A phase 1 study of veliparib (ABT-888) plus weekly carboplatin and paclitaxel in advanced solid malignancies, with an expansion cohort in triple negative breast cancer (TNBC) (ETCTN 8620)

BACKGROUND

Veliparib is a poly-ADP-ribose polymerase (PARP) inhibitor, and it has clinical activity with every 3 weeks carboplatin and paclitaxel. In breast cancer, weekly paclitaxel is associated with improved overall survival. We aimed to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of veliparib with weekly carboplatin and paclitaxel as well as safety, pharmacokinetics, and preliminary clinical activity in triple negative breast cancer (TNBC).

METHODS

Patients with locally advanced/metastatic solid tumors and adequate organ function were eligible. A standard 3 + 3 dose-escalation design was followed by a TNBC expansion cohort. Veliparib doses ranging from 50 to 200 mg orally bid were tested with carboplatin (AUC 2) and paclitaxel (80 mg/m2) given weekly in a 21-day cycle. Adverse events (AE) were evaluated by CTCAE v4.0, and objective response rate (ORR) was determined by RECIST 1.1.

RESULTS

Thirty patients were enrolled, of whom 22 had TNBC. Two dose-limiting toxicities were observed. The RP2D was determined to be 150 mg PO bid veliparib with weekly carboplatin and paclitaxel 2 weeks on, 1 week off, based on hematologic toxicity requiring dose reduction in the first 5 cycles of treatment. The most common grade 3/4 AEs included neutropenia, anemia, and thrombocytopenia. PK parameters of veliparib were comparable to single-agent veliparib. In 23 patients with evaluable disease, the ORR was 65%. In 19 patients with TNBC with evaluable disease, the ORR was 63%.

CONCLUSION

Veliparib can be safely combined with weekly paclitaxel and carboplatin, and this triplet combination has promising clinical activity.

Optimal two-stage designs for exploratory basket trials

The primary goal of an exploratory oncology clinical trial is to identify an effective drug for further development. To account for tumor indication selection error, multiple tumor indications are often selected for simultaneous testing in a basket trial. In this article, we propose optimal and minimax two-stage basket trial designs for exploratory clinical trials. Inactive tumor indications are pruned in stage 1 and the active tumor indications are pooled at end of stage 2 to assess overall effectiveness of the test drug. The proposed designs explicitly control the type I and type II error rates with closed-form sample size formula. They can be viewed as a natural extension of Simon's optimal and minimax two-stage designs for single arm trials to multi-arm basket trials. A simulation study shows that the proposed design method has desirable operating characteristics as compared to other commonly used design methods for exploratory basket trials.

Breast conservation after neoadjuvant chemotherapy for triple-negative breast cancer: Surgical results from an international randomized trial (BrighTNess)

514

Background: Neoadjuvant systemic therapy (NST) increases the frequency of breast-conserving therapy (BCT) in stage II-III breast cancer, but there is little data on how often it converts patients (pts) from BCT-ineligible (BCT-I) to BCT-eligible (BCT-E) and on the impact of other factors on surgical choices. We collected surgical assessment and management data from an international randomized trial of NST in triple-negative breast cancer (TNBC). Methods: Women with operable TNBC were randomized to veliparib (V) with carboplatin (C) and paclitaxel (P), placebo with C and P or placebo with P followed by doxorubicin and cyclophosphamide. The surgeons assessed BCT candidacy by clinico-radiographic criteria before and after NST; surgical management was at surgeon and patient discretion. We assessed interactions between BCT eligibility pre- and post-NST, germline BRCA mutation ( gBRCA) status, continent of treatment and achievement of pathologic complete response(pCR) and percentage of pts who underwent BCT versus mastectomy. Results: Pre- and post-NST surgical assessments were available for 604 pts who underwent surgery. BCT rates are listed in the Table. The BCT rate was 68% among pts deemed BCT-E after NST. pCR rates were identical between BCT-E pts who chose BCT (55%) vs. mastectomy (53%). Of 141 pts deemed BCT-I at baseline, 75 (53%) converted to BCT-E but only 42 (56%) of these opted for BCT. pCR rates were 49% in BCT-E converts vs. 36% in those remained BCT-I. gBRCA pts (n = 84) were less likely to choose BCT even if they were BCT-E. Pts treated in North America (NA) were less likely to choose BCT (55% vs. 80% for Europe and Asia P<0.0001) even among non- gBRCA considered BCT-E post-NST (61% vs. 85% P<0.0001). Conclusions: This largest prospective analysis of the impact of NST in TNBC demonstrates a conversion rate from BCT-I to BCT-E of 53%. BCT rates were lower in pts with gBRCA; the much higher mastectomy rate among BCT-E pts in NA merits investigation. Clinical trial information: NCT02032277. [Table: see text]

Phase 3 study evaluating efficacy and safety of veliparib (V) plus carboplatin (Cb) or Cb in combination with standard neoadjuvant chemotherapy (NAC) in patients (pts) with early stage triple-negative breast cancer (TNBC)

520

Background: Clinical studies suggest that TNBC is sensitive to DNA-damaging agents, including Cb. V is a potent PARP inhibitor that may enhance the antitumor activity of such agents. We present primary response data from a phase 3 randomized, placebo-controlled study (NCT02032277) evaluating the addition of V + Cb or Cb to neoadjuvant paclitaxel (P) followed by doxorubicin + cyclophosphamide (AC). Methods: Pts with histologically confirmed, invasive TNBC (T2–T4 N0–2 or T1 N1–2) amenable to surgical resection were randomized 2:1:1 to (Arm A) P 80 mg/m2 weekly + Cb AUC 6 mg/mL/min q3 weeks + V 50 mg PO BID; (Arm B) P + Cb + PO placebo; or (Arm C) P + IV placebo + PO placebo, for 12 weeks followed by AC (60 mg/m2 or 600 mg/m2 q2 or 3 weeks) × 4. Primary endpoint was pathologic complete response (pCR) in breast and nodes with > 80% power at 2-sided α of 0.05 using pair-wise comparisons for A vs B and A vs C to detect significant treatment effects using Χ2 test; secondary endpoint was rate of conversion to eligibility for breast conservation surgery (BCS). Adverse events (AEs) were assessed with NCI CTCAE V4.0. Results: Six hundred thirty-four pts (median age 50 years; range 22–79) were randomized to Arms A (n = 316), B (n = 160), or C (n = 158). Baseline characteristics were well balanced. No pCR difference was observed between Arms A and B (53.2% vs 57.5% p = 0.36), but pCR in Arm A was higher than Arm C (53.2% vs 31.0% p < 0.001). In non-prespecified analysis, pCR in Arm B was also higher than Arm C (57.5% vs 31.0% p < 0.001). Among pts ineligible for BCS at screening (n = 141), 62% were eligible after NAC in Arm A vs 44% each in Arms B (p = 0.13) and C (p = 0.14). Grade 3–4 AEs (Arms A/B/C, 86%/85%/45%) and serious AEs (30%/27%/14%) neutropenia, thrombocytopenia, anemia, nausea, and vomiting were increased with the addition of Cb; V did not impact toxicity. Median cycles of NAC were not reduced with V + Cb + P or Cb + P vs P. Conclusions: Addition of V to neoadjuvant Cb + P followed by AC did not increase pCR rate in breast and nodes in stage II–III TNBC, while addition of V + Cb or Cb alone to P followed by AC did. Cb (+/– V) increased toxicity but did not impact delivery of NAC. Clinical trial information: NCT02032277.

Abstract P4-22-02: Evaluation of veliparib (V) and temozolomide (TMZ) in a phase 2 randomized study of the efficacy and tolerability of V+TMZ or carboplatin (C) and paclitaxel (P) vs placebo (Plc)+C/P in patients (pts) with BRCA1 or BRCA2 mutations and metastatic breast cancer

Background: V is a potent, poly(ADP-ribose) polymerase (PARP) inhibitor that obstructs DNA damage repair. BRCA1/2 tumors are defective in homologous recombination, which leads to more error-prone mechanisms of DNA repair and increased sensitivity to PARP inhibition. V enhances the antitumor activity of alkylating agents such as TMZ in preclinical models. In addition, V+TMZ showed promising activity in a single-arm phase 2 study in pts with BRCA1/2 mutations. This phase 2 trial (NCT01506609) investigated the efficacy and tolerability of V+TMZ (or V+C/P) compared to Plc+C/P in pts with locally recurrent or metastatic breast cancer harboring a BRCA1 or BRCA2 mutation. Results from the primary analysis for the V+TMZ arm vs Plc+C/P are presented, and the V+C/P vs Plc+C/P results will be presented separately.

Methods: Male and female pts aged ≥18 years with histologically confirmed locally recurrent or metastatic breast cancer were randomized 1:1:1 to: 1) V 40 mg BID D1–7 + TMZ 150–200 mg/m2 QD D1–5, 28-D cycle; 2) V 120 mg BID D1–7 + C AUC 6, D3 and P 175 mg/m2, D3, 21-D cycle; 3) placebo BID D1–7 + C/P. Key eligibility criteria included known deleterious BRCA1/2 mutation, ≤2 prior chemotherapies for metastatic disease, no prior platinum agent, and no CNS metastases. Randomization was stratified by hormone receptor status, prior cytotoxic therapy (yes vs no), and ECOG PS (0–1 vs 2). The primary endpoint was progression-free survival (PFS) per RECIST 1.1 by independent review. Overall survival (OS), objective response rate (ORR), and safety/tolerability were also evaluated.

Results: A total of 290 pts (284 BRCA+ per central lab) were randomized (V+TMZ, n=94 [91 BRCA+]). Baseline demographics and disease characteristics were comparable among treatment arms; 41.3% of pts had triple-negative breast cancer (TNBC) and 31.7% had received &gt;2 prior regimens. Median study drug exposure was 6 cycles for the V+TMZ arm and 10 cycles for the Plc+C/P arm. Median PFS, median OS (interim), and ORR for V+TMZ were inferior to Plc+C/P (PFS 7.4 vs 12.3 mo, OS 19.1 vs 25.0 mo, and ORR 28.6% vs 61.3%). In pts with TNBC, median PFS was 5.5 (3.1–8.5) mo; 8.4 (6.8–10.6) mo for pts with non-TNBC. Treatment-emergent adverse events (AEs) of interest occurring differentially with V+TMZ are shown in Table 1. Grade ≥3 AEs in ≥30% of pts in the V+TMZ arm were thrombocytopenia (48%) and neutropenia (37%).

Conclusions: V+TMZ provided durable responses, with less neutropenia, alopecia, and neuropathy than Plc+C/P; however, PFS, OS, and ORR were inferior in the TMZ arm compared to C/P.

Table 1Treatment-Emergent AEs, n (%)V+TMZ, n=93Plc+C/P, n=96Neutropenia46 (50)71 (74)Alopecia10 (11)55 (57)Peripheral neuropathy11 (12)56 (58)Thrombocytopenia73 (79)67 (70)Nausea70 (75)56 (58)

Citation Format: Diéras V, Han HS, Robson ME, Palácová M, Marcom PK, Jager A, Bondarenko I, Citrin D, Campone M, Telli ML, Domchek SM, Friedlander M, Kaufman B, Ratajczak C, Coates A, Bonnet P, Qin Q, Qian J, Giranda VL, Shepherd SP, Puhalla S, Isakoff SJ. Evaluation of veliparib (V) and temozolomide (TMZ) in a phase 2 randomized study of the efficacy and tolerability of V+TMZ or carboplatin (C) and paclitaxel (P) vs placebo (Plc)+C/P in patients (pts) with BRCA1 or BRCA2 mutations and metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-02.

A randomized Phase II study of veliparib with temozolomide or carboplatin/paclitaxel versus placebo with carboplatin/paclitaxel in BRCA1/2 metastatic breast cancer: design and rationale

Veliparib is an orally administered poly(ADP-ribose) polymerase inhibitor that is being studied in Phase I–III clinical trials, including Phase III studies in non-small-cell lung cancer, ovarian cancer and breast cancer. Tumor cells with deleterious BRCA1 or BRCA2 mutations are deficient in homologous recombination DNA repair and are intrinsically sensitive to platinum therapy and poly(ADP-ribose) polymerase inhibitors. We describe herein the design and rationale of a Phase II trial investigating whether the addition of veliparib to temozolomide or carboplatin/paclitaxel provides clinical benefit over carboplatin/paclitaxel with placebo in patients with locally recurrent or metastatic breast cancer harboring a deleterious BRCA1 or BRCA2 germline mutation (Trial registration: EudraCT 2011-002913-12, NCT01506609).

Phase III randomized, placebo-controlled trial of carboplatin (C) and paclitaxel (P) with/without veliparib (ABT-888) in HER2- BRCA-associated locally advanced or metastatic breast cancer (BC)

155

Background: BRCA-mutated tumors are more susceptible to platinum therapy and PARP inhibitors due to underlying defects in homologous recombination repair of DNA damage. In preclinical models the potent oral PARP1/2 inhibitor veliparib was shown to enhance sensitivity to C and to have single-agent activity in BRCA+ cell lines. Phase 1 trials suggest promising antitumor activity and acceptable toxicity of veliparib plus C/P in triple-negative BC (Puhalla et al. Cancer Res 2012;72:PD09-06) and single-agent activity of veliparib in BRCA+ BC (Somlo et al. J Clin Oncol 2014;32:abstr. 1021). This phase III trial assesses efficacy and toxicity of veliparib plus C/P vs C/P alone in patients with HER2− BRCA-associated locally advanced or metastatic BC (NCT02163694). Methods: Phase III randomized, double-blind, placebo-controlled, multicenter trial. Eligible patients (female or male; ≥ 18 years) have HER2−metastatic/locally advanced unresectable BC with (suspected) deleterious BRCA1/2 germline mutations and received 2 or fewer prior lines of DNA-damaging chemotherapy for metastatic BC. In addition, patients must have received ≤ 1 prior line of platinum therapy (any setting) without progression within 12 months of completing treatment. Patients are randomized 2:1 to C/P with veliparib or C/P with placebo, stratified by estrogen and/or progesterone receptor expression, prior platinum therapy, and central nervous system metastases. Veliparib (120 mg p.o. BID) or placebo will be given on Days −2 to 5, C (AUC 6 mg/mL/min i.v.) on Day 1, and P (80 mg/m2i.v.) on Days 1, 8, and 15 (21-day cycles). Treatment continues until unacceptable toxicity or progressive disease (PD). Patients in the placebo arm who discontinue due to PD are eligible for crossover to veliparib monotherapy. The primary objective is to assess if the addition of veliparib to C/P increases progression-free survival; additional objectives include evaluation of overall survival, clinical benefit rate, objective response rate, quality of life, and safety. Enrollment began in July 2014 with a planned sample size of 270 patients. Clinical trial information: NCT02163694.

Randomized phase II study evaluating veliparib (ABT-888) with temozolomide in patients with metastatic melanoma

BACKGROUND

Veliparib (ABT-888) is a potent, orally bioavailable, small-molecule inhibitor of the DNA repair enzymes poly ADP-ribose polymerase-1 and -2. Veliparib enhances the efficacy of temozolomide (TMZ) and other cytotoxic agents in preclinical tumor models.

PATIENTS AND METHODS

In this multicenter, double-blind trial, adults with unresectable stage III or IV metastatic melanoma were randomized 1:1:1 to TMZ plus veliparib 20 or 40 mg, or placebo twice daily. Efficacy end points included progression-free survival (PFS), overall survival (OS), and objective response rate (ORR).

RESULTS

Patients (N = 346) were randomized between February 2009 and January 2010. Median [95% confidence interval (CI)] PFS was 3.7 (3.0-5.5), 3.6 (1.9-4.1), and 2 (1.9-3.7) months in the 20-mg, 40-mg, and placebo arms, respectively. Median (95% CI) OS was 10.8 (9.0-13.1), 13.6 (11.4-15.9), and 12.9 (9.8-14.3) months, respectively; ORR was 10.3%, 8.7%, and 7.0%. Exploratory analyses showed patients with low ERCC1 expression had longer PFS when TMZ was combined with veliparib. Toxicities were as expected for TMZ. The frequencies of thrombocytopenia, neutropenia, and leukopenia were significantly increased in the veliparib groups. Grade 3 or 4 adverse events, mainly hematologic toxicities, were seen in 55%, 63%, and 41% of patients in the 20-mg, 40-mg, and placebo arms, respectively.

CONCLUSIONS

Median PFS with 20 and 40 mg veliparib almost doubled numerically compared with placebo, but the improvements did not reach statistical significance. OS was not increased with veliparib. Toxicities were similar to TMZ monotherapy, but with increased frequency.

Population pharmacokinetic modeling of veliparib (ABT-888) in patients with non-hematologic malignancies

BACKGROUND AND OBJECTIVE

Veliparib (ABT-888) is a potent oral inhibitor of Poly(ADP-ribose) polymerase enzyme that is currently in development for the treatment of non-hematologic and hematologic malignancies. This analysis characterizes the population pharmacokinetics of veliparib, including developing a structural pharmacokinetic model and testing patient demographics and covariates for potential influence on veliparib pharmacokinetics in patients with non-hematologic malignancies.

METHODS

The analysis dataset included 3,542 veliparib concentration values from 325 patients with non-hematologic malignancies enrolled in three phase I and one phase II studies. Population pharmacokinetic modeling was performed using NONMEM. The likelihood ratio test was used for comparison of nested models, and visual predictive check was employed for model qualification. Covariates tested included body size measures, creatinine clearance (CLCR), formulation, age, sex, race, liver function tests, and coadministration with temozolomide.

RESULTS

A one-compartment model with first-order absorption and elimination adequately described veliparib pharmacokinetics. The final model included fixed effects for CLCR on veliparib oral clearance (CL/F) and lean body mass (LBM) on volume of distribution (V d/F). CL/F and V d/F were 20.9 L/h (for a CLCR of 100 mL/min) and 173 L (for an LBM of 56 kg), respectively.

CONCLUSION

Only LBM and CLCR were found to be determinants of veliparib V d/F and CL/F, respectively. Dosage adjustments of veliparib on the basis of body size, age, sex, race, liver function, and temozolomide coadministration are not necessary in patients with non-hematologic malignancies. This is the first study to characterize the population pharmacokinetics of veliparib, and the developed model will be used to conduct simulations and evaluate veliparib exposure-response relationships.

Outcome of BRCA 1/2-mutated (BRCA+) and triple-negative, BRCA wild type (BRCA-wt) breast cancer patients in a phase I study of single-agent veliparib (V)

135

Background: Veliparib (V) (ABT-888) is an oral, potent inhibitor of PARP 1/2. PARP inhibitors have preclinical and clinical efficacy in BRCA+ malignancies. There are genotypic and phenotypic similarities between BRCA+ cancers, serous ovarian cancer and basal-like breast cancer and we postulated that these tumors types may be similarly sensitive to single-agent PARP inhibition. This study sought to establish the maximum tolerated dose (MTD), dose -limiting toxicities (DLT), pharmacokinetic and pharmocodynamic properties, and preliminary efficacy of chronically-dosed V in 2 cohorts of patients, BRCA+ and BRCA-wt (consisting of serous ovarian cancer and triple-negative breast cancer (TNBC). Methods: A 3+3 dose escalation phase I trial was performed. Nine dose levels (DL) were planned, and dose escalation started at 50 mg BID to a maximum of 500 mg BID to determine a maximum tolerated dose (MTD) and recommended phase II dose (RP2D). V was administered orally continuously on a 28 day cycle. BRCA+ and BRCA-wt patients were enrolled in 2 separate cohorts with 2 separate escalations. Results: 98 (70 BRCA+ and 28 BRCA-wt) pts have been enrolled. The maximum administered dose (MAD) was 500mg BID and the MTD/RP2D is 400mg BID for both cohorts. 59 BRCA+ pts and 24 BRCA-wt pts (21 TNBC and 3 ovary) were evaluable for response. ORR was defined as CR+PR and clinical benefit rate (CBR) as CR+PR+SD > 6 months. Results are summarized in the table. Conclusions: There is evidence of anti-tumor activity with V comparable to that of other PARP inhibitors in the BRCA+ population. There was indication of dose responsiveness with greater activity in this population at higher doses. There is less activity in the mostly TNBC, BRCA-wt population, although there was evidence of benefit in a small number of patients. Ongoing tissue correlative studies will help to identify potential mechanisms of sensitivity and resistance. Clinical trial information: NCT00892736. [Table: see text]

PARP inhibitors attenuate chemotherapy-induced painful neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major toxicity of chemotherapy treatment for which no therapy is approved. Poly(ADP-ribose) polymerase (PARP)1/2 are nuclear enzymes activated upon DNA damage, and PARP1/2 inhibition provides resistance against DNA damage. A role for PARP inhibition in sensory neurotransmission has also been established. PARP inhibitors attenuate pain-like behaviors and neuropathy-associated decreased peripheral nerve function in diabetic models. The hypothesis tested was that PARP inhibition protects against painful neuropathy. The objective of this study was to investigate whether the novel, selective PARP1/2 inhibitors (ABT-888 and related analogues) would attenuate development of mechanical allodynia in vincristine-treated rats. PARP inhibitors were dosed for 2 days, and then co-administered with vincristine for 12 days. Mechanical allodynia was observed in rats treated with vincristine. PARP1/2 inhibition significantly attenuated development of mechanical allodynia and reduced poly ADP-ribose (PAR) activation in rat skin. The data presented here show that PARP inhibition attenuates vincristine-induced mechanical allodynia in rats, and supports that PARP inhibition may represent a novel therapeutic approach for CIPN.

A phase I clinical trial of veliparib and temozolomide in children with recurrent central nervous system tumors: A Pediatric Brain Tumor Consortium report

2036

Background: A phase I trial of veliparib (ABT-888), an oral poly(ADP-ribose) polymerase (PARP) inhibitor, and temozolomide (TMZ) was conducted in children with recurrent brain tumors to: 1) estimate the maximum tolerated doses (MTD) or recommended phase II doses (RP2D) of veliparib and TMZ using the Continual Reassessment Method; 2) describe the toxicities of this regimen; and 3) evaluate plasma pharmacokinetics (PK) and peripheral blood mononuclear cell (PBMC) PARP inhibition after veliparib treatment. Methods: TMZ was given once daily and veliparib twice daily for 5 days, every 28 days. Five veliparib/TMZ dose levels were studied: 20/180; 15/180; 15/150; 20/135; and 25/135 mg/m2/dose, respectively. Baseline and serial veliparib PK samples were obtained on days 1 and 4. PBMC poly(ADP-ribose) (PAR) levels were also measured using an ELISA assay. A total of 12 subjects were enrolled at the RP2D. Results: Thirty-one patients (29 evaluable) with a median age of 7.0 years (range 1.3-19.8) were enrolled. Dose-limiting toxicities (DLT) included grade 4 neutropenia and thrombocytopenia at the 20/180 and 15/180 mg/m2/dose levels. Based on the toxicity profile, PKs and PBMC PAR results, the RP2D were veliparib, 25 mg/m2 BID, and TMZ, 135 mg/m2/day, for 5 days every 28 days. No objective responses were observed, although 4 subjects had SD > 6 months duration, including one patient each with glioblastoma multiforme, anaplastic ependymoma, pilocytic astrocytoma, and optic pathway glioma. At the veliparib RP2D, the PK parameters included: Cmax, 1.2 ± 0.7 µM; AUC0-12 hr, 1.53 ± 0.61 µg•hr/mL; and Cl/F, 173 ± ml/min/m2. PARP inhibition was observed in PBMC but did not correlate with veliparib dose levels. Conclusions: The combination of veliparib and TMZ was well tolerated in children with recurrent CNS tumors. Veliparib PK parameters at RP2D are similar to those in adults. PBMC PARP inhibition did not correlate with veliparib dose levels, perhaps due to the smaller number of patients at each dose level and the technical limitations of specimen collection/processing and the ELISA assay. A phase II trial of veliparib/TMZ in children with recurrent primary brain tumors is planned. Clinical trial information: NCT00946335.

Phase I adult brain tumor consortium (ABTC) trial of ABT-888 (veliparib), temozolomide (TMZ), and radiotherapy (RT) for newly diagnosed glioblastoma multiforme (GBM) including pharmacokinetic (PK) data

2065

Background: ABTC conducted a dose finding trial of ABT-888, an orally administered Poly(ADP-ribose) polymerase [PARP] inhibitor, during daily TMZ with post-operative RT for GBM. PARP is important in repair pathways for RT induced DNA injury and TMZ induced alkylation at N7-methylguanine and N3-methyldenine. Methods: An initial safety group (no concurrent RT), received ABT-888 10 mg BID po during 42 days of daily TMZ 75 mg/m2. After this, the planned dosing steps included ABT-888 BID concurrent with standard RT and TMZ, with planned ABT-888 dose escalation or de-escalation based on observed toxicity. Dose limiting toxicity (DLT) is ≥ grade 3 non-hematologic or neurologic not responding to steroids, and hematologic ANC<500/mm3 and platelets (PLT) < 25K/mm3. The pharmacokinetics (PK) of ABT-888 were characterized for dose 1 and at steady-state. Results: Without concurrent RT, DLT (thrombocytopenia) occurred in 1/6 patients. With concurrent RT/TMZ and ABT-888 10 mg BID, 4/12 patients had DLT (thrombocytopenia). As per the planned dose de-escalation, ABT-888 10 mg BID was then given every other week during TMZ/RT. This resulted in 3/6 patients with DLT (2 thrombocytopenia, 1 neutropenia). The hematologic toxicity with this regimen was judged high enough that accrual was discontinued. In the setting of continuous dosing for 6 weeks, the total body clearance of ABT-888 for the first dose (27.5±9.5 L/h, n = 15) and at steady-state after BID dosing (23.5±10.4 L/h, n = 18) were similar. Accumulation for BID dosing was 56±33%. Steady-state peak and trough concentrations of the drug in plasma were 66±29 ng/mL and 18±10 ng/mL, respectively. Additional PK data will be presented. Conclusions: Administering ABT-888 BID po in combination with standard RT/TMZ was not tolerable in GBM patients as a result of hematologic toxicity. ABT-888 PK in GBM patients were very similar to findings reported for solid tumor patients. There is strong scientific rationale for continued development of an appropriate dosing regimen for this agent in the initial therapy of GBM. Clinical trial information: NCT00770471.

Phase I study of ABT-888 in combination with carboplatin and gemcitabine in subjects with advanced solid tumors

2584^

Background: Veliparib (V) is an oral inhibitor of poly(ADP-ribose) polymerases (PARP)-1 and -2, which are essential for base excision repair of ssDNA breaks. BRCA deficient tumors are more sensitive to PARP inhibitors when used as monotherapy or in combination with DNA-damaging agents. The objectives of this study were to determine the maximum tolerated dose (MTD), pharmacokinetic interactions, and safety/tolerability profile of V in combination with carboplatin (C) and gemcitabine (G). Methods: Eligibility criteria included patients (pts) with metastatic or unresectable solid tumors for which C/G was a treatment option. During the study, eligibility was amended to limit prior chemotherapy regimens to ≤ 2. C AUC 4 /G 800 mg/m2was given intravenously on Day 1 and G given on Day 8 of 21 day cycles. To assess tolerability of C/G prior to V, V was started in Cycle 2. When C/G was stopped, pts could stay on monotherapy V until progression. Dose-escalation used a Bayesian continual reassessment method. Results: 59 pts (51 female, median age 52) were enrolled. The most common tumor types were ovarian (n=39) and breast (n=10). Germline BRCA mutations were known in 24 ovarian pts. 58 pts had prior chemotherapy (1-6 regimens, median 2), and 51 had prior platinum. Grade 3/4 AEs in >10% of pts were neutropenia, thrombocytopenia, anemia, and leukopenia. Dose limiting toxicities were thrombocytopenia (n=3) and neutropenia at V 310 mg twice daily (BID) and thrombocytopenia at 250 mg BID. Other frequent AEs were nausea, constipation, and fatigue. Preliminary results showed co-administration of V did not affect C or G pharmacokinetics. Treatment cycles (range, median) were 1-28, 5 for V; 2-10, 5 for C; and 2-10, 4 for G. Day 8 G was stopped in some pts to improve tolerability. 28 pts stayed on monotherapy V (1-23 cycles). Partial and complete responses were seen in 11 and 2 pts. Response rates were 47% (8/17) in known BCRA deficient ovarian, 25% (3/12) in other ovarian, and 13% (2/15) in other evaluable pts. Conclusions: V combined with C and G was tolerated with a safety profile similar to C and G alone. The MTD was V 250 mg BID, C AUC 4.0, G 800 mg/m2. Promising anti-tumor activity was observed in BRCA deficient ovarian pts. Clinical trial information: NCT01063816.

Hit to Lead optimization of a novel class of squarate-containing polo-like kinases inhibitors

A high throughput screening (HTS) hit, 1 (Plk1 K(i)=2.2 μM) was optimized and evaluated for the enzymatic inhibition of Plk-1 kinase. Molecular modeling suggested the importance of adding a hydrophobic aromatic amine side chain in order to improve the potency by a classic kinase H-donor-acceptor binding mode. Extensive SAR studies led to the discovery of 49 (Plk1 K(i)=5 nM; EC(50)=1.05 μM), which demonstrated moderate efficacy at 100 mpk in a MiaPaCa tumor model, with no overt toxicity.

A phase I study of veliparib (ABT-888) in combination with carboplatin and paclitaxel in advanced solid malignancies

3049

Background: Veliparib (ABT-888, NSC 737664) is an orally available inhibitor of poly(ADP-ribose) polymerase (PARP)-1 and -2: enzymes that recruit base excision repair machinery to single-stranded DNA breaks. Expression of PARP-1 may be increased in cancer cells and confer resistance to DNA-damaging agents. The objectives of this phase I study included determination of the recommended phase 2 dose (RP2D), maximum tolerated dose (MTD), dose limiting toxicity (DLT) and pharmacokinetics (PK) of veliparib in combination with paclitaxel (P) and carboplatin (C). Methods: Eligibility criteria included advanced solid tumors, ≤ 3 prior chemotherapy regimens for advanced disease, ECOG performance status 0-2. Veliparib was given PO BID on days 1-7 of each 21 day cycle, and P and C were administered on day 3. In dose levels 1-7, veliparib was not given during cycle 1 to serve as intra-patient control for toxicity and PK assessment, and DLT was evaluated during cycle 2. A standard “3+3” dose escalation was utilized starting at veliparib 20 mg BID, P 150 mg/m2, C AUC 5. Plasma concentrations of veliparib, P and C were determined by LC-MS/MS and AAS during cycle 1 and 2. Results: To date, 68 patients have been enrolled. Tumor types included lung (15), breast (14), melanoma (10), squamous cell of head/neck (7), and urothelial (5). Toxicities observed were expected with C plus P chemotherapy, including neutropenia, thrombocytopenia, peripheral neuropathy. DLTs were seen in 2 out of 7 evaluable patients at the maximum administered dose: veliparib 120 mg BID, P 200 mg/m2, C AUC 6, (febrile neutropenia, hyponatremia). Veliparib 80 mg, P 200 mg/m2, C AUC 6 was well tolerated with 1 out of 9 DLT (febrile neutropenia). Median number of cycles was 5 (1-17). Partial response was seen in 11 (Lung-2, breast-2, melanoma-2, urothelial-2, head and neck, gastric, unknown primary) and complete response in 1 patient with breast cancer and 1 patient with urothelial cancer. Stable disease was observed in 35 patients. Veliparib did not affect the PK disposition of P or C. Conclusions: Veliparib in combination with P and C was well-tolerated with a safety profile similar to P and C alone. Promising anti-tumor activity was observed in several tumor types.

A phase I study of chronically dosed, single-agent veliparib (ABT-888) in patients (pts) with either BRCA 1/2-mutated cancer (BRCA+), platinum-refractory ovarian cancer, or basal-like breast cancer (BRCA-wt)

3054

Background: Veliparib (ABT-888) is an oral, potent inhibitor of PARP 1/2. Preclinically, PARP inhibitors have activity in tumors with defective homologous recombination (HR), particularly those that are BRCA+. Reduced levels of BRCA expression have been observed in ovarian cancer and basal-like breast cancer, which share genotypic and phenotypic similarities with BRCA+ cancers. We postulated that these tumors types may be similarly sensitive to single-agent PARP inhibition. This study sought to establish the maximum tolerated dose (MTD), dose limiting toxicities (DLT), pharmacokinetic and pharmocodynamic properties, and preliminary efficacy of chronically-dosed veliparib. Methods: A 3+3 dose escalation phase I trial was performed. Nine dose levels (DL) were planned, and dose escalation started at 50 mg BID to a maximum of 500 mg BID. Veliparib was administered orally continuously on a 28 day cycle. Results: 63 pts have been enrolled to date. Thirty-eight were BRCA+ (20 ovary, 12 breast, 2 pancreas, and one each - prostate, peritoneal, fallopian tube, endometrial); 25 BRCA-wt. (21 breast, 4 ovarian). DLTs occurred at the following dose levels: BRCA+: gr. 2 thrombocytopenia at 50 mg BID; BRCA+: gr.3 Nausea/vomiting at 400 mg BID; BRCA-wt: gr 2 seizure at 400 mg BID. The MTD has not been determined and 500 mg BID is presently enrolling. Notable toxicities have included low-grade fatigue and nausea. PK was linear and non-saturable with t ½ of 5 h. The number of cycles administered ranged from 1- 15, median 2. In BRCA+ pts, there were 2 partial responses (breast, ovarian) and 10 pts had evidence of prolonged SD ≥ 4 months. In BRCA-wt pts, there was 1 PR (breast) and 7 pts with SD≥ 4 months. Correlative studies, including assessment of PAR inhibition and BRCA methylation status, are ongoing. Conclusions: Veliparib is tolerable on a continuous oral dosing schedule with evidence of anti-tumor activity seen in BRCA+ and BRCA-wt tumors. A mandatory biopsy expansion cohort is planned at the recommended phase II dose, which will allow further insights regarding efficacy and mechanisms of resistance to PARP inhibition.

ABT-888 (veliparib) in combination with weekly carboplatin and paclitaxel in advanced solid tumors

TPS1138

Background: The combination of paclitaxel and carboplatin is widely used for the treatment of patients with advanced solid tumors of diverse histologies. In breast cancer patients, a weekly regimen of paclitaxel has shown greater efficacy with comparable safety, when compared to every-three-weeks dosing (ECOG 1199). ABT-888 (veliparib) is an oral inhibitor of poly-ADP-ribose polymerase (PARP). Inhibition of PARP has been shown in preclinical studies to potentiate the effect of cytotoxic agents which induce DNA damage, such as platinum agents. The preclinical synergy of carboplatin with veliparib and the efficacy of the combination of paclitaxel with carboplatin supports exploration of this triplet regimen. Methods: This 3+3 phase I trial will seek to determine the maximum tolerated dose (MTD) of the combination of carboplatin (AUC 2), paclitaxel (80 mg/m2), and veliparib in patients with advanced solid tumors. Veliparib will be escalated beginning at 50 mg PO BID to a maximum of 200mg PO BID. Treatment will be given on a weekly basis over a 21-day cycle. There will be an expansion cohort of 6-12 patients with triple negative breast cancer at the maximum tolerated dose. This group of patients will undergo mandatory pre- and post-cycle 1 tumor biopsies. Secondary aims of the study include safety and toxicity of the combination, its pharmacokinetic and pharmacodynamic effects, documentation of any anti-tumor response, and assessment of the characteristics of the tumor specimens obtained in the expansion cohort that may contribute to efficacy. The latter will include whole genome microarray analysis to evaluate expression of genes involved in DNA repair pathways. Currently, the recommended phase II dose has not been determined and enrollment is ongoing on the last planned dose level (veliparib 200 mg BID).

Phase I safety and pharmacokinetic (PK) study of veliparib in combination with whole brain radiation therapy (WBRT) in patients (pts) with brain metastases

2013

Background: Veliparib is an oral PARP-1 and -2 inhibitor that enhances the antitumor activity of DNA damaging agents including radiation therapy in vivo. In pre-clinical models, veliparib crosses the blood-brain barrier. This ongoing phase I dose-escalation study evaluates the safety, PK, and provides preliminary antitumor activity of veliparib in combination with WBRT in pts with brain metastases. Methods: Pts with brain metastases from non-CNS primary solid malignancy, adequate organ function, RPA Class 2, and KPS ≥70 were treated with WBRT (37.5 Gy in 15 fractions or 30 Gy in 10 fractions) QD with veliparib BID with every fraction of WBRT in escalating doses of 10, 20, 30, 50, 100, 150, and 200 mg; the final WBRT fraction was followed by 1 extra day of veliparib. Safety, PK, and tumor response by RECIST were assessed. Results: At the time of reporting 59 pts (M/F, 21/38; median age 57 y) had been treated. Baseline KPS was 70, 80, 90, and 100 in 6.8, 32.2, 40.7, and 20.3% pts, respectively; primary tumor types were breast (n=20), NSCLC (n=20), melanoma (n=9), colorectal (n=2), and others (n=8); 71.2% pts had multiple lesions; and 18.6% had prior brain SRS. Grade 3/4 treatment-emergent adverse events (TEAEs; ≥5%) were fatigue (6.8%), anemia (5.1%), hyponatraemia (5.1%), and thrombocytopenia (5.1%); other TEAEs (≥20%) were fatigue (57.6%), headache (42.4%), nausea (40.7%), alopecia (28.8%), vomiting (22%), radiation skin reactions (22%), and decreased appetite (22%). PK of veliparib were approximately dose-proportional, with oral clearance of 21.6 ± 14.2 L/h (mean ± SD, n=45), minimal drug accumulation at day 15, and no significant effect of food on bioavailability. Tumor response was evaluable in 48 pts. Best tumor response and median survival were 37.5% and 10 months (m) for NSCLC, and 52.9% and 12.5 m for breast cancer (excluding pts with leptomeningeal disease). Conclusions: Addition of veliparib up to 200 mg BID was well tolerated with concurrent WBRT and dose escalation ongoing. The PK of veliparib was dose proportional with no food effect. Preliminary antitumor activity is encouraging and informative for the design of more definitive trials.

Pilot study of veliparib (ABT-888) with temozolomide (TMZ) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

224

Background: Castration-resistant PC tumors exhibit increased PARP activity (critical enzymes for DNA damage repair). Veliparib is a novel, oral, potent inhibitor of PARP-1 and PARP-2. Preclinically, resistance to oral TMZ treatment in the PC3-Luc prostate cancer mouse model was reversed when mice were treated with veliparib. Based on the synergistic interaction, we evaluated the efficacy and safety of veliparib + TMZ in mCRPC pts.

Methods: Eligible pts had mCRPC, PSA>2 ng/mL, progressed on at least one docetaxel based therapy and adequate organ function. Pts received veliparib 40 mg BID Days (D) 1-7 and TMZ D1-5 in 28D cycle (C) until disease progression (PD) or unacceptable toxicities. Tumor response was assessed every 8 weeks. Primary objective: Efficacy based on rate of PSA decline of 30% or greater. Secondary objectives: safety, RECIST objective response rate, progression-free survival (PFS), overall survival (OS) and biomarker analyses. A sample size of 25 pts provided 76% power to differentiate between PSA response rates of 5 and 20% at 1-sided type I error rate of 0.1.

Results: 26 pts were enrolled; median age 67 years [55, 81]; median baseline PSA 107 ng/ml (6.9, 4584.4); 7/26 (27%) had 2 prior therapies. Median Cs of veliparib + TMZ received were 2 (range 1–9). Most frequent treatment related adverse events (AE) were fatigue (50%), nausea (38%) and constipation (23%). Grade 3/4 AEs in >10% of pts was thrombocytopenia (15%). All pts are off therapy. 25 pts were PSA response evaluable; 2 pts had a confirmed PSA response; 1 pt had a 37% decrease in PSA while the other pt had a 96% decrease in PSA and a 40% reduction in tumor size. 4/25 pts had stable disease for a minimum of 4 months (m). Median PFS was 2.1 m [95% CI: 1.8, 3.9]; 11/26 pts have died with median OS of 9.1 m [95% CI: 5.5, 11.7]. There was a negative correlation between change from baseline in circulating tumor cells and PFS.

Conclusions: Veliparib + TMZ were well tolerated with evidence of some activity. Due to lack of activity of TMZ in CRPC,veliparib-induced potentiation of TMZ may not be clinically significant. Other combinations will be explored with higher doses of veliparib. Biomarker data will be presented.

Ubiquitin-specific cysteine protease 2a (USP2a) regulates the stability of Aurora-A

The ubiquitin/proteasome pathway plays critical roles in virtually all aspects of cell biology. Enzymes of the ubiquitin pathway add (ligases) or remove (deubiquitinases) ubiquitin tags to or from their target proteins in a selective fashion. USP2a is a member of a subfamily of deubiquitinases, called ubiquitin-specific cysteine proteases (USPs). Although USP2a has been reported to be a bona fide oncogene that regulates the stability of MDM2, MDMX, and FAS, it is likely that there are other unidentified substrates for USP2a. In this study, we show that USP2a mediates mitotic progression by regulating the stability of Aurora-A. Through cell-based screening of a USP siRNA library, we discovered that knockdown of USP2a reduced the protein levels of Aurora-A. USP2a interacts with Aurora-A directly in vitro and in vivo. In addition, Aurora-A is a substrate for USP2a in vitro and in vivo. Our study provides a novel mechanism for the role of USP2a in mediating the stability of Aurora-A.

Optimization of phenyl-substituted benzimidazole carboxamide poly(ADP-ribose) polymerase inhibitors: identification of (S)-2-(2-fluoro-4-(pyrrolidin-2-yl)phenyl)-1H-benzimidazole-4-carboxamide (A-966492), a highly potent and efficacious inhibitor

We have developed a series of phenylpyrrolidine- and phenylpiperidine-substituted benzimidazole carboxamide poly(ADP-ribose) polymerase (PARP) inhibitors with excellent PARP enzyme potency as well as single-digit nanomolar cellular potency. These efforts led to the identification of (S)-2-(2-fluoro-4-(pyrrolidin-2-yl)phenyl)-1H-benzimidazole-4-carboxamide (22b, A-966492). Compound 22b displayed excellent potency against the PARP-1 enzyme with a K(i) of 1 nM and an EC(50) of 1 nM in a whole cell assay. In addition, 22b is orally bioavailable across multiple species, crosses the blood-brain barrier, and appears to distribute into tumor tissue. It also demonstrated good in vivo efficacy in a B16F10 subcutaneous murine melanoma model in combination with temozolomide and in an MX-1 breast cancer xenograft model both as a single agent and in combination with carboplatin.

Plasma and cerebrospinal fluid pharmacokinetics of ABT-888 after oral administration in non-human primates

PURPOSE

ABT-888 inhibits poly(ADP-ribose) polymerase (PARP) and may enhance the efficacy of chemotherapy and radiation in CNS tumors. We studied the plasma and cerebrospinal fluid (CSF) pharmacokinetics (PK) of ABT-888 in a non-human primate (NHP) model that is highly predictive of human CSF penetration.

METHODS

ABT-888, 5 mg/kg, was administered orally to three NHPs. Serial blood and CSF samples were obtained. Plasma and CSF concentrations of ABT-888 were measured using LC/MS/MS, and the resulting concentration versus time data were evaluated using non-compartmental and compartmental PK methods.

RESULTS

The CSF penetration of ABT-888 was 57+/-7% (mean+/-SD). The peak ABT-888 concentration in the plasma was 0.62+/-0.18 microM. Plasma and CSF AUC0-infinity were 3.7+/-1.7 and 2.1+/-0.8 microM h. PARP inhibition in peripheral blood mononuclear cells was evident 2 h after ABT-888 administration.

CONCLUSION

The CSF penetration of ABT-888 after oral administration was 57%. Plasma and CSF concentrations were in the range that has been shown to inhibit PARP activity in vivo in humans.

Discovery and SAR of substituted 3-oxoisoindoline-4-carboxamides as potent inhibitors of poly(ADP-ribose) polymerase (PARP) for the treatment of cancer

Through conformational restriction of a benzamide by formation of a seven-membered hydrogen-bond with an oxindole carbonyl group, a series of PARP inhibitors was designed for appropriate orientation for binding to the PARP surface. This series of compounds with a 3-oxoisoindoline-4-carboxamide core structure, displayed modest to good activity against PARP-1 in both intrinsic and cellular assays. SAR studies at the lactam nitrogen of the pharmacophore have suggested that a secondary or tertiary amine is important for cellular potency. An X-ray structure of compound 1e bound to the protein confirmed the formation of a seven-membered intramolecular hydrogen bond. Though revealed previously in peptides, this type of seven-membered intramolecular hydrogen bond is rarely observed in small molecules. Largely due to the formation of the intramolecular hydrogen bond, the 3-oxoisoindoline-4-carboxamide core structure appears to be planar in the X-ray structure. An additional hydrogen bond interaction of the piperidine nitrogen to Gly-888 also contributes to the binding affinity of 1e to PARP-1.

Immunohistochemical detection of poly(ADP-ribose) polymerase inhibition by ABT-888 in patients with refractory solid tumors and lymphomas

PURPOSE

Targeting the poly (ADP-ribose) polymerase (PARP) pathway for cancer treatment has been an active area of pre-clinical and clinical research. We aimed to determine whether the PARP inhibitor ABT-888 hits its therapeutic target in tumors by immunohistochemistry during a Phase 0 trial conducted at the National Cancer Institute.

EXPERIMENTAL DESIGN

The expression of poly (ADP-ribose) (PAR) and full size PARP-1 were quantitatively examined by immunohistochemistry in paraffin-embedded tumor biopsies at baseline and 3-24 h after a single oral dose (25 or 50 mg) of ABT-888.

RESULTS

Baseline PAR levels were moderate to high in three patients with non-Hodgkin lymphomas, and one each with small cell lung cancer, squamous cell carcinoma of the tongue and melanoma; low in two patients with cutaneous T-cell lymphoma and one with adenocarcinoma of external ear canal. A significant decrease in PAR (median decrease 30.2, range -13.1 to -69.8) was achieved after drug administration (n = 6 pairs; p = 0.03), whereas an increase in PARP-1 expression was observed in five of the six tumors. This resulted in a decrease in the ratio of PAR to PARP-1 in tumor biopsies (median -6.76, range -0.41 to -22.59; p = 0.03).

CONCLUSIONS

ABT-888 hits its therapeutic target by significantly reducing PAR levels and the ratio of PAR to PARP-1 in human tumor cells detected by immunohistochemistry. Baseline tumor PAR levels vary considerably among patients who entered this phase 0 study. This underscores a need to investigate baseline PAR levels in association with response in future preclinical and clinical studies.

ABT-888 confers broad in vivo activity in combination with temozolomide in diverse tumors

PURPOSE

ABT-888, currently in phase 2 trials, is a potent oral poly(ADP-ribose) polymerase inhibitor that enhances the activity of multiple DNA-damaging agents, including temozolomide (TMZ). We investigated ABT-888+TMZ combination therapy in multiple xenograft models representing various human tumors having different responses to TMZ.

EXPERIMENTAL DESIGN

ABT-888+TMZ efficacy in xenograft tumors implanted in subcutaneous, orthotopic, and metastatic sites was assessed by tumor burden, expression of poly(ADP-ribose) polymer, and O(6)-methylguanine methyltransferase (MGMT).

RESULTS

Varying levels of ABT-888+TMZ sensitivity were evident across a broad histologic spectrum of models (55-100% tumor growth inhibition) in B-cell lymphoma, small cell lung carcinoma, non-small cell lung carcinoma, pancreatic, ovarian, breast, and prostate xenografts, including numerous regressions. Combination efficacy in otherwise TMZ nonresponsive tumors suggests that TMZ resistance may be overcome by poly(ADP-ribose) polymerase inhibition. Profound ABT-888+TMZ efficacy was seen in experimental metastases models that acquired resistance to TMZ. Moreover, TMZ resistance was overcome in crossover treatments, indicating that combination therapy may overcome acquired TMZ resistance. Neither tumor MGMT, mismatch repair, nor poly(ADP-ribose) polymer correlated with the degree of sensitivity to ABT-888+TMZ.

CONCLUSIONS

Robust ABT-888+TMZ efficacy is observed across a spectrum of tumor types, including orthotopic and metastatic implantation. As many TMZ nonresponsive tumors proved sensitive to ABT-888+TMZ, this novel combination may broaden the clinical use of TMZ beyond melanoma and glioma. Although TMZ resistance may be influenced by MGMT, neither MGMT nor other mechanisms of TMZ resistance (mismatch repair) precluded sensitivity to ABT-888+TMZ. Underlying mechanisms of TMZ resistance in these models are not completely understood but likely involve mechanisms independent of MGMT.

Acquired resistance to combination treatment with temozolomide and ABT-888 is mediated by both base excision repair and homologous recombination DNA repair pathways

Many established cancer therapies involve DNA-damaging chemotherapy or radiotherapy. Gain of DNA repair capacity of the tumor represents a common mechanism used by cancer cells to survive DNA-damaging therapy. Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme that is activated by DNA damage and plays a critical role in base excision repair. Inhibition of PARP represents an attractive approach for the treatment of cancer. Previously, we have described the discovery and characterization of a potent PARP inhibitor, ABT-888. ABT-888 potentiates the activity of DNA-damaging agents such as temozolomide (TMZ) in a variety of preclinical models. We report here the generation of HCT116 cells resistant to treatment with TMZ and ABT-888 (HCT116R cells). HCT116R cells exhibit decreased H2AX phosphorylation in response to treatment with TMZ and ABT-888 relative to parental HCT116 cells. Microarray and Western blot studies indicate that HCT116R cells have decreased PARP-1 and elevated Rad51 expression levels. HCT116R cells are dependent on Rad51 for proliferation and survival, as shown by inhibition of proliferation and induction of apoptosis upon treatment with Rad51 small interfering RNA. In addition, HCT116R cells are more resistant to radiation than the parental HCT116 cells. Our study suggests that cancer cells upregulate the homologous recombination DNA repair pathway to compensate for the loss of base excision repair, which may account for the observed resistance to treatment with TMZ and ABT-888.

Synthesis and SAR of novel tricyclic quinoxalinone inhibitors of poly(ADP-ribose)polymerase-1 (PARP-1)

Based on screening hit 1, a series of tricyclic quinoxalinones have been designed and evaluated for inhibition of PARP-1. Substitutions at the 7- and 8-positions of the quinoxalinone ring led to a number of compounds with good enzymatic and cellular potency. The tricyclic quinoxalinone class is sensitive to modifications of both the amine substituent and the tricyclic core. The synthesis and structure-activity relationship studies are presented.

Phase 0 clinical trial of the poly (ADP-ribose) polymerase inhibitor ABT-888 in patients with advanced malignancies

PURPOSE

We conducted the first phase 0 clinical trial in oncology of a therapeutic agent under the Exploratory Investigational New Drug Guidance of the US Food and Drug Administration. It was a first-in-human study of the poly (ADP-ribose) polymerase (PARP) inhibitor ABT-888 in patients with advanced malignancies.

PATIENTS AND METHODS

ABT-888 was administered as a single oral dose of 10, 25, or 50 mg to determine the dose range and time course over which ABT-888 inhibits PARP activity in tumor samples and peripheral blood mononuclear cells, and to evaluate ABT-888 pharmacokinetics. Blood samples and tumor biopsies were obtained pre- and postdrug administration for evaluation of PARP activity and pharmacokinetics. A novel statistical approach was developed and utilized to study pharmacodynamic modulation as the primary end point for trials of limited sample size.

RESULTS

Thirteen patients with advanced malignancies received the study drug; nine patients underwent paired tumor biopsies. ABT-888 demonstrated good oral bioavailability and was well tolerated. Statistically significant inhibition of poly (ADP-ribose) levels was observed in tumor biopsies and peripheral blood mononuclear cells at the 25-mg and 50-mg dose levels.

CONCLUSION

Within 5 months of study activation, we obtained pivotal biochemical and pharmacokinetic data that have guided the design of subsequent phase I trials of ABT-888 in combination with DNA-damaging agents. In addition to accelerating the development of ABT-888, the rapid conclusion of this trial demonstrates the feasibility of conducting proof-of-principle phase 0 trials as part of an alternative paradigm for early drug development in oncology.

Discovery of the Poly(ADP-ribose) polymerase (PARP) inhibitor 2-[(R)-2-methylpyrrolidin-2-yl]-1H-benzimidazole-4-carboxamide (ABT-888) for the treatment of cancer

We have developed a series of cyclic amine-containing benzimidazole carboxamide PARP inhibitors with a methyl-substituted quaternary center at the point of attachment to the benzimidazole ring system. These compounds exhibit excellent PARP enzyme potency as well as single-digit nanomolar cellular potency. These efforts led to the identification of 3a (2-[(R)-2-methylpyrrolidin-2-yl]-1H-benzimidazole-4-carboxamide, ABT-888), currently in human phase I clinical trials. Compound 3a displayed excellent potency against both the PARP-1 and PARP-2 enzymes with a K(i) of 5 nM and in a C41 whole cell assay with an EC(50) of 2 nM. In addition, 3a is aqueous soluble, orally bioavailable across multiple species, and demonstrated good in vivo efficacy in a B16F10 subcutaneous murine melanoma model in combination with temozolomide (TMZ) and in an MX-1 breast cancer xenograft model in combination with either carboplatin or cyclophosphamide.

Inhibition of Akt inhibits growth of glioblastoma and glioblastoma stem-like cells

A commonly activated signaling cascade in many human malignancies, including glioblastoma multiforme, is the Akt pathway. This pathway can be activated via numerous upstream alterations including genomic amplification of epidermal growth factor receptor, PTEN deletion, or PIK3CA mutations. In this study, we screened phosphatidylinositol 3-kinase/Akt small-molecule inhibitors in an isogenic cell culture system with an activated Akt pathway secondary to a PIK3CA mutation. One small molecule, A-443654, showed the greatest selective inhibition of cells with the mutant phenotype. Based on these findings, this inhibitor was screened in vitro against a panel of glioblastoma multiforme cell lines. All cell lines tested were sensitive to A-443654 with a mean IC(50) of approximately 150 nmol/L. An analogue of A-443654, methylated at a region that blocks Akt binding, was on average 36-fold less active. Caspase assays and dual flow cytometric analysis showed an apoptotic mechanism of cell death. A-443654 was further tested in a rat intracranial model of glioblastoma multiforme. Animals treated intracranially with polymers containing A-443654 had significantly extended survival compared with control animals; animals survived 79% and 43% longer than controls when A-443654-containing polymers were implanted simultaneously or in a delayed fashion, respectively. This small molecule also inhibited glioblastoma multiforme stem-like cells with similar efficacy compared with traditionally cultured glioblastoma multiforme cell lines. These results suggest that local delivery of an Akt small-molecule inhibitor is effective against experimental intracranial glioma, with no observed resistance to glioblastoma multiforme cells grown in stem cell conditions.

Potentiation of temozolomide cytotoxicity by poly(ADP)ribose polymerase inhibitor ABT-888 requires a conversion of single-stranded DNA damages to double-stranded DNA breaks

Poly(ADP-ribose) polymerase (PARP) senses DNA breaks and facilitates DNA repair via the polyADP-ribosylation of various DNA binding and repair proteins. We explored the mechanism of potentiation of temozolomide cytotoxicity by the PARP inhibitor ABT-888. We showed that cells treated with temozolomide need to be exposed to ABT-888 for at least 17 to 24 hours to achieve maximal cytotoxicity. The extent of cytotoxicity correlates with the level of double-stranded DNA breaks as indicated by gammaH2AX levels. In synchronized cells, damaging DNA with temozolomide in the presence of ABT-888 during the S phase generated high levels of double-stranded breaks, presumably because the single-stranded DNA breaks resulting from the cleavage of the methylated nucleotides were converted into double-stranded breaks through DNA replication. As a result, treatment of temozolomide and ABT-888 during the S phase leads to higher levels of cytotoxicity. ABT-888 inhibits poly(ADP-ribose) formation in vivo and enhances tumor growth inhibition by temozolomide in multiple models. ABT-888 is well tolerated in animal models. ABT-888 is currently in clinical trials in combination with temozolomide.

The PARP inhibitor, ABT-888 potentiates temozolomide: correlation with drug levels and reduction in PARP activity in vivo

ABT-888 is a potent, orally bioavailable PARP-1/2 inhibitor shown to potentiate DNA damaging agents. The ability to potentiate temozolomide (TMZ) and develop a biological marker for PARP inhibition was evaluated in vivo. Doses/schedules that achieve TMZ potentiation in the B16F10 syngeneic melanoma model were utilized to develop an ELISA to detect a pharmacodynamic marker, ADP ribose polymers (pADPr), after ABT 888 treatment. ABT-888 enhanced TMZ antitumor activity, in a dose-proportional manner with no observed toxicity (44-75% tumor growth inhibition vs. TMZ monotherapy), but did not show single agent activity. Extended ABT-888 dosing schedules showed no advantage compared to simultaneous TMZ administration. Efficacy correlated with plasma/tumor drug concentrations. Intratumor drug levels correlated with a dose-proportional/time-dependent reduction in pADPr. Potentiation of TMZ activity by ABT-888 correlated with drug levels and inhibition of PARP activity in vivo. ABT-888 is in Phase 1 trials using a validated ELISA based on the assay developed here to assess pharmacological effect.

Isoxazolo[3,4-b]quinoline-3,4(1H,9H)-diones as unique, potent and selective inhibitors for Pim-1 and Pim-2 kinases: chemistry, biological activities, and molecular modeling

A series of isoxazolo[3,4-b]quinoline-3,4(1H,9H)-diones were synthesized as potent inhibitors against Pim-1 and Pim-2 kinases. The structure-activity-relationship studies started from a high-throughput screening hit and was guided by molecular modeling of inhibitors in the active site of Pim-1 kinase. Installing a hydroxyl group on the benzene ring of the core has the potential to form a key hydrogen bond interaction to the hinge region of the binding pocket and thus resulted in the most potent inhibitor, 19, with K(i) values at 2.5 and 43.5 nM against Pim-1 and Pim-2, respectively. Compound 19 also exhibited an activity profile with a high degree of kinase selectivity.