TrkC; TrkB; TrkA

Larotrectinib (LOXO-101) is an ATP-competitive oral inhibitor that targets the three isoforms of the tropomyosin-related kinase (TRK) family of receptor kinases (TRKA, B, and C). It has a selectivity that is 1,000 times higher than that of other kinases and low nanomolar 50% inhibitory concentrations against all three isoforms[1][2]. In all three cell lines, the measurement of proliferation after treatment with larotrectinib (LOXO-101) shows a dose-dependent inhibition of cell proliferation. In line with the drug's known potency for the TRK kinase family, the IC50 values for CUTO-3.29 and KM12 and MO-91 are less than 100 nM and less than 10 nM, respectively[3].

Larotrectinib (LOXO-101) exhibits 60-65% plasma protein binding and 33-100% oral bioavailability in rat and monkey experiments. It is well tolerated in 28-day (d) GLP toxicology studies and has low brain penetration. Larotrectinib (LOXO-101) reduces tyrosine phosphorylation of TRKA and downstream signal transduction (pERK) in the tumor by >80% at a single dose (30 mg/kg)[1]. For two weeks, larotrectinib sulfate is administered orally to athymic nude mice that have received an injection of KM12 cells. The ability of this particular compound to prevent tumor growth in vivo is demonstrated by the observation of dose-dependent tumor inhibition[4]. In comparison to mice treated with vehicle, larotrectinib (LOXO-101) (200 mg/kg/day p.o. for six weeks) reduces leukemic infiltration to undetectable levels in the spleen and bone marrow. Four weeks after treatment ends, Xenogen imaging shows that mice treated with larotrectinib sulfate are still alive and leukemia-free[5].

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Etv6-NTRK3/+, CD19-Cre mice developed aggressive disease with 100% penetrance and a median latency of 38 days (n=27). The average body weight of Etv6-NTRK3/+, CD19-Cre mice was significantly reduced compared to age-matched Etv6-NTRK3/+ controls (13.9 vs 20.2g, p<0.001). We observed increased spleen weight in Etv6-NTRK3/+, CD19-Cre mice compared to controls (142 vs 71mg, p=0.02), but no difference in peripheral white blood counts (9.7 vs 13.4 x 109/L, p=0.3). Presence of the Etv6-NTRK3 fusion was confirmed in bone marrow samples by RT-PCR. Immunophenotyping of bone marrow indicated arrest at the pre-B stage (Hardy stage C: B220+, CD19+, CD43+, BP1+, IgM-), recapitulating human ALL. Pathological analysis using hematoxylin and eosin and B220 staining showed infiltration of leukemic cells into the bone marrow, spleen, liver and lung. Interestingly, we observed extensive infiltration of leukemic cells into the central nervous system, specifically ventral to the thoracic and lumbar vertebrae, and the meninges within the brain. Copy number alteration and sequence mutation analysis is currently being performed to determine additional genetic lesions. Leukemia cells from the bone marrow displayed constitutive activation of the MAPK pathway via pERK1/2.[3]

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Using a PDX model of ETV6-NTRK3, it was demonstrate that treatment with Larotrectinib (LOXO-101) (200mg/kg/day p.o for six weeks) reduced leukemic infiltration to undetectable levels in the bone marrow (0 vs 75.8% human CD45/CD19 bone marrow blasts, n=5 each group) and spleen compared to vehicle-treated mice (splenic weight 316 vs 20mg, p<0.001). Notably, treatment with dexamethasone had a modest effect against this tumor (average 55.3% bone marrow blasts and spleen weight 134mg, n=5). Mice treated with LOXO-101 were still alive and leukemia-free four weeks after the cessation of treatment, as determined by Xenogen imaging.[3]

LOXO-101 is a small molecule with a cellular potency of 2 to 20 nM against the TRKA, TRKB, and TRKC kinases that was created to block the ATP binding site of the TRK family of receptors. Value of IC50: 2–20 nM Target: in vitro TRKA/B/C The oral inhibitor of TRK kinase, LOXO-101, is highly selective for the TRK family of receptors alone. Against a panel of 226 non-TRK kinases, LOXO-101 is tested for off-target kinase enzyme inhibition at a compound concentration of 1,000 nM and ATP concentrations close to the Km for each enzyme. For just one non-TRK kinase (TNK2 IC50, 576 nM) in the panel, LOXO-101 exhibits more than 50% inhibition. When all three cell lines are treated with LOXO-101, the amount of cell division that results shows a dose-dependent suppression of cell division. Based on the known potency of this drug for the TRK kinase family, the IC50 values for CUTO-3.29 and KM12 and MO-91 are less than 100 nM and less than 10 nM, respectively.

Ba/F3 cells expressing EV or MPRIP-NTRK1 (RIP-TRKA) were lysed following a 5-hour treatment with the indicated drug doses (Larotrectinib (LOXO-101; ARRY-470); G, gefitinib 1,000 nM) or DMSO control. For western bolt analysis, the cell lysate is used.

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Methods: For in vitro studies, kinase fusions were expressed in IL3 dependent Ba/F3 cells. To generate a genetically engineered mouse model, we used a previously reported conditional knockin model of Etv6-NTRK3 (Cancer Cell 2007;12:542-558), whereby the human portion of NTRK3 cDNA encoding the tyrosine kinase domain was inserted into exon 6 of the mouse Etv6 locus, downstream of a floxed transcriptional terminator sequence. Expression of the Etv6-NTRK3 protein was accomplished using Cre-recombinase driven by the B-lineage promoter CD19. Phosphoflow cytometry analysis and sensitivity to Larotrectinib (LOXO-101; ARRY-470) was assessed in vitro. Researchers next assessed the in vitro efficacy of the TRK inhibitors crizotinib, which also inhibits ALK, and a more specific inhibitor,Larotrectinib (LOXO-101; ARRY-470). Compared to crizotinib (IC50 205 nM), Larotrectinib (LOXO-101; ARRY-470) was 10 times more potent against BaF3-ETV6-NTRK3 cells (IC5017 nM), and had no effect on other kinase fusions (ABL1, ABL2, CSF1R, FLT3, JAK2) up to 10µM. In addition, LOXO-101 was remarkably selective for TRK A, B and C in a cytotoxicity screen of 77 human cancer cell lines as compared to crizotinib. Using a PDX model of ETV6-NTRK3, we demonstrate that treatment with LOXO-101 (200mg/kg/day p.o for six weeks) reduced leukemic infiltration to undetectable levels in the bone marrow (0 vs 75.8% human CD45/CD19 bone marrow blasts, n=5 each group) and spleen compared to vehicle-treated mice (splenic weight 316 vs 20mg, p<0.001). Notably, treatment with dexamethasone had a modest effect against this tumor (average 55.3% bone marrow blasts and spleen weight 134mg, n=5). Mice treated with LOXO-101 were still alive and leukemia-free four weeks after the cessation of treatment, as determined by Xenogen imaging.

Mice: Throughout the investigation, arthymic nude mice are employed. The mice are given a subcutaneous injection of 5x10⁵ KM12 cells into the dorsal flank region. Tumor volume is measured directly with calipers and is computed using the following formula: length × (width⁵)/2. Mice are randomly chosen to receive either diluent, 60 mg/kg/dose, or 200 mg/kg/dose of Larotrectinib (LOXO-101) after the tumor has established and reached a size of 150–200 mm⁵. For 14 days, larotrectinib (LOXO-101) is given orally via gavage once a day. Three, six, and twenty-four hours after the final dosage, tissue and blood are extracted[4].

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To generate a genetically engineered mouse model, we used a previously reported conditional knockin model of Etv6-NTRK3 (Cancer Cell 2007;12:542-558), whereby the human portion of NTRK3 cDNA encoding the tyrosine kinase domain was inserted into exon 6 of the mouse Etv6 locus, downstream of a floxed transcriptional terminator sequence. Expression of the Etv6-NTRK3 protein was accomplished using Cre-recombinase driven by the B-lineage promoter CD19. A patient derived xenograft (PDX) model of ETV6-NTRK3 was established by engrafting primary human ALL cells expressing luciferase into NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice. Phosphoflow cytometry analysis and sensitivity to LOXO-101 was assessed in vitro and in vivo.[3]

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A patient derived xenograft (PDX) model of ETV6-NTRK3 was established by engrafting primary human ALL cells expressing luciferase into NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice. Phosphoflow cytometry analysis and sensitivity to LOXO-101 was assessed in vivo.[3]

Absorption
The mean absolute bioavailability of larotrectinib capsules is approximately 34% (range: 32-37%). In adult patients who received larotrectinib capsules 100 mg twice daily, Cmax was achieved at about one hour after dosing and steady-state was reached within three days. The mean steady-state Cmax and AUC0-24h of larotrectinib capsules was 788 ng/mL and 4351 ng*h/mL, respectively. In healthy subjects, the AUC of the larotrectinib oral solution was similar to that of the capsules and the Cmax was 36% greater with the oral solution. As compared to a fasted state, the administration of larotrectinib in healthy subjects alongside a high-fat meal resulted in a similar AUC and a reduction in Cmax of 35%.

Route of Elimination
Following oral administration of a single 100 mg dose of radiolabeled larotrectinib in healthy subjects, 58% (5% unchanged) of the administered radioactivity was recovered in feces and 39% (20% unchanged) was recovered in urine.

Volume of Distribution
Following intravenous administration to healthy subjects, the mean volume of distribution of larotrectinib at steady-state was approximately 48L.

Clearance
The mean clearance CL/F of larotrectinib is 98 L/h.

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Metabolism / Metabolites
Larotrectinib is metabolized predominantly by CYP3A4. Following oral administration of a single 100 mg dose of radiolabeled larotrectinib in healthy subjects, the major circulating drug components in plasma were unchanged larotrectinib (19%) and an O-linked glucuronide (26%).

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Biological Half-Life
In healthy subjects, the half-life of larotrectinib following oral administration is 2.9 hours.

Hepatotoxicity
In early clinical trials in a total of 176 patients with various forms of solid tumors which had an NTRK gene fusion, elevations in serum aminotransferase levels occurred in 45% of patients treated with larotrectinib. Serum aminotransferase levels rose to above 5 times ULN in 6% of patients and led to early discontinuation in 2%. Serum aminotransferase elevations typically arose after 4 to 12 weeks of treatment, but usually without jaundice or alkaline phosphatase elevations. Most elevations resolved within 4 to 8 weeks and discontinuations were uncommon. Restarting larotrectinib at a reduced dose after resolution of the aminotransferase abnormalities was generally well tolerated and did not lead to recurrence of liver injury. Cases with jaundice and symptoms during larotrectinib therapy have not been reported, but the clinical experience with this kinase inhibitor has been limited and prelicensure clinical trials were carried out with careful clinical monitoring.
Likelihood score: E* (unproven but suspected 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 larotrectinib during breastfeeding. The manufacturer recommends that breastfeeding be discontinued during larotrectinib therapy and for 1 week after the last 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
Larotrectinib is 70% bound to human plasma proteins _in vitro_ and binding is independent of drug concentration. The blood-to-plasma concentration ratio is 0.9.

[1]. LOXO-101, a pan TRK inhibitor, For The Treatment Of TRK-driven Cancers.

[2]. Infantile Fibrosarcoma With NTRK3-ETV6 Fusion Successfully Treated With the Tropomyosin-Related Kinase Inhibitor LOXO-101. Pediatr Blood Cancer. 2016 Aug;63(8):1468-70.

[3]. Genetic Modeling and Therapeutic Targeting of ETV6-NTRK3 with Loxo-101in Acute Lymphoblastic Leukemia. Blood 2016 128:278.

[4]. An Oncogenic NTRK Fusion in a Patient with Soft-Tissue Sarcoma with Response to the Tropomyosin-Related Kinase Inhibitor LOXO-101. Cancer Discov. 2015 Oct;5(10):1049-57.

Larotrectinib Sulfate is the sulfate salt form of larotrectinib, an orally available, tropomyosin receptor kinase (Trk) inhibitor, with potential antineoplastic activity. Upon administration, larotrectinib binds to Trk, thereby preventing neurotrophin-Trk interaction and Trk activation, which results in both the induction of cellular apoptosis and the inhibition of cell growth in tumors that overexpress Trk. Trk, a receptor tyrosine kinase activated by neurotrophins, is mutated in a variety of cancer cell types and plays an important role in tumor cell growth and survival.
See also: Larotrectinib (has active moiety).

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Drug Indication
Vitrakvi as monotherapy is indicated for the treatment of adult and paediatric patients with solid tumours that display a Neurotrophic Tyrosine Receptor Kinase (NTRK) gene fusion,who have a disease that is locally advanced, metastatic or where surgical resection is likely to result in severe morbidity, andwho have no satisfactory treatment options.

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Infantile fibrosarcoma (IFS) is a rare pediatric cancer typically presenting in the first 2 years of life. Surgical resection is usually curative and chemotherapy is active against gross residual disease. However, when recurrences occur, therapeutic options are limited. We report a case of refractory IFS with constitutive activation of the tropomyosin-related kinase (TRK) signaling pathway from an ETS variant gene 6-neurotrophin 3 receptor gene (ETV6-NTRK3) gene fusion. The patient enrolled in a pediatric Phase 1 trial of LOXO-101, an experimental, highly selective inhibitor of TRK. The patient experienced a rapid, radiographic response, demonstrating the potential for LOXO-101 to provide benefit for IFS harboring NTRK gene fusions.[2] Oncogenic TRK fusions induce cancer cell proliferation and engage critical cancer-related downstream signaling pathways. These TRK fusions occur rarely, but in a diverse spectrum of tumor histologies. LOXO-101 is an orally administered inhibitor of the TRK kinase and is highly selective only for the TRK family of receptors. Preclinical models of LOXO-101 using TRK-fusion-bearing human-derived cancer cell lines demonstrate inhibition of the fusion oncoprotein and cellular proliferation in vitro, and tumor growth in vivo. The tumor of a 41-year-old woman with soft-tissue sarcoma metastatic to the lung was found to harbor an LMNA-NTRK1 gene fusion encoding a functional LMNA-TRKA fusion oncoprotein as determined by an in situ proximity ligation assay. In a phase I study of LOXO-101 (ClinicalTrials.gov no. NCT02122913), this patient's tumors underwent rapid and substantial tumor regression, with an accompanying improvement in pulmonary dyspnea, oxygen saturation, and plasma tumor markers. Significance: TRK fusions have been deemed putative oncogenic drivers, but their clinical significance remained unclear. A patient with a metastatic soft-tissue sarcoma with an LMNA-NTRK1 fusion had rapid and substantial tumor regression with a novel, highly selective TRK inhibitor, LOXO-101, providing the first clinical evidence of benefit from inhibiting TRK fusions.[4]

C21H22F2N6O2.H2O4S

526.51

526.144

C, 47.91; H, 4.59; F, 7.22; N, 15.96; O, 18.23; S, 6.09

1223405-08-0

Larotrectinib;1223403-58-4;(R)-Larotrectinib;1223404-68-9

67330085

Light yellow to brown solid powder

3.451

4

11

3

36

741

2

S(=O)(=O)(O[H])O[H].FC1C([H])=C([H])C(=C([H])C=1[C@@]1([H])C([H])([H])C([H])([H])C([H])([H])N1C1C([H])=C([H])N2C(=C(C([H])=N2)N([H])C(N2C([H])([H])C([H])([H])[C@@]([H])(C2([H])[H])O[H])=O)N=1)F

PXHANKVTFWSDSG-QLOBERJESA-N

InChI=1S/C21H22F2N6O2.H2O4S/c22-13-3-4-16(23)15(10-13)18-2-1-7-28(18)19-6-9-29-20(26-19)17(11-24-29)25-21(31)27-8-5-14(30)12-27;1-5(2,3)4/h3-4,6,9-11,14,18,30H,1-2,5,7-8,12H2,(H,25,31);(H2,1,2,3,4)/t14-,18+;/m0./s1

(3S)-N-[5-[(2R)-2-(2,5-difluorophenyl)pyrrolidin-1-yl]pyrazolo[1,5-a]pyrimidin-3-yl]-3-hydroxypyrrolidine-1-carboxamide;sulfuric acid

ARRY 470 sulfate; ARRY-470 sulfate; ARRY470 sulfate; LOXO-101 sulfate; Larotrectinib sulfate; LOXO101 sulfate; LOXO 101 sulfate; LOXO-101; LOXO101; ARRY-470; RDF76R62ID; (S)-N-(5-((R)-2-(2,5-difluorophenyl)pyrrolidin-1-yl)pyrazolo[1,5-a]pyrimidin-3-yl)-3-hydroxypyrrolidine-1-carboxamide sulfate; UNII-RDF76R62ID; ARRY470; ARRY 470; trade name: Vitrakvi

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: ≥ 3.25 mg/mL (6.17 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 32.5 mg/mL clear DMSO stock solution to 400 μL of PEG300 and mix evenly; then add 50 μL of Tween-80 to the above solution and mix evenly; then add 450 μL of 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: ≥ 3.25 mg/mL (6.17 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 32.5 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: ≥ 3.25 mg/mL (6.17 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 32.5 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: ≥ 2.5 mg/mL (4.75 mM) (saturation unknown) in 5% DMSO + 40% PEG300 + 5% Tween80 + 50% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
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 5: ≥ 2.5 mg/mL (4.75 mM) (saturation unknown) in 5% DMSO + 95% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
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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 (Please use freshly prepared in vivo formulations for optimal results.)