Analysis of KIT mutations in sporadic and familial gastrointestinal stromal tumors: therapeutic implications through protein modeling.
OBJECTIVE
Gastrointestinal stromal tumors (GIST) are characterized by expressing a gain-of-function mutation in KIT, and to a lesser extent, PDGFR. Imatinib mesylate, a tyrosine kinase inhibitor, has activity against GISTs that contain oncogenic mutations of KIT. In this study, KIT and PDGFRalpha mutation status was analyzed and protein modeling approaches were used to assess the potential effect of KIT mutations in response to imatinib therapy.


METHODS
Genomic DNA was isolated from GIST tumors. Exons 9, 11, 13, and 17 of c-KIT and exons 12, 14, and 18 of PDGFRalpha were evaluated for oncogenic mutations. Protein modeling was used to assess mutations within the juxtamembrane region and the kinase domain of KIT.


RESULTS
Mutations in KIT exons 9, 11, and 13 were identified in GISTs with the majority of changes involving the juxtamembrane region of KIT. Molecular modeling indicates that mutations in this region result in disruption of the KIT autoinhibited conformation, and lead to gain-of-function activation of the kinase. Furthermore, a novel germ-line mutation in KIT was identified that is associated with an autosomal dominant predisposition to the development of GIST.


CONCLUSIONS
We have used protein modeling and structural analyses to elucidate why patients with GIST tumors containing exon 11 mutations are the most responsive to imatinib mesylate treatment. Importantly, mutations detected in this exon and others displayed constitutive activation of KIT. Furthermore, we have found tumors that are both KIT and PDGFRalpha mutation negative, suggesting that additional, yet unidentified, abnormalities may contribute to GIST tumorigenesis.
Tarn
Chi
C
Department of Medical Oncology, Basic Sciences, and Pathology, Fox Case Cancer Center, Philadelphia, Pennsylvania, USA.
Merkel
Erin
E
Canutescu
Adrian A
AA
Shen
Wei
W
Skorobogatko
Yuliya
Y
Heslin
Martin J
MJ
Eisenberg
Burton
B
Birbe
Ruth
R
Patchefsky
Arthur
A
Dunbrack
Roland
R
Arnoletti
J Pablo
JP
von Mehren
Margaret
M
Godwin
Andrew K
AK
D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001549:Benzamides; D002471:Cell Transformation, Neoplastic; D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D004273:DNA, Neoplasm / Q000032:analysis*; D005260:Female; D046152:Gastrointestinal Stromal Tumors / Q000235:genetics* / Q000503:physiopathology; D018095:Germ-Line Mutation; D006801:Humans; D000068877:Imatinib Mesylate; D008297:Male; D008875:Middle Aged; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010375:Pedigree; D010879:Piperazines / Q000494:pharmacology*; D010982:Platelet-Derived Growth Factor / Q000096:biosynthesis / Q000235:genetics; D011487:Protein Conformation; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis / Q000235:genetics*; D011743:Pyrimidines / Q000494:pharmacology*
D000970:Antineoplastic Agents; D001549:Benzamides; D004273:DNA, Neoplasm; D010879:Piperazines; D010982:Platelet-Derived Growth Factor; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit