bmn-673 and Lung-Neoplasms

SCLC accounts for 15% of lung cancer worldwide. Characterised by early dissemination and rapid development of chemo-resistant disease, less than 5% of patients survive 5 years. Despite 3 decades of clinical trials there has been no change to the standard platinum and etoposide regimen for first line treatment developed in the 1970's. The exceptionally high number of genomic aberrations observed in SCLC combined with the characteristic rapid cellular proliferation results in accumulation of DNA damage and genomic instability. To flourish in this precarious genomic context, SCLC cells are reliant on functional DNA damage repair pathways and cell cycle checkpoints. Current cytotoxic drugs and radiotherapy treatments for SCLC have long been known to act by induction of DNA damage and the response of cancer cells to such damage determines treatment efficacy. Recent years have witnessed improved understanding of strategies to exploit DNA damage and repair mechanisms in order to increase treatment efficacy. This review will summarise the rationale to target DNA damage response in SCLC, the progress made in evaluating novel DDR inhibitors and highlight various ongoing challenges for their clinical development in this disease.

Topics: Aurora Kinases; Azepines; Benzimidazoles; Carbolines; Cell Cycle Checkpoints; Cell Proliferation; Cytotoxins; DNA Damage; DNA Repair; Etoposide; Genomic Instability; Heterocyclic Compounds, 4 or More Rings; Humans; Lung Neoplasms; Molecular Targeted Therapy; Phthalazines; Piperazines; Poly(ADP-ribose) Polymerase Inhibitors; Protein Kinase Inhibitors; Pyrimidines; Rad51 Recombinase; Small Cell Lung Carcinoma

This signal finding study (S1400G) was designed to evaluate the efficacy of talazoparib in advanced stage squamous cell lung cancer harboring homologous recombination repair deficiency.. The full eligible population (FEP) had tumors with a deleterious mutation in any of the study-defined homologous recombination repair genes and without prior exposure to a PARP inhibitor. The primary analysis population (PAP) is a subset of FEP with alteration in ATM, ATR, BRCA1, BRCA2, or PALB2. Treatment consisted of talazoparib 1 mg daily continuously in 21-day cycles. A 2-stage design with exact 93% power and 1-sided 0.07 type I error required enrollment of 40 patients in the PAP in order to rule out an overall response rate (ORR) of 15% or less if the true ORR is ≥ 35%.. The study enrolled 47 patients in the FEP, of whom 24 were in the PAP. The median age for the FEP was 66.7 years; 83% were male and 85% white. ORR in the PAP was 4% (95% confidence interval [CI], 0, 21) with disease control rate of 54% (95% CI, 33, 74). Median progression-free survival and overall survival were 2.4 months (95% CI, 1.5-2.8) and 5.2 months (95% CI, 4.0-10), respectively. In the FEP, ORR was 11% (95% CI, 3.6, 23), the disease control rate was 51% (95% CI, 36, 66), and the median duration of response was 1.8 months (95% CI, 1.3, 4.2). Median progression-free and overall survival were 2.5 months and 5.7 months, respectively.. S1400G failed to show sufficient level of efficacy for single agent talazoparib in a biomarker defined subset of squamous lung cancer with homologous recombination repair deficiency.

Topics: Adult; Aged; Aged, 80 and over; Carcinoma, Non-Small-Cell Lung; Carcinoma, Squamous Cell; Female; Humans; Lung Neoplasms; Male; Middle Aged; Neoplasm Staging; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Progression-Free Survival; Recombinational DNA Repair; Survival Rate; Treatment Outcome

Preclinical data suggest that poly(ADP-ribose) polymerase (PARP) inhibitors have synergistic activity when combined with immune checkpoint inhibitors (ICIs); however, it is unknown which tumor types or molecular subtypes may benefit from this combination.. To investigate responses associated with the combination of avelumab and talazoparib in different tumor types and/or molecular subtypes.. In this phase 1b and 2 basket nonrandomized controlled trial, patients with advanced solid tumors were enrolled in the following cohorts: non-small cell lung cancer (NSCLC); DNA damage response (DDR)-positive NSCLC; triple-negative breast cancer (TNBC); hormone receptor-positive, human epidermal growth factor receptor 2 (ERBB2)-negative, DDR-positive breast cancer; recurrent, platinum-sensitive ovarian cancer (OC); recurrent, platinum-sensitive, BRCA1/2-altered OC; urothelial cancer; metastatic castration-resistant prostate cancer (mCRPC); DDR-positive mCRPC; and BRCA1/2- or ATM-altered solid tumors. Data were analyzed between June 17, 2021, and August 6, 2021.. All patients in phases 1b and 2 received avelumab plus talazoparib.. The phase 1b primary end point was dose-limiting toxic effects. The phase 2 primary end point was objective response, measured as objective response rate (ORR). Secondary end points included safety, time to response, duration of response (DOR), progression-free survival, time to prostate-specific antigen progression and PSA response of 50% or greater (for mCRPC), cancer antigen 125 response (for OC), pharmacokinetics, immunogenicity, and biomarkers.. A total of 223 patients (mean [SD] age, 63.2 [11.0] years; 117 [52.5%] men) were treated, including 12 patients in phase 1b and 211 patients in phase 2. The recommended phase 2 dose was avelumab 800 mg every 2 weeks plus talazoparib 1 mg once daily. In phase 2, the ORR was 18.2% (95% CI, 5.2%-40.3%) in patients with TNBC; 34.8% (95% CI, 16.4%-57.3%) in patients with HR-positive, ERBB2-negative, and DDR-positive BC; and 63.6% (95% CI, 30.8%-89.1%) in patients with platinum-sensitive, BRCA1/2-altered OC. Responses occurred more frequently in patients with BRCA1/2-altered tumors. Durable responses were observed in patients with TNBC (median [range] DOR, 11.1 [3.4-20.4] months); HR-positive, ERBB2-negative, and DDR-positive BC (median [range] DOR, 15.7 [3.9 to ≥20.6] months); and BRCA1/2-altered OC (median DOR not reached; range, 5.6 to ≥18.4 months). The most common grade 3 or greater treatment-related adverse events were anemia (75 patients [33.6%]), thrombocytopenia (48 patients [21.5%]), and neutropenia (31 patients [13.9%]).. This nonrandomized controlled trial found that ORRs for avelumab plus talazoparib were comparable with those with PARP inhibitor or ICI monotherapy. Prolonged DOR in patients with TNBC; HR-positive, ERBB2-negative, and DDR-positive BC; and BRCA1/2-altered OC warrant further investigation in randomized clinical trials. These data highlight the importance of prospective patient selection in future studies of ICI and PARP-inhibitor combinations.. ClinicalTrials.gov Identifier: NCT03330405.

Topics: Antibodies, Monoclonal; Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; Female; Humans; Immunotherapy; Lung Neoplasms; Male; Middle Aged; Poly(ADP-ribose) Polymerase Inhibitors; Prospective Studies; Prostatic Neoplasms, Castration-Resistant; Triple Negative Breast Neoplasms

Poly ADP ribose polymerase (PARP) inhibitors are mainly used in treating BRCA-mutant cancers, and their application in novel therapies to expand their benefit is of interest in personalized medicine. A recent report showed that pharmacological targeting of PARP increases the sensitivity of cancer cells to EGFR inhibition, but the therapeutic value of this combination has not been fully determined. We propose a strategy of combining PARP inhibitors with bispecific antibodies that target both EGFR and Notch signalling, highlighting the difficulties posed by deregulation of Notch signalling and the enrichment of cancer stem cells (CSCs) during therapy. In the present study, we showed that although PARP plus EGFR targeting led to more penetrant and durable responses in the non-small cell lung cancer (NSCLC) PDX model, it influenced the enrichment of stem-like cells and their relative proportion. Stem-like cells were significantly inhibited in vitro and in vivo by EGFR/Notch-targeting bispecific antibodies. These bispecific antibodies were effective in PDX models and showed promise in cell line models of NSCLC, where they delayed the development of acquired resistance to cetuximab and talazoparib. Moreover, combining EGFR/Notch-targeting bispecific antibodies and talazoparib had a more substantial antitumour effect than the combination of talazoparib and cetuximab in a broad spectrum of epithelial tumours. EGFR/Notch bispecific antibodies decrease the subpopulation of stem-like cells, reduce the frequency of tumour-initiating cells, and downregulate mesenchymal gene expression. These findings suggest that combining EGFR and Notch signalling blockade can potentially increase the response to PARP blockade.

Topics: Antibodies, Bispecific; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cetuximab; ErbB Receptors; Humans; Lung Neoplasms; Neoplastic Stem Cells; Poly(ADP-ribose) Polymerase Inhibitors

Topics: Antineoplastic Agents; Humans; Lung Neoplasms; Phthalazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Small Cell Lung Carcinoma

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.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Carcinoma, Non-Small-Cell Lung; Cytochrome P-450 Enzyme System; Drug Resistance, Multiple; Humans; Lung Neoplasms; Neoplasm Proteins

Patient mortality rates have remained stubbornly high for the past decades in small cell lung cancer (SCLC) because of having no standard targeted therapies with confirmed advantages at present. Poly [ADP-ribose] polymerase (PARP) inhibitors have shown promise in preclinical models but have had unsatisfactory clinical results in SCLC. By RNA-seq and isobaric tags for relative and absolute quantification (ITRAQ), we revealed that PARP1 inhibition led to the relocalization of forkhead box-O3a (FOXO3a) from nuclear to cytoplasm. By performing co-Immunoprecipitation (co-IP) and CRISPR-Cas9-mediated knockout plasmid we showed that FOXO3a was subject to exportin 1 (XPO1)-dependent nuclear export. We demonstrated the effects of the PARP inhibitor BMN673 on apoptosis and DNA damage were markedly enhanced by simultaneous inhibition of XPO1 in vitro. The combination of BMN673 and the XPO1 inhibitor selinexor inhibited primary SCLC cell proliferation in mini-patient-derived xenotransplants (miniPDXs) and markedly inhibited tumor growth without significant toxicity in xenograft models. The efficacy was enhanced for more than 2.5 times, compared to the single agent. Based on these findings, we further designed a novel dual PARP-XPO1 inhibitor and showed its effectiveness in SCLC. In this work, we illustrated that combining a PARP inhibitor with an XPO1 inhibitor is associated with significantly improved efficacy and tolerability. Dual PARP-XPO1 inhibition restored the FOXO3a balance and activity in SCLC. Collectively, targeting PARP1 and XPO1 opens new avenues for therapeutic intervention against SCLC, warranting further investigation in potential clinical trials.

Topics: Active Transport, Cell Nucleus; Animals; Cell Line, Tumor; Cell Nucleus; Cell Proliferation; Cell Survival; Cytoplasm; Drug Synergism; Exportin 1 Protein; Female; Forkhead Box Protein O3; Gene Expression Regulation, Neoplastic; Humans; Hydrazines; Karyopherins; Lung Neoplasms; Mice; Phthalazines; Receptors, Cytoplasmic and Nuclear; Small Cell Lung Carcinoma; Triazoles; Xenograft Model Antitumor Assays

Small cell lung cancer (SCLC) is an aggressive type of lung cancer with high mortality that is caused by frequent relapses and acquired resistance. Despite that several target-based approaches with potential therapeutic impact on SCLC have been identified, numerous targeted drugs have not been successful in providing improvements in cancer patients when used as single agents. A combination of targeted therapies could be a strategy to induce maximum lethal effects on cancer cells. As a starting point in the development of new drug combination strategies for the treatment of SCLC, we performed a mid-throughput screening assay by treating a panel of SCLC cell lines with BETi or AKi in combination with PARPi or EZH2i. We observed drug synergy between I-BET762 and Talazoparib, BETi and PARPi, respectively, in SCLC cells. Combinatorial efficacy was observed in

Topics: Antineoplastic Agents; Benzodiazepines; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cells, Cultured; DNA Damage; Drug Synergism; Humans; Lung Neoplasms; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors

Up to 40% of lung adenocarcinoma have been reported to lack ataxia-telangiectasia mutated (ATM) protein expression. We asked whether ATM-deficient lung cancer cell lines are sensitive to poly-ADP ribose polymerase (PARP) inhibitors and determined the mechanism of action of olaparib in ATM-deficient A549 cells.. We analysed drug sensitivity data for olaparib and talazoparib in lung adenocarcinoma cell lines from the Genomics of Drug Sensitivity in Cancer (GDSC) project. We deleted ATM from A549 lung adenocarcinoma cells using CRISPR/Cas9 and determined the effects of olaparib and the ATM/Rad3-related (ATR) inhibitor VE-821 on cell viability.. IC. Patients with tumours characterised by ATM-deficiency may benefit from treatment with a PARP inhibitor in combination with an ATR inhibitor.

Topics: Adenocarcinoma; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Ataxia Telangiectasia Mutated Proteins; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Clustered Regularly Interspaced Short Palindromic Repeats; Gene Deletion; Histones; Humans; Lung Neoplasms; Mutation; Nitroso Compounds; Phosphorylation; Phthalazines; Piperazines; Poly(ADP-ribose) Polymerase Inhibitors; Pyrazines; Pyrimidines; RNA, Messenger; Sulfones; Tumor Suppressor Protein p53

A minority of cancers have breast cancer gene (BRCA) mutations that confer sensitivity to poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis), but the role for PARPis in BRCA-proficient cancers is not well established. This suggests the need for novel combination therapies to expand the use of these drugs. Recent reports that low doses of DNA methyltransferase inhibitors (DNMTis) plus PARPis enhance PARPi efficacy in BRCA-proficient AML subtypes, breast, and ovarian cancer open up the possibility that this strategy may apply to other sporadic cancers. We identify a key mechanistic aspect of this combination therapy in nonsmall cell lung cancer (NSCLC): that the DNMTi component creates a BRCAness phenotype through downregulating expression of key homologous recombination and nonhomologous end-joining (NHEJ) genes. Importantly, from a translational perspective, the above changes in DNA repair processes allow our combinatorial PARPi and DNMTi therapy to robustly sensitize NSCLC cells to ionizing radiation in vitro and in vivo. Our combinatorial approach introduces a biomarker strategy and a potential therapy paradigm for treating BRCA-proficient cancers like NSCLC.

Topics: Animals; Antineoplastic Agents; BRCA1 Protein; BRCA2 Protein; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Combined Modality Therapy; DNA Modification Methylases; DNA Repair; Drug Therapy, Combination; Enzyme Inhibitors; Female; Homologous Recombination; Humans; Lung Neoplasms; Male; Mice; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Radiation, Ionizing

Poly (ADP-ribose) polymerase (PARP) inhibitors have demonstrated great promise in the treatment of patients with deficiencies in homologous recombination (HR) DNA repair, such as those with loss of BRCA1 or BRCA2 function. However, emerging studies suggest that PARP inhibition can also target HR-competent cancers, such as non-small-cell lung cancer (NSCLC), and that the therapeutic effect of PARP inhibition may be improved by combination with chemotherapy agents. In our study, it was found that PARP inhibitors talazoparib (BMN-673) and olaparib (AZD-2281) both had synergistic activity with the common first-line chemotherapeutic gemcitabine in a panel of lung cancer cell lines. Furthermore, the combination demonstrated significant in vivo antitumor activity in an H23 xenograft model of NSCLC compared to either agent as monotherapy. This synergism occurred without loss of HR repair efficiency. Instead, the combination induced synergistic single-strand DNA breaks, leading to accumulation of toxic double-strand DNA lesions in vitro and in vivo. Our study elucidates the underlying mechanisms of synergistic activity of PARP inhibitors and gemcitabine, providing a strong motivation to pursue this combination as an improved therapeutic regimen.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; BRCA1 Protein; BRCA2 Protein; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Deoxycytidine; DNA Damage; Drug Synergism; Female; Gemcitabine; Humans; Lung Neoplasms; Male; Mice; Mice, Nude; Phthalazines; Piperazines; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Recombinational DNA Repair; Xenograft Model Antitumor Assays

Insufficient chemotherapy response and rapid disease progression remain concerns for small-cell lung cancer (SCLC). Oncologists rely on serial CT scanning to guide treatment decisions, but this cannot assess in vivo target engagement of therapeutic agents. Biomarker assessments in biopsy material do not assess contemporaneous target expression, intratumoral drug exposure, or drug-target engagement. Here, we report the use of PARP1/2-targeted imaging to measure target engagement of PARP inhibitors in vivo. Using a panel of clinical PARP inhibitors, we show that PARP imaging can quantify target engagement of chemically diverse small molecule inhibitors in vitro and in vivo. We measure PARP1/2 inhibition over time to calculate effective doses for individual drugs. Using patient-derived xenografts, we demonstrate that different therapeutics achieve similar integrated inhibition efficiencies under different dosing regimens. This imaging approach to non-invasive, quantitative assessment of dynamic intratumoral target inhibition may improve patient care through real-time monitoring of drug delivery.

Topics: Animals; Cell Line, Tumor; Dose-Response Relationship, Drug; Humans; Lung Neoplasms; Mice, Inbred NOD; Mice, Knockout; Mice, SCID; Molecular Targeted Therapy; Phthalazines; Piperazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Positron Emission Tomography Computed Tomography; Small Cell Lung Carcinoma; Xenograft Model Antitumor Assays

Poly (ADP-ribose) polymerase (PARP) inhibitors have been shown to enhance the radiosensitivity of cancer cells in vitro in a replication-dependent manner. Their in vivo radiosensitizing effects have also been demonstrated in preclinical tumor models. However, whether PARP inhibition can enhance the response to radiation therapy in normal tissues has been largely neglected. We hypothesized that PARP inhibition might also potentiate the response of replicating normal tissues to radiation therapy. In this study, we examined the normal tissue response in mice treated with PARP inhibitors (BMN673 or AZD2281) in combination with thoracic irradiation.. The antitumor effects of fractionated irradiation (5 Gy × 4) in combination with BMN673 were evaluated in nude mice bearing established Calu-6 human lung cancer xenografts. The normal tissue response was evaluated in C57BL6 mice that were treated with BMN673 or AZD2281 combined with fractionated irradiation, 5 Gy × 4, delivered to the whole thorax. Body weight and histology of the esophagus and skin in the field of irradiation were examined. The DNA damage response in the esophagus and skin was assessed by γH2AX immunohistochemistry.. While PARP inhibition enhanced irradiation-induced tumor growth inhibition in nude mice, it was also associated with significant body weight loss and increased damage to the esophagus and skin within the field of irradiation in C57BL6 mice. PARP inhibition compromised the repair of irradiation-induced DNA damage in the esophagus and skin.. Although PARP inhibition enhanced the antitumor response to fractionated irradiation, it also enhanced the irradiation response in replicating normal tissues. Therefore, our study suggests that additional caution may be warranted in the clinical development of combination therapies using PARP inhibitors and radiation therapy, in particular where the field of irradiation includes the esophagus.

Topics: Animals; Combined Modality Therapy; DNA Damage; Esophagus; Female; Heterografts; Histones; Humans; Lung Neoplasms; Mice; Mice, Inbred C57BL; Mice, Nude; Organs at Risk; Phthalazines; Piperazines; Poly(ADP-ribose) Polymerase Inhibitors; Radiation Injuries, Experimental; Radiation-Sensitizing Agents; Skin; Weight Loss

Excision repair cross-complementation group 1 (ERCC1) is a DNA repair enzyme that is frequently defective in non-small cell lung cancer (NSCLC). Although low ERCC1 expression correlates with platinum sensitivity, the clinical effectiveness of platinum therapy is limited, highlighting the need for alternative treatment strategies. To discover new mechanism-based therapeutic strategies for ERCC1-defective tumours, we performed high-throughput drug screens in an isogenic NSCLC model of ERCC1 deficiency and dissected the mechanism underlying ERCC1-selective effects by studying molecular biomarkers of tumour cell response. The high-throughput screens identified multiple clinical poly (ADP-ribose) polymerase 1 and 2 (PARP1/2) inhibitors, such as olaparib (AZD-2281), niraparib (MK-4827) and BMN 673, as being selective for ERCC1 deficiency. We observed that ERCC1-deficient cells displayed a significant delay in double-strand break repair associated with a profound and prolonged G₂/M arrest following PARP1/2 inhibitor treatment. Importantly, we found that ERCC1 isoform 202, which has recently been shown to mediate platinum sensitivity, also modulated PARP1/2 sensitivity. A PARP1/2 inhibitor-synthetic lethal siRNA screen revealed that ERCC1 deficiency was epistatic with homologous recombination deficiency. However, ERCC1-deficient cells did not display a defect in RAD51 foci formation, suggesting that ERCC1 might be required to process PARP1/2 inhibitor-induced DNA lesions before DNA strand invasion. PARP1 silencing restored PARP1/2 inhibitor resistance in ERCC1-deficient cells but had no effect in ERCC1-proficient cells, supporting the hypothesis that PARP1 might be required for the ERCC1 selectivity of PARP1/2 inhibitors. This study suggests that PARP1/2 inhibitors as a monotherapy could represent a novel therapeutic strategy for NSCLC patients with ERCC1-deficient tumours.

Topics: Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; Cell Line; Cell Line, Tumor; DNA Breaks, Double-Stranded; DNA Repair; DNA-Binding Proteins; Endonucleases; Enzyme Inhibitors; G2 Phase Cell Cycle Checkpoints; High-Throughput Screening Assays; Humans; Indazoles; Lung Neoplasms; Phthalazines; Piperazines; Piperidines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Protein Isoforms; Rad51 Recombinase; RNA Interference; RNA, Small Interfering

Small cell lung carcinoma (SCLC) is an aggressive malignancy affecting nearly 30,000 people annually in the United States. We have previously identified elevated PARP1 levels in SCLC and demonstrated in vitro sensitivity to the PARP inhibitors AZD 2281 and AG014699. Here, we evaluate activity of a novel, potent PARP inhibitor, BMN 673, and identify markers of response as a basis for developing predictive markers for clinical application.. Inhibition of SCLC proliferation by BMN 673 was assayed in vitro and effects on tumor growth were measured in SCLC xenograft models. Protein expression and pathway activation was assessed by reverse phase protein array and western blot analysis. PARP inhibition was confirmed using a PAR ELISA.. We demonstrate striking, single agent activity of BMN 673 in SCLC cell lines and xenografts, with single agent BMN 673 exhibiting in vivo activity similar to cisplatin. Sensitivity to BMN 673 was associated with elevated baseline expression levels of several DNA repair proteins, whereas greater drug resistance was observed in SCLC models with baseline activation of the PI3K/mTOR pathway. Furthermore, we developed and confirmed these data with a novel "DNA repair score" consisting of a group of 17 DNA repair proteins.. Elevated expression of multiple DNA repair proteins, as well as a corresponding "DNA repair protein score," predict response to BMN 673 in in vitro SCLC models. These observations complement recent work in which PI3K inhibition sensitizes breast cancer models to PARP inhibition, suggesting cooperation between DNA repair and PI3K pathways.

Topics: Animals; Cell Line, Tumor; Cell Proliferation; Cell Survival; Disease Models, Animal; DNA Repair; Enzyme Activation; Female; Humans; Lung Neoplasms; Mice; Mice, Inbred BALB C; Mice, Nude; Neoplasm Transplantation; Phosphatidylinositol 3-Kinases; Phthalazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Small Cell Lung Carcinoma; TOR Serine-Threonine Kinases; Xenograft Model Antitumor Assays