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Ref Type Journal Article
PMID (25847190)
Authors Smith CC, Zhang C, Lin KC, Lasater EA, Zhang Y, Massi E, Damon LE, Pendleton M, Bashir A, Sebra R, Perl A, Kasarskis A, Shellooe R, Tsang G, Carias H, Powell B, Burton EA, Matusow B, Zhang J, Spevak W, Ibrahim PN, Le MH, Hsu HH, Habets G, West BL, Bollag G, Shah NP
Title Characterizing and Overriding the Structural Mechanism of the Quizartinib-Resistant FLT3 "Gatekeeper" F691L Mutation with PLX3397.
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Abstract Text Tyrosine kinase domain mutations are a common cause of acquired clinical resistance to tyrosine kinase inhibitors (TKI) used to treat cancer, including the FLT3 inhibitor quizartinib. Mutation of kinase "gatekeeper" residues, which control access to an allosteric pocket adjacent to the ATP-binding site, has been frequently implicated in TKI resistance. The molecular underpinnings of gatekeeper mutation-mediated resistance are incompletely understood. We report the first cocrystal structure of FLT3 with the TKI quizartinib, which demonstrates that quizartinib binding relies on essential edge-to-face aromatic interactions with the gatekeeper F691 residue, and F830 within the highly conserved Asp-Phe-Gly motif in the activation loop. This reliance makes quizartinib critically vulnerable to gatekeeper and activation loop substitutions while minimizing the impact of mutations elsewhere. Moreover, we identify PLX3397, a novel FLT3 inhibitor that retains activity against the F691L mutant due to a binding mode that depends less vitally on specific interactions with the gatekeeper position.We report the first cocrystal structure of FLT3 with a kinase inhibitor, elucidating the structural mechanism of resistance due to the gatekeeper F691L mutation. PLX3397 is a novel FLT3 inhibitor with in vitro activity against this mutation but is vulnerable to kinase domain mutations in the FLT3 activation loop.

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Molecular Profile Treatment Approach
Gene Name Source Synonyms Protein Domains Gene Description Gene Role
Therapy Name Drugs Efficacy Evidence Clinical Trials
Pexidartinib Pexidartinib 54 7
Drug Name Trade Name Synonyms Drug Classes Drug Description
Pexidartinib Turalio PLX3397|CML-261 CSF1R Inhibitor 28 FLT3 Inhibitor 65 KIT Inhibitor 57 Turalio (pexidartinib) inhibits multiple receptor tyrosine kinases, including KIT, CSF1R, FLT3, and FLT3/ITD, which may inhibit growth in cancer cells (PMID: 22294205, PMID: 25993548, PMID: 25847190). Turalio (pexidartinib) is FDA approved for use in patients with symptomatic tenosynovial giant cell tumor (FDA.gov).
Gene Variant Impact Protein Effect Variant Description Associated with drug Resistance
FLT3 D698N missense unknown FLT3 D698N lies within the protein kinase domain of the Flt3 protein (UniProt.org). D698N has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190, PMID: 24623852), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 D839A missense unknown FLT3 D839A lies within the activation loop in the protein kinase domain of the Flt3 protein (PMID: 25837374). D839A has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 D839G missense gain of function FLT3 D839G lies within the protein kinase domain activation loop of the Flt3 protein (UniProt.org). D839G results in constitutive phosphorylation of Flt3, activation of Akt and Mapk signaling, leading to transformation of cultured cells (PMID: 24608088), and has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190). Y
FLT3 D839H missense unknown FLT3 D839H lies within the protein kinase domain of the Flt3 protein (UniProt.org). D839H has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 D839N missense unknown FLT3 D839N lies within the activation loop of the protein kinase domain of the Flt3 protein (PMID: 25837374). D839N has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Nov 2023). Y
FLT3 E708G missense unknown FLT3 E708G lies within the protein kinase domain of the Flt3 protein (UniProt.org). E708G has been identified in sequencing studies (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023).
FLT3 G846R missense unknown FLT3 G846R lies within the activation loop of the protein kinase domain of the Flt3 protein (PMID: 25837374). G846R has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 M664I missense unknown FLT3 M664I lies within the protein kinase domain of the Flt3 protein (UniProt.org). M664I has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 M837_D839delinsGRH indel unknown FLT3 M837_D839delinsGRH results in a deletion of three amino acids in the protein kinase domain of the Flt3 protein from amino acids 837 to 839, combined with the insertion of three amino acids at the same site (UniProt.org). M837_D839delinsGRH has been associated with drug resistance when co-occurring with FLT3 internal tandem duplication (FLT3-ITD) (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Nov 2023).
FLT3 N609K missense unknown FLT3 N609K lies within the cytoplasmic domain of the Flt3 protein (UniProt.org). N609K has been identified in sequencing studies (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023).
FLT3 N676S missense unknown FLT3 N676S lies within the protein kinase domain of the Flt3 protein (UniProt.org). N676S has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190, PMID: 15374944, PMID: 31790499), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 N841K missense unknown FLT3 N841K lies within the activation loop of the protein kinase domain of the Flt3 protein (PMID: 25837374). N841K has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190, PMID: 25487917), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 R845G missense unknown FLT3 R845G lies within the activation loop of the protein kinase domain of the Flt3 protein (PMID: 25837374). R845G has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190, PMID: 30962949), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023). Y
FLT3 S652G missense unknown FLT3 S652G lies within the protein kinase domain of the Flt3 protein (UniProt.org). S652G has been identified in sequencing studies (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Oct 2023).
FLT3 T628I missense unknown FLT3 T628I lies within the protein kinase domain of the Flt3 protein (UniProt.org). T628I has been identified in sequencing studies (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Nov 2023).
FLT3 T820A missense unknown FLT3 T820A lies within the protein kinase domain of the Flt3 protein (UniProt.org). T820A has been identified in the scientific literature (PMID: 25847190), but has not been biochemically characterized and therefore, its effect on Flt3 protein function is unknown (PubMed, Dec 2023).
FLT3 Y842H missense gain of function FLT3 Y842H lies within the protein kinase domain of the Flt3 protein (UniProt.org). Y842H results in increased phosphorylation of Flt3, activation of Stat5 and Mapk, and transformation of cultured cells (PMID: 14604974), and is associated with acquired resistance in the context of FLT3-ITD (PMID: 25847190, PMID: 22504184, PMID: 29187377). Y
FLT3 Y842S missense gain of function - predicted FLT3 Y842S lies within the activation loop of the protein kinase domain of the Flt3 protein (PMID: 25837374). Y842S has been demonstrated to occur as a secondary resistance mutation in the context of FLT3 internal tandem duplication (FLT3-ITD) mutations (PMID: 25847190), and results in increased catalytic activity and autophosphorylation of the Flt3 kinase domain in in vitro assays, and therefore, is predicted to lead to a gain of Flt3 protein function (PMID: 31943770). Y
Molecular Profile Indication/Tumor Type Response Type Therapy Name Approval Status Evidence Type Efficacy Evidence References
FLT3 exon 14 ins FLT3 D835N Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D835N were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 N841K Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/N841K mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D839A Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D839A mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 M664I FLT3 F691L Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/M664I mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins Advanced Solid Tumor sensitive Pexidartinib Preclinical Actionable In a preclinical study, PLX3397 inhibited proliferation of transformed cells expressing FLT3-ITD in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D839G Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, FLT3 D839G conferred resistance to PLX3397 when expressed in a compound mutation with FLT3-ITD in cell culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D839G Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD /F691L/D839G mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 R845G Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/R845G mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 M664I Advanced Solid Tumor decreased response Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 M664I displayed reduced sensitivity to PLX3397 relative to cells expressing FLT3-ITD in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 Y842C Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/Y842C mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 Y842H Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/Y842H mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D835N Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D835N mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835V Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D835V were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D839A Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D839A were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 N676S FLT3 F691L Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/N676S mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L leukemia sensitive Pexidartinib Preclinical Actionable In a preclinical study, PLX3397 inhibited proliferation of human leukemia cells harboring both FLT3-ITD and FLT3 F691L in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D698N Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D698N mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D835Y Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D835Y mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 Y842C Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, FLT3 Y842C conferred resistance to PLX3397 when expressed in a compound mutation with FLT3-ITD in cell culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835F Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D835F were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 M837_D839delinsGRH leukemia predicted - resistant Pexidartinib Case Reports/Case Series Actionable In a clinical case study, a leukemia patient with FLT3-ITD positive leukemia initially responded to Pexidartinib (PLX3397), but experienced relapse after emergence of a compound FLT3 M837_D839delinsGRH mutation on the FLT3-ITD allele (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835H Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, FLT3 D835H conferred resistance to PLX3397 in transformed cells when expressed as a compound mutation with FLT3-ITD in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D835E Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a FLT3 ITD with D835E and F691L were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 N676S Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 N676S were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D698N Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D698N were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 S652G leukemia predicted - resistant Pexidartinib Case Reports/Case Series Actionable In a clinical case study, a patient with FLT3-ITD positive leukemia initially responded to Pexidartinib (PLX3397), but experienced relapse after emergence of a FLT3 S652G mutation on the same allele as FLT3-ITD (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 Y842S Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/Y842S mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835Y leukemia predicted - resistant Pexidartinib Case Reports/Case Series Actionable In a clinical case study, a patient with FLT3-ITD positive leukemia initially responded to Pexidartinib (PLX3397) therapy, but experienced relapse after emergence of FLT3 D835Y on the same allele as the FLT3-ITD mutation (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 G846R Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/G846R mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D839N Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D839N were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 D835V Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3 D835V were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835E Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D835E were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 Y842H Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 Y842H were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D835H Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D835H mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 N841K Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 N841K were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 Y842S Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 Y842S were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 R834Q Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 R834Q were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 R845G Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 R845G were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835G Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D835G were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835Y Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, FLT3 D835Y conferred resistance to PLX3397 when expressed in a compound mutation with FLT3-ITD in cell culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 R834Q Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/R834Q mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 G846R Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD with FLT3 G846R were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L Advanced Solid Tumor sensitive Pexidartinib Preclinical Actionable In a preclinical study, PLX3397 inhibited growth of transformed cells expressing a compound FLT3 F691L/FLT3-ITD mutation in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins leukemia sensitive Pexidartinib Preclinical - Cell line xenograft Actionable In a preclinical study, PLX3397 inhibited proliferation of human leukemia cells harboring FLT3-ITD in culture and in cell line xenograft models (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D839H Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3-ITD along with FLT3 D839H were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D839N Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D839N were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 D835Y Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing FLT3 D835Y were resistant to PLX3397 in culture (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 D835H leukemia resistant Pexidartinib Clinical Study Actionable In a clinical study, a patient with FLT3-ITD positive leukemia initially responded to PLX3397, but experienced relapse after emergence of a FLT3 D835H mutation on the same allele as the FLT3-ITD mutation (PMID: 25847190). 25847190
FLT3 exon 14 ins FLT3 F691L FLT3 D835G Advanced Solid Tumor resistant Pexidartinib Preclinical Actionable In a preclinical study, transformed cells expressing a compound FLT3-ITD/F691L/D835G mutation were resistant to PLX3397 in culture (PMID: 25847190). 25847190