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==Crystal structure of KIT kinase domain with a small molecule inhibitor, PLX9486 (bezuclastinib) in the DFG-in state==
<StructureSection load='7khk' size='340' side='right'caption='[[7khk]], [[Resolution|resolution]] 2.34&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[7khk]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=7KHK OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=7KHK FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 2.34&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=WEJ:4,5-dimethyl-N-(2-phenyl-1H-pyrrolo[2,3-b]pyridin-5-yl)-1H-pyrazole-3-carboxamide'>WEJ</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=7khk FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=7khk OCA], [https://pdbe.org/7khk PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=7khk RCSB], [https://www.ebi.ac.uk/pdbsum/7khk PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=7khk ProSAT]</span></td></tr>
</table>
== Disease ==
[https://www.uniprot.org/uniprot/KIT_HUMAN KIT_HUMAN] Defects in KIT are a cause of piebald trait (PBT) [MIM:[https://omim.org/entry/172800 172800]; also known as piebaldism. PBT is an autosomal dominant genetic developmental abnormality of pigmentation characterized by congenital patches of white skin and hair that lack melanocytes.<ref>PMID:1376329</ref> <ref>PMID:1370874</ref> <ref>PMID:1717985</ref> <ref>PMID:7687267</ref> <ref>PMID:8680409</ref> <ref>PMID:9029028</ref> <ref>PMID:9450866</ref> <ref>PMID:9699740</ref> <ref>PMID:11074500</ref>   Defects in KIT are a cause of gastrointestinal stromal tumor (GIST) [MIM:[https://omim.org/entry/606764 606764].<ref>PMID:9029028</ref> <ref>PMID:9697690</ref> <ref>PMID:9438854</ref> <ref>PMID:11505412</ref> <ref>PMID:15824741</ref>   Defects in KIT have been associated with testicular germ cell tumor (TGCT) [MIM:[https://omim.org/entry/273300 273300]. A common solid malignancy in males. Germ cell tumors of the testis constitute 95% of all testicular neoplasms.<ref>PMID:9029028</ref>   Defects in KIT are a cause of acute myelogenous leukemia (AML) [MIM:[https://omim.org/entry/601626 601626]. AML is a malignant disease in which hematopoietic precursors are arrested in an early stage of development. Note=Somatic mutations that lead to constitutive activation of KIT are detected in AML patients. These mutations fall into two classes, the most common being in-frame internal tandem duplications of variable length in the juxtamembrane region that disrupt the normal regulation of the kinase activity. Likewise, point mutations in the kinase domain can result in a constitutively activated kinase.<ref>PMID:9029028</ref> 
== Function ==
[https://www.uniprot.org/uniprot/KIT_HUMAN KIT_HUMAN] Tyrosine-protein kinase that acts as cell-surface receptor for the cytokine KITLG/SCF and plays an essential role in the regulation of cell survival and proliferation, hematopoiesis, stem cell maintenance, gametogenesis, mast cell development, migration and function, and in melanogenesis. In response to KITLG/SCF binding, KIT can activate several signaling pathways. Phosphorylates PIK3R1, PLCG1, SH2B2/APS and CBL. Activates the AKT1 signaling pathway by phosphorylation of PIK3R1, the regulatory subunit of phosphatidylinositol 3-kinase. Activated KIT also transmits signals via GRB2 and activation of RAS, RAF1 and the MAP kinases MAPK1/ERK2 and/or MAPK3/ERK1. Promotes activation of STAT family members STAT1, STAT3, STAT5A and STAT5B. Activation of PLCG1 leads to the production of the cellular signaling molecules diacylglycerol and inositol 1,4,5-trisphosphate. KIT signaling is modulated by protein phosphatases, and by rapid internalization and degradation of the receptor. Activated KIT promotes phosphorylation of the protein phosphatases PTPN6/SHP-1 and PTPRU, and of the transcription factors STAT1, STAT3, STAT5A and STAT5B. Promotes phosphorylation of PIK3R1, CBL, CRK (isoform Crk-II), LYN, MAPK1/ERK2 and/or MAPK3/ERK1, PLCG1, SRC and SHC1.<ref>PMID:7520444</ref> <ref>PMID:9528781</ref> <ref>PMID:10397721</ref> <ref>PMID:12444928</ref> <ref>PMID:12878163</ref> <ref>PMID:12511554</ref> <ref>PMID:17904548</ref> <ref>PMID:19265199</ref> <ref>PMID:21640708</ref> <ref>PMID:21135090</ref> 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
Importance: Many cancer subtypes, including KIT-mutant gastrointestinal stromal tumors (GISTs), are driven by activating mutations in tyrosine kinases and may initially respond to kinase inhibitors but frequently relapse owing to outgrowth of heterogeneous subclones with resistance mutations. KIT inhibitors commonly used to treat GIST (eg, imatinib and sunitinib) are inactive-state (type II) inhibitors. Objective: To assess whether combining a type II KIT inhibitor with a conformation-complementary, active-state (type I) KIT inhibitor is associated with broad mutation coverage and global disease control. Design, Setting, and Participants: A highly selective type I inhibitor of KIT, PLX9486, was tested in a 2-part phase 1b/2a trial. Part 1 (dose escalation) evaluated PLX9486 monotherapy in patients with solid tumors. Part 2e (extension) evaluated PLX9486-sunitinib combination in patients with GIST. Patients were enrolled from March 2015 through February 2019; data analysis was performed from May 2020 through July 2020. Interventions: Participants received 250, 350, 500, and 1000 mg of PLX9486 alone (part 1) or 500 and 1000 mg of PLX9486 together with 25 or 37.5 mg of sunitinib (part 2e) continuously in 28-day dosing cycles until disease progression, treatment discontinuation, or withdrawal. Main Outcomes and Measures: Pharmacokinetics, safety, and tumor responses were assessed. Clinical efficacy end points (progression-free survival and clinical benefit rate) were supplemented with longitudinal monitoring of KIT mutations in circulating tumor DNA. Results: A total of 39 PLX9486-naive patients (median age, 57 years [range, 39-79 years]; 22 men [56.4%]; 35 [89.7%] with refractory GIST) were enrolled in the dose escalation and extension parts. The recommended phase 2 dose of PLX9486 was 1000 mg daily. At this dose, PLX9486 could be safely combined with 25 or 37.5 mg daily of sunitinib continuously. Patients with GIST who received PLX9486 at a dose of 500 mg or less, at the recommended phase 2 dose, and with sunitinib had median (95% CI) progression-free survivals of 1.74 (1.54-1.84), 5.75 (0.99-11.0), and 12.1 (1.34-NA) months and clinical benefit rates (95% CI) of 14% (0%-58%), 50% (21%-79%), and 80% (52%-96%), respectively. Conclusions and Relevance: In this phase 1b/2a nonrandomized clinical trial, type I and type II KIT inhibitors PLX9486 and sunitinib were safely coadministered at the recommended dose of both single agents in patients with refractory GIST. Results suggest that cotargeting 2 complementary conformational states of the same kinase was associated with clinical benefit with an acceptable safety profile. Trial Registration: ClinicalTrials.gov Identifier: NCT02401815.

Association of Combination of Conformation-Specific KIT Inhibitors With Clinical Benefit in Patients With Refractory Gastrointestinal Stromal Tumors: A Phase 1b/2a Nonrandomized Clinical Trial.,Wagner AJ, Severson PL, Shields AF, Patnaik A, Chugh R, Tinoco G, Wu G, Nespi M, Lin J, Zhang Y, Ewing T, Habets G, Burton EA, Matusow B, Tsai J, Tsang G, Shellooe R, Carias H, Chan K, Rezaei H, Sanftner L, Marimuthu A, Spevak W, Ibrahim PN, Inokuchi K, Alcantar O, Michelson G, Tsiatis AC, Zhang C, Bollag G, Trent JC, Tap WD JAMA Oncol. 2021 Jul 8. pii: 2781610. doi: 10.1001/jamaoncol.2021.2086. PMID:34236401<ref>PMID:34236401</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 7khk" style="background-color:#fffaf0;"></div>

==See Also==
*[[Tyrosine kinase 3D structures|Tyrosine kinase 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Zhang Y]]