middle Aged; Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors

This phase I study investigated talazoparib pharmacokinetics (PK) and safety in patients with advanced solid tumours and varying degrees of hepatic function.. 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.. 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.. 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.

Topics: Humans; Liver Diseases; Neoplasms; Phthalazines

Inhibitors of poly(ADP-ribose) polymerase (PARP) proteins potentiate antitumor activity of platinum chemotherapy. This study sought to determine the safety and tolerability of PARP inhibitor talazoparib with carboplatin and paclitaxel.. Forty-three patients were treated. The MTD for both schedules was talazoparib 250mcg daily. The main toxicity was myelosuppression including grade 3/4 hematologic treatment-related adverse events (TRAEs). Dose modification occurred in 87% and 100% of patients for schedules A and B, respectively. Discontinuation due to TRAEs was 13% in schedule A and 10% in B. Ten out of 22 evaluable patients in schedule A and 5/16 patients in schedule B had a complete or partial response. Twelve out of 43 patients received ≥6 cycles of talazoparib after induction, with a 13-month median duration of maintenance.. We have established the recommended phase II dose of Talazoparib at 250mcg on a 3- or 7-day schedule with carboplatin AUC6 and paclitaxel 80 mg/m

Topics: Antineoplastic Combined Chemotherapy Protocols; Carboplatin; Humans; Neoplasms; Paclitaxel; Poly(ADP-ribose) Polymerases

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.. 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.. 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 (C. 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).

Topics: Adult; Aged; Antineoplastic Agents; Asian People; Dose-Response Relationship, Drug; Humans; Japan; Maximum Tolerated Dose; Middle Aged; Neoplasm Grading; Neoplasm Metastasis; Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors

Talazoparib combined with irinotecan and temozolomide demonstrated efficacy in a murine Ewing sarcoma model. Based on these data, we conducted a phase I trial of talazoparib and irinotecan with/without temozolomide in paediatric patients with recurrent/refractory solid malignancies.. Cohorts of 3-6 patients with recurrent/refractory solid malignancies received escalating doses of oral talazoparib and intravenous irinotecan (arm A) and oral talazoparib, oral temozolomide and intravenous irinotecan (arm B) in a 3 + 3 design. Talazoparib was administered on days 1-6, and intravenous irinotecan and oral temozolomide were administered on days 2-6, of a 21-day course. Serum for talazoparib and irinotecan pharmacokinetics was obtained during course 1. UGT1A1 polymorphism and Schlafen family member 11 (SLFN11) immunohistochemical staining were performed.. Forty-one patients (20 males; median age, 14.6 years; 24 with recurrent disease) were evaluable for dose escalation. Twenty-nine and 12 patients were treated on arm A and arm B, respectively, for a total of 208 courses. The most common diagnosis was Ewing sarcoma (53%). The most common ≥grade III haematologic toxicities in arms A and B included neutropenia (78% and 31%, respectively) and thrombocytopenia (42% and 31%, respectively). In arms A and B, febrile neutropenia (24% and 14%, respectively) and diarrhoea (21% and 7%, respectively) were the most common ≥grade III non-hematologic toxicities. Six patients (Ewing sarcoma [5 patients] and synovial sarcoma [1 patient]) had a response (1 with a complete response, 5 with a partial response). The objective response rates were 10.3% (arm A) and 25% (arm B). Pharmacokinetic testing demonstrated no evidence of drug-drug interaction between talazoparib and irinotecan. UGT1A1 was not related to response. SLFN11 positivity was associated with best response to therapy.. The combination of talazoparib and irinotecan with/without temozolomide is feasible and active in Ewing sarcoma, and further investigation is warranted.

Topics: Adolescent; Adult; Antineoplastic Combined Chemotherapy Protocols; Child; Child, Preschool; Female; Humans; Irinotecan; Male; Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Temozolomide; Young Adult

This paper describes the pharmacokinetics (PK), mass balance, metabolic profiling, and safety of talazoparib after a single oral dose of

Topics: Administration, Oral; Adult; Aged; Aged, 80 and over; Carbon Radioisotopes; Feces; Female; Half-Life; Humans; Male; Middle Aged; Neoplasms; Phthalazines

In this issue of Cell Chemical Biology, Palve et al. (2022) identified PARP16 as a non-canonical therapeutic target of the PARP1 inhibitor talazoparib, which synergizes with the WEE1 inhibitor adavosertib to enhance its efficacy. The dual targeting of PARP1 and PARP16 may explain the greater efficacy of talazoparib in some cancers.

Topics: Antineoplastic Agents; Humans; Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors

The synthetic lethal association between BRCA deficiency and poly (ADP-ribose) polymerase (PARP) inhibition supports PARP inhibitor (PARPi) clinical efficacy in BRCA-mutated tumors. PARPis also demonstrate activity in non-BRCA mutated tumors presumably through induction of PARP1-DNA trapping. Despite pronounced clinical response, therapeutic resistance to PARPis inevitably develops. An abundance of knowledge has been built around resistance mechanisms in BRCA-mutated tumors, however, parallel understanding in non-BRCA mutated settings remains insufficient. In this study, we find a strong correlation between the epithelial-mesenchymal transition (EMT) signature and resistance to a clinical PARPi, Talazoparib, in non-BRCA mutated tumor cells. Genetic profiling demonstrates that SNAI2, a master EMT transcription factor, is transcriptionally induced by Talazoparib treatment or PARP1 depletion and this induction is partially responsible for the emerging resistance. Mechanistically, we find that the PARP1 protein directly binds to SNAI2 gene promoter and suppresses its transcription. Talazoparib treatment or PARP1 depletion lifts PARP1-mediated suppression and increases chromatin accessibility around SNAI2 promoters, thus driving SNAI2 transcription and drug resistance. We also find that depletion of the chromatin remodeler CHD1L suppresses SNAI2 expression and reverts acquired resistance to Talazoparib. The PARP1/CHD1L/SNAI2 transcription axis might be therapeutically targeted to re-sensitize Talazoparib in non-BRCA mutated tumors.

Topics: Antineoplastic Agents; Chromatin; DNA Helicases; DNA-Binding Proteins; Humans; Neoplasms; Phthalazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Snail Family Transcription Factors

G-quadruplexes (G4s) are DNA or RNA structures formed by guanine-rich repeating sequences. Recently, G4s have become a highly attractive therapeutic target for BRCA-deficient cancers. Here, we show that a substituted quinolone amide compound, MTR-106, stabilizes DNA G-quadruplexes in vitro. MTR-106 displayed significant antiproliferative activity in homologous recombination repair (HR)-deficient and PARP inhibitor (PARPi)-resistant cancer cells. Moreover, MTR-106 increased DNA damage and promoted cell cycle arrest and apoptosis to inhibit cell growth. Importantly, its oral and i.v. administration significantly impaired tumor growth in BRCA-deficient xenograft mouse models. However, MTR-106 showed modest activity against talazoparib-resistant xenograft models. In rats, the drug rapidly distributes to tissues within 5 min, and its average concentrations were 12-fold higher in the tissues than in the plasma. Overall, we identified MTR-106 as a novel G-quadruplex stabilizer with high tissue distribution, and it may serve as a potential anticancer agent.

Topics: Animals; Antineoplastic Agents; BRCA1 Protein; BRCA2 Protein; Cell Line, Tumor; Cell Survival; DNA Repair; Drug Resistance, Neoplasm; G-Quadruplexes; Humans; Male; Mice; Mice, Nude; Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Rats; Rats, Sprague-Dawley; Xenograft Model Antitumor Assays

The exploitation of GLU988 and LYS903 residues in PARP1 as targets to design isoquinolinone (I & II) and naphthyridinone (III) analogues is described. Compounds of structure I have good biochemical and cellular potency but suffered from inferior PK. Constraining the linear propylene linker of structure I into a cyclopentene ring (II) offered improved PK parameters, while maintaining potency for PARP1. Finally, to avoid potential issues that may arise from the presence of an anilinic moiety, the nitrogen substituent on the isoquinolinone ring was incorporated as part of the bicyclic ring. This afforded a naphthyridinone scaffold, as shown in structure III. Further optimization of naphthyridinone series led to identification of a novel and highly potent PARP1 inhibitor 34, which was further characterized as preclinical candidate molecule. Compound 34 is orally bioavailable and displayed favorable pharmacokinetic (PK) properties. Compound 34 demonstrated remarkable antitumor efficacy both as a single-agent as well as in combination with chemotherapeutic agents in the BRCA1 mutant MDA-MB-436 breast cancer xenograft model. Additionally, compound 34 also potentiated the effect of agents such as temozolomide in breast cancer, pancreatic cancer and Ewing's sarcoma models.

Topics: Animals; Antineoplastic Agents; Binding Sites; Cell Line, Tumor; Cell Survival; Half-Life; Humans; Mice; Mice, Inbred BALB C; Molecular Docking Simulation; Naphthyridines; Neoplasms; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Quinolones; Structure-Activity Relationship; Transplantation, Heterologous

Poly (ADP-ribose) polymerase (PARP) plays a significant role in DNA repair responses; therefore, this enzyme is targeted by PARP inhibitors in cancer therapy. Here we have developed a number of fused tetra- or pentacyclic dihydrodiazepinoindolone derivatives with excellent PARP enzymatic and cellular PARylation inhibition activities. These efforts led to the identification of pamiparib (BGB-290,

Topics: Animals; Binding Sites; Carbazoles; Cell Proliferation; Dogs; Female; Fluorenes; Half-Life; Humans; Indoles; Isoenzymes; Mice; Microsomes; Molecular Docking Simulation; Neoplasms; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Rats; Structure-Activity Relationship; Xenograft Model Antitumor Assays

Poly(ADP-ribose) polymerase (PARP) inhibitors have been developed to treat cancers associated with somatic BRCA mutations and germline genetic aberrations involved in the DNA damage response. The efficacy, tolerability, and pharmacokinetic/pharmacodynamic (PK/PD) profile of talazoparib, a potent small-molecule PARP inhibitor, was established in 4 clinical studies in cancer patients (2 phase 1 studies PRP-001 and PRP-002, the phase 2 ABRAZO trial, and the phase 3 EMBRACA trial). The current study aimed to describe the population PK of talazoparib and identify covariates that affect talazoparib PK in patients with advanced cancers using pooled data from these 4 studies. Talazoparib PK was well characterized by a 2-compartment model with first-order absorption and absorption lag time. Based on covariate analysis, no dose adjustment for talazoparib is required based on a patient's age, sex, baseline body weight, Asian race, the presence of mild renal or hepatic impairment, or use of acid-reducing agents. A reduced 0.75-mg daily dose is recommended for patients taking a potent P-glycoprotein inhibitor and those with moderate renal impairment. Insufficient data were available to establish dosing recommendations for patients with severe renal and moderate or severe hepatic impairment. The PK of a single 1-mg talazoparib capsule is comparable with 4 0.25-mg capsules. Talazoparib can be taken with or without food. These data provide support for dosing recommendations and labeling information for talazoparib.

Topics: Administration, Oral; Adolescent; Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Biological Availability; Clinical Trials, Phase I as Topic; Clinical Trials, Phase II as Topic; Clinical Trials, Phase III as Topic; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Humans; Male; Middle Aged; Multicenter Studies as Topic; Neoplasm Staging; Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Young Adult

In vitro data show that talazoparib is a substrate for P-glycoprotein (P-gp) and breast cancer resistance protein transporters. This open-label, 2-arm, drug-drug interaction Phase 1 study in patients with advanced solid tumours assessed the effect of a P-gp inhibitor (itraconazole) and a P-gp inducer (rifampicin) on the pharmacokinetics of a single dose of talazoparib. The safety and tolerability of a single dose of talazoparib with and without itraconazole or rifampicin were also assessed.. Thirty-six patients were enrolled (Arm A [itraconazole], n = 19; Arm B [rifampicin], n = 17). Patients in both arms received 2 single oral doses of talazoparib (0.5 mg, Arm A; 1 mg, Arm B) alone and with multiple daily oral doses of itraconazole (Arm A) or rifampicin (Arm B).. Coadministration of itraconazole and talazoparib increased talazoparib area under the plasma concentration-time profile from time 0 extrapolated to infinity by ~56% and maximum observed plasma concentration by ~40% relative to talazoparib alone. Coadministration of rifampicin and talazoparib increased talazoparib maximum observed plasma concentration by approximately 37% (geometric mean ratio 136.6% [90% confidence interval 103.2-180.9]); area under the curve was not affected relative to talazoparib alone (geometric mean ratio 102.0% [90% confidence interval 94.0-110.7]). Talazoparib had an overall safety profile consistent with that observed in prior studies in which talazoparib was administered as a single dose.. Coadministration of itraconazole increased talazoparib plasma exposure compared to talazoparib alone. A reduced talazoparib dose is recommended if coadministration of potent P-gp inhibitors cannot be avoided. Similar exposure was observed when talazoparib was administered alone and with rifampicin suggesting that the effect of rifampicin on talazoparib exposure is limited.

Topics: Area Under Curve; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; Drug Interactions; Humans; Neoplasm Proteins; Neoplasms; Phthalazines

Polypharmacology plays an important role in defining response and adverse effects of drugs. For some mechanisms, experimentally mapping polypharmacology is commonplace, although this is typically done within the same protein class. Four PARP inhibitors have been approved by the FDA as cancer therapeutics, yet a precise mechanistic rationale to guide clinicians on which to choose for a particular patient is lacking. The four drugs have largely similar PARP family inhibition profiles, but several differences at the molecular and clinical level have been reported that remain poorly understood. Here, we report the first comprehensive characterization of the off-target kinase landscape of four FDA-approved PARP drugs. We demonstrate that all four PARP inhibitors have a unique polypharmacological profile across the kinome. Niraparib and rucaparib inhibit DYRK1s, CDK16 and PIM3 at clinically achievable, submicromolar concentrations. These kinases represent the most potently inhibited off-targets of PARP inhibitors identified to date and should be investigated further to clarify their potential implications for efficacy and safety in the clinic. Moreover, broad kinome profiling is recommended for the development of PARP inhibitors as PARP-kinase polypharmacology could potentially be exploited to modulate efficacy and side-effect profiles.

Topics: Antineoplastic Agents; Binding Sites; Cyclin-Dependent Kinases; Dyrk Kinases; HEK293 Cells; Humans; Indazoles; Indoles; Isoenzymes; Molecular Docking Simulation; Neoplasms; Phthalazines; Piperazines; Piperidines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Polypharmacology; Protein Binding; Protein Interaction Domains and Motifs; Protein Serine-Threonine Kinases; Protein Structure, Secondary; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Substrate Specificity

PARP1 inhibitors (PARPis) are used clinically during cancer therapy and are thought to exert their cytotoxicity through PARP1 polymerase inhibition and PARP1-DNA trapping. Here, we showed no significant correlation between PARP1-DNA trapping and cytotoxicity induced by PARPis. We complemented PARP1-knockout sublines with wild-type PARP1 and 11 mutants with different point mutations that affect the polymerase activity. When examining the PARPi talazoparib, the induced cytotoxicity was highly significantly correlated with cellular PARP1 polymerase activity, but not with its PARP1-DNA trapping or polymerase inhibition. Similarly, talazoparib's PARP1-DNA trapping revealed significant correlation with the polymerase activity rather than its inhibition. Differently, however, when evaluating purified wild-type and mutated PARP1, we identified an almost linear relationship between PARPis' inhibiting PARP1 dissociation from DNA and their cytotoxicity in 17 cancer cell lines. In contrast, no significant correlation existed between PARP1 polymerase inhibition in the histone-based systems and the cytotoxicity. After careful comparisons on different methods and detection targets, we conclude that the PARPi-mediated increase in PARP1-DNA binding by inhibiting autoPARylation of PARP1 on DNA rather than in PARP1-DNA trapping is correlated with PARPi's cytotoxicity. Accordingly, we established a new PARPi screening model that more closely predicts cytotoxicity.

Topics: Cell Line, Tumor; DNA, Neoplasm; Drug Screening Assays, Antitumor; Gene Knockdown Techniques; Humans; NAD; Neoplasms; Phthalazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors

The aims of this study were (i) to evaluate the effect of talazoparib (1 mg once daily) on cardiac repolarization in patients with advanced solid tumors by assessing corrected QT interval (QTc) and (ii) to examine the relationship between plasma talazoparib concentration and QTc. In this open-label phase 1 study, patients had continuous 12-lead ECG recordings at baseline followed by time-matched continuous ECG recordings and collection of talazoparib plasma pharmacokinetic samples predose and at 1, 2, 4, and 6 h postdose on treatment days 1 and 22 and before talazoparib administration on day 2. ECG recordings were submitted for independent central review where triplicate 10-s ECGs, extracted up to 15 min before pharmacokinetic samples, were assessed for RR, PR, QRS, and QT intervals and ECG morphology. QT interval was corrected for heart rate using Fridericia's (QTcF) and Bazett's (QTcB) formulae. Linear mixed-effects modeling was used to examine the relationship between QTc and RR interval change from baseline and plasma talazoparib concentration. Thirty-seven patients received talazoparib. Mean change in QTcF from time-matched baseline ranged from -3.5 to 6.9 ms, with the greatest change 1 h postdose on day 22. No clinically relevant changes in PR, QRS, QTcB, QTcF, or RR intervals, heart rate, or ECG morphology were observed. No concentration-dependent effect on heart rate or QTc was observed. No deaths, permanent treatment discontinuations due to adverse events were reported. Talazoparib (1 mg once daily) had no clinically relevant effects on cardiac repolarization.

Topics: Electrocardiography; Female; Follow-Up Studies; Heart Rate; Humans; Male; Middle Aged; Neoplasms; Phthalazines; Prognosis

A synthetic lethality-based strategy has been developed to identify therapeutic targets in cancer harboring tumor-suppressor gene mutations, as exemplified by the effectiveness of poly ADP-ribose polymerase (PARP) inhibitors in BRCA1/2-mutated tumors. However, many synthetic lethal interactors are less reliable due to the fact that such genes usually do not perform fundamental or indispensable functions in the cell. Here, we developed an approach to identifying the "essential lethality" arising from these mutated/deleted essential genes, which are largely tolerated in cancer cells due to genetic redundancy. We uncovered the cohesion subunit SA1 as a putative synthetic-essential target in cancers carrying inactivating mutations of its paralog, SA2. In SA2-deficient Ewing sarcoma and bladder cancer, further depletion of SA1 profoundly and specifically suppressed cancer cell proliferation, survival, and tumorigenic potential. Mechanistically, inhibition of SA1 in the SA2-mutated cells led to premature chromatid separation, dramatic extension of mitotic duration, and consequently, lethal failure of cell division. More importantly, depletion of SA1 rendered those SA2-mutated cells more susceptible to DNA damage, especially double-strand breaks (DSBs), due to reduced functionality of DNA repair. Furthermore, inhibition of SA1 sensitized the SA2-deficient cancer cells to PARP inhibitors in vitro and in vivo, providing a potential therapeutic strategy for patients with SA2-deficient tumors.

Topics: Animals; Antigens, Nuclear; Cell Cycle Proteins; Cell Line, Tumor; Chromosomal Proteins, Non-Histone; Cohesins; DNA Breaks, Double-Stranded; Female; Gene Knockdown Techniques; Genes, Essential; Humans; Mice; Mice, Nude; Mutation; Neoplasms; Nuclear Proteins; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Protein Subunits; Sarcoma, Ewing; Urinary Bladder Neoplasms; Xenograft Model Antitumor Assays

Although PARP inhibitors (PARPi) target homologous recombination defective tumours, drug resistance frequently emerges, often via poorly understood mechanisms. Here, using genome-wide and high-density CRISPR-Cas9 "tag-mutate-enrich" mutagenesis screens, we identify close to full-length mutant forms of PARP1 that cause in vitro and in vivo PARPi resistance. Mutations both within and outside of the PARP1 DNA-binding zinc-finger domains cause PARPi resistance and alter PARP1 trapping, as does a PARP1 mutation found in a clinical case of PARPi resistance. This reinforces the importance of trapped PARP1 as a cytotoxic DNA lesion and suggests that PARP1 intramolecular interactions might influence PARPi-mediated cytotoxicity. PARP1 mutations are also tolerated in cells with a pathogenic BRCA1 mutation where they result in distinct sensitivities to chemotherapeutic drugs compared to other mechanisms of PARPi resistance (BRCA1 reversion, 53BP1, REV7 (MAD2L2) mutation), suggesting that the underlying mechanism of PARPi resistance that emerges could influence the success of subsequent therapies.

Topics: Aged; Animals; BRCA1 Protein; Cell Line, Tumor; CRISPR-Cas Systems; DNA Mutational Analysis; Drug Resistance, Neoplasm; Female; Humans; Mice; Mice, Inbred BALB C; Mice, Nude; Mouse Embryonic Stem Cells; Mutagenesis; Neoplasms; Phthalazines; Point Mutation; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Precision Medicine; Whole Genome Sequencing; Xenograft Model Antitumor Assays; Zinc Fingers

The observation that BRCA1- and BRCA2-deficient cells are sensitive to inhibitors of poly(ADP-ribose) polymerase (PARP) has spurred the development of cancer therapies that use these inhibitors to target deficiencies in homologous recombination

Topics: Animals; BRCA1 Protein; Cell Line; CRISPR-Cas Systems; DNA Damage; DNA Repair; DNA Replication; DNA Topoisomerases, Type I; Female; Gene Editing; Genes, BRCA1; Genome; HeLa Cells; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Mice; Neoplasms; Phthalazines; Piperazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Prostatic Neoplasms; Ribonuclease H; Ribonucleotides; Synthetic Lethal Mutations; Xenograft Model Antitumor Assays

Poly(ADP-ribose) polymerases (PARPs) are involved in DNA repair following damage by endogenous or exogenous processes. It has become clear over the past decade that inhibition of PARP in the context of defects in other DNA repair mechanisms provide a tumor specific way to kill cancer cells. We describe the rationale for this approach and the design and discovery of niraparib, a potent PARP-1/2 inhibitor with good cell based activity, selectivity for cancer over normal cells, and oral bioavailability. Niraparib was characterized in a number of preclinical models before moving to phase I clinical trials, where it showed excellent human pharmacokinetics suitable for once a day oral dosing, achieved its pharmacodynamic target for PARP inhibition, and had promising activity in cancer patients. It is currently being tested in phase 3 clinical trials as maintenance therapy in ovarian cancer and as a treatment for breast cancer.

Topics: Animals; BRCA1 Protein; BRCA2 Protein; Drug Discovery; Enzyme Inhibitors; Homologous Recombination; Humans; Indazoles; Models, Molecular; Neoplasms; Piperidines; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases