KIT D816V (IC50 = 0.27 nM); PDGFRA D842V (IC50 = 0.24 nM)

Avapritinib (BLU-285) exhibits dose-dependent antitumor efficacy and is well tolerated in vivo. With 10 mg/kg once daily oral dosing of Avapritinib, complete inhibition of tumor growth and ≥75% inhibition of KIT kinase is observed in the aggressive KIT exon 17 mutant driven P815 mastocytoma model grown as a solid tumor allograft and in a disseminated model of disease. Throughout the course of the 24-day dosage period, the disease burden in the vehicle control animals increases 86-fold, with widespread disease visible in the femurs, pelvis, and circulating in peripheral blood. This is measured by whole body luciferase imaging (photons/second/mm2). Throughout the course of the trial, avapritinib, at both oral dosages of 10 or 30 mg/kg once daily, significantly lowers the burden of disease. At either 10 or 30 mg/kg, avapritinib causes tumor regression in all animals, and by the end of the study, disease abrogation in multiple animals is indistinguishable from background signal measurements. This in vivo model shows that avapritinib is also well tolerated, and it has no negative effects on body weight at any dose[3].

Biochemical in vitro activity of avapritinib (BLU-285) on the KIT exon 17 mutant enzyme, KIT D816V (IC50=0.27 nM), has been demonstrated.

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LanthaScreen binding assays[2]
Serially diluted compounds, KIT protein, and anti–glutathione S-transferase–Europium antibody were incubated with tracer as follows: KIT WT, V560G, and D820E proteins with tracer 222 and KIT D816E, A829P, and D816V with Tracer 178. Plates were incubated at 25°C for 60 min and read on a PerkinElmer EnVision with two excitation flashes and two emission reads: λex = 350 nm, λem = 665 nm; λex = 350 nm, λem = 615 nm.[2]

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KINOMEscan binding assays[2]
Compounds were screened at 3 μM concentration against a panel of 392 WT kinase constructs using the KINOMEscan assay platform at DiscoveRx, as previously described.

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Hotspot kinase profiling assays[2]
In vitro kinase profiling of KIT and PDGFRA constructs was performed at Reaction Biology Corporation. Kinase/substrate pairs, serially diluted compounds, and any additional cofactors required were prepared in a reaction buffer at their respective Michaelis constant (Km) for ATP. 33P-ATP (10 mCi/ml) was added to initiate the reaction, followed by the detection of kinase activity by a filter-binding method.

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KIT exon 17 mutants conferring ligand-independent constitutive kinase activity are known drivers of disease in both solid tumors and hematologic malignancies. KIT Exon 17 mutations have been identified in several human diseases such as systemic mastocytosis (SM), as resistance mutations in second and third line gastrointestinal stromal tumor (GIST), and certain subsets of acute myeloid leukemia (AML). We have developed BLU-285, a potent and selective exon 17 mutant KIT kinase inhibitor. BLU-285 has demonstrated biochemical in vitro activity on the KIT exon 17 mutant enzyme, KIT D816V (half-maximal inhibitory concentration [IC50] = 0.27 nM). Cellular activity of BLU-285 on KIT D816 mutants was measured by autophosphorylation in the human mast cell leukemia cell line HMC1.2, and the P815 mouse mastocytoma cell line with IC50= 4 and 22 nM, respectively.[3]

Autophosphorylation in the human mast cell leukemia cell line HMC1.2 and the mouse mastocytoma cell line P815, with IC50 values of 4 and 22 nM, respectively, is used to assess the cellular activity of avapritinib on KIT D816 mutants. Avapritinib potently inhibits cellular proliferation (IC50=75 nM), downstream signaling, and KIT N822K mutant autophosphorylation (IC50=40 nM) in Kasumi-1 cells, a t(8;21)-positive AML cell line with a KIT exon 17 N822K mutation.

Mice: The effectiveness of avapritinib (BLU-285) in KIT exon 17-mutated CBF-AML is evaluated in a femoral injection model of Kasumi-1 luc⁺ AML NOG SCID mice. Mice are dosed with avapritinib orally once daily at 10 mg/kg or 30 mg/kg through day 45 after a 21-day post-injection latency period.

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All animal studies were performed under IACUC guidelines established at each respective institution where the study was conducted. Avapritinib (BLU-28) was formulated in 0.5% carboxymethyl cellulose + 1% Tween 80. Dasatinib was formulated in 50% propylene glycol. Imatinib was formulated in sterile water. Regorafenib was formulated in a PEG400/125 mM methanesulfonic acid (MSA) mixture at 80:20 ratio. MSA (125 mM) was prepared in water. Sunitinib was formulated in 50 mM citrate buffer (pH 3.5). The P815 xenograft study was performed at WuXi AppTec in Shanghai, China. BALB/c nude mice were inoculated with 1 × 106 P815 cells subcutaneously at the right flank. When the average tumor size reached about 75 mm3, treatment with test article began. Ten animals were treated per group. Tumors were measured to assess antitumor activity. For PK/PD analysis, plasma and tumors were collected from three mice per group. The GIST exon 11/17 (model 2007031011) and exon 11/13 (model GS11331) xenograft studies were performed at Crown Biosciences. Nonobese diabetic–severe combined immunodeficient mice were inoculated with 100,000 to 125,000 viable cells subcutaneously into the rear flank. Animals were randomized when average tumor volume reached 150 to 200 mm3, followed by oral dosing of compounds. Eleven animals were treated per group. Plasma and tumor samples were collected from three animals per group. [2]

Absorption, Distribution and Excretion
A 300mg oral dose of avapritinib reaches a Cmax of 813ng/mL with a Tmax of 2.0-4.1h and an AUC of 15400h\*ng/mL.
Avapritinib is 70% eliminated in the feces with 11% as the unchanged drug and 18% eliminated in the urine with 0.23% as the unchanged drug.
The mean apparent volume of distribution is 1200L.
The mean apparent oral clearance of avapritinib is 19.5L/h.

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Metabolism / Metabolites
Avapritinib is metabolized mainly by CYP3A4 and CYP2C9 _in vitro_. A 310mg oral dose is recovered as 49% unchanged drug, 35% hydroxy glucuronide metabolite, and 14% oxidatively deaminated metabolite.

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Biological Half-Life
The half life of avapritinib is 32-57h.

Hepatotoxicity
In the prelicensure clinical trials of avapritinib in patients with GIST harboring the PDGFRA D842V mutation, ALT elevations arose in 20% of patients but were usually self-limited and mild. ALT elevations above 5 times the upper limit of normal (ULN) were uncommon, being found in 1% to 3% of treated patients. In the open label trials supporting the approval of avapritinib, there were no instances of clinically apparent liver injury, hepatic failure or deaths from liver injury. Avapritinib is associated with frequent elevations in serum bilirubin, but the increases are largely indirect and resolve rapidly with discontinuation.
Likelihood score: E* (unproven but suspected rare cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No information is available on the clinical use of avapritinib during breastfeeding. Because avapritinib is 98.8% bound to plasma proteins, the amounts in milk are likely to be low. However, the manufacturer recommends avoiding breastfeeding during therapy and for 2 weeks following the final dose.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
Avapritinib is 98.8% protein bound in serum.

[1]. Avapritinib: A Selective Inhibitor of KIT and PDGFRα that Reverses ABCB1 and ABCG2-MediatedMultidrug Resistance in Cancer Cell Lines. Mol Pharm. 2019 Jul 1;16(7):3040-3052.

[2]. A precision therapy against cancers driven by KIT/PDGFRA mutations. Sci Transl Med. 2017 Nov 1;9(414). pii: eaao1690.

[3]. Blu-285, a Potent and Selective Inhibitor for Hematologic Malignancies with KIT Exon 17 Mutations.Blood 2015 126:568.

Avapritinib, or BLU-285, is a selective tyrosine kinase inhibitor of KIT and platelet derived growth factor receptor alpha indicated for the treatment of unresectable, metastatic gastrointestinal stromal tumors and advanced systemic mastocytosis. It is one of the first medications available for the treatment of multidrug resistant cancers. Avapritinib shares a similar mechanism with [ripretinib]. Avapritinib was granted FDA approval on 9 January 2020 and EMA approval on 24 September 2020.
Avapritinib is a Kinase Inhibitor. The mechanism of action of avapritinib is as a Tyrosine Kinase Inhibitor, and Cytochrome P450 2C9 Inhibitor, and P-Glycoprotein Inhibitor, and Breast Cancer Resistance Protein Inhibitor, and Multidrug and Toxin Extrusion Transporter 1 Inhibitor, and Multidrug and Toxin Extrusion Transporter 2 K Inhibitor, and Bile Salt Export Pump Inhibitor.
Avapritinib is a tyrosine kinase receptor inhibitor that targets mutant forms of several genes (KIT, PDGFRA) involved in gastrointestinal stromal tumors which are often found in refractory cases. Serum aminotransferase elevations arise in a small proportion of patients treated with the highest doses of avapritinib, but episodes of clinically apparent liver injury have not been reported with its use.
Avapritinib is an orally bioavailable inhibitor of specific mutated forms of platelet-derived growth factor receptor alpha (PDGFR alpha; PDGFRa) and mast/stem cell factor receptor c-Kit (SCFR), with potential antineoplastic activity. Upon oral administration, avapritinib specifically binds to and inhibits specific mutant forms of PDGFRa and c-Kit, including the PDGFRa D842V mutant and various KIT exon 17 mutants. This results in the inhibition of PDGFRa- and c-Kit-mediated signal transduction pathways and the inhibition of proliferation in tumor cells that express these PDGFRa and c-Kit mutants. PDGFRa and c-Kit, protein tyrosine kinases and tumor-associated antigens (TAAs), are mutated in various tumor cell types; they play key roles in the regulation of cellular proliferation.

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Drug Indication
Avapritinib is indicated for the treatment of adults with unresectable or metastatic GIST harboring a platelet-derived growth factor receptor alpha (PDGFRA) exon 18 mutation, including PDGFRA D842V mutations. It is also used to treat adult patients with advanced systemic mastocytosis (AdvSM). AdvSM includes patients with aggressive systemic mastocytosis (ASM), systemic mastocytosis with an associated hematological neoplasm (SM-AHN), and mast cell leukemia. However, it is not recommended for the treatment of patients with AdvSM with platelet counts of less than 50 X 109 L.
Ayvakyt is indicated as monotherapy for the treatment of adult patients with unresectable or metastatic gastrointestinal stromal tumours (GIST) harbouring the platelet-derived growth factor receptor alpha (PDGFRA) D842V mutation.
Treatment of all conditions included in the category of malignant neoplasms (except haematopoietic and lymphoid tissue neoplasms)
Treatment of mastocytosis

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Mechanism of Action
Avapritinib has a negative modulating effect on the transporters ABCB1 and ABCG2, which mediate the multidrug resistance phenotype of some cancers. This modulation may be due to interactions of avapritinib with the drug binding pocket of these transporters. Negative modulation of these transporters, resensitizes cancerous cells to treatment with chemotherapeutic agents like [paclitaxel].

C26H27FN10

498.5580

498.24

C, 62.64; H, 5.46; F, 3.81; N, 28.09

1703793-34-3

118023034

White to off-white solid powder

1.9

1

9

5

37

752

1

C[C@](C1=CC=C(C=C1)F)(C2=CN=C(N=C2)N3CCN(CC3)C4=NC=NN5C4=CC(=C5)C6=CN(N=C6)C)N

DWYRIWUZIJHQKQ-SANMLTNESA-N

InChI=1S/C26H27FN10/c1-26(28,20-3-5-22(27)6-4-20)21-13-29-25(30-14-21)36-9-7-35(8-10-36)24-23-11-18(16-37(23)33-17-31-24)19-12-32-34(2)15-19/h3-6,11-17H,7-10,28H2,1-2H3/t26-/m0/s1

(1S)-1-(4-fluorophenyl)-1-[2-[4-[6-(1-methylpyrazol-4-yl)pyrrolo[2,1-f][1,2,4]triazin-4-yl]piperazin-1-yl]pyrimidin-5-yl]ethanamine

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: ≥ 2.5 mg/mL (5.01 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 25.0 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: ≥ 2.5 mg/mL (5.01 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 25.0 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 3: ≥ 2.5 mg/mL (5.01 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (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 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 2% DMSO+40% PEG 300+2% Tween 80+ddH2O: 4mg/mL

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