RET^WT (IC50 = 1.29 nM); RET^V804M (IC50 = 1.97 nM ); RET^V804M (IC50 = 0.99 nM)

ONT-380 has nanomolar activity against purified HER2 enzyme and is approximately 500-fold selective for HER2 versus EGFR in cell-based assays. ONT-380 (ARRY-380) selectively inhibits the receptor tyrosine kinase HER2 relative to EGFR. In HER2 overexpressing cell lines, ONT-380 blocks proliferation and the phosphorylation of HER2 and its downstream effector, Akt. By contrast, in the EGFR overexpressing cell lines, it weakly inhibits phosphorylation and proliferation, demonstrating that ONT-380 may have potential to block HER2 signaling without causing the toxicities of EGFR inhibition.

In the ARRY-380-treated-group, 75% of the animals are alive on Day 43. ARRY-380 and its active metabolite causes a significant reduction in brain pErbB2 (80%). ARRY-380 demonstrates significant dose-related tumor growth inhibition (TGI; 50% at 50 mg/kg/d and 96% at 100 mg/kg/d) with numerous partial regressions (>50% reduction from baseline size) at the higher dose level in 9/12 animals. ARRY-380 (50 mg/kg/d) in combination with trastuzumab shows a 98% TGI with complete regressions in 9/12 animals and two partial regressions. At dose of 100 mg/kg/d of ARRY-380 in combination with trastuzumab, there is 100% TGI and all animals have complete responses.

Irbinitinib, formerly known as ARRY-380 and ONT-380 or Tucatinib, is a potent and selective small molecule inhibitor of HER2 with IC50 value of 8 nM, it is equally potent against truncated p95-HER2, and is 500-fold more selective for HER2 versus EGFR. Irbinitinib acts by blocking the proliferation and phosphorylation of HER2 and its downstream effector, Akt. By contrast, in the EGFR overexpressing cell lines, it weakly inhibits phosphorylation and proliferation, demonstrating that Irbinitinib may have potential to block HER2 signaling without causing the toxicities of EGFR inhibition. Therefore, it has the potential to be used as an anticancer agent.

ONT-380 has nanomolar activity against purified HER2 enzyme and is approximately 500-fold selective for HER2 versus EGFR in cell-based assays. In the EGFR overexpressing cell lines, it weakly inhibits phosphorylation and proliferation, demonstrating that Irbinitinib may have potential to block HER2 signaling without causing the toxicities of EGFR inhibition.

Experimental Design: [1]
ONT-380 was administered twice daily (BID) in continuous 28-day cycles. After a modified 3+3 dose-escalation design determined the MTD, the expansion cohort was enrolled. PK properties of ONT-380 and a metabolite were determined. Response was evaluated by Response Evaluation Criteria in Solid Tumors (RECIST).

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Results: [1]
Fifty patients received ONT-380 (escalation = 33; expansion = 17); 43 patients had HER2+ MBC. Median prior anticancer regimens = 5. Dose-limiting toxicities of increased transaminases occurred at 800 mg BID, thus 600 mg BID was the MTD. Common AEs were usually Grade 1/2 in severity and included nausea (56%), diarrhea (52%), fatigue (50%), vomiting (40%) constipation, pain in extremity and cough (20% each). 5 patients (19%) treated at MTD had grade 3 AEs (increased transaminases, rash, night sweats, anemia, and hypokalemia). The half-life of ONT-380 was 5.38 hours and increases in exposure were approximately dose proportional. In evaluable HER2+ MBC (n = 22) treated at doses ≥ MTD, the response rate was 14% [all partial response (PR)] and the clinical benefit rate (PR + stable disease ≥ 24 weeks) was 27%.

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200 mg/kg/d; oral

Mice with SKOV-3 tumor

Absorption, Distribution and Excretion
The Tmax for tucatinib ranges from 1 to 4 hours. One pharmacokinetic study revealed a Cmax of 1120 ng/mL after a dose of 350 mg twice daily with a Tmax ranging from 1 to 3 hours. The AUCtau was reported to be about 7120 hours×ng/mL.
In a study of radiolabled tucatinib, about 86% of the total dose was excreted in the feces and 4.1% was found in the urine. About 16% of the tucatinib dose recovered in the feces was identified as unchanged tucatinib.
The volume of distribution of tucatinib is about 1670 L. This drug penetrates the blood-brain barrier.
The apparent clearance is 148 L/h.

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Metabolism / Metabolites
Tucatinib is metabolized by CYP2C8 with some contributions from CYP3A.

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Biological Half-Life
A pharmacokinetic study revealed a half-life of approximately 5.38 hours. Prescribing information mentions a geometric mean half-life of about 8.21 hours.

Hepatotoxicity
In the prelicensure clinical trials of tucatinib in combination with trastuzumab and capecitabine in patients with metastatic and unresectable HER2 positive breast cancer, liver test abnormalities were frequent although usually self-limited and mild. Some degree of ALT elevations arose in 46% of those receiving tucatinib vs 27% treated with trastuzumab and capecitabine alone. Peak ALT levels rose to above 5 times the upper limit of normal (ULN) in 8% of the tucatinib treated subjects but in less than 1% of controls receiving trastuzumab and capecitabine alone. In a controlled trial enrolling 612 patients with breast cancer, 9 tucatinib treated patients developed ALT elevations and hyperbilirubinemia. Upon further evaluation, however, none of these cases of suspected significant liver injury were considered due to tucatinib, all patients having other possible reasons for liver injury and jaundice. There were no cases of tucatinib-associated liver failure or hepatotoxicity leading to death in any of the prelicensure studies. The product label for tucatinib recommends monitoring for routine liver tests before and every 3 weeks during therapy, and as clinically indicated.
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 tucatinib during breastfeeding. The manufacturer recommends that breastfeeding be discontinued during tucatinib therapy and for 1 week after the last dose. However, tucatinib is used in combination with trastuzumab and capecitabine. It is recommended that breastfeeding be suspended for 7 months after the use of trastuzumab.
◉ 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
Tucatinib is about 97% bound to plasma proteins.

[1]. Phase 1 Study of ONT-380, a HER2 Inhibitor, in Patients with HER2+ Advanced Solid Tumors, with an Expansion Cohort in HER2+ Metastatic Breast Cancer (MBC). Clin Cancer Res. 2017 Jan 4. pii: clincanres.1496.2016.

[2]. Abstract: In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 852. doi:1538-7445.AM2012-852.

[3]. In Vivo Activity of ARRY-380, a Potent, Small Molecule Inhibitor of ErbB2 in Combination with RP-56976. Cancer Research.

Tucatinib is a kinase inhibitor drug used with [trastuzumab] and [capecitabine] in the treatment of unresectable or metastatic HER-2 positive breast cancer. It was developed by Seattle Genetics and approved by the FDA on April 17, 2020. Tucatinib is a promising new treatment for patients with metastatic breast cancer who have not responded adequately to other chemotherapy regimens.
Tucatinib is a Kinase Inhibitor. The mechanism of action of tucatinib is as a Tyrosine Kinase Inhibitor, and Cytochrome P450 3A Inhibitor, and P-Glycoprotein Inhibitor, and Cytochrome P450 2C8 Inhibitor.
Tucatinib is tyrosine kinase inhibitor that targets the human epidermal growth factor receptor 2 (HER2) and is used in combination with other antineoplastic agents in the treatment of refractory, advanced or metastatic HER2 positive breast and colorectal cancer. Serum aminotransferase elevations are common during therapy with tucatinib, but it has not been linked to episodes of clinically apparent liver injury with jaundice.
Tucatinib is an orally bioavailable inhibitor of the human epidermal growth factor receptor tyrosine kinase ErbB-2 (also called HER2) with potential antineoplastic activity. Tucatinib selectively binds to and inhibits the phosphorylation of ErbB-2, which may prevent the activation of ErbB-2 signal transduction pathways, resulting in growth inhibition and death of ErbB-2-expressing tumor cells. ErbB-2 is overexpressed in a variety of cancers and plays an important role in cellular proliferation and differentiation.

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Drug Indication
Tucatinib is indicated with [trastuzumab] and [capecitabine] for the treatment of adults diagnosed with advanced unresectable or metastatic HER2-positive breast cancer. This includes patients with brain metastases and those who have received one or more prior anti-HER2-based regimens in the metastatic setting. It is also indicated in combination with trastuzumab for the treatment of adult patients with RAS wild-type HER2-positive unresectable or metastatic colorectal cancer that has progressed following treatment with fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy. This indication is approved under accelerated approval; thus, it is contingent upon verification and description of clinical benefit in confirmatory trials.
Tukysa is indicated in combination with trastuzumab and capecitabine for the treatment of adult patients with HER2‑positive locally advanced or metastatic breast cancer who have received at least 2 prior anti‑HER2 treatment regimens.
Treatment of solid tumours
Treatment of breast malignant neoplasms

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Mechanism of Action
Mutations in the HER-2 gene are observed in some types of breast carcinoma. Tucatinib inhibits the tyrosine kinase enzyme of the HER-2 gene. Mutations of tyrosine kinase in the HER-2 gene lead to cascade effects of increased cell signaling and proliferation, resulting in malignancy. Results of in vitro studies show that tucatinib inhibits the phosphorylation of both HER-2 and HER-3, leading to downstream changes in MAPK and AKT signaling and cell proliferation. Anti-tumor activity occured in the cells that expressed HER-2. In vivo, tucatinib has been shown to inhibit HER-2 expressing tumors, likely by the same mechanism.

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Pharmacodynamics
By inhibiting tyrosine kinase, tucatinib exerts anti-tumor activity, reducing the size of HER-2 positive breast cancer tumors. In clinical trials, the regimen of tucatinib and [trastuzumab] showed enhanced activity both in vitro and in vivo when compared to either drug administered by itself.

C26H24N8O2

480.2022

480.202

C, 64.99; H, 5.03; N, 23.32; O, 6.66

937263-43-9

Tucatinib hemiethanolate;1429755-56-5

51039094

White to yellow solid powder

1.4±0.1 g/cm3

1.729

3.62

2

8

6

36

796

0

N1C2C(=CC(NC3OCC(C)(C)N=3)=CC=2)C(NC2C=C(C)C(OC3=CC4N(N=CN=4)C=C3)=CC=2)=NC=1

SDEAXTCZPQIFQM-UHFFFAOYSA-N

InChI=1S/C26H24N8O2/c1-16-10-17(5-7-22(16)36-19-8-9-34-23(12-19)28-15-30-34)31-24-20-11-18(4-6-21(20)27-14-29-24)32-25-33-26(2,3)13-35-25/h4-12,14-15H,13H2,1-3H3,(H,32,33)(H,27,29,31)

6-N-(4,4-dimethyl-5H-1,3-oxazol-2-yl)-4-N-[3-methyl-4-([1,2,4]triazolo[1,5-a]pyridin-7-yloxy)phenyl]quinazoline-4,6-diamine

ONT 380; ARRY380; ONT380; ARRY 380; ONT-380; Irbinitinib; ARRY-380; Tukysa; Tucatinib

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: ~96 mg/mL ( ~199.8 mM）
Water: <15 mg/mL
Ethanol: Insoluble

Solubility in Formulation 1: ≥ 2.62 mg/mL (5.45 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 2: ≥ 2.62 mg/mL (5.45 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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Solubility in Formulation 3: 2.08 mg/mL (4.33 mM) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (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 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 4: 2.08 mg/mL (4.33 mM) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (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 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 5: ≥ 2.08 mg/mL (4.33 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 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 6: 5%DMSO+40%PEG300+5%Tween 80+50%ddH2O：0.8mg/ml

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Solubility in Formulation 7: 10 mg/mL (20.81 mM) in 30 % SBE-β-CD (add these co-solvents sequentially from left to right, and one by one), Suspension solution; with ultrasonication.

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