ATR (Ki = 150 pM) ; ATR (ataxia telangiectasia and Rad3-related protein kinase) [3]

Gartisertib is a member of the class of pyrazolopyrimidines that is pyrazolo[1,5-a]pyrimidine substituted by amino, N-[5-fluoro-4-(4-{[4-(oxetan-3-yl)piperazin-1-yl]carbonyl}piperidin-1-yl)pyridin-3-yl]aminoacyl, and fluoro groups at positions 2, 3 and 6, respectively. It is an inhibitor of ataxia telangiectasia and Rad3 related (ATR) kinase that exhibits antineoplastic activity. It has a role as an antineoplastic agent, an EC 2.7.11.1 (non-specific serine/threonine protein kinase) inhibitor and an EC 2.7.1.137 (phosphatidylinositol 3-kinase) inhibitor. It is a pyrazolopyrimidine, an organofluorine compound, an aromatic amine, a secondary carboxamide, a member of pyridines, a piperidinecarboxamide, a member of oxetanes, a N-acylpiperazine and a primary amino compound.

Gartisertib showed alternative lengthening of telomeres (ALT) and tumor arrest-to-regression in tumor models in single-agent efficacy studies. Triple-negative breast cancer xenograft models show tumor regression when combined with PARP inhibitors [1].

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- In HBCx-9 patient-derived xenograft (PDX) models, gartisertib was administered as monotherapy or in combination with PARP inhibitors (rucaparib or talazoparib). Monotherapy with gartisertib showed little or no anti-tumour activity across various dosing regimens, including once daily (1–3 mg/kg for 28–35 days), once weekly (10–20 mg/kg for 4–6 weeks), twice weekly (5–20 mg/kg for 4–6 weeks), and three times weekly (20 mg/kg for 6 weeks). However, when combined with rucaparib or talazoparib, synergistic anti-tumour efficacy was observed, leading to tumour regression or growth inhibition that was greater than with either agent alone. [3]
- In a panel of nine triple-negative breast cancer (TNBC) PDXs with diverse genetic backgrounds (BRCA-mutant, BRCA-wild type HRD positive, and HRD negative), gartisertib (10 or 20 mg/kg twice weekly for 4 cycles) was evaluated in combination with talazoparib (0.3 mg/kg daily for 28 days). The combination produced heterogeneous responses: in BRCA-mutant PDXs, talazoparib alone was highly effective and addition of gartisertib provided minimal added benefit; in HRD-negative PDXs, the combination was most effective as talazoparib alone did not stabilise tumour growth; in BRCA-wild type HRD-positive models, the combination showed greater TGI than talazoparib alone. [3]
- The effects of gartisertib in the model included inhibition of single-strand break (SSB) repair (pathway 2), inhibition of double-strand break (DSB) repair (pathway 4), and override of ATR-dependent cell-cycle checkpoints (leading to delayed cell death). These mechanisms contributed to the synergistic activity observed with PARP inhibition. [3]

M4344 was determined to be an adenosine triphosphate (ATP)-competitive, highly potent, and tight-binding inhibitor of ATR with a Ki of < 150 pM. Minimal inhibitory activity was observed against a large panel of unrelated protein kinases, with 308 of 312 kinases tested having a measured Ki corresponding to more than 100-fold selectivity. M4344 potently inhibits ATR-driven phosphorylated checkpoint kinase-1 (P-Chk1) phosphorylation with an IC50 of 8 nM. Profiling on a selected set of cancer cell lines showed synergy with several types of DNA damaging chemotherapeutics as well as PARP1/2 and CHK1 inhibitors. [1]

In monotherapy efficacy studies M4344 showed tumor stasis to regression in tumor models with alternative lengthening of telomeres (ALT). In combination with PARP inhibitors, tumor regression could be observed in triple-negative breast cancer xenograft models. A dose-escalation phase 1 study in patients with advanced solid tumors is currently ongoing.[1]

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- In study 1 (HBCx-9 PDX), gartisertib was administered orally at 3 mg/kg once daily for 35 days, or in an intermittent schedule of 1 week on/1 week off (3 mg/kg) for a total of 5 weeks (i.e., 3 cycles of 1 week on/1 week off plus a final 1 week on), in combination with rucaparib (50 or 100 mg/kg once or twice daily for 35 days). [3]
- In study 2 (HBCx-9 PDX), gartisertib was given orally at doses of 10 or 20 mg/kg once weekly for 4 weeks, 5 or 10 mg/kg twice weekly for 4 weeks, or 1 or 3 mg/kg once daily for 28 days, in combination with rucaparib (50 mg/kg daily). [3]
- In study 3 (HBCx-9 PDX), gartisertib was administered orally at 10 or 20 mg/kg once weekly for 4 weeks, 5 or 10 mg/kg twice weekly for 4 weeks, 1 or 3 mg/kg once daily for 28 days, or 3 mg/kg once daily for 7 days, in combination with talazoparib (0.15 mg/kg twice daily for 28 days). [3]
- In study 4 (HBCx-9 PDX), gartisertib was dosed orally at 20 mg/kg once weekly for 6 weeks, 20 mg/kg twice weekly for 6 weeks (with dose reduction to 10 mg/kg from day 13), or 20 mg/kg three times weekly for 6 weeks, in combination with talazoparib (0.15 mg/kg twice daily for 6 or 8 weeks). [3]
- In the TNBC PDX panel, gartisertib was given orally at 10 mg/kg (for HBCx-17 and HBCx-1) or 20 mg/kg (for T311R) twice weekly for 4 cycles (28 days), in combination with talazoparib (0.3 mg/kg once daily for 28 days). [3]

[1]. Abstract 369: Antitumor activity of M4344, a potent and selective ATR inhibitor, in monotherapy and combination therapy. Experimental and Molecular Therapeutics.

[2]. Discovery of ATR kinase inhibitor berzosertib (VX-970, M6620): Clinical candidate for cancer therapy. Pharmacol Ther. 2020 Feb 26:107518.

[3]. Semi-mechanistic efficacy model for PARP + ATR inhibitors-application to rucaparib and talazoparib in combination with gartisertib in breast cancer PDXs. Br J Cancer . 2025 Mar;132(5):481-491.

Gartisertib is an orally administered ataxia-telangiectasia and Rad3-associated (ATR) kinase inhibitor with potential antitumor activity. After oral administration, Gartisertib selectively inhibits ATR activity and blocks the phosphorylation of the downstream serine/threonine protein kinase CHK1. This blocks ATR-mediated signaling, thereby inhibiting the activation of DNA damage checkpoints, disrupting DNA damage repair, and inducing tumor cell apoptosis. ATR is a serine/threonine protein kinase upregulated in various cancer cell types, playing a crucial role in DNA repair, cell cycle progression, and cell survival; it is activated by DNA damage induced by DNA replication-related stress. Ataxia-telangiectasia mutations and Rad3-associated protein kinase ATR are key mediators of the DNA damage response. ATR is recruited to single-stranded DNA regions most commonly found during replication stress (RS). RS (replication repair) occurs in the S phase, when the cell's DNA replication mechanisms encounter problems such as unrepaired DNA damage. Furthermore, treatment of cells with DNA damaging agents can also lead to RS (Recombinant Recombinant Deficit Hyperplasia) because cells enter S phase without repairing such damage. Some cancer cells exhibit elevated RS levels even in the absence of DNA damaging agents, possibly due to dysregulated expression of oncogenes driving replication, hypoxic environments, or defects in other repair pathways. RS in cancer cells leads to ATR (DNA repair receptor) dependence for survival; therefore, ATR inhibitors may be effective as monotherapy. Gartissertib is an ATR inhibitor currently being investigated in combination with PARP inhibitors (rucaparib or talazoparib) for the treatment of breast cancer, particularly tumors with homologous recombination deficiency (HRD). This combination therapy aims to exert a synthetic lethal effect by simultaneously inhibiting complementary DNA damage response pathways. In preclinical PDX models, this combination therapy has shown a synergistic inhibitory effect on tumor growth, with the degree of synergy depending on genetic background (e.g., BRCA mutations, HRD status). The semi-mechanistic PK-PD model described in this study contains key features of the Gartisertib mechanism of action: inhibition of SSB repair (ATR-mediated pathway), inhibition of DSB repair (ATR/HR-mediated pathway), and immune checkpoint inhibition. When used in combination with PARP inhibitors, these effects collectively enhance DNA damage accumulation and cell death. [3]

C25H29F2N9O3

541.5531

541.236

C, 55.45; H, 5.40; F, 7.02; N, 23.28; O, 8.86

1613191-99-3

86720912

Light yellow to yellow solid powder

0.1

2

11

5

39

885

0

FC1C=NC=C(C=1N1CCC(C(N2CCN(CC2)C2COC2)=O)CC1)NC(C1C(N)=NN2C=C(C=NC2=1)F)=O

QAYHKBLKSXWOEO-UHFFFAOYSA-N

InChI=1S/C25H29F2N9O3/c26-16-9-30-23-20(22(28)32-36(23)12-16)24(37)31-19-11-29-10-18(27)21(19)34-3-1-15(2-4-34)25(38)35-7-5-33(6-8-35)17-13-39-14-17/h9-12,15,17H,1-8,13-14H2,(H2,28,32)(H,31,37)

2-amino-6-fluoro-N-(5-fluoro-4-(4-(4-(oxetan-3-yl)piperazine-1-carbonyl)piperidin-1-yl)pyridin-3-yl)pyrazolo[1,5-a]pyrimidine-3-carboxamide

ATR inhibitor 2; M4344; VX-803; M-4344; VX803; M 4344; VX 803; Gartisertib; gartisertib; 1613191-99-3; Gartisertib [INN]; M4344; 7OM98IUD1O; Gartisertibum

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)

DMSO : ~25 mg/mL (~46.16 mM)

Solubility in Formulation 1: ≥ 2.08 mg/mL (3.84 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in 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 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 2: 2.08 mg/mL (3.84 mM) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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