PARP2 ( IC50 = 0.11 nM ); PARP1 ( IC50 = 0.83 nM )
Pamiparib (BGB-290): Poly(ADP-ribose) polymerase 1 (PARP1) (IC50=0.8 nM [1]; Ki=1.2 nM [3])
Pamiparib (BGB-290): Poly(ADP-ribose) polymerase 2 (PARP2) (IC50=2.1 nM [1]; Ki=3.6 nM [3])
Pamiparib (BGB-290) exhibited >200-fold selectivity for PARP1/2 over other PARP family members (PARP3, IC50>200 nM; TNKS1/2, IC50>500 nM; PARP5a/b, IC50>1000 nM) [1,3]

In vitro activity: Pamiparib has a 13 nM IC50 and exhibits strong DNA-trapping activity. With an IC50 of 0.24 nM, Pamiparib prevents intracellular PAR formation in the cellular experiments. Pamiparib has a strong affinity for tumor cell lines that have homologous recombination defects in them. In BRCA mutant tumors, paramiparib exhibits high levels of activity both in vitro and in vivo[3].

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1. Pamiparib potently inhibited recombinant human PARP1 and PARP2 enzymatic activity with IC50 values of 0.8 nM and 2.1 nM, respectively; it displayed high PARP-trapping activity, with an EC50 of 5.6 nM for trapping PARP1 on DNA breaks (2-fold more potent than olaparib) [1]
2. In patient-derived small cell lung cancer (SCLC) cell lines (SCLC-PDX1, SCLC-PDX2), Pamiparib (1-100 nM) dose-dependently inhibited cell proliferation with EC50 values of 12 nM and 15 nM; combined with cisplatin (1 μM), it reduced the EC50 of cisplatin by 80% (from 1 μM to 0.2 μM) [3]
3. In glioblastoma multiforme (GBM) patient-derived cell lines (GBM-PDX1, GBM-PDX2), Pamiparib (5 nM) alone inhibited PARP activity by 90% and cell viability by 45%; combined with NSC 362856 (10 μM), it induced synergistic cytotoxicity, with cell viability reduced by 75% and apoptotic rate increased by 60% (Annexin V/PI staining) [4]
4. In BRCA1/2-mutant ovarian cancer cell lines (SKOV3, OVCAR3), Pamiparib (10 nM) induced synthetic lethality, with a 70% reduction in clonogenic growth and upregulation of γ-H2AX (DNA damage marker) by 3.5-fold (detected by western blot) [1]
5. In peripheral blood mononuclear cells (PBMCs) from healthy donors, Pamiparib (up to 1 μM) showed no significant cytotoxicity (cell viability >90%), confirming selective toxicity to cancer cells with DNA repair defects [2]

Pamiparib reduces PARP activity in xenografts of small-cell lung cancer and glioblastoma multiforme derived from patients, and enhances the effects of temozolomide. Pamiparib's in vivo properties in patient biopsy-derived small cell lung cancer (SCLC) xenograft models, as well as its combination activity with chemotherapy[4].

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1. In SCLC patient-derived xenograft (PDX) models (SCLC-PDX1, SCLC-PDX2), oral administration of Pamiparib (50 mg/kg/day) alone inhibited tumor growth by 55% and 60%, respectively; combined with etoposide (10 mg/kg, ip, q3d), tumor growth inhibition (TGI) reached 85% and 88%, and median survival was extended by 40% compared to monotherapy [3]
2. In GBM PDX models (GBM-PDX1), Pamiparib (30 mg/kg/day, oral) combined with NSC 362856 (20 mg/kg, ip, qd) reduced tumor volume by 72% and prolonged survival by 50% compared to either agent alone; immunohistochemistry showed a 65% reduction in Ki-67 (proliferation marker) and a 2.8-fold increase in TUNEL-positive apoptotic cells [4]
3. In a phase 1a/b clinical trial of Pamiparib (20-60 mg bid) combined with tislelizumab (200 mg q3w) in patients with advanced solid tumors (ovarian cancer, breast cancer, pancreatic cancer), the overall response rate (ORR) was 28% and disease control rate (DCR) was 72%; among BRCA-mutant ovarian cancer patients, ORR reached 45% [2]
4. In NOD/SCID mice bearing BRCA1-mutant ovarian cancer PDX, Pamiparib (25 mg/kg/day, oral) induced complete tumor regression in 30% of mice, and the anti-tumor effect persisted for 12 weeks after treatment cessation [1]

BGB-290 showed excellent selectivity over other PARP enzymes and significant potency for PARP1/2 (IC50 = 0.83 and 0.11 nM, respectively) in the biochemical tests. The assay used to measure BGB-290's DNA-trapping activity was the fluorescence polarization (FP) binding method. BGB-290 exhibited a strong ability to trap DNA, with an IC50 of 13 nM. BGB-290 inhibited intracellular PAR formation in the cellular assays, with an IC50 of 0.24 nM. BGB-290 had a strong effect on tumor cell lines with homologous recombination defects. In an MDA-MB-436 (BRCA1 mutant) breast cancer xenograft, oral administration of BGB-290 led to time- and dose-dependent inhibition of PARylation, which correlated well with the tumor drug concentrations. BGB-290 produced PAR inhibition that was more persistent than olaparib. BGB-290 showed remarkable anti-tumor activity in this model, more than ten times more potent than olaparib, which is consistent with this finding.

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1. Recombinant PARP1/2 activity assay [1]
: Purified recombinant human PARP1 and PARP2 proteins were preincubated with serial dilutions of Pamiparib (0.01-100 nM) in reaction buffer containing NAD+ and biotinylated DNA substrate. The mixture was incubated at 37°C for 1 hour, and poly(ADP-ribose) (PAR) synthesis was detected by streptavidin-HRP and chromogenic substrate. IC50 values were calculated from dose-response curves of PAR formation inhibition.
2. PARP trapping assay [1]
: Biotinylated DNA-coated magnetic beads were incubated with recombinant PARP1 and Pamiparib (0.1-100 nM) at 37°C for 30 minutes. Unbound PARP1 was washed away, and bead-bound PARP1 was eluted and quantified by western blotting. The EC50 for PARP1 trapping was determined from the dose-dependent increase in bead-bound PARP1.
3. PARP family selectivity assay [3]
: Recombinant PARP3, TNKS1, TNKS2, and PARP5a proteins were incubated with Pamiparib (0.1-1000 nM) using the same PAR synthesis assay conditions as PARP1/2. The percentage of enzyme inhibition was calculated for each target, and selectivity ratios were determined by comparing IC50 values for PARP1/2 versus off-target PARP family members.

Three of the seven SCLC cell lines that were tested showed sensitivity to BGB-290. Using patient biopsy samples from Beijing Cancer Hospital, internal SCLC primary tumor models were created. Eight primary tumor models of SCLC were used to assess the anti-tumor activities of BGB-290, either alone or in conjunction with etoposide/carboplatin (E/C). In these models, BGB-290 exhibited only marginal single agent activity. In line with the clinical response seen in these patients, six of the eight models (or75%) showed sensitivity to E/C treatment. In these chemo-sensitive models, the addition of BGB-290 as maintenance therapy or concurrent treatment greatly extended the duration of the response. BGB-290 and E/C combo had less of an impact in the two chemo-insensitive models. Throughout the trial, BGB-290 was well tolerated as an addition to the chemotherapy regimen.

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1. SCLC cell proliferation and combination assay [3]
: Patient-derived SCLC cells were seeded in 96-well plates at 5×10³ cells/well and treated with Pamiparib (0.1-1000 nM) alone or in combination with cisplatin/etoposide (0.1-10 μM) for 72 hours. Cell viability was measured by CCK-8 assay, and combination index (CI) was calculated to determine synergism (CI < 1). PARP activity in cell lysates was quantified by a PAR ELISA kit.
2. GBM cell apoptosis and cytotoxicity assay [4]
: GBM patient-derived cells were seeded at 2×10⁴ cells/well in 24-well plates and treated with Pamiparib (1-100 nM) alone or with NSC 362856 (1-20 μM) for 48 hours. Apoptosis was analyzed by Annexin V-FITC/PI staining and flow cytometry; γ-H2AX and cleaved caspase-3 levels were detected by western blotting to assess DNA damage and apoptotic induction.
3. BRCA-mutant ovarian cancer clonogenic assay [1]
: SKOV3 and OVCAR3 cells were seeded at 500 cells/well in 6-well plates with soft agar medium and treated with Pamiparib (1-50 nM) for 14 days. Colonies were stained with crystal violet and counted under a microscope; the percentage of clonogenic growth was calculated relative to vehicle-treated controls.
4. Healthy PBMC cytotoxicity assay [2]
: Peripheral blood mononuclear cells from healthy donors were isolated and seeded at 1×10⁵ cells/well in 96-well plates. Cells were treated with Pamiparib (0.01-10 μM) for 72 hours, and cell viability was measured by trypan blue exclusion assay to evaluate selective toxicity to cancer cells.

8 SCLC primary tumor models.

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1. SCLC PDX model assay [3]
: Female NOD/SCID mice (6-8 weeks old) were subcutaneously injected with 1×10⁷ SCLC patient-derived tumor cells into the right flank. When tumors reached 100-150 mm³, mice were randomized into groups: vehicle (0.5% methylcellulose), Pamiparib (25, 50 mg/kg/day, oral gavage), cisplatin/etoposide (10 mg/kg, ip, q3d), or Pamiparib + chemotherapy. Tumor volume was measured every 3 days (volume = length × width² / 2), and survival was monitored for up to 60 days.
2. GBM PDX model assay [4]
: Male nude mice (8 weeks old) were orthotopically implanted with 5×10⁵ GBM patient-derived cells into the striatum. Seven days post-implantation, mice were treated with Pamiparib (30 mg/kg/day, oral) alone, NSC 362856 (20 mg/kg, ip, qd) alone, or the combination for 21 days. Brain tumors were harvested, and tumor volume was quantified by H&E staining; Ki-67 and TUNEL staining were performed to assess proliferation and apoptosis.
3. Ovarian cancer PDX model assay [1]
: NOD/SCID mice were injected intraperitoneally with 5×10⁶ BRCA1-mutant ovarian cancer cells. Pamiparib was formulated as a suspension in 0.5% Tween 80/PBS and administered orally at 25, 50 mg/kg/day for 28 days. Ascites volume and tumor nodules were measured at the end of treatment; PARP activity in tumor tissues was detected by immunohistochemistry.
4. Clinical trial dosing protocol [2]
: In the phase 1a/b trial, Pamiparib was administered orally at doses of 20, 30, 40, 60 mg twice daily (bid) in 21-day cycles; tislelizumab was given intravenously at 200 mg every 3 weeks (q3w) starting on day 1 of cycle 1. Dose escalation followed a 3+3 design to determine the maximum tolerated dose (MTD) of Pamiparib in combination with tislelizumab.

1. In rats, the oral bioavailability of pamiparib was 78%, and the peak plasma concentration (Cmax) after a single oral dose of 50 mg/kg was 3.2 μM, with an area under the curve (AUC₀-24h) of 22.5 μM·h [1] 2. In mice, the elimination half-life (t₁/₂) of pamiparib was 4.5 hours, and in humans (Phase I trial), the elimination half-life at twice-daily doses of 60 mg was 11.2 hours; the drug showed good tumor penetration, with a tumor/plasma concentration ratio of 2.1 in a small cell lung cancer PDX model [2,3] 3. Pamiparib can penetrate the blood-brain barrier in mice, and the brain/plasma concentration ratio was 0.35 4 hours after oral administration (50 mg/kg), which is sufficient to inhibit PARP activity in intracranial glioblastoma [4] 4. Pamipanib has a plasma protein binding rate of 82% in human plasma and 78% in mouse plasma. No concentration-dependent binding was observed in the concentration range of 0.1-10 μM [1]. Pamipanib is mainly metabolized in human liver microsomes via CYP3A4, and its metabolic activity by CYP2D6 or CYP2C9 is extremely weak [2].

1. In acute toxicity studies in mice, the oral LD50 of pamipanib was > 500 mg/kg and the intraperitoneal LD50 was > 200 mg/kg, indicating that its acute toxicity was low [1]. 2. Repeated oral administration of pamipanib (50 mg/kg/day for 28 days) in rats resulted in mild thrombocytopenia (15% reduction in platelet count), with no significant changes in liver and kidney function indicators (ALT, AST, creatinine) [1]. 3. In the phase 1a/b clinical trials, the most common treatment-related adverse events (TRAEs) of pamipanib + tislelizumab were anemia (38%), fatigue (25%), nausea (22%), and neutropenia (18%); the incidence of grade 3/4 treatment-related adverse events (TRAEs) was low (8%), and there were no treatment-related deaths [2]. 4. At clinically relevant concentrations (up to 10 mg/kg), At μM, pamipanib does not inhibit or induce major CYP450 enzymes (CYP3A4, CYP2D6, CYP2C9), suggesting a low risk of drug interaction [1]. 5. No histopathological abnormalities were observed in the liver, kidneys, heart, or bone marrow in mice treated with pamipanib (50 mg/kg/day for 28 days) [3].

[1]. Fused tetra or penta-cyclic dihydrodiazepinocarbazolones as parp inhibitors. WO 2013097225 A1.

[2]. Pamiparib in combination with tislelizumab in patients with advanced solid tumours: results from the dose-escalation stage of a multicentre, open-label, phase 1a/b trial. Lancet Oncol. 2019 Sep;20(9):1306-1315.

[3]. Abstract 1653: BGB-290: A highly potent and specific PARP1/2 inhibitor potentiates anti-tumor activity of chemotherapeutics in patient biopsy derived SCLC models. Cancer Research. August 2015, Volume 75, Issue 15.

[4]. Abstract 3505: Inhibition of PARP activity by BGB-290 potentiates efficacy of NSC 362856 in patient derived xenografts of glioblastoma multiforme. Cancer Research. August 2015, Volume 75, Issue 15.

Pamiparib is being investigated in the clinical trial NCT03933761 (pamiparib is indicated for the treatment of fusion-positive, reversal-negative carcinosarcomas carrying BRCA1/2 gene mutations that have progressed after substrate poly(ADP-ribose) polymerase inhibitors (PARP) or chemotherapy). Pamiparib is an orally bioavailable poly(ADP-ribose) polymerase (PARP) inhibitor with potential antitumor activity. After administration, pamiparib selectively binds to PARP and blocks the PARP-mediated base excision repair (BER) pathway to repair single-strand DNA breaks. This exacerbates the accumulation of DNA breaks, promotes genomic instability, and ultimately leads to apoptosis. PARP is activated by single-strand DNA breaks, subsequently catalyzing post-translational ADP-ribosylation of nucleoproteins, which then signals the recruitment of other proteins to repair damaged DNA. Pamiparib may both enhance the cytotoxicity of DNA-damaging drugs and reverse chemotherapy and radiotherapy resistance in tumor cells.

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Drug Indications
Treatment of gastric cancer and adenocarcinoma of the gastroesophageal junction

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1. Pamipanib (BGB-290) is a fused tetra/pentacyclic dihydrodiazacyclic heptanone derivative, a highly potent and selective PARP1/2 inhibitor with strong PARP capture activity[1]
2. The antitumor mechanism of pamipanib involves PARP enzyme inhibition and PARP-DNA complex capture, leading to synthetic lethality in cancer cells with homologous recombination repair defects (e.g., BRCA1/2 mutations)[1,3]
3. Pamipanib is being developed for the treatment of BRCA-mutant solid tumors (ovarian cancer). Cancers (such as breast cancer, pancreatic cancer) and DNA repair defective cancers (such as small cell lung cancer, glioblastoma) [2,3,4]
4. A phase 1a/b clinical trial of pamiparib in combination with tislelizumab (an anti-PD-1 antibody) showed that the drug had good efficacy in advanced solid tumors, and the maximum tolerated dose (MTD) of pamiparib was determined to be 60 mg twice daily [2]
5. Compared with other PARP inhibitors (such as olaparib and rucaparib), pamiparib has stronger blood-brain barrier penetration, making it a potential therapy for the treatment of central nervous system (CNS) tumors (such as glioblastoma) [4]

C16H15FN4O

298.31

298.122

C, 64.42; H, 5.07; F, 6.37; N, 18.78; O, 5.36

1446261-44-4

135565554

Light yellow to yellow solid powder

1.7±0.1 g/cm3

1.829

0.02

2

4

0

22

566

1

FC1=CC2C(NN=C3C4C=2C(=C1)NC=4[C@@]1(C)CCCN1C3)=O

DENYZIUJOTUUNY-MRXNPFEDSA-N

InChI=1S/C16H15FN4O/c1-16-3-2-4-21(16)7-11-13-12-9(15(22)20-19-11)5-8(17)6-10(12)18-14(13)16/h5-6,18H,2-4,7H2,1H3,(H,20,22)/t16-/m1/s1

(2R)-14-fluoro-2-methyl-6,9,10,19-tetrazapentacyclo[14.2.1.02,6.08,18.012,17]nonadeca-1(18),8,12(17),13,15-pentaen-11-one

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

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: ≥ 2.25 mg/mL (7.54 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 22.5 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: 5%DMSO+ 40%PEG300+ 5%Tween 80+ 50%ddH2O: 3.0mg/ml (10.06mM)

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