The New England Journal of Medicine

Numéro : Volume 348(13), 27 March 2003, p 1201-1214
Copyright : Copyright (C) 2003 Massachusetts Medical Society. All rights reserved.
Type de publication : [Original Articles]
DOI : 10.1056/NEJMoa025217
ISSN : 0028-4793
Accès : 00006024-200303270-00002

A Tyrosine Kinase Created by Fusion of the PDGFRA and FIP1L1 Genes as a Therapeutic Target of Imatinib in Idiopathic Hypereosinophilic Syndrome

Cools, Jan; DeAngelo, Daniel J.; Gotlib, Jason; Stover, Elizabeth H.; Legare, Robert D.; Cortes, Jorges; Kutok, Jeffrey; Clark, Jennifer; Galinsky, Ilene; Griffin, James D.; Cross, Nicholas C.P.; Tefferi, Ayalew; Malone, James; Alam, Rafeul; Schrier, Stanley L.; Schmid, Janet; Rose, Michal; Vandenberghe, Peter; Verhoef, Gregor; Boogaerts, Marc; Wlodarska, Iwona; Kantarjian, Hagop; Marynen, Peter; Coutre, Steven E.; Stone, Richard; Gilliland, D. Gary.
Informations sur l'auteur
From Brigham and Women's Hospital and Harvard Medical School, Boston (J. Cools, E.H.S., J.K., J. Clark, D.G.G.); the Dana-Farber Cancer Institute, Boston (D.J.D., J. Clark, I.G., J.D.G., R.S., D.G.G.); Stanford University School of Medicine, Stanford, Calif. (J.G., J.M., S.L.S., S.E.C.); Women and Infants Hospital, Brown University School of Medicine, Providence, R.I., and Westerly Hospital, Westerly, R.I. (R.D.L.); M.D. Anderson Cancer Center, Houston (J. Cortes, H.K.); the Wessex Regional Genetics Laboratory, Salisbury, United Kingdom (N.C.P.C.); Mayo Clinic, Rochester, Minn. (A.T.); National Jewish Medical and Research Center, Denver (R.A.); Tulane University School of Medicine, New Orleans (J.S.); Yale University School of Medicine, New Haven, Conn. (M.R.); University Hospital Leuven, Leuven, Belgium (P.V., G.V., M.B.); Flanders Interuniversity Institute for Biotechnology, Leuven, Belgium (J. Cools, P.M.); Center for Human Genetics, Leuven, Belgium (I.W.); and Howard Hughes Medical Institute, Brigham and Women's Hospital, Boston (D.G.G.). Address reprint requests to Dr. Gilliland at the Harvard Institutes of Medicine, 4 Blackfan Cir., Rm. 418, Boston, MA 02115 (gilliland@hihg. med.harvard.edu) or to Dr. Stone at the Dana-Farber Cancer Institute, 44 Binney St., Boston, MA 02115 ([email protected]).

Abstract

Background: Idiopathic hypereosinophilic syndrome involves a prolonged state of eosinophilia associated with organ dysfunction. It is of unknown cause. Recent reports of responses to imatinib in patients with the syndrome suggested that an activated kinase such as ABL, platelet-derived growth factor receptor (PDGFR), or KIT, all of which are inhibited by imatinib, might be the cause.

Methods: We treated 11 patients with the hypereosinophilic syndrome with imatinib and identified the molecular basis for the response.

Results: Nine of the 11 patients treated with imatinib had responses lasting more than three months in which the eosinophil count returned to normal. One such patient had a complex chromosomal abnormality, leading to the identification of a fusion of the Fip1-like 1 (FIP1L1) gene to the PDGFR(alpha) (PDGFRA) gene generated by an interstitial deletion on chromosome 4q12. FIP1L1-PDGFR(alpha) is a constitutively activated tyrosine kinase that transforms hematopoietic cells and is inhibited by imatinib (50 percent inhibitory concentration, 3.2 nM). The FIP1L1-PDGFRA fusion gene was subsequently detected in 9 of 16 patients with the syndrome and in 5 of the 9 patients with responses to imatinib that lasted more than three months. Relapse in one patient correlated with the appearance of a T674I mutation in PDGFRA that confers resistance to imatinib.

Conclusions: The hypereosinophilic syndrome may result from a novel fusion tyrosine kinase - FIP1L1-PDGFR(alpha) - that is a consequence of an interstitial chromosomal deletion. The acquisition of a T674I resistance mutation at the time of relapse demonstrates that FIP1L1-PDGFR(alpha) is the target of imatinib. Our data indicate that the deletion of genetic material may result in gain-of-function fusion proteins.

N Engl J Med 2003;348: 1201-14.



The hypereosinophilic syndrome is a rare hematologic disorder with sustained overproduction of eosinophils in the bone marrow, eosinophilia, tissue infiltration, and organ damage. The diagnosis is based on the criteria of Chusid et al. [1]: sustained eosinophilia (more than 1500 eosinophils per cubic millimeter) for more than six months; the absence of other causes of eosinophilia, including parasitic infections and allergies; and signs and symptoms of organ involvement, most frequently the heart, the central and peripheral nervous system, the lungs, and the skin. The syndrome is more common in men than women (ratio, 9:1) and occurs predominantly between the ages of 20 and 50 years. Total leukocyte counts are usually less than 25,000 per cubic millimeter, with 30 to 70 percent eosinophils. Bone marrow eosinophils are increased (30 to 60 percent), but myeloblasts are usually not. [2] It has been difficult to assess the clonality of the hypereosinophilic syndrome, but some cases are clonally derived, as demonstrated by clonal karyotypic abnormalities and X-inactivation assays. [3,4]

Treatment of the hypereosinophilic syndrome attempts to limit organ damage by controlling the eosinophil count and includes prednisone, hydroxyurea, interferon alfa, and cytotoxic chemotherapy. In most cases, however, the disorder is fatal. Recently, it was reported that four of five cases responded to imatinib mesylate (Gleevec, Novartis). [5] Imatinib, a 2-phenylaminopyrimidine-based tyrosine kinase inhibitor, [6] has been approved for the treatment of BCR-ABL-positive chronic myeloid leukemia (CML) and acute lymphoblastic leukemia. [7,8] Besides the ABL tyrosine kinase, imatinib also inhibits the type III transmembrane receptors KIT and platelet-derived growth factor receptor (PDGFR) (beta). [6,9,10] Hence, imatinib is also a promising new treatment for gastrointestinal stromal tumors, which frequently harbor activating mutations in the KIT gene, [11,12] and chronic myeloproliferative diseases with rearrangements of the gene for PDGFR(beta) (PDGFRB). [13] The clinical response to imatinib suggests that the hypereosinophilic syndrome may also be associated with constitutive activation of ABL, KIT, PDGFR, or an as yet unidentified target. Therefore, we evaluated the response to imatinib in patients with the hypereosinophilic syndrome and the molecular basis of the response.

Methods

Patients and Treatment

The study was conducted from June 2001 to October 2002. We studied 16 patients who had received a diagnosis of the hypereosinophilic syndrome and 1 who had acute myelogenous leukemia with marrow fibrosis that developed from a rapidly progressive hypereosinophilic myeloproliferative disorder (Table 1). Only Patients 1 through 11, who had symptomatic disease, were treated with imatinib, at a dose of 100 to 400 mg per day. Patients 12 through 17 were not treated with imatinib. No patient concurrently received cytotoxic therapy.

Table 1 Table 1 Opens a popup window Opens a popup window Opens a popup window

Written informed consent was obtained for the prospective accrual of clinical data and the collection of biologic specimens for analysis of genes known to be inhibited by imatinib. Complete hematologic remission was defined by a white-cell count of less than 10,000 per cubic millimeter, a platelet count of more than 100,000 per cubic millimeter, the presence of fewer than 5 percent eosinophils in the peripheral blood and bone marrow, the absence of blasts and promyelocytes in the peripheral blood, and the absence of extramedullary involvement.

Fluorescence in Situ Hybridization

Fluorescence in situ hybridization was performed as described previously. [14] Probes were obtained from the Roswell Park Cancer Institute libraries RPCI6 and RPCI11 (http://www.chori.org/BACPAC).

Rapid Amplification of Complementary DNA Ends

Trizol (Invitrogen) was used to extract RNA from white cells. DNA was extracted with use of the QIAmp DNA blood Maxi Kit (Qiagen). First-strand complementary DNA (cDNA) was synthesized from 2 microg of total RNA with the use of the Superscript first-strand synthesis system (Invitrogen) with a gene-specific primer or random primers. Rapid amplification of cDNA ends was performed as previously described [15] with primers PDGFRA-R1 for cDNA synthesis and PDGFRA-R2 and PDGFRA-R3 for a nested polymerase chain reaction (PCR).

PCR assay

Fusion of the Fip1-like 1 (FIP1L1) gene to the PDGFR(alpha) (PDGFRA) gene was confirmed on cDNA by nested PCR with the use of primer pairs FIP1L1-F4 and PDGFRA-R1 and FIP1L1-F5 and PDGFRA-R2. The reciprocal fusion was detected with the use of primer pairs PDGFRA-F5 and FIP1L1-R1 and PDGFRA-F3 and FIP1L1-R2. Amplification of the fusion gene at the DNA level was performed with use of the Expand Long template PCR system (Roche). For mutation analysis of the FIP1L1-PDGFRA fusion gene in Patient 5, the gene was amplified with primers FIP1L1-F5 and PDGFRA-R12. Exon 15 of PDGFRA was amplified with primers PDGFRA-F14 and PDGFRA-R15. PCR products were cloned in a pGEM-T-easy plasmid (Promega) and sequenced with use of an ABI sequencer (Perkin Elmer). Long-distance inverse PCR was performed as previously described, [16] with use of an AseI digest (New England Biolabs) and primer pairs LDI1 and PDGFRA-R2 in the first PCR and LDI2 and PDGFRA-R3 in the nested PCR.

Constructs

The open reading frame of the FIP1L1-PDGFRA fusion gene was amplified by PCR from cDNA from Patient 1 with use of the proofreading enzyme HF-2 (Clontech) and primers FIP1L1-Fc and PDGFRA-Rc. This PCR product was cloned in the retroviral vector MSCV-EGFP (kindly provided by W. Pear, University of Pennsylvania). Constructs with point mutations, constructs with deletion mutations, and epitope-tagged constructs were obtained by PCR from the FIP1L1-PDGFRA clone and cloned into MSCV-EGFP. Similarity searches were performed with use of the BLAST program (http://www.ncbi.nlm.nih.gov/BLAST).

Cell Culture

293T cells were grown in Dulbecco's modified Eagle's medium with 10 percent fetal-calf serum, and Ba/F3 cells were grown in RPMI medium with 10 percent fetal-calf serum and 1 ng of mouse interleukin-3 per milliliter. Production of retroviral supernatant and transduction have been described previously. [17] Interleukin-3-independent growth was assessed by plating transduced Ba/F3 cells in interleukin-3-free medium, after the cells were washed three times in phosphate-buffered saline. Imatinib was stored as a 10 mM stock solution in water and diluted in RPMI medium for use. For Western blotting, Ba/F3 cells were incubated in the presence of imatinib for 90 minutes before lysis. For dose-response curves, Ba/F3 cells were incubated for 24 hours in the presence of imatinib, and the number of viable cells at the start and at the end was determined with the Celltiter96AQ(ueous))One solution proliferation assay (Promega). Dose-response curves were fitted with use of OriginPro 6.1 software (OriginLab).

Western Blotting

Immunoprecipitation was performed with use of anti-MYC antibody (Cell Signaling) and protein G agarose (Roche). Each procedure involved 6 million Ba/F3 cells with stable expression of MYC-tagged wild-type FIP1L1-PDGFR(alpha) fusion protein or the T674I mutant. Cells were lysed in lysis buffer (Cell Signaling) containing 1 mM sodium orthovanadate, 20 (mu)M phenylarsine oxide (Calbiochem), and protease inhibitors (complete tablets, Roche). For Western blotting, Ba/F3 cells were collected, lysed in loading buffer (Cell Signaling), separated by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, and transferred to membranes. The following antibodies were used: anti-phospho-ERK1/2, anti-phospho-STAT5 and antiphosphotyrosine (P-Tyr-100/102, Cell Signaling), anti-PDGFR(alpha) (Upstate), anti-STAT5b (Santa-Cruz), antimouse peroxidase, and antirabbit peroxidase (Amersham Pharmacia Biotech). Detection was performed with use of the Western Lightning system (Perkin Elmer).

Primers

The following primers were used: PDGFRA-F3, 5'gagcgagaaccgagagctc; PDGFRA-F5, 5'caaagtggaggagaccatcg; PDGFRA-F14, 5'gaacattgtaaacttgctggg; PDGFRA-R1, 5'tgagagcttgtttttcactgga; PDGFRA-R2, 5'gggaccggcttaatccatag; PDGFRA-R3, 5'ggctgttccttcaaccacct; PDGFRA-R12, 5'catagctccgtgctttca; PDGFRA-R15, 5'catagctccgtgtgctttca; PDGFRA-Rc, 5'cgaattcccagttacaggaagctgtct; FIP1L1-Fc, 5'tggatcccggccatgtcggccggcgag; FIP1L1-F4, 5'acctggtgctgatctttctgat; FIP1L1-F5, 5'aaagaggatacgaatgggacttg; FIP1L1-R1, 5'agtgctgacagtcggaggag; FIP1L1-R2, 5'gagctcctggagggaaaaac; LDI1, 5'gaacgtacgatgtttggtttcca; LDI2, 5'gtctctaatcccatccaggttgc; GAPDH-F, 5'tggaaatcccatcaccatct; and GAPDH-R, 5'gtcttctgggtggcagtgat.

Results

Response to Imatinib in Patients with Hypereosinophilic Syndrome

The median age of the 11 patients (9 men and 2 women) who received imatinib was 46 years (range, 28 to 61) (Table 1). Prior therapies included corticosteroids in 9, hydroxyurea in 10, interferon alfa in 5, cytotoxic chemotherapy in 2, cyclosporine in 1, and radiotherapy for extramedullary disease in 2. Patients had one or more of the following: endomyocardial fibrosis or restrictive cardiomyopathy, gastrointestinal involvement, central nervous system or paraspinal disease, pulmonary involvement, skin involvement, hepatosplenomegaly, and thrombosis. The median eosinophil count at presentation was 14,500 per cubic millimeter (range, 4960 to 53,000). Nine patients had a normal karyotype; one patient had t(1;4)(q44;q12), and the patient with leukemia had trisomy 8, trisomy 19, add2q, and del6q. All patients were BCR-ABL-negative on cytogenetic analysis or fluorescence in situ hybridization. Imatinib was initiated at doses ranging from 100 to 400 mg daily. A complete hematologic remission was achieved in 10 of 11 patients after a median of 4 weeks (range, 1 to 12), although 1 of the 10 had only a transient response, which lasted several weeks, and had no response to an increased dose of imatinib. The response lasted more than 3 months in the other nine patients (median duration, 7 months; range, 3 to 15). Analysis of a bone marrow aspirate and biopsy specimen obtained before therapy from Patient 5, who had a response, showed hypereosinophilia, with the large hypolobated eosinophils characteristic of the hypereosinophilic syndrome. After therapy, there was extensive necrosis, Charcot-Leyden crystals, and patchy, normal hematopoiesis. This patient relapsed at five months, with recurrent cytogenetic abnormalities.

Cloning of FIP1L1-PDGFRA

Patient DNA was analyzed for activating mutations in known targets of imatinib: PDGFRA, PDGFRB, and KIT. [6,9,10] No mutations were found in exons encoding the activation loops or juxtamembrane domains (data not shown). One patient (Patient 1) had t(1;4)(q44;q12). The combination of this patient's response to imatinib and translocation at 4q12, a region where PDGFRA and KIT are located, prompted investigation of their involvement. Fluorescence in situ hybridization showed that a probe spanning the KIT locus (586A2) was translocated to the der(1) chromosome, indicating that the break point was centromeric to KIT. A probe at the CHIC2 locus (200D9), centromeric to PDGFRA, [18] was deleted (Figure 1B). Taken together, these results indicated the presence of a translocation associated with a deletion on 4q12 with a break point near PDGFRA.

Figure 1 Figure 1 Opens a popup window Opens a popup window Opens a popup window

To determine whether a chimeric PDGFRA transcript was present, we performed 5' rapid amplification of cDNA ends on the sequence, encoding the kinase domain of PDGFRA. [19] Sequence analysis of the resultant products revealed that the kinase domain of PDGFRA was fused to an uncharacterized gene (GenBank accession number NM_030917), encoding a putative 520-amino-acid protein that most closely resembled Fip1, an essential component of the Saccharomyces cerevisiae polyadenylation machinery. [20] Therefore, we named the human gene FIP1L1 (Fip1-like 1). According to data from Expressed Sequence Tags (http://www.ncbi.nlm.nih.gov/dbEST) and Ensembl (http://www.ensembl.org), FIP1L1 is widely expressed and undergoes alternative splicing. The FIP1L1-PDGFRA fusion gene was in-frame and fused the first 233 amino acids of FIP1L1 to the last 523 amino acids of PDGFR(alpha) (Figure 1 and Figure 2).

Figure 2 Figure 2 Opens a popup window Opens a popup window Opens a popup window

Surprisingly, FIP1L1 was not located on chromosome 1, as might have been expected owing to a reciprocal translocation, but was approximately 800 kb upstream of PDGFRA on 4q12 (NCBI contig NT_022853) (Figure 3). Taken together, this information indicated that the fusion gene was created by either del(4)(q12) or t(4;4)(q12;q12) rather than t(1;4)(q44;q12). The fusion of FIP1L1 and PDGFRA was confirmed by reverse-transcriptase-PCR on RNA and PCR on DNA from Patient 1 (Figure 1D and Figure 4A). The reciprocal PDGFRA-FIP1L1 fusion gene was not detected in RNA or DNA, strongly suggesting that the fusion was the consequence of an interstitial deletion (Figure 1D and Figure 4A).

Figure 3 Figure 3 Opens a popup window Figure 4 Figure 4 Opens a popup window Opens a popup window

Incidence of FIP1L1-PDGFRA in the Hypereosinophilic Syndrome

An additional four of nine patients for whom pretreatment RNA or DNA was available had the FIP1L1-PDGFRA fusion gene. Four of six patients with the hypereosinophilic syndrome who did not receive imatinib were also found to have the gene on the basis of RNA or DNA analysis (Figure 1 and Figure 4). Thus, the FIP1L1-PDGFRA fusion gene occurred in 9 of our 16 patients (56 percent).

Sequence analysis of DNA from peripheral-blood samples from seven of nine patients with the fusion gene confirmed that all break points in PDGFRA occurred in exon 12 and that cryptic splice sites were used within introns of FIP1L1 or within exon 12 of PDGFRA, to allow splicing between exons of FIP1L1 and the interrupted exon 12 of PDGFRA (Figure 4). Attempts to amplify the reciprocal fusion genes on RNA and DNA were unsuccessful, indicating that all fusions were the result of a deletion on 4q12 and not of t(4;4) (Figure 1 and Figure 4).

Relapse during Imatinib Treatment Associated with an Acquired Mutation in PDGFRA

Patient 5, who relapsed during imatinib treatment, harbored the FIP1L1-PDGFRA fusion gene initially and at the time of relapse. We hypothesized that relapse might be attributable to mutations in the PDGFR(alpha) moiety that conferred resistance to imatinib. Sequence analysis of the PDGFR(alpha) kinase domain at the time of relapse showed that the fusion protein had acquired a T674I mutation (Figure 2B). This mutation occurred in the ATP-binding region of PDGFR(alpha) at the same position as the T315I mutation in BCR-ABL [21,22] (Figure 2C), which is known to confer resistance to imatinib in that context. [21-23]

Effect of FIP1L1-PDGFR(alpha)

The expression of FIP1L1-PDGFR(alpha) transformed the murine hematopoietic cell line Ba/F3 to interleukin-3-independent growth (Figure 5B) and was constitutively tyrosine-phosphorylated in these cells (Figure 5D). Deletion of the FIP1L1 moiety (amino acids 4 to 233) abrogated this type of growth, indicating that this part of the fusion protein was essential for the activation of the chimeric kinase. Further mutational analysis showed that the first 29 amino acids of FIP1L1 (encoded by exon 1) were necessary and sufficient to activate the PDGFR(alpha) kinase domain (Figure 5B). Analysis of the phosphorylation status of ERK1 or ERK2 and STAT5 indicated that STAT5, but not ERK, was a downstream target of FIP1L1-PDGFR(alpha) (Figure 5E, and data not shown).

Figure 5 Figure 5 Opens a popup window Opens a popup window Opens a popup window

Inhibition of FIP1L1-PDGFR(alpha) Kinase Activity and Resistance to Imatinib

To confirm that FIP1L1-PDGFR(alpha) was a target of imatinib, we tested the effect of imatinib on the growth of Ba/F3 cells expressing FIP1L1-PDGFR(alpha) or FIP1L1-PDGFR(alpha) harboring the T674I mutation (Figure 5C). Ba/F3 cells expressing FIP1L1-PDGFR(alpha) were efficiently inhibited by much lower concentrations of imatinib than Ba/F3 cells expressing BCR-ABL. The concentration of imatinib required to inhibit cells transformed by FIP1L1-PDGFR(alpha) by 50 percent (IC(50))) was 3.2 nM, whereas the IC(50)) for BCR-ABL was 582 nM. [23] These data indicate that FIP1L1-PDGFR(alpha) is more sensitive to inhibition by imatinib than is BCR-ABL and correlate with the findings that the effective dose of imatinib is lower in patients with the hypereosinophilic syndrome (100 mg per day) than in patients with BCR-ABL-positive CML (300 to 400 mg per day). As compared with Ba/F3 cells expressing wild-type FIP1L1-PDGFR(alpha), Ba/F3 cells expressing the FIP1L1-PDGFR(alpha) T674I mutant were more than 1000 times as resistant to imatinib, with a cellular IC(50)) of 7498 nM (Figure 5C ).

Consistent with these findings, imatinib inhibited tyrosine phosphorylation of FIP1L1-PDGFR(alpha) and its downstream target STAT5 with an IC(50)) of approximately 5 nM (Figure 5D and Figure 5E, respectively), whereas inhibition of the T674I mutant required concentrations of imatinib that were at least 1000 times as high (10,000 and 5000 nM, respectively) (Figure 5F and Figure 5G). STAT5 phosphorylation was restored by the addition of interleukin-3 (Figure 5E and Figure 5G), demonstrating the specificity of imatinib in this context. Taken together, these data demonstrate that the PDGFR(alpha) kinase domain is a direct target of imatinib in patients with the hypereosinophilic syndrome.

Discussion

Constitutive activation of tyrosine kinases is a key element in the pathogenesis of myeloproliferative diseases. In most cases the mutant kinases have been identified by cloning recurrent chromosomal translocation break points. Examples include the BCR-ABL, [24] ETV6-PDGFR(beta), [25] HIP1-PDGFR(beta), [26] ETV6-JAK2, [27] and H4-PDGFR(beta) [28] fusion proteins. The hypereosinophilic syndrome is a myeloproliferative syndrome, but most patients present with an apparently normal karyotype. We found a gene rearrangement, which is not evident on standard karyotyping, that results in a novel FIP1L1-PDGFR(alpha) fusion protein.

The FIP1L1-PDGFRA gene rearrangement is a clonal abnormality that raises several questions about the classification of eosinophilic syndromes. World Health Organization (WHO) criteria indicate that patients with clonally derived eosinophils should be classified as having chronic eosinophilic leukemia rather than the hypereosinophilic syndrome. On the basis of these criteria, at least seven of our patients with the hypereosinophilic syndrome should be reclassified as having chronic eosinophilic leukemia. Furthermore, it is plausible that most patients with the hypereosinophilic syndrome, or at least those with imatinib-sensitive disease, will have clonally derived eosinophils. It may therefore be appropriate to reevaluate the WHO classification in the light of our observations.

Several lines of evidence argue that the FIP1L1-PDGFR(alpha) fusion protein is a cause of the hypereosinophilic syndrome. First, it was found in a majority of our patients and has the biologic properties of other tyrosine kinase fusion proteins that are implicated in the pathogenesis of myeloproliferative disease. Second, most patients with the hypereosinophilic syndrome had a response to imatinib, a potent inhibitor of PDGFR(alpha), PDGFR(beta), KIT, and ABL. [10] Most such patients have a response to lower doses of imatinib than those required for the induction of hematologic and cytogenetic responses in patients with BCR-ABL-positive CML (e.g., 100 mg daily vs. 400 mg daily). [8] This difference correlates with the lower IC(50)) of FIP1L1-PDGFR(alpha) than BCR-ABL. Third, clinical relapse and resistance to imatinib in a patient with the hypereosinophilic syndrome were associated with the acquisition of a point mutation in the ATP-binding domain of the FIP1L1-PDGFR(alpha) fusion protein that confers resistance to imatinib. The T674I substitution is analogous to the T315I mutation in the ABL kinase that occurs in some patients with BCR-ABL-positive CML in whom resistance to imatinib develops [21] and thus demonstrates that FIP1L1-PDGFR(alpha) is the therapeutic target of imatinib in the hypereosinophilic syndrome.

Nine of 11 patients with the hypereosinophilic syndrome had responses to imatinib that lasted more than three months, but only 5 of these 9 had a detectable FIP1L1-PDGFRA fusion. The basis for a response to imatinib in the other four patients is not known, but there are several possibilities. First, break points for the deletion may be widely distributed within the FIP1L1 gene. Our biochemical data indicate that a deletion that incorporated only the first exon of FIP1L1 would be sufficient to activate the PDGFR(alpha) kinase domain. However, reverse-transcriptase-PCR screening for such FIP1L1-PDGFRA variants was negative in these patients. Second, another gene near FIP1L1 could form a fusion protein with PDGFR(alpha). Detailed fluorescence in situ hybridization with probes that span the deleted region will resolve this question, but we have not yet identified alternative fusion partners for PDGFRA. Third, in some patients with the hypereosinophilic syndrome, the KIT gene, located approximately 400 kb downstream of PDGFRA, may be fused to FIP1L1. KIT is also sensitive to imatinib [10]; thus, a FIP1L1-KIT fusion protein in patients with the hypereosinophilic syndrome should also result in a clinical response. However, we have been unable to identify such a FIP1L1-KIT fusion gene in the four patients who had a response to imatinib but who did not have the FIP1L1-PDGFRA fusion gene. Fourth, a similar, cytogenetically silent gene rearrangement may occur, involving either ABL or PDGFR(beta) in some patients. Finally, an as yet unidentified kinase that is inhibited by imatinib may be constitutively activated by a mutation. Further analysis will be required to evaluate these possibilities.

Cloning of the FIP1L1-PDGFRA gene rearrangement identified chromosomal interstitial deletion as a novel molecular mechanism for a gain-of-function fusion gene. Most investigations of the loss of heterozygosity in human tumors have focused on the loss of function of one or both alleles of a putative tumor-suppressor gene. Our data suggest that a comprehensive analysis of human tumors for small deletions that may result in gain-of-function fusion genes should be undertaken.

Supported in part by grants from the National Institutes of Health (CA66996 and DK50654, to Dr. Gilliland; T32GMO7753-24, to Ms. Stover; and K23HL04409, to Dr. Gotlib); by a grant from the Leukemia and Lymphoma Society (to Dr. Gilliland); by a grant from the Fonds voor Wetenschapdelijk Onderzoek-Vlaanderen (G.0121.00, to Dr. Marynen); and by the Belgian American Educational Foundation and the Commission for Educational Exchange between the United States and Belgium. Dr. Cools is a postdoctoral researcher and Dr. Vandenberghe is a senior clinical investigator of the Fonds voor Wetenschapdelijk Onderzoek-Vlaanderen. Dr. Gilliland is an Associate Investigator of the Howard Hughes Medical Institute.

We are indebted to Ursula Pluys, Riet Somers, and Alexis Bywater for technical and administrative assistance, and to Marie Maerevoet, M.D., Lucienne Michaux, M.D., and Achiel Vanhoof, M.D. for contribution of patient samples and clinical care.

REFERENCES

1. Chusid MJ, Dale DC, West BC, Wolff SM. The hypereosinophilic syndrome: analysis of fourteen cases with review of the literature. Medicine (Baltimore) 1975;54:1-27. [Context Link]

2. Weller PF, Bubley GJ. The idiopathic hypereosinophilic syndrome. Blood 1994;83:2759-79. [Context Link]

3. Luppi M, Marasca R, Morselli M, Barozzi P, Torelli G. Clonal nature of hypereosinophilic syndrome. Blood 1994;84:349-50. [Context Link]

4. Chang HW, Leong KH, Koh DR, Lee SH. Clonality of isolated eosinophils in the hypereosinophilic syndrome. Blood 1999;93:1651-7. [Context Link]

5. Gleich GJ, Leiferman KM, Pardanani A, Tefferi A, Butterfield JH. Treatment of hypereosinophilic syndrome with imatinib mesilate. Lancet 2002;359:1577-8. [Context Link]

6. Buchdunger E, Zimmermann J, Mett H, et al. Inhibition of the Abl protein-tyrosine kinase in vitro and in vivo by a 2-phenylaminopyrimidine derivative. Cancer Res 1996; 56:100-4. [Context Link]

7. Druker BJ, Sawyers CL, Kantarjian H, et al. Activity of a specific inhibitor of the BCR-ABL tyrosine kinase in the blast crisis of chronic myeloid leukemia and acute lymphoblastic leukemia with the Philadelphia chromosome. N Engl J Med 2001;344:1038-42. [Erratum, N Engl J Med 2001;345:232.] [Context Link]

8. Druker BJ, Talpaz M, Resta DJ, et al. Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia. N Engl J Med 2001;344:1031-7. Ovid Full Text [Context Link]

9. Carroll M, Ohno-Jones S, Tamura S, et al. CGP 57148, a tyrosine kinase inhibitor, inhibits the growth of cells expressing BCR-ABL, TEL-ABL, and TEL-PDGFR fusion proteins. Blood 1997;90:4947-52. [Context Link]

10. Buchdunger E, Cioffi CL, Law N, et al. Abl protein-tyrosine kinase inhibitor STI571 inhibits in vitro signal transduction mediated by c-kit and platelet-derived growth factor receptors. J Pharmacol Exp Ther 2000;295:139-45. [Context Link]

11. Tuveson DA, Willis NA, Jacks T, et al. STI571 inactivation of the gastrointestinal stromal tumor c-KIT oncoprotein: biological and clinical implications. Oncogene 2001;20:5054-8. [Context Link]

12. Demetri GD, von Mehren M, Blanke CD, et al. Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors. N Engl J Med 2002;347:472-80. Ovid Full Text [Context Link]

13. Apperley JF, Gardembas M, Melo JV, et al. Response to imatinib mesylate in patients with chronic myeloproliferative diseases with rearrangements of the platelet-derived growth factor receptor beta. N Engl J Med 2002;347:481-7. Ovid Full Text [Context Link]

14. Dierlamm J, Wlodarska I, Michaux L, et al. Successful use of the same slide for consecutive fluorescence in situ hybridization experiments. Genes Chromosomes Cancer 1996;16:261-4. [Context Link]

15. Cools J, Bilhou-Nabera C, Wlodarska I, et al. Fusion of a novel gene, BTL, to ETV6 in acute myeloid leukemias with a t(4;12) (q11-q12;p13). Blood 1999;94:1820-4. [Context Link]

16. Willis TG, Jadayel DM, Coignet LJ, et al. Rapid molecular cloning of rearrangements of the IGHJ locus using long-distance inverse polymerase chain reaction. Blood 1997;90:2456-64. [Context Link]

17. Schwaller J, Frantsve J, Aster J, et al. Transformation of hematopoietic cell lines to growth-factor independence and induction of a fatal myelo- and lymphoproliferative disease in mice by retrovirally transduced TEL/JAK2 fusion gene. EMBO J 1998; 17:5321-33. [Context Link]

18. Cools J, Mentens N, Odero MD, et al. Evidence for position effects as a variant ETV6-mediated leukemogenic mechanism in myeloid leukemias with a t(4;12) (q11- q12;p13) or t(5;12)(q31;p13). Blood 2002;99:1776-84. [Context Link]

19. Kawagishi J, Kumabe T, Yoshimoto T, Yamamoto T. Structure, organization, and transcription units of the human alpha- platelet-derived growth factor receptor gene, PDGFRA. Genomics 1995;30:224-32. [Context Link]

20. Preker PJ, Lingner J, Minvielle-Sebastia L, Keller W. The FIP1 gene encodes a component of a yeast pre-mRNA polyadenylation factor that directly interacts with poly(A) polymerase. Cell 1995;81:379-89. Full Text [Context Link]

21. Gorre ME, Mohammed M, Ellwood K, et al. Clinical resistance to STI-571 cancer therapy caused by BCR-ABL gene mutation or amplification. Science 2001;293:876-80. Buy Now [Context Link]

22. Shah NP, Nicoll JM, Nagar B, et al. Multiple BCR-ABL kinase domain mutations confer polyclonal resistance to the tyrosine kinase inhibitor imatinib (STI571) in chronic phase and blast crisis chronic myeloid leukemia. Cancer Cell 2002;2:117-25. Full Text [Context Link]

23. Roumiantsev S, Shah NP, Gorre ME, et al. Clinical resistance to the kinase inhibitor STI-571 in chronic myeloid leukemia by mutation of Tyr-253 in the Abl kinase domain P-loop. Proc Natl Acad Sci U S A 2002;99:10700-5. [Context Link]

24. de Klein A, van Kessel AG, Grosveld G, et al. A cellular oncogene is translocated to the Philadelphia chromosome in chronic myelocytic leukaemia. Nature 1982;300:765-7. [Context Link]

25. Golub TR, Barker GF, Lovett M, Gilliland DG. Fusion of PDGF receptor beta to a novel ets-like gene, tel, in chronic myelomonocytic leukemia with t(5;12) chromosomal translocation. Cell 1994;77:307-16. [Context Link]

26. Ross TS, Bernard OA, Berger R, Gilliland DG. Fusion of Huntingtin interacting protein 1 to platelet-derived growth factor beta receptor (PDGFbetaR) in chronic myelomonocytic leukemia with t(5;7) (q33;q11.2). Blood 1998;91:4419-26. [Context Link]

27. Peeters P, Raynaud SD, Cools J, et al. Fusion of TEL, the ETS-variant gene 6 (ETV6), to the receptor-associated kinase JAK2 as a result of t(9;12) in a lymphoid and t(9;15;12) in a myeloid leukemia. Blood 1997;90:2535-40. [Context Link]

28. Schwaller J, Anastasiadou E, Cain D, et al. H4(D10S170), a gene frequently rearranged in papillary thyroid carcinoma, is fused to the platelet-derived growth factor receptor beta gene in atypical chronic myeloid leukemia with t(5;10)(q33;q22). Blood 2001;97:3910-8. [Context Link]



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