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PDF file - 1.2MB, This file contains additional data on tumor responses to olaparib treatment (Fig. S1 and S2), pH2AX stainings on treated and untreated tumors (Fig. S3), analysis of mutations in 53BP1 (Fig. S4 and S7B), characterization of cell lines (Fig. S5), RAD51 and 53BP1 IRIFs in tumors and cell lines (Fig. S6 and S7), 53BP1 in topotecan-resistant tumors (Fig. S8) and tumor responses to AZD2461 treatment (Fig. S9 and S10).

PDF file - 1641K, Supplementary figure 1. Stereospecific targeting of PARP by BMN 673. Supplementary figure 2. Lack of effect of PARP inhibition on ATP concentration. Supplementary figure 3. Flow cytometry analyses after treatment with different PARP inhibitors. Supplementary figure 4. Stereospecific poisoning of PARP by BMN 673.

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Inhibition of PARP is a promising therapeutic strategy for homologous recombination–deficient tumors, such as BRCA1-associated cancers. We previously reported that BRCA1-deficient mouse mammary tumors may acquire resistance to the clinical PARP inhibitor (PARPi) olaparib through activation of the P-glycoprotein drug efflux transporter. Here, we show that tumor-specific genetic inactivation of P-glycoprotein increases the long-term response of BRCA1-deficient mouse mammary tumors to olaparib, but these tumors eventually developed PARPi resistance. In a fraction of cases, this resistance is caused by partial restoration of homologous recombination due to somatic loss of 53BP1. Importantly, PARPi resistance was minimized by long-term treatment with the novel PARP inhibitor AZD2461, which is a poor P-glycoprotein substrate. Together, our data suggest that restoration of homologous recombination is an important mechanism for PARPi resistance in BRCA1-deficient mammary tumors and that the risk of relapse of BRCA1-deficient tumors can be effectively minimized by using optimized PARP inhibitors.Significance: In this study, we show that loss of 53BP1 causes resistance to PARP inhibition in mouse mammary tumors that are deficient in BRCA1. We hypothesize that low expression or absence of 53BP1 also reduces the response of patients with BRCA1-deficient tumors to PARP inhibitors. Cancer Discov; 3(1); 68–81. ©2012 AACR.See related commentary by Fojo and Bates, p. 20This article is highlighted in the In This Issue feature, p. 1

PDF file - 28K, Information on all antibodies and primers that were used in this study

Anti-PARP drugs were initially developed as catalytic inhibitors to block the repair of DNA single-strand breaks. We recently reported that several PARP inhibitors have an additional cytotoxic mechanism by trapping PARP–DNA complexes, and that both olaparib and niraparib act as PARP poisons at pharmacologic concentrations. Therefore, we have proposed that PARP inhibitors should be evaluated based both on catalytic PARP inhibition and PARP–DNA trapping. Here, we evaluated the novel PARP inhibitor, BMN 673, and compared its effects on PARP1 and PARP2 with two other clinical PARP inhibitors, olaparib and rucaparib, using biochemical and cellular assays in genetically modified chicken DT40 and human cancer cell lines. Although BMN 673, olaparib, and rucaparib are comparable at inhibiting PARP catalytic activity, BMN 673 is ∼100-fold more potent at trapping PARP–DNA complexes and more cytotoxic as single agent than olaparib, whereas olaparib and rucaparib show similar potencies in trapping PARP–DNA complexes. The high level of resistance of PARP1/2 knockout cells to BMN 673 demonstrates the selectivity of BMN 673 for PARP1/2. Moreover, we show that BMN 673 acts by stereospecific binding to PARP1 as its enantiomer, LT674, is several orders of magnitude less efficient. BMN 673 is also approximately 100-fold more cytotoxic than olaparib and rucaparib in combination with the DNA alkylating agents methyl methane sulfonate (MMS) and temozolomide. Our study demonstrates that BMN 673 is the most potent clinical PARP inhibitor tested to date with the highest efficiency at trapping PARP–DNA complexes. Mol Cancer Ther; 13(2); 433–43. ©2013 AACR.

Purpose: Oral administration of the alkylating agent cyclophosphamide at low doses, metronomic dosing, is well tolerated, with efficacy in multiple tumor types. PARP inhibition potentiates effects of cyclophosphamide in preclinical models. We conducted a phase I trial of the PARP inhibitor veliparib and metronomic cyclophosphamide in patients with refractory solid tumors and lymphoid malignancies.Experimental Design: Objectives were to establish the safety and maximum tolerated dose (MTD) of the combination; characterize veliparib pharmacokinetics (PK); measure poly(ADP-ribose) (PAR), a product of PARP, in tumor biopsies and peripheral blood mononuclear cells (PBMC); and measure the DNA-damage marker γH2AX in PBMCs and circulating tumor cells (CTC). Cyclophosphamide was administered once daily in 21-day cycles in combination with veliparib administered once daily for 7, 14, or 21 days.Results: Thirty-five patients were enrolled. The study treatment was well tolerated, and the MTD was established as veliparib 60 mg with cyclophosphamide 50 mg given once daily. Seven patients had partial responses; an additional six patients had disease stabilization for at least six cycles. PAR was significantly decreased in PBMCs (by at least 50%) and tumor biopsies (by at least 80%) across dose levels (DL); γH2AX levels were increased in CTCs from seven of nine patients evaluated after drug administration.Conclusions: The combination of veliparib with metronomic cyclophosphamide is well tolerated and shows promising activity in a subset of patients with BRCA mutations. A phase II trial of the combination compared with single-agent cyclophosphamide is ongoing in BRCA-positive ovarian cancer, triple-negative breast cancer, and low-grade lymphoma. Clin Cancer Res; 18(6); 1726–34. ©2012 AACR.

Supplemental Figure S2. PAR levels in patient PBMC samples. Data shown in dark red are from patients who reported deleterious BRCA mutations, data shown in dark blue are from patients reporting wildtype BRCA status, and data in grey are from patients with unknown BRCA status.

7 tables and 3 figure legends

Relationship between AUC and Cmax after single dose (A)

Supplementary Table 1 Pharmacokinetic parametersa of veliparib and its main metabolite (A- 925088) when veliparib was given orally alone on cycle 2 day -1 or in combination with irinotecan on cycle 2 day 8

Supplementary Figure Legends

Supplementary Data from A Phase I Clinical Trial of the Poly(ADP-ribose) Polymerase Inhibitor Veliparib and Weekly Topotecan in Patients with Solid Tumors

Proteomic outcomes

Supplementary Methods and Supplementary Figures

Supplementary Figure S2. Dose-exposure relationships.

Supplementary Methods, including numbered supplementary methods figures and figure legends

All supplementary files together

Supplementary Figures S1-S6; Supplementary Data; Supplementary Tables S1-S3.

Purpose: To determine the safety and tolerability of olaparib with cisplatin and gemcitabine, establish the maximum tolerated dose (MTD), and evaluate the pharmacodynamic and pharmacokinetic profile of the combination.Experimental Design: We conducted a phase I study of olaparib with cisplatin and gemcitabine in patients with advanced solid tumors. Treatment at dose level 1 (DL1) consisted of olaparib 100 mg orally every 12 hours on days 1 to 4, gemcitabine 500 mg/m2 on days 3 and 10, and cisplatin 60 mg/m2 on day 3. PAR levels were measured in peripheral blood mononuclear cells (PBMC).Results: Dose-limiting toxicities (DLT) in two of three patients at DL1 included thrombocytopenia and febrile neutropenia. The protocol was amended to enroll patients treated with ≤2 prior severely myelosuppressive chemotherapy regimens and treated with olaparib 100 mg once daily on days 1 to 4 (DL−1). No DLTs were seen in six patients at DL−1. Because of persistent thrombocytopenia and neutropenia following a return to DL1, patients received 100 mg olaparib every 12 hours on day 1 only. No hematologic DLTs were observed; nonhematologic DLTs included gastrointestinal bleed, syncope, and hypoxia. Of 21 patients evaluable for response, two had partial response. Olaparib inhibited PARP in PBMCs and tumor tissue, although PAR levels were less effectively inhibited when olaparib was used for a short duration.Conclusions: Olaparib in combination with cisplatin and gemcitabine is associated with myelosuppression even at relatively low doses. Modified schedules of olaparib in chemotherapy naive patients will have to be explored with standard doses of chemotherapy. Clin Cancer Res; 18(8); 2344–51. ©2012 AACR.

Relationship between veliparib exposure-% CFB in PAR levels in PBMC (A) and �B in PAR levels-ORR (B)

Supplementary Table 2 Pharmacokinetic parametersa of irinotecan and its main active metabolite SN-38 when irinotecan was administered as a 1.5-h intravenous infusion (100 mg/m2) alone on cycle 1 day 1 or in combination with veliparib on cycle 2 day 8

Purpose:To determine the dose limiting toxicities (DLT), maximum tolerated dose (MTD), and recommended phase II dose (RP2D) of veliparib in combination with weekly topotecan in patients with solid tumors. Correlative studies were included to assess the impact of topotecan and veliparib on poly(ADP-ribose) levels in peripheral blood mononuclear cells, serum pharmacokinetics of both agents, and potential association of germline repair gene mutations with outcome.Experimental Design:Eligible patients had metastatic nonhematologic malignancies with measurable disease. Using a 3 + 3 design, patients were treated with veliparib orally twice daily on days 1–3, 8–10, and 15–17 and topotecan intravenously on days 2, 9, and 16 every 28 days. Tumor responses were assessed by RECIST.Results:Of 58 patients enrolled, 51 were evaluable for the primary endpoint. The MTD and RP2D was veliparib 300 mg twice daily on days 1–3, 8–10, and 15–17 along with topotecan 3 mg/m2 on days 2, 9, and 16 of a 28-day cycle. DLTs were grade 4 neutropenia lasting >5 days. The median number of cycles was 2 (1–26). The objective response rate was 10%, with 1 complete and 4 partial responses. Twenty-two patients (42%) had stable disease ranging from 4 to 26 cycles. Patients with germline BRCA1, BRCA2, or RAD51D mutations remained on study longer than those without homologous recombination repair (HRR) gene mutations (median 4 vs. 2 cycles).Conclusions:Weekly topotecan in combination with veliparib has a manageable safety profile and appears to warrant further investigation.

Purpose: A phase I trial of veliparib in combination with topotecan plus carboplatin (T+C) demonstrated a 33% objective response rate in patients with hematological malignancies. The objective is to perform exposure–response analysis to inform the phase II trial design.Experimental Design: Pharmacokinetic, efficacy, and safety data from 95 patients, who were administered 10 to 100 mg b.i.d. doses of veliparib for either 8, 14, or 21 days with T+C, were utilized for exposure–efficacy (objective response and overall survival) and exposure–safety (≥grade 3 mucositis) analysis. Multivariate cox proportional hazards and logistic regression analyses were conducted. The covariates evaluated were disease status, duration of treatment, and number of prior therapies.Results: The odds of having objective response were 1.08-fold with 1,000 ng/hr/mL increase in AUC, 1.8-fold with >8 days treatment, 2.8-fold in patients with myeloproliferative neoplasms (MPN), and 0.5-fold with ≥2 prior therapies. Based on analysis of overall survival, hazard of death decreased by 1.5% for 1,000 ng/hr/mL increase in AUC, 39% with >8 days treatment, 44% in patients with MPN, while increased by 19% with ≥2 prior therapies. The odds of having ≥grade 3 mucositis increased by 29% with 1,000 ng.h/mL increase in AUC.Conclusions: Despite shallow exposure–efficacy relationship, doses lower than 80 mg do not exceed veliparib single agent preclinical IC50. Shallow exposure–mucositis relationship also supports the 80-mg dose. Based on benefit/risk assessment, veliparib at a dose of 80 mg b.i.d. for at least 14 days in combination with T+C is recommended to be studied in MPN patients. Clin Cancer Res; 23(21); 6421–9. ©2017 AACR.

Supplemental Figure S1. A, pretreatment bone marrow samples were treated diluent (-) with 10 μM melphalan (+) for 6 h and analyzed by immmunoblotting for FANCD2, ubiquitinated FANCD2 (Ub-FANCD2) and, as a loading control, heat shock protein 90 (HSP90). Supplemental Figure S2. A, Aliquots of whole cell lysates containing 5 x 106 pretreatment marrow mononuclear cells from the indicated patients were subjected to SDS-PAGE and blotting for the indicated antigens (lanes 5-12). Supplemental Figure S3. A, PAR suppression in PBMCs at various veliparib dose levels as a function of times during therapy. B, PAR suppression in PBMCs at 2 hours post dosing on day 1 and its relationship to clinical response. C, PAR suppression as assessed in bone marrow aspirates. Supplemental Table S1. MPN-Associated Leukemia Characteristics Supplemental Table S2 Accumulation of γH2AX in Viable Peripheral Blood CD34+ Cells Following Veliparib Administration at 80 mg Twice Daily Relative to Pretreatment (Day 0) Levels of DNA Damage

Supplementary Expression Data. Individual expression values for all 211 genes interrogated in the tumor tissue of 55 patients.

Purpose: Phosphorylated histone H2AX (γH2AX) serves as a biomarker for formation of DNA double-strand break repair complexes. A quantitative pharmacodynamic immunofluorescence assay for γH2AX was developed, validated, and tested in human tumor xenograft models with the use of clinically relevant procedures.Experimental Design: The γH2AX immunofluorescence assay uses a novel data quantitation and image processing algorithm to determine the extent of nuclear-specific γH2AX staining in tumor needle biopsies and hair follicles collected from mice bearing topotecan-responsive A375 xenografts. After method validation with the topoisomerase I (Top1) inhibitor topotecan, the assay was used to compare pharmacodynamic properties of three structurally related indenoisoquinoline Top1 inhibitors.Results: γH2AX response to topotecan was quantified over a 60-fold dose range (0.016-1.0 times the murine single-dose maximum tolerated dose), and significant pharmacodynamic response was measured at the mouse equivalent of the 1.5 mg/m2 clinical dose as well as the lowest dose tested. Responses were within a time window amenable for biopsy collection in clinical trials. These studies enabled characterization of dose and time responses for three indenoisoquinolines, resulting in selection of two for clinical evaluation. γH2AX response to Top1 inhibitors in hair follicles was also observable above a minimal dose threshold.Conclusions: Our γH2AX assay is sufficiently accurate and sensitive to quantify γH2AX in tumor samples and will be used in correlative studies of two indenoisoquinolines in a phase I clinical trial at the National Cancer Institute. Data suggest that hair follicles may potentially serve as a surrogate tissue to evaluate tumor γH2AX response to Top1 inhibitors. Clin Cancer Res; 16(22); 5447–57. ©2010 AACR.

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Purpose: PARP is essential for recognition and repair of DNA damage. In preclinical models, PARP inhibitors modulate topoisomerase I inhibitor–mediated DNA damage. This phase I study determined the MTD, dose-limiting toxicities (DLT), pharmacokinetics (PK), and pharmacodynamics (PD) of veliparib, an orally bioavailable PARP1/2 inhibitor, in combination with irinotecan.Experimental Design: Patients with advanced solid tumors were treated with 100 mg/m2 irinotecan on days 1 and 8 of a 21-day cycle. Twice-daily oral dosing of veliparib (10–50 mg) occurred on days 3 to 14 (cycle 1) and days −1 to 14 (subsequent cycles) followed by a 6-day rest. PK studies were conducted with both agents alone and in combination. Paired tumor biopsies were obtained after irinotecan alone and veliparib/irinotecan to evaluate PARP1/2 inhibition and explore DNA damage signals (nuclear γ-H2AX and pNBS1).Results: Thirty-five patients were treated. DLTs included fatigue, diarrhea, febrile neutropenia, and neutropenia. The MTD was 100 mg/m2 irinotecan (days 1 and 8) combined with veliparib 40 mg twice daily (days −1–14) on a 21-day cycle. Of 31 response-evaluable patients, there were six (19%) partial responses. Veliparib exhibited linear PK, and there were no apparent PK interactions between veliparib and irinotecan. At all dose levels, veliparib reduced tumor poly(ADP-ribose) (PAR) content in the presence of irinotecan. Several samples showed increases in γ-H2AX and pNBS1 after veliparib/irinotecan compared with irinotecan alone.Conclusions: Veliparib can be safely combined with irinotecan at doses that inhibit PARP catalytic activity. Preliminary antitumor activity justifies further evaluation of the combination. Clin Cancer Res; 22(13); 3227–37. ©2016 AACR.

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Purpose: Veliparib, a PARP inhibitor, demonstrated clinical activity in combination with oral cyclophosphamide in patients with BRCA-mutant solid tumors in a phase I trial. To define the relative contribution of PARP inhibition to the observed clinical activity, we conducted a randomized phase II trial to determine the response rate of veliparib in combination with cyclophosphamide compared with cyclophosphamide alone in patients with pretreated BRCA-mutant ovarian cancer or in patients with pretreated primary peritoneal, fallopian tube, or high-grade serous ovarian cancers (HGSOC).Experimental Design: Adult patients were randomized to receive cyclophosphamide alone (50 mg orally once daily) or with veliparib (60 mg orally once daily) in 21-day cycles. Crossover to the combination was allowed at disease progression.Results: Seventy-five patients were enrolled and 72 were evaluable for response; 38 received cyclophosphamide alone and 37 the combination as their initial treatment regimen. Treatment was well tolerated. One complete response was observed in each arm, with three partial responses (PR) in the combination arm and six PRs in the cyclophosphamide alone arm. Genetic sequence and expression analyses were performed for 211 genes involved in DNA repair; none of the detected genetic alterations were significantly associated with treatment benefit.Conclusion: This is the first trial that evaluated single-agent, low-dose cyclophosphamide in HGSOC, peritoneal, fallopian tube, and BRCA-mutant ovarian cancers. It was well tolerated and clinical activity was observed; the addition of veliparib at 60 mg daily did not improve either the response rate or the median progression-free survival. Clin Cancer Res; 21(7); 1574–82. ©2015 AACR.

Table describing details of drug screen

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Purpose:The Wee1 kinase inhibitor adavosertib abrogates cell-cycle arrest, leading to cell death. Prior testing of twice-daily adavosertib in patients with advanced solid tumors determined the recommended phase II dose (RPh2D). Here, we report results for once-daily adavosertib.Patients and Methods:A 3 + 3 dose-escalation design was used, with adavosertib given once daily on days 1 to 5 and 8 to 12 in 21-day cycles. Molecular biomarkers of Wee1 activity, including tyrosine 15–phosphorylated Cdk1/2 (pY15-Cdk), were assessed in paired tumor biopsies. Whole-exome sequencing and RNA sequencing of remaining tumor tissue identified potential predictive biomarkers.Results:Among the 42 patients enrolled, the most common toxicities were gastrointestinal and hematologic; dose-limiting toxicities were grade 4 hematologic toxicity and grade 3 fatigue. The once-daily RPh2D was 300 mg. Six patients (14%) had confirmed partial responses: four ovarian, two endometrial. Adavosertib plasma exposures were similar to those from twice-daily dosing. On cycle 1 day 8 (pre-dose), tumor pY15-Cdk levels were higher than baseline in four of eight patients, suggesting target rebound during the day 5 to 8 dosing break. One patient who progressed rapidly had a tumor WEE1 mutation and potentially compensatory PKMYT1 overexpression. Baseline CCNE1 overexpression occurred in both of two responding patients, only one of whom had CCNE1 amplification, and in zero of three nonresponding patients.Conclusions:We determined the once-daily adavosertib RPh2D and observed activity in patients with ovarian or endometrial carcinoma, including two with baseline CCNE1 mRNA overexpression. Future studies will determine whether CCNE1 overexpression is a predictive biomarker for adavosertib.

Single-agent outcomes

Supplementary Methods, Supplementary Fig. S1 (Mean adavosertib plasma concentrations for QD vs. BID schedules), Supplementary Fig. S2 (Example PD biomarker immunofluorescence images), Supplementary Fig. S3 (CCNE1 tumor alteration frequency IMPACT data), Supplementary Fig. S4 (Independence of tumor CCNE1 mRNA expression and CCNE1 CNA in TCGA ovarian and endometrial cohorts), Supplementary Table S1 (DLTs), Supplementary Table S2 (Non-DLT dose reductions), Supplementary Table S3 (Responses and baseline genomic characteristics for patients with ovarian carcinoma and prior PARP inhibitor therapy), Supplementary Table S4 (Mean Cycle 1 Day 1 PK parameters), Supplementary Table S5 (Patient tumor mutations identified by WES), Supplementary References

Correlation between objective response rate (ORR) and overall survival (OS)

Supplementary Methods, Tables S1 and S2, Figure Legend

Supplementary Figure S4. Assessment of pNBS1 in the exploratory multiplex immunofluorescence assay.

Metabolic outcomes

Purpose: The PARP inhibitor veliparib delays DNA repair and potentiates cytotoxicity of multiple classes of chemotherapy drugs, including topoisomerase I inhibitors and platinating agents. This study evaluated veliparib incorporation into leukemia induction therapy using a previously described topotecan/carboplatin backbone.Experimental Design: Employing a 3+3 trial design, we administered escalating doses of veliparib combined with topotecan + carboplatin in relapsed or refractory acute leukemias, aggressive myeloproliferative neoplasms (MPN), and chronic myelomonocytic leukemia (CMML).Results: A total of 99 patients received veliparib 10–100 mg orally twice daily on days 1–8, 1–14, or 1–21 along with continuous infusion topotecan 1.0–1.2 mg/m2/d + carboplatin 120–150 mg/m2/d on days 3–7. The MTD was veliparib 80 mg twice daily for up to 21 days with topotecan 1.2 mg/m2/d + carboplatin 150 mg/m2/d. Mucositis was dose limiting and correlated with high veliparib concentrations. The response rate was 33% overall (33/99: 14 CR, 11 CRi, 8 PR) but was 64% (14/22) for patients with antecedent or associated aggressive MPNs or CMML. Leukemias with baseline DNA repair defects, as evidenced by impaired DNA damage–induced FANCD2 monoubiquitination, had improved survival [HR = 0.56 (95% confidence interval, 0.27–0.92)]. A single 80-mg dose of veliparib, as well as veliparib in combination with topotecan + carboplatin, induced DNA damage as manifested by histone H2AX phosphorylation in CD34+ leukemia cells, with greater phosphorylation in cells from responders.Conclusions: The veliparib/topotecan/carboplatin combination warrants further investigation, particularly in patients with aggressive MPNs, CMML, and MPN- or CMML-related acute leukemias. Clin Cancer Res; 23(4); 899–907. ©2016 AACR.

Purpose: Although many cancers are showing remarkable responses to targeted therapies, pediatric sarcomas, including Ewing sarcoma, remain recalcitrant. To broaden the therapeutic landscape, we explored the in vitro response of Ewing sarcoma cell lines against a large collection of investigational and approved drugs to identify candidate combinations.Experimental Design: Drugs displaying activity as single agents were evaluated in combinatorial (matrix) format to identify highly active, synergistic drug combinations, and combinations were subsequently validated in multiple cell lines using various agents from each class. Comprehensive metabolomic and proteomic profiling was performed to better understand the mechanism underlying the synergy. Xenograft experiments were performed to determine efficacy and in vivo mechanism.Results: Several promising candidates emerged, including the combination of small-molecule PARP and nicotinamide phosphoribosyltransferase (NAMPT) inhibitors, a rational combination as NAMPTis block the rate-limiting enzyme in the production of nicotinamide adenine dinucleotide (NAD+), a necessary substrate of PARP. Mechanistic drivers of the synergistic cell killing phenotype of these combined drugs included depletion of NMN and NAD+, diminished PAR activity, increased DNA damage, and apoptosis. Combination PARPis and NAMPTis in vivo resulted in tumor regression, delayed disease progression, and increased survival.Conclusions: These studies highlight the potential of these drugs as a possible therapeutic option in treating patients with Ewing sarcoma. Clin Cancer Res; 23(23); 7301–11. ©2017 AACR.

Supplementary Figure S3. pNBS1 staining post-combination treatment is limited to tumor cells.

Purpose:Only one chemical class of topoisomerase I (TOP1) inhibitors is FDA approved, the camptothecins with irinotecan and topotecan widely used. Because of their limitations (chemical instability, drug efflux-mediated resistance, and diarrhea), novel TOP1 inhibitors are warranted. Indenoisoquinoline non-camptothecin topoisomerase I (TOP1) inhibitors overcome chemical instability and drug resistance that limit camptothecin use. Three indenoisoquinolines, LMP400 (indotecan), LMP776 (indimitecan), and LMP744, were examined in a phase I study for lymphoma-bearing dogs to evaluate differential efficacy, pharmacodynamics, toxicology, and pharmacokinetics.Experimental Design:Eighty-four client-owned dogs with lymphomas were enrolled in dose-escalation cohorts for each indenoisoquinoline, with an expansion phase for LMP744. Efficacy, tolerability, pharmacokinetics, and target engagement were determined.Results:The MTDs were 17.5 mg/m2 for LMP 776 and 100 mg/m2 for LMP744; bone marrow toxicity was dose-limiting; up to 65 mg/m2 LMP400 was well-tolerated and MTD was not reached. None of the drugs induced notable diarrhea. Sustained tumor accumulation was observed for LMP744; γH2AX induction was demonstrated in tumors 2 and 6 hours after treatment; a decrease in TOP1 protein was observed in most lymphoma samples across all compounds and dose levels, which is consistent with the fact that tumor response was also observed at low doses LMP744. Objective responses were documented for all indenoisoquinolines; efficacy (13/19 dogs) was greatest for LMP744.Conclusions:These results demonstrate proof-of-mechanism for indenoisoquinoline TOP1 inhibitors supporting their further clinical development. They also highlight the value of the NCI Comparative Oncology Program (https://ccr.cancer.gov/Comparative-Oncology-Program) for evaluating novel therapies in immunocompetent pets with cancers.

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A phase I trial of ABT-888 (veliparib), a PARP inhibitor, in combination with topotecan, a topoisomerase I–targeted agent, was carried out to determine maximum tolerated dose (MTD), safety, pharmacokinetics, and pharmacodynamics of the combination in patients with refractory solid tumors and lymphomas. Varying schedules and doses of intravenous topotecan in combination with ABT-888 (10 mg) administered orally twice a day (BID) were evaluated. Plasma and urine pharmacokinetics were assessed and levels of poly(ADP-ribose) (PAR) and the DNA damage marker γH2AX were measured in tumor and peripheral blood mononuclear cells (PBMC). Twenty-four patients were enrolled. Significant myelosuppression limited the ability to coadminister ABT-888 with standard doses of topotecan, necessitating dose reductions. Preclinical studies using athymic mice carrying human tumor xenografts also informed schedule changes. The MTD was established as topotecan 0.6 mg/m2/d and ABT-888 10 mg BID on days one to five of 21-day cycles. Topotecan did not alter the pharmacokinetics of ABT-888. A more than 75% reduction in PAR levels was observed in 3 paired tumor biopsy samples; a greater than 50% reduction was observed in PBMCs from 19 of 23 patients with measurable levels. Increases in γH2AX response in circulating tumor cells (CTC) and PBMCs were observed in patients receiving ABT-888 with topotecan. We show a mechanistic interaction of a PARP inhibitor, ABT-888, with a topoisomerase I inhibitor, topotecan, in PBMCs, tumor, and CTCs. Results of this trial reveal that PARP inhibition can modulate the capacity to repair topoisomerase I–mediated DNA damage in the clinic. Cancer Res; 71(17); 5626–34. ©2011 AACR.