PARP-2 ( Ki = 2.9 nM ); PARP-1 ( Ki = 5.2 nM )
Veliparib exhibits no effect on SIRT2 (>5 μM). [1] With an EC50 of 2 nM, veliparib suppresses PARP activity in C41 cells[2]. In H460 cells exposed to and not exposed to light, veliparib lowers PAR levels. DNA repair and clonogenesis in H460 cells are inhibited by PARP-1 inhibition. When veliparib is combined with radiation therapy, H460 cells exhibit increased sequestration and autophagy [3]. In H1299, DU145, and 22RV1 cells, veliparib decreases PARP activity; this suppression is correlated with p53 function. In clonogenic H1299 cells, veliparib (10 μM) reduces quarter fraction (SF) by 43%. In oxygenated H1299 cells, velibib distributes radiation efficiently. In hypoxia-irradiated cells such H1299, DU145, and 22RV1, veliparib can disconnect SF[4].

Veliparib exhibits no effect on SIRT2 (>5 μM). [1] With an EC50 of 2 nM, veliparib suppresses PARP activity in C41 cells[2]. In H460 cells exposed to and not exposed to light, veliparib lowers PAR levels. DNA repair and clonogenesis in H460 cells are inhibited by PARP-1 inhibition. When veliparib is combined with radiation therapy, H460 cells exhibit increased sequestration and autophagy [3]. In H1299, DU145, and 22RV1 cells, veliparib decreases PARP activity; this suppression is correlated with p53 function. In clonogenic H1299 cells, veliparib (10 μM) reduces quarter fraction (SF) by 43%. In oxygenated H1299 cells, velibib distributes radiation efficiently. In hypoxia-irradiated cells such H1299, DU145, and 22RV1, veliparib can disconnect SF[4].

Veliparib has a 56%–92% postcranial bioavailability in mice, SD spray, beagle dogs, and cynomolgus monkeys[1]. Tumor growth delay is improved in the NCI-H460 xenograft model by veliparib (25 mg/kg, ip). Veliparib can lessen tumor vascularization when combined with radiation therapy [3]. Veliparib, at dosages of 3 and 12.5 mg/kg, decreased intratumoral PAR levels in A375 and Colo829 xenograft models by more than 95%; this suppression was reversible over time [4].\n

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\n\nVeliparib (ABT-888) potentiates temozolomide in a syngeneic melanoma model. [1]
\nTemozolomide is a newer generation of cytotoxic alkylating agent that is currently used to treat central nervous system malignancies and melanoma. The pharmacokinetic profile of temozolomide is similar between mice and humans, and this allows studies in mice at similar exposures to those achieved in humans. This is important because preclinical models best predict clinical outcomes when plasma drug concentrations of the cytotoxic agents are similar to those seen in humans. Consequently, a dose of 50 to 62.5 mg/kg/d temozolomide was used, and this dose closely mimics human exposure at the clinically relevant dose of 200 mg/m2 (oral, q.d.×5) when measured by either area under the concentration curve (AUC) or Cmax. At this dose range, no overt toxicity (e.g., excessive weight loss, ruffled coats, dehydration, etc.) was observed in mice. [1]
\n\nThe B16 model, which is relatively resistant to most chemotherapeutics, is moderately sensitive to temozolomide and its sensitivity can be enhanced with PARP inhibitors. Veliparib (ABT-888), administered orally, significantly potentiated the temozolomide efficacy in a dose-dependent manner (Fig. 2A). Maximum potentiation was seen at day 19 with % T/C values (versus temozolomide) of 10 (P = 0.0003), 16 (P < 0.0001), and 23 (P < 0.0001) for the 25, 12.5, and 3.1 mg/kg/d Veliparib (ABT-888) combination groups, respectively. The combinations were well tolerated with maximum body weight loss of 11% for the 25 mg/kg/d ABT-888 and temozolomide combination compared with 7% for temozolomide and 2% for ABT-888. The mice rapidly regained weight once the dosing period ended. [1]
\n\nTo establish the steady-state concentration necessary for in vivo activity, Veliparib (ABT-888) was administered as a continuous infusion in combination with 50 mg/kg/d temozolomide. ABT-888 at doses of 25 to 1 mg/kg/d all significantly potentiated the temozolomide monotherapy (Fig. 2B). Maximum potentiation was seen at day 17 with % T/C values (versus temozolomide) of 13 (P < 0.0001), 12 (P < 0.0001), 16 (P < 0.0001), 39 (P = 0.0033), and 63 (not significant) for the 25, 12.5, 5, 1, and 0.3 mg/kg/d ABT-888 combination groups, respectively. A higher dose of 50 mg/kg/d ABT-888 could not be evaluated with temozolomide because this combination resulted in skin toxicity at the OMP implantation site. The 25 and 12.5 mg/kg/d ABT-888 combination treatments were equivalent in activity, thereby defining the maximally efficacious dose as 12.5 mg/kg/d in this model. Maximum weight loss for the combination groups was 1% compared with a 5% gain for temozolomide. [1]

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\n\nIn vivo inhibition of PAR. [1]
\nActivation of PARP in response to DNA damage results in ribosylation of various substrate proteins. To show inhibition of PARP activity in vivo, tumors from mice treated with Veliparib (ABT-888) were analyzed for levels of PAR by Western blot. B16F10 tumor-bearing mice were treated with either vehicle, temozolomide alone, or in combination with ABT-888 (Fig. 2C), similar to doses used in the efficacy study (Fig. 2A). A decrease in PAR proteins in tumors from animals treated with either ABT-888 alone or in combination with temozolomide was observed, indicating the ability of ABT-888 to inhibit PARP activity in vivo.\n[1]
\nVeliparib (ABT-888) potentiates temozolomide in a syngeneic glioma model. ABT-888 also potentiates temozolomide in a 9L orthotopic rat glioma model. Maximum efficacy was seen at day 14 using magnetic resonance imaging (Fig. 3A and C). ABT-888 at 50 mg/kg/d in combination with temozolomide reduced tumor volume by 63%, which was 44% better than temozolomide alone (P < 0.005). Tumor growth inhibition with ABT-888 was dose dependent (Fig. 3A and B). The combination of 50 mg/kg/d dose of ABT-888 with temozolomide significantly prolonged animal survival versus temozolomide with a median survival of 19 and 22 days, respectively (P < 0.0132, log-rank test; Fig. 3B). ABT-888 as a single agent at 50 mg/kg/d was not efficacious in this model (data not shown). The combinations were well tolerated with maximum weight losses of only 9% for the combination compared with 8% for temozolomide.\n

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\nVeliparib (ABT-888) potentiates platinum agents. [1]
\nThe ability of ABT-888 to potentiate the efficacy of platinum-based agents was investigated in the MX-1 breast carcinoma xenograft model. This line was derived from a 29-year-old female with a poorly differentiated mammary carcinoma. Internal sequencing efforts at Abbott have determined that MX-1 has BRCA1 deletions. A novel BRCA1 variant (BRCA1 33636delGAAA) was detected that would result in a frameshift mutation predicted to introduce a chain terminator and truncate the protein at residue 999. Two previously described nonsynomous single-nucleotide polymorphisms were also detected in BRCA2 (BRCA2 16864A>C, Asn289His, and BRCA2 221847A>G, Asn991Asp), both of which have been described in Chinese Breast Cancer families.\n
\nVeliparib (ABT-888) induced a pronounced potentiation of cisplatin activity (Fig. 4A). At day 68 when all mice were still present in each combination group, no significant differences were noted between the 5, 25, and 50 mg/kg/d combinations with cisplatin. However, at the end of the trial, ABT-888 at 5, 25, and 50 mg/kg/d in combination with cisplatin showed an increase in cures (8/9, 8/9, and 6/9 animals, respectively), whereas the cisplatin monotherapy had only 3/9 cures (no measurable tumors at end of the trial). Both the 5 and 25 mg/kg/d ABT-888 plus cisplatin were significantly different than cisplatin alone (P = 0.049, Fisher's exact test), whereas the 50 mg/kg/d ABT-888 was not significantly different from 5 and 25 mg/kg/d treatment combinations. The vehicle and ABT-888 monotherapy groups had no cures. This dose-response study showed that maximal potentiation was reached at 5 mg/kg/d ABT-888. Potentiation of platinum agents was confirmed in a second MX-1 study using carboplatin. Carboplatin is a second-generation platinum, less toxic anticancer drug and is currently the standard of care for treating lung, ovarian, and head and neck cancers. ABT-888 administered at 25 mg/kg/d via OMPs caused a pronounced potentiation of carboplatin at 10 and 15 mg/kg/d as reflected by tumor volumes (Fig. 4B). Compared with carboplatin treatment groups at day 38, the %T/C values were 34 (P = 0.011) and 18 (P < 0.0001) for the carboplatin 15 and 10 mg/kg/d combinations with ABT-888, respectively. The 10 mg/kg/d carboplatin/ABT-888 combination regressed tumor volumes from day 26, whereas carboplatin monotherapy had only a modest tumor inhibition.\n
\nBecause Veliparib (ABT-888) showed a pronounced potentiation of carboplatin at 10 mg/kg/d, a separate study was undertaken to determine the dose-response relationship of ABT-888 at a fixed carboplatin dose. ABT-888 potentiated the activity of 10 mg/kg/d carboplatin (q4d×3) with %T/C values (versus carboplatin) at day 42 of 9 (P < 0.0005), 22 (P = 0.0014), and 42 (P = 0.012) for the 50, 25, and 12.5 mg/kg/d combinations of ABT-888 and carboplatin (data not shown). The 5 and 1 mg/kg/d doses of ABT-888 did not potentiate carboplatin.\n

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\nVeliparib (ABT-888) potentiates cyclophosphamide. [1]
\nIn the MX-1 model, ABT-888 administered at 25 mg/kg/d via OMPs not only potentiated cyclophosphamide at 12.5 mg/kg/d on days 20, 24, and 27 schedule (Fig. 4C) but also caused tumor regression, whereas the cyclophosphamide monotherapy only slightly delayed tumor growth. The %T/C values of this combination (versus cyclophosphamide) at day 38 was 35 (P = 0.0011). Cyclophosphamide was not effective at 5 mg/kg/d and ABT-888 did not potentiate the cytotoxic agent at this dose. In a separate confirmatory study, ABT-888 at 25 mg/kg/d enhanced the efficacy of cyclophosphamide (12.5 mg/kg/d, q4d×3) but potentiation was not shown at 12.5 mg/kg/d of ABT-888. The %T/C values of combinations (versus carboplatin) at day 42 were 53 (P = 0.018), 91 (not significant), and 100 (not significant) for the 25, 12.5, and 5 mg/kg/d doses of ABT-888 combinations, respectively (data not shown).
\n\nThe ability of Veliparib (ABT-888) to potentiate the efficacy of cyclophosphamide was also evaluated in the DOHH-2 B-cell lymphoma flank xenograft model. DOHH-2 is a lymphoma line with the t(14;18) translocation that results in expression of high levels of Bcl-2 and is sensitive to cyclophosphamide. However, ABT-888 did not potentiate cyclophosphamide using an array of cytotoxic schedules (q.d.×1, q.d.×4, q4d×2, and q4d×3) and dosing schemes (data not shown), although cyclophosphamide showed single-agent activity. These data indicate that ABT-888 is not a potentiator of cyclophosphamide in the DOHH-2 model.\n

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\nVeliparib (ABT-888)potentiates radiation. [1]
\nHCT-116 is a human colon cancer line that has been very well characterized for radiation sensitivity, including growth delay, cell cycle arrest, and apoptosis. ABT-888 administered via OMPs at 25 mg/kg/d potentiated fractionated radiation (2 Gy/d × 10 days) with a median survival time of 36 days compared with 23 days (P < 0.036, log-rank test) from radiation alone (Fig. 5). Although ABT-888 did not enhance median survival (34 days) at 12.5 mg/kg/d (P = 0.06), this treatment group did have one cure (no palpable tumor) when the study was terminated on day 65. ABT-888 was also tested at 5 and 1 mg/kg/d in combination with radiation but these groups were not significantly different than radiation alone. Overall, ABT-888 showed a dose response in combination with radiation (P = 0.0165, log-rank trend).

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In a Phase I clinical trial involving patients with recurrent gynecologic cancer and triple-negative breast cancer, Veliparib was administered orally in combination with intravenous Pegylated Liposomal Doxorubicin (PLD). The study employed a 3+3 dose-escalation design to determine the Recommended Phase 2 Dose (RP2D).[5]
Veliparib was administered twice daily (BID) on days 1-14, and PLD was administered intravenously on day 1 of a 28-day cycle. The starting dose was 50 mg BID of veliparib with 40 mg/m² PLD. The determined RP2D was Veliparib 200 mg BID on days 1–14 with PLD 40 mg/m² on day 1.[5]
Antitumor activity was observed in both sporadic and BRCA-deficient cancers. Among 44 enrolled patients, two BRCA mutation carriers (one with primary peritoneal cancer, one with ovarian cancer) achieved a Complete Response (CR). Eight patients achieved a Partial Response (PR), and 14 had Stable Disease (SD). The overall response rate was 23% (10/44).[5]
Progression-free survival (PFS) for all ovarian cancer patients was 4.7 months. Overall median survival for ovarian cancer patients was 24 months. No significant difference in PFS or OS was found between BRCA mutation carriers and non-carriers, nor between platinum-sensitive and platinum-resistant patients in this study.[5]

In PARP assays, 50 mM Tris (pH 8.0), 1 mM DTT, 1.5 μM [³H]NAD⁺ (1.6 μCi/mmol), 200 nM biotinylated histone H1, 200 nM slDNA, and 1 nM PARP-1 or 4 nM PARP-2 enzyme are added to a buffer. After 1.5 mM benzamide is added to stop the reaction, the reaction is moved to streptavidin Flash plates and counted using a TopCount microplate scintillation counter.

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Using a commercial assay kit, PARP1 enzyme activity is measured; however, instead of using the PARP1 protein that comes with the kit, cell lysates containing either the wild-type PARP1 or the PARP Y907 mutant are used. Each reaction receives 500 ng of the entire lysate. Veliparib (ABT-888), a PARP inhibitor, has a dosage range of 0.01 to 1,000 μM. A plate reader is used to measure the PARP enzyme activity of both wild-type and mutant samples following their incubation with the substrate[2].

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In vitro PARP and SIRT assays. PARP assays were conducted in a buffer containing 50 mmol/L Tris (pH 8.0), 1 mmol/L DTT, 1.5 μmol/L [3H]NAD+ (1.6 μCi/mmol), 200 nmol/L biotinylated histone H1, 200 nmol/L slDNA, and 1 nmol/L PARP-1 or 4 nmol/L PARP-2 enzyme. Reactions were terminated with 1.5 mmol/L benzamide, transferred to streptavidin Flash plates, and counted using a TopCount microplate scintillation counter.[1]
Nicotinamide [2,5′,8-3H]adenine dinucleotide and streptavidin SPA beads were purchased from xxx Biosciences. Recombinant human PARP purified from Escherichia coli and 6-Biotin-17-NAD+ were purchased from xxx. NAD+, histone, aminobenzamide, 3-aminobenzamide, and calf thymus DNA (dcDNA) were from xxx. Stem loop oligonucleotide (slDNA) CACAAGTGTTGCATTCCTC-TCTGAAGTTAAGACCTATGCAGAGAGGAATGCAACACTTGTG, containing MCAT sequence (italics), was obtained from Qiagen. The oligonucleotides were dissolved to 1 mmol/L in annealing buffer containing 10 mmol/L Tris-HCl (pH 7.5), 1 mmol/L EDTA, and 50 mmol/L NaCl, incubated for 5 min at 95°C, and followed by annealing at 45°C for 45 min. Histone H1 (95% electrophoretically pure) was purchased from yyy. Biotinylated histone H1 was prepared by treating the protein with Sulfo-NHS-LC-Biotin. SIRT2 assays were conducted as described previously.

Cellular PARP Assay[2]
C41 cells were treated with test compound for 30 min in a 96-well plate. PARP was activated by damaging DNA with 1 mM H2O2 for 10 min. Cells were washed with ice-cold PBS once and fixed with prechilled methanol/acetone (7:3) at −20 °C for 10 min. After air-drying, plates were rehydrated with PBS and blocked using 5% nonfat dry milk in PBS-tween (0.05%) (blocking solution) for 30 min at room temperature. Cells were incubated with anti-PAR antibody 10H (1:50) in blocking solution at room temperature for 60 min followed by washing with PBS-Tween20 5 times and incubation with goat antimouse fluorescein 5(6)-isothiocyanate (FITC)-coupled antibody (1:50) and 1 μg/mL 4′,6-diamidino-2-phenylindole (DAPI) in blocking solution at room temperature for 60 min. After washing with PBS-Tween20 5 times, analysis was performed using an fmax Fluorescence Microplate Reader set at the excitation and emission wavelength for FITC or the excitation and emission wavelength for DAPI. PARP activity (FITC signal) was normalized with cell numbers (DAPI).

In order to conduct syngeneic studies on B16F10, a mixture of 6×10⁴ cells and 50% Matrigel is injected subcutaneously (20 g) into the flank of 6- to 8-week-old female C57BL/6 mice. In order to conduct cisplatin efficacy studies, fragments (20–30 mm³) of human tumors taken from spontaneously growing tumors in nude mouse hosts are trocar-implanted in female nude mice. In the studies involving carboplatin and MX-1 cyclophosphamide, 200 μL of a 1:10 dilution of tumor brei in 45% Matrigel and 45% Spinner MEM is administered to female scid mice as an injection. Tumors are allowed to grow to the specified size in these well-established tumor studies, after which they are randomized to therapy groups. Male scid mice are given a s.c. injection of 1×10⁶ cells mixed with 50% Matrigel to be used in DOHH-2 xenograft studies. Veliparib is administered orally or continuously via s.c. insertion of a 14-day Alzet OMP model 2002 in a pH 4.0-adjusted 0.9% NaCl solution. Doses of Veliparib are determined based on the OMP's daily delivery rate of 12 μL. The formulation of temozolomide, cisplatin, carboplatin, and cyclophosphamide is done in accordance with the advice of the manufacturers.

Pharmacokinetic Results [5]
Unpaired two-sided t-tests were used to compare the pharmacokinetic parameters of the twice-daily dose ≥200 mg group (high-dose veliparib group, n=18) and the twice-daily dose <200 mg group (low-dose veliparib group, n=7). 25 of the 31 patients had complete samples and underwent pharmacokinetic studies. We found that the AUC/mg (area under the plasma drug concentration-time curve) of PLD was positively correlated with the veliparib dose (p=0.001), while the PLD clearance rate (CL) was negatively correlated with the veliparib dose (p=0.001). When patients were analyzed in low-dose and high-dose groups, the mean (standard deviation) half-life (hours) in the low-dose group was significantly shorter than that in the high-dose group, at 83.2 (33.2) hours and 108.6 (24.88) hours, respectively (p = 0.042); the mean PLD clearance (mL/h) in the low-dose group was significantly higher than that in the high-dose group, at 35.9 (15.9) mL/h and 14.2 (4.3) mL/h, respectively (p < 0.0001). Similarly, the PLD AUC/mg dose (mg·h/L) in the low-dose group was also significantly lower than that in the high-dose group, at 35.0 (14.7) mL/h and 74.9 (18.3) mL/h, respectively (p < 0.0001). In the extended cohort, pharmacokinetic data for veliparib were evaluable in 13 patients (see Supplementary Materials). The half-life on day 1 was 4.1 hours, slightly shorter than the 5.3 hours on day 8. The apparent clearance on day 8 was 15.4 L/h, and the apparent volume of distribution was 121 L, both calculated using the AUC_0-12 on day 8. To accommodate the dose reduction between day 1 and day 8, the exposure was dose-normalized. Results showed statistically significant differences between the C_max on day 1 and the predicted C_max on day 8 (Figure 3A, p=0.0022), and between the AUC_0-∞ on day 1 and the AUC_0-12 on day 8 (Figure 3B, p=0.0151). The observed cumulative rate was 1.2 times lower than the expected cumulative rate calculated based on the observed half-life and the 12-hour dosing interval. The observed Cmax cumulative ratio was 0.865, AUC0–12 was 0.816, and AUC0–12/AUC0−∞ was 0.666. In an extended pharmacokinetic (PK) cohort study, 13 patients received veliparib (200 mg twice daily) and PLD (40 mg/m²). PK sampling for veliparib was performed on day 1 of cycle 2 (in combination with PLD) and day 8 of cycle 2 (veliparib alone). Blood samples were collected before administration and at 0.5, 1, 1.5, 2, 3, 4, 6, and 8 hours after administration. [5] Plasma concentrations of veliparib were analyzed using a validated LC-MS method. Pharmacokinetic parameters were determined using a non-compartmental model. [5]
On day 1 of cycle 2 (in combination with PLD), the mean (standard deviation) half-life (t_1/2) was 4.1 (1.4) hours, the apparent clearance (CL/F) was 10.9 (6.6) L/h, and the AUC_0-∞ was 22.6 (9.2) µg/mL·h. [5]
On day 8 of cycle 2 (velipanib alone), the mean (standard deviation) half-life was 5.3 (1.9) hours, the apparent clearance was 15.4 (4.8) L/h, the apparent volume of distribution (Vd/F) was 120.6 (62.8) L, and the AUC_0-12 was 13.3 (4.0) µg/mL·h. [5]
Co-administration with PLD on day 1 appeared to reduce the apparent clearance of veripab (10.9 L/h), compared to 15.4 L/h when administered alone on day 8, suggesting that co-administration with PLD may improve the bioavailability of veripab. The observed Cmax and AUC cumulative ratios were lower than predicted based on half-life. [5]
There is a pharmacokinetic interaction between veripab and PLD. When the dose of veripab is ≥200 mg BID, the exposure (AUC) of PLD is significantly increased, while its clearance is significantly decreased, while no increase is observed at doses <200 mg BID. [5]

Most patients (39%) received veliparib at 200 mg twice daily (the final dose after dose reduction), and 70% received PLD at 40 mg/m². In group B, 20 patients (49%) and in group A, 2 patients (67%) had their veliparib or PLD doses reduced due to adverse events, including those experiencing dose-limiting toxicities (DLTs). Table 3 lists the adverse events. While Grade 1 and 2 toxicities were common, only 10% of patients experienced Grade 3 or 4 toxicities. The most common Grade 3 and 4 adverse events included: anemia (4 cases, 10%); neutropenia (4 cases, 10%); hand-foot syndrome (HFS) (4 cases, 10%); nausea (2 cases, 5%); vomiting (2 cases, 5%); neuropathy (2 cases, 5%); and elevated transaminases (2 cases, 5%). Five patients (11%) discontinued treatment due to toxicities. In Group A, one patient developed grade 4 cardiac tamponade after receiving 200 mg veliparib twice daily and 40 mg/m² pegylated interferon (after one cycle). Cytological examination of the pericardial effusion showed positive malignant cells. In patients in Level B, treatment was discontinued for the following reasons: no improvement in thrombocytopenia after 24 cycles of 50 mg veliparib BID and 22.5 mg/m² PLD; grade 3 hand-foot syndrome after 32 cycles of 50 mg veliparib BID and 22.5 mg/m² PLD; a decrease in left ventricular ejection fraction (LVEF) of 52% (pre-treatment LVEF was 72%) after 5 cycles of 200 mg veliparib BID and 40 mg/m² PLD; and no improvement in leukopenia after 2 cycles of 300 mg veliparib BID and 40 mg/m² PLD. [5] Overall, the combination of veliparib and PLD was well tolerated. Grade 3 or 4 toxicities were observed in 10% of patients (4/44). The most common Grade 3/4 adverse events were anemia (10%), neutropenia (10%), hand-foot syndrome (HFS) (10%), nausea (5%), vomiting (5%), neuropathy (5%), and elevated transaminases (5%). [5] The most common (>30% of patients) drug-related adverse events of any grade were fatigue (83%), nausea (71%), leukopenia (41%), anemia (41%), weight loss/anorexia (39%), constipation (32%), taste disturbance (32%), elevated AST (32%), and hand-foot syndrome (HFS) (29%). [5] Five patients (11%) discontinued treatment due to toxicity. Dose-limiting toxicities (DLTs) included nausea, vomiting, dehydration, anorexia, abdominal pain, headache, dizziness, and fatigue. No dose-limiting toxicities (DLTs) were observed, and none of these toxicities were hematologic. [5] Two BRCA mutation carriers developed secondary oral squamous cell carcinoma 2 and 2.5 years after completing treatment with velipoparib and liposomal aspirin (PLD) (PLD cumulative doses of 1153 mg and 857 mg, respectively). One of the patients also developed esophageal squamous cell carcinoma 3 years after treatment. The authors noted that this may be related to the combination therapy, especially considering the observed pharmacokinetic interactions leading to increased PLD exposure. [5]

[1]. ABT-888, an orally active poly(ADP-ribose) polymerase inhibitor that potentiates DNA-damaging agents in preclinical tumor models. Clin Cancer Res. 2007 May 1;13(9):2728-37.

[2]. 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. J Med Chem. 2009 Jan 22;52(2):514-23.

[3]. Inhibition of poly(ADP-ribose) polymerase enhances cell death and improves tumor growth delay in irradiated lung cancer models. Clin Cancer Res. 2007 May 15;13(10):3033-42.

[4]. Preclinical Modeling of a Phase 0 Clinical Trial: Qualification of a Pharmacodynamic Assay of Poly (ADP-Ribose) Polymerase in Tumor Biopsies of Mouse Xenografts. Clin Cancer Res. Author manuscript; available in PMC 2009 Nov 1.

[5]. Phase I and Pharmacokinetic Study of Veliparib, a PARP Inhibitor, and Pegylated Liposomal Doxorubicin (PLD) in Recurrent Gynecologic Cancer and Triple Negative Breast Cancer with Long-Term Follow-Up. Cancer Chemother Pharmacol. 2020 Feb 13;85(4):741–751

Velipanib is a benzimidazole derivative with a carbamoyl group substituted at the C-4 position and a (2R)-2-methylpyrrolidone-2-yl substituted at the C-2 position. It is a potent, orally bioavailable PARP inhibitor. It is an EC 2.4.2.30 (NAD(+) ADP-ribosyltransferase) inhibitor. Velipanib is a poly(ADP-ribose) polymerase (PARP)-1 and -2 inhibitor with chemosensitizing and antitumor activity. At therapeutic concentrations, ABT-888, as a single agent, does not have antiproliferative activity; it inhibits DNA repair by inhibiting PARP, thereby enhancing the cytotoxicity of DNA-damaging agents. PARP ribozymes are activated by DNA single-strand or double-strand breaks, leading to poly(ADP-ribosyl)ation of other nuclear DNA-binding proteins involved in DNA repair; poly(ADP-ribosyl)ation facilitates efficient DNA repair and improves the survival rate of proliferating cells under mild genotoxic stress (e.g., oxidants, alkylating agents, or ionizing radiation).

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Drug Indications
Treatment of high-grade gliomas; treatment of fallopian tube cancer; treatment of ovarian cancer; treatment of peritoneal cancer; treatment of lung cancer (small cell lung cancer and non-small cell lung cancer)
Vilipanib is a benzimidazole derivative with a carbamoyl group substituted at the C-4 position and a (2R)-2-methylpyrrolidone-2-yl substituted at the C-2 position. It is a potent, orally bioavailable PARP inhibitor. It is an EC 2.4.2.30 (NAD(+) ADP-ribosyltransferase) inhibitor.
Vilipanib is a poly(ADP-ribose) polymerase (PARP)-1 and -2 inhibitor with chemosensitizing and antitumor activity. ABT-888 does not have antiproliferative activity as a single agent at therapeutic concentrations; it inhibits DNA repair and enhances the cytotoxicity of DNA-damaging agents by inhibiting PARP. PARP ribozymes are activated by DNA single-strand or double-strand breaks, leading to the polymerization (ADP-ribosylation) of other nuclear DNA-binding proteins involved in DNA repair. Polymerization (ADP-ribosylation) facilitates efficient DNA repair and promotes the survival of proliferating cells under mild genotoxic stress (e.g., oxidants, alkylating agents, or ionizing radiation).

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Drug Indications
Treatment of high-grade gliomas
Treatment of fallopian tube cancer, ovarian cancer, peritoneal cancer
Treatment of lung cancer (small cell lung cancer and non-small cell lung cancer)
Treatment of breast cancer.

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Objective: To evaluate the preclinical pharmacokinetics and antitumor efficacy of ABT-888, a novel orally bioavailable poly(ADP-ribose) polymerase (PARP) inhibitor. Experimental Design: In vitro potency was determined using PARP-1 and PARP-2 enzyme activity assays. In syngeneic and xenograft models, we evaluated the in vivo efficacy of ABT-888 in combination with temozolomide, platinum-based drugs, cyclophosphamide, and ionizing radiation. Results showed that ABT-888 is a potent inhibitor of PARP-1 and PARP-2, with Ki values of 5.2 and 2.9 nmol/L, respectively. This compound exhibits good oral bioavailability and can cross the blood-brain barrier. In a B16F10 subcutaneous injection mouse melanoma model, ABT-888 significantly enhanced the efficacy of temozolomide. PARP inhibitors significantly improved the efficacy of temozolomide at doses as low as 3.1 mg/kg/day with ABT-888, reaching maximum efficacy at 25 mg/kg/day. In a 9L orthotopic rat glioma model, temozolomide monotherapy showed minimal efficacy, while the combination of ABT-888 and temozolomide significantly delayed tumor progression. In the MX-1 breast cancer xenograft model (BRCA1 deletion and BRCA2 mutation), ABT-888 enhanced the efficacy of cisplatin, carboplatin, and cyclophosphamide, leading to tumor regression; while monotherapy with equivalent doses of cytotoxic drugs showed only mild tumor suppression. Furthermore, in the HCT-116 colon cancer model, ABT-888 enhanced the efficacy of radiotherapy (2 Gy/dx, 10 fractions). ABT-888 did not demonstrate monotherapy activity in any of the models. Conclusion: ABT-888 is a potent PARP inhibitor with good oral bioavailability, crosses the blood-brain barrier, and enhances the efficacy of temozolomide, platinum-based drugs, cyclophosphamide, and radiotherapy in both idiopathic and xenograft tumor models. This broad-spectrum chemotherapeutic and radiotherapy-enhancing effect makes this compound a highly attractive candidate for clinical evaluation. [1]

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Evaluate the preclinical pharmacokinetics and antitumor efficacy of a novel orally bioavailable poly(ADP-ribose) polymerase (PARP) inhibitor, ABT-888. Experimental design: In vitro efficacy was determined by PARP-1 and PARP-2 enzyme activity assays. In syngeneic and xenograft models, we evaluated the in vivo efficacy of ABT-888 in combination with temozolomide, platinum-based drugs, cyclophosphamide, and ionizing radiation. Results showed that ABT-888 was a potent inhibitor of PARP-1 and PARP-2, with Ki values of 5.2 and 2.9 nmol/L, respectively. This compound exhibits good oral bioavailability and can cross the blood-brain barrier. In a B16F10 subcutaneous injection mouse melanoma model, ABT-888 significantly enhanced the efficacy of temozolomide. PARP inhibitors significantly improved the efficacy of temozolomide at ABT-888 doses as low as 3.1 mg/kg/day, reaching maximum efficacy at 25 mg/kg/day. In a 9L orthotopic rat glioma model, temozolomide monotherapy showed minimal efficacy, while the combination of ABT-888 and temozolomide significantly delayed tumor progression. In an MX-1 breast cancer xenograft model (BRCA1 deletion and BRCA2 mutation), ABT-888 enhanced the efficacy of cisplatin, carboplatin, and cyclophosphamide, leading to regression of established tumors; while the same doses of cytotoxic drugs alone showed only mild tumor suppression. In addition, ABT-888 enhanced the efficacy of radiotherapy (2 Gy/dx, 10 fractions) in the HCT-116 colon cancer model. ABT-888 did not show single-drug activity in any of the models. Conclusion: ABT-888 is a potent PARP inhibitor with good oral bioavailability, crosses the blood-brain barrier, and enhances the efficacy of temozolomide, platinum-based drugs, cyclophosphamide, and radiotherapy in both homologous and xenograft tumor models. This compound has broad chemosensitizing and radiosensitizing effects, making it a highly attractive candidate for clinical evaluation. [1]

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Poly(ADP-ribose) polymerase (PARP) inhibitors have become promising therapies for a variety of diseases, including cancer, in clinical trials. One PARP inhibitor, olaparib (Lynparza, AstraZeneca), was recently approved by the FDA for the treatment of ovarian cancer with BRCA gene mutations. BRCA1 and BRCA2 play crucial roles in repairing DNA double-strand breaks, and the lack of BRCA proteins makes cancer cells more sensitive to PARP inhibitors. This study shows that receptor tyrosine kinase c-Met binds to PARP1 and phosphorylates its Tyr907 site (PARP1 pTyr907 or pY907). PARP1 pY907 can enhance the enzymatic activity of PARP1 and reduce its binding to PARP inhibitors, thereby making cancer cells resistant to PARP inhibitors. The combination of c-Met and PARP1 inhibitors synergistically inhibits the growth of breast cancer cells and xenografts in vitro, and we have also observed a similar synergistic effect in a lung cancer xenograft model. These results suggest that the abundance of PARP1 pY907 may predict tumor resistance to PARP inhibitors, and that combination therapy with c-Met and PARP inhibitors may benefit patients with high c-Met expression in tumors who are unresponsive to PARP inhibitors alone. [2]

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Early studies of first-generation poly(ADP-ribose) polymerase (PARP) inhibitors have shown that they have certain therapeutic potential in the treatment of mustard gas (SM) injury. Currently, several novel and promising PARP inhibitors are undergoing clinical trials for cancer treatment, making them a hot research topic again. However, the role of PARP-1 in SM-induced injury remains unclear. This study uses the highly effective and specific PARP inhibitor ABT-888 as an example to explore the role of PARP inhibitors in SM injury. Results showed that in both the mouse ear vesicle model (MEVM) and HaCaT cell models, the PARP inhibitor ABT-888 alleviated SM-induced cell damage. ABT-888 significantly reduced SM-induced edema and epidermal necrosis in the MEVM model. In the HaCaT cell model, ABT-888 reduced SM-induced NAD(+)/ATP depletion and apoptosis/necrosis. Subsequently, we investigated the mechanism of action of PARP-1 in SM injury by knocking down PARP-1 in HaCaT cells. The results showed that PARP-1 knockdown protected cell viability and downregulated apoptosis checkpoints following SM injury, including p-JNK, p-p53, Caspase 9, Caspase 8, c-PARP, and Caspase 3. Furthermore, AKT activation inhibited autophagy by regulating mTOR. Our results indicate that SM exposure significantly inhibits Akt/mTOR pathway activation. PARP-1 knockdown reversed SM-induced Akt/mTOR pathway inhibition. In summary, our findings suggest that the protective effect of PARP-1 downregulation in SM injury may be related to its regulation of apoptosis, necrosis, energy crisis, and autophagy. However, it is noteworthy that the PARP inhibitor ABT-888 further enhanced H2AX (S139) phosphorylation after SM exposure, suggesting that we should exercise extreme caution when using PARP inhibitors in the treatment of SM injury due to the exacerbation of DNA damage. [3]

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Vilipanib is an oral PARP-1 and PARP-2 inhibitor. PARP-1 and PARP-2 are ribozymes involved in DNA damage recognition and repair, particularly base excision repair. PARP inhibitors can enhance the efficacy of DNA damage drugs such as doxorubicin. [5]
This phase I study (NCI 8475 protocol, NCT01145430) was a multicenter, open-label trial that enrolled patients with recurrent ovarian/fallopian tube/primary peritoneal cancer or metastatic triple-negative breast cancer. [5]
The study was divided into two groups: group A (patients who had previously received PLD treatment) and group B (patients who had not previously received PLD treatment). Only patients with breast cancer were included in group B. [5]
The authors concluded that although antitumor activity was observed, the long-term occurrence of squamous cell carcinoma and the observed pharmacokinetic interaction between veliparib and PLD suggest that research should focus on other targeted combination therapies to improve efficacy. Further development of such specific combination therapy regimens is discouraged. [5]

C13H18CL2N4O

317.21

316.085

C, 49.22; H, 5.72; Cl, 22.35; N, 17.66; O, 5.04

912445-05-7

912444-00-9; 912445-05-7 (HCl)

45480520

White to off-white solid powder

3

5

3

2

20

348

1

C(C1C=CC=C2N=C([C@@]3(NCCC3)C)NC=12)(=O)N.Cl

DSBSVDCHFMEYBX-FFXKMJQXSA-N

InChI=1S/C13H16N4O.2ClH/c1-13(6-3-7-15-13)12-16-9-5-2-4-8(11(14)18)10(9)17-12;;/h2,4-5,15H,3,6-7H2,1H3,(H2,14,18)(H,16,17);2*1H/t13-;;/m1../s1

2-[(2R)-2-methylpyrrolidin-2-yl]-1H-benzimidazole-4-carboxamide;dihydrochloride

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 100 mg/mL (315.25 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)