Activity of AMN107, a novel aminopyrimidine tyrosine kinase inhibitor, against human FIP1L1-PDGFR-alpha-expressing cells

The Progress of Small Molecule Targeting BCR-ABL in the Treatment of Chronic Myeloid Leukemia

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease. According to the American Cancer Society's 2021 cancer data report, new cases of CML account for about 15% of all leukemias. CML is generally divided into three stages: chronic phase, accelerated phase, and blast phase. Nearly 90% of patients are diagnosed as a chronic phase. Allogeneic stem cell transplantation and chemotherapeutic drugs, such as interferon IFN-α were used as the earliest treatments for CML. However, they could generate obvious side effects, and scientists had to seek new treatments for CML. A new era of targeted therapy for CML began with the introduction of imatinib, the first-generation BCR-ABL kinase inhibitor. However, the ensuing drug resistance and mutant strains led by T315I limited the further use of imatinib. With the continuous advancement of research, tyrosine kinase inhibitors (TKI) and BCR-ABL protein degraders with novel structures and therapeutic mechanisms have been discovered. From biological macromolecules to classical target protein inhibitors, a growing number of compounds are being developed to treat chronic myelogenous leukemia. In this review, we focus on summarizing the current situation of a series of candidate small-molecule drugs in CML therapy, including TKIs and BCR-ABL protein degrader. The examples provided herein describe the pharmacology activity of small-molecule drugs. These drugs will provide new enlightenment for future treatment directions.

Adverse events associated with nilotinib in chronic myeloid leukemia: mechanisms and management strategies

Introduction: Nilotinib is a second-generation tyrosine kinase inhibitor (TKI) targeting BCR/ABL, which is used for the first-line treatment of newly diagnosed chronic myeloid leukemia (CML) patients and the second-line treatment of most CML patients who are resistant or intolerant to prior therapy that includes imatinib. In addition to common adverse reactions, long-term use of nilotinib shows some toxicities that are different from those of occurring during other BCR/ABL TKI treatments, such as cardiovascular toxicity. It is life-threatening, which would affect not only the choice of initial treatment of CML patients but also the safety of long-term medication.Areas covered: Through searching literature and reports from PubMed and clinical trials, here we review a profile of the adverse effects induced by nilotinib. We also discuss the potential molecular toxicological mechanisms and clinical management, which may provide strategies to prevent or intervene the toxicity associated with nilotinib.Expert opinion: Severe adverse effects associated with nilotinib limit its long-term clinical application. However, the exact mechanisms underlying these toxicities remain unclear. Future research should focus on the developing strategies to reduce the toxicities of nilotinib as well as to avoid similar toxicity in the development of new drugs.

Loss of epigenetic regulator TET2 and oncogenic KIT regulate myeloid cell transformation via PI3K pathway

Mutations in KIT and TET2 are associated with myeloid malignancies. We show that loss of TET2-induced PI3K activation and -increased proliferation is rescued by targeting the p110α/δ subunits of PI3K. RNA-Seq revealed a hyperactive c-Myc signature in Tet2-/- cells, which is normalized by inhibiting PI3K signaling. Loss of TET2 impairs the maturation of myeloid lineage-derived mast cells by dysregulating the expression of Mitf and Cebpa, which is restored by low-dose ascorbic acid and 5-azacytidine. Utilizing a mouse model in which the loss of TET2 precedes the expression of oncogenic Kit, similar to the human disease, results in the development of a non-mast cell lineage neoplasm (AHNMD), which is responsive to PI3K inhibition. Thus, therapeutic approaches involving hypomethylating agents, ascorbic acid, and isoform-specific PI3K inhibitors are likely to be useful for treating patients with TET2 and KIT mutations.

Platelet-derived growth factor receptors (PDGFRs) fusion genes involvement in hematological malignancies

PURPOSE

To investigate oncogenic platelet-derived growth factor receptor(PDGFR) fusion genes involvement in hematological malignancies, the advances in the PDGFR fusion genes diagnosis and development of PDGFR fusions inhibitors.

METHODS

Literature search was done using terms "PDGFR and Fusion" or "PDGFR and Myeloid neoplasm" or 'PDGFR and Lymphoid neoplasm' or "PDGFR Fusion Diagnosis" or "PDGFR Fusion Targets" in databases including PubMed, ASCO.org, and Medscape.

RESULTS

Out of the 36 fusions detected, ETV6(TEL)-PDGFRB and FIP1L1-PDGFRA fusions were frequently detected, 33 are as a result of chromosomal translocation, FIP1L1-PDGFRA and EBF1-PDGFRB are the result of chromosomal deletion and CDK5RAP2- PDGFRΑ is the result of chromosomal insertion. Seven of the 34 rare fusions have detectable reciprocals.

CONCLUSION

RNA aptamers are promising therapeutic target of PDGFRs and diagnostic tools of PDGFRs fusion genes. Also, PDGFRs have variable prospective therapeutic strategies including small molecules, RNA aptamers, and interference therapeutics as well as development of adaptor protein Lnk mimetic drugs.

Antitumor activity of S116836, a novel tyrosine kinase inhibitor, against imatinib-resistant FIP1L1-PDGFRα-expressing cells

The FIP1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRα) fusion oncogene is the driver factor in a subset of patients with hypereosinophilic syndrome (HES)/chronic eosinophilic leukemia (CEL). Most FIP1L1-PDGFRα-positive patients respond well to the tyrosine kinase inhibitor (TKI) imatinib. Resistance to imatinib in HES/CEL has been described mainly due to the T674I mutation in FIP1L1-PDGFRα, which is homologous to the imatinib-resistant T315I mutation in BCR-ABL. Development of novel TKIs is imperative to overcome resistance to imatinib. We synthesized S116836, a novel TKI. In this study, we evaluated the antitumor activity of S116836 in FIP1L1-PDGFRα-expressing cells. The results showed that S116836 potently inhibited PDGFRα and its downstream signaling molecules such as STAT3, AKT, and Erk1/2. S116836 effectively inhibited the growth of the WT and T674I FIP1L1-PDGFRα-expressing neoplastic cells in vitro and in nude mouse xenografts. Moreover, S116836 induced intrinsic pathway of apoptosis as well as the death receptor pathway, coincided with up-regulation of the proapoptotic BH3-only protein Bim-EL through the Erk1/2 pathway. In conclusion, S116836 is active against WT and T674I FIP1L1-PDGFRα-expressing cells, and may be a prospective agent for the treatment of HES/CEL.

A preclinical study demonstrating the efficacy of nilotinib in inhibiting the growth of pediatric high-grade glioma

Solid tumors arising from malignant transformation of glial cells are one of the leading causes of central nervous system tumor-related death in children. Recurrence in spite of rigorous surgical and chemoradiation therapies remains a major hurdle in management of these tumors. Here, we investigate the efficacy of the second-generation receptor tyrosine kinase inhibitor nilotinib as a therapeutic option for the management of pediatric gliomas. We have utilized two independent pediatric high-grade glioma cell lines with either high platelet-derived growth factor receptor alpha (PDGFRα) or high PDGFRβ expression in in vitro assays to investigate the specific downstream effects of nilotinib treatment. Using in vitro cell-based assays we show that nilotinib inhibits PDGF-BB-dependent activation of PDGFRα. We further show that nilotinib is able to decrease cell proliferation and anchorage-independent growth via suppression of AKT and ERK1/2 signaling pathways. Our results suggest that nilotinib may be effective for management of a PDGFRα-dependent group of pediatric gliomas.

Identification of Ponatinib as a potent inhibitor of growth, migration, and activation of neoplastic eosinophils carrying FIP1L1-PDGFRA

In chronic eosinophilic leukemia, the transforming oncoprotein FIP1L1-PDGFRA is a major target of therapy. In most patients, the tyrosine kinase inhibitor (TKI) imatinib induces complete remission. For patients who are intolerant or resistant, novel TKIs have been proposed. We examined the in vitro effects of 14 kinase blockers on growth and function of EOL-1 cells, a FIP1L1-PDGFRA(+) eosinophil cell line. Major growth-inhibitory effects were seen with all PDGFR-blocking agents, with IC50 values in the low nanomolar range: ponatinib, 0.1-0.2 nmol/L; sorafenib, 0.1-0.2 nmol/L; masitinib, 0.2-0.5 nmol/L; nilotinib, 0.2-1.0 nmol/L; dasatinib, 0.5-2.0 nmol/L; sunitinib, 1-2 nmol/L; midostaurin, 5-10 nmol/L. These drugs were also found to block activation of PDGFR-downstream signaling molecules, including Akt, S6, and STAT5 in EOL-1 cells. All effective TKIs produced apoptosis in EOL-1 cells as determined by microscopy, Annexin-V/PI, and caspase-3 staining. In addition, PDGFR-targeting TKIs were found to inhibit cytokine-induced migration of EOL-1 cells. In all bioassays used, ponatinib was found to be the most potent compound in EOL-1 cells. In addition, ponatinib was found to downregulate expression of the activation-linked surface antigen CD63 on EOL-1 cells and to suppress the growth of primary neoplastic eosinophils. We also examined drug effects on Ba/F3 cells expressing two clinically relevant, imatinib-resistant, mutant forms of FIP1L1-PDGFRA, namely T674I and D842V. Strong inhibitory effects on both mutants were seen only with ponatinib. In summary, novel PDGFR-targeting TKIs may be alternative agents for the treatment of patients with imatinib-resistant chronic eosinophilic leukemia. Although several different PDGFR-targeting agents are effective, the most potent drug appears to be ponatinib.

Effect of the tyrosine kinase inhibitor nilotinib in patients with hypereosinophilic syndrome/chronic eosinophilic leukemia: analysis of the phase 2, open-label, single-arm A2101 study

PURPOSE

Hypereosinophilic syndrome (HES) and chronic eosinophilic leukemia (CEL) are characterized by sustained overproduction of eosinophils and organ dysfunction. CEL involves the presence of clonal genetic markers, such as a fusion of FIP1-like 1 protein and platelet-derived growth factor receptor α (FIP1L1-PDGFRα, or F/P) or PDGFRα-activating mutations.

METHODS

Sixteen patients with HES/CEL were enrolled in the phase 2 nilotinib registration trial (NCT00109707) and treated with nilotinib 400 mg twice daily. The median duration of treatment was 95 days (range 3-1,079).

RESULTS

Twelve patients had HES: 1 achieved a complete hematologic response (CHR), 3 achieved stable disease, 3 had progressive disease, and 5 were not evaluable for response. Four patients had CEL: 2 with the F/P fusion and 2 with PDGFRα-activating mutations. Both patients with an F/P fusion achieved a CHR; 1 also achieved a complete molecular response (CMR). Of the 2 patients with PDGFRα-activating mutations, 1 had stable disease and the other achieved CMR. At 24 months, overall survival in the HES group was 75.0 % (95 % CI 50.5-100.0) and no patients in the CEL group died. Median survival was not yet reached after a median follow-up of 32 months. The most common grade 3/4 hematologic laboratory abnormalities were lymphocytopenia (31.3 %) and neutropenia (25.0 %). The most common drug-related nonhematologic grade 3/4 adverse event was pruritus, which occurred in 2 patients (12.5 %).

CONCLUSIONS

Nilotinib 400 mg twice daily was effective in some patients with HES/CEL regardless of F/P mutation status, and the safety profile was consistent with other nilotinib studies.

Review of current classification, molecular alterations, and tyrosine kinase inhibitor therapies in myeloproliferative disorders with hypereosinophilia

Recent advances in our understanding of the molecular mechanisms underlying hypereosinophilia have led to the development of a ‘molecular’ classification of myeloproliferative disorders with eosinophilia. The revised 2008 World Health Organization classification of myeloid neoplasms included a new category called “myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB or FGFR1.” Despite the molecular heterogeneity of PDGFR (platelet-derived growth factor receptor) rearrangements, tyrosine kinase inhibitors at low dose induce rapid and complete hematological remission in the majority of these patients. Other kinase inhibitors are promising. Further discoveries of new molecular alterations will direct the development of new specific inhibitors. In this review, an update of the classifications of myeloproliferative disorders associated with hypereosinophilia is discussed together with open and controversial questions. Molecular mechanisms and promising results of tyrosine kinase inhibitor treatments are reviewed.

The challenge of developing robust drugs to overcome resistance

Drug resistance is problematic in microbial disease, viral disease and cancer. Understanding at the outset that resistance will impact the effectiveness of any new drug that is developed for these disease categories is imperative. In this Feature, we detail approaches that have been taken with selected drug targets to reduce the susceptibility of new drugs to resistance mechanisms. We will also define the concepts of robust drugs and resilient targets, and discuss how the design of robust drugs and the selection of resilient targets can lead to successful strategies for combating resistance.

Nilotinib: a novel, selective tyrosine kinase inhibitor

The development of tyrosine kinase inhibitors (TKIs) for the treatment of chronic myelogenous leukemia (CML) was based on the discovery that CML stem and progenitor cells overexpress the abnormal fusion protein kinase BCR-ABL. The prototype TKI, imatinib, selectively inhibits BCR-ABL, as well as several other kinases, including stem cell factor receptor (KIT), discoidin domain receptor (DDR), platelet-derived growth factor receptor (PDGFR), and colony-stimulating factor receptor-1 (CSF-1R). Although the management of CML improved dramatically with the introduction of imatinib, not all patients benefit from treatment because of resistance or intolerance. Consequently, research efforts have focused on developing more potent TKIs with the ability to circumvent imatinib resistance. Nilotinib, a second-generation oral TKI, was rationally designed based on the crystal structure of imatinib to be highly active against a wide range of imatinib-resistant BCR-ABL mutants and is approved for the treatment of newly diagnosed or imatinib-resistant or -intolerant CML, and has shown superiority over imatinib in first-line treatment for newly diagnosed CML. Furthermore, the activity of nilotinib against KIT and PDGFRα has led to its evaluation in advanced gastrointestinal stromal tumors (GIST). The purpose of this review is to describe the development of nilotinib, providing a structural explanation for the differential activity of nilotinib and imatinib in GIST. Activity of nilotinib against KIT and PDGFR and emerging evidence of differences in cellular uptake between nilotinib and imatinib are discussed.

Nilotinib: evaluation and analysis of its role in chronic myeloid leukemia

Nilotinib, formally known as AMN107, is a second-generation tyrosine kinase inhibitor, rationally designed from its revolutionary parent compound imatinib, to produce a 30–40-fold enhancement in the inhibition of the BCR–ABL1-derived oncoprotein associated with chronic myeloid leukemia. In clinical trials, nilotinib has proven to be a useful agent in the treatment of imatinib-refractory disease and was initially approved by both the US FDA and EMA in 2007 for use in adults as a second-line therapy. More recently, data from the first randomized controlled trials of the front-line use of nilotinib in newly diagnosed patients with chronic phase chronic myeloid leukemia have demonstrated superiority in the rates of major molecular responses at 12 months over the gold standard–imatinib 400 mg. As such, in June 2010, the FDA granted accelerated approval for its use in newly diagnosed Philadelphia chromosome-positive chronic myeloid leukemia. Nilotinib is well tolerated, with a favorable side-effect profile. With the emergence of supportive trial data, it is likely to have a leading role both in the front-line management of newly presenting patients and in the second-line treatment of patients resistant to or intolerant of imatinib and other second-line agents.

Nilotinib: optimal therapy for patients with chronic myeloid leukemia and resistance or intolerance to imatinib

Chronic myeloid leukemia (CML) is the consequence of a single balanced translocation that produces the BCR-ABL fusion oncogene which is detectable in over 90% of patients at presentation. The BCR-ABL inhibitor imatinib mesylate (IM) has improved survival in all phases of CML and is the standard of care for newly diagnosed patients in chronic phase. Despite the very significant therapeutic benefits of IM, a small minority of patients with early stage disease do not benefit optimally while IM therapy in patients with advanced disease is of modest benefit in many. Diverse mechanisms may be responsible for IM failures, with point mutations within the Bcr-Abl kinase domain being amongst the most common resistance mechanisms described in patients with advanced CML. The development of novel agents designed to overcome IM resistance, while still primarily targeted on BCR-ABL, led to the creation of the high affinity aminopyrimidine inhibitor, nilotinib. Nilotinib is much more potent as a BCR-ABL inhibitor than IM and inhibits both wild type and IM-resistant BCR-ABL with significant clinical activity across the entire spectrum of BCR-ABL mutants with the exception of T315I. The selection of a second generation tyrosine kinase inhibitor to rescue patients with imatinib failure will be based on several factors including age, co-morbid medical problems and ABL kinase mutational profile. It should be noted that while the use of targeted BCR-ABL kinase inhibitors in CML represents a paradigm shift in CML management these agents are not likely to have activity against the quiescent CML stem cell pool. The purpose of this review is to summarize the pre-clinical and clinical data on nilotinib in patients with CML who have failed prior therapy with IM or dasatinib.

Hypereosinophilic syndrome: current approach to diagnosis and treatment

Hypereosinophilic syndrome is a heterogeneous group of rare disorders characterized by marked blood or tissue eosinophilia resulting in a wide variety of clinical manifestations. Although the existence of clinical subtypes (or variants) of HES has been appreciated for some time, the recent characterization of some of these variants at the molecular and immunologic levels has demonstrated dramatic differences in disease pathogenesis, response to treatment, and prognosis depending on the etiology of the eosinophilia. This, together with the availability of novel targeted therapies, including tyrosine kinase inhibitors and monoclonal antibodies, has fundamentally altered the approach to the diagnosis and treatment of HES.

How I treat hypereosinophilic syndromes

Hypereosinophilic syndromes (HESs) are a heterogeneous group of uncommon disorders characterized by marked peripheral eosinophilia and end organ manifestations attributable to the eosinophilia or unexplained in the clinical setting. Whereas corticosteroids remain the mainstay of treatment for most patients, recent diagnostic advances and the development of novel targeted therapies, including tyrosine kinase inhibitors and humanized monoclonal antibodies, have increased the complexity of therapeutic decisions in HESs. This review presents a treatment-based approach to the diagnosis and classification of patients with peripheral blood eosinophilia of 1.5 x 10(9)/L (1500/mm3) or higher and discusses the role of currently available therapeutic agents in the treatment of these patients.

Nilotinib: a phenylamino-pyrimidine derivative with activity against BCR-ABL, KIT and PDGFR kinases

The BCR-ABL kinase inhibitor imatinib mesylate is currently the standard therapy for patients with chronic myeloid leukemia (CML). However, mutations within the ABL kinase domain interfering with drug binding have been identified as the main mechanism of resistance to imatinib. Multiple distinct BCR-ABL kinase mutant isoforms conferring varying degrees of resistance to tyrosine kinase inhibitors have been reported. Nilotinib is a tyrosine kinase inhibitor 30-fold more potent than imatinib against BCR-ABL kinase. Nilotinib is active against a wide range of imatinib-resistant BCR-ABL mutant isoforms, except for T315I. Results from Phase II studies of nilotinib for patients with CML after failure or intolerance to imatinib therapy have shown a favorable toxicity profile and confirmed the high efficacy of nilotinib in this setting. Studies addressing the activity of nilotinib in newly-diagnosed patients with CML are underway. Furthermore, nilotinib is a potent inhibitor of KIT and PDGFR kinases. Here, we review the preclinical development of nilotinib and the activity of this agent in patients with CML and in tumors driven by KIT and/or PDGFR mutant kinases, such as gastrointestinal stromal tumors and some forms of clonal hypereosinophilia.

Refining targeted therapies in chronic myeloid leukemia: development and application of nilotinib, a step beyond imatinib

The BCR-ABL kinase inhibitor imatinib mesylate is currently the standard therapy for patients with chronic myeloid leukemia (CML). Despite the remarkable results achieved with imatinib for the treatment of CML, the emergence of resistance to this drug has become a significant problem. Mutations within the ABL kinase domain have been identified as the main mechanism of resistance to imatinib. Other mechanisms include genomic amplification of BCR-ABL and modulation of drug efflux or influx transporters. Several strategies have been developed to overcome the problem of imatinib resistance, including dose escalation of imatinib, combination treatments, or novel targeted agents. Nilotinib is a tyrosine kinase inhibitor 30-fold more potent than imatinib, active against a wide range of mutant clones, except T315I. Phase I-II trials of nilotinib showed high activity in imatinib-resistant CML and Ph+ acute lymphoblastic leukemia. We here review the development of nilotinib and the activity of this agent in CML patients and in other forms of sensitive neoplasms.

Ki11502, a novel multitargeted receptor tyrosine kinase inhibitor, induces growth arrest and apoptosis of human leukemia cells in vitro and in vivo

Ki11502 is a novel multitargeted receptor tyrosine kinase (RTK) inhibitor with selectivity against platelet-derived growth factor receptor alpha/beta (PDGFRalpha/beta). Ki11502 (0.1-1 nM, 2 days) profoundly caused growth arrest, G(0)/G(1) cell-cycle arrest, and apoptosis associated with down-regulation of Bcl-2 family proteins in the eosinophilic leukemia EOL-1 cells having the activated FIP1-like 1/PDGFRalpha fusion gene. Ki11502 decreased levels of p-PDGFRalpha and its downstream signals, including p-Akt, p-ERK, and p-STAT5, in EOL-1 cells. Of note, Ki11502 was also active against imatinib-resistant PDGFRalphaT674I mutant. In addition, Ki11502 inhibited proliferation of biphenotipic leukemia MV4-11 and acute myelogenous leukemia MOLM13 and freshly isolated leukemia cells having activating mutations in FMS-like tyrosine kinase 3 (FLT3). This occurred in parallel with the drug inhibiting FLT3 and its downstream signal pathways, as measured by fluorescence-activated cell sorting using the phospho-specific antibodies. In addition, Ki11502 totally inhibited proliferation of EOL-1 cells growing as tumor xenografts in SCID mice without any noticeable adverse effects. Taken together, Ki11502 has profound antiproliferative effects on select subsets of leukemia including those possessing imatinib-resistant mutation.

Sorafenib inhibits the imatinib-resistant KITT670I gatekeeper mutation in gastrointestinal stromal tumor

PURPOSE

Resistance is commonly acquired in patients with metastatic gastrointestinal stromal tumor who are treated with imatinib mesylate, often due to the development of secondary mutations in the KIT kinase domain. We sought to investigate the efficacy of second-line tyrosine kinase inhibitors, such as sorafenib, dasatinib, and nilotinib, against the commonly observed imatinib-resistant KIT mutations (KIT(V654A), KIT(T670I), KIT(D820Y), and KIT(N822K)) expressed in the Ba/F3 cellular system.

EXPERIMENTAL DESIGN

In vitro drug screening of stable Ba/F3 KIT mutants recapitulating the genotype of imatinib-resistant patients harboring primary and secondary KIT mutations was investigated. Comparison was made to imatinib-sensitive Ba/F3 KIT mutant cells as well as Ba/F3 cells expressing only secondary KIT mutations. The efficacy of drug treatment was evaluated by proliferation and apoptosis assays, in addition to biochemical inhibition of KIT activation.

RESULTS

Sorafenib was potent against all imatinib-resistant Ba/F3 KIT double mutants tested, including the gatekeeper secondary mutation KIT(WK557-8del/T670I), which was resistant to other kinase inhibitors. Although all three drugs tested decreased cell proliferation and inhibited KIT activation against exon 13 (KIT(V560del/V654A)) and exon 17 (KIT(V559D/D820Y)) double mutants, nilotinib did so at lower concentrations.

CONCLUSIONS

Our results emphasize the need for tailored salvage therapy in imatinib-refractory gastrointestinal stromal tumors according to individual molecular mechanisms of resistance. The Ba/F3 KIT(WK557-8del/T670I) cells were sensitive only to sorafenib inhibition, whereas nilotinib was more potent on imatinib-resistant KIT(V560del/V654A) and KIT(V559D/D820Y) mutant cells than dasatinib and sorafenib.

Novel Abl kinase inhibitors in chronic myeloid leukemia in blastic phase and Philadelphia chromosome-positive acute lymphoblastic leukemia

Chronic myeloid leukemia (CML) is characterized by the presence of the Philadelphia chromosome, which is associated with a balanced translocation involving chromosomes 9 and 22 to produce a fusion gene (bcr-abl) that gives rise to a constitutively activated Abl tyrosine kinase. This kinase led to the discovery of several small-molecule inhibitors, imatinib being the first and most successful of these. Resistance to imatinib results in some patients from Abl kinase point mutations. Overcoming imatinib resistance represents one of the biggest challenges facing clinicians in the modern management of CML. In this review, we discuss the current understanding of CML pathophysiology and mechanisms of imatinib resistance and how advancing this knowledge has led to the design of novel therapies in the area of blastic phase CML and Philadelphia chromosome-positive acute lymphoblastic leukemia with previous imatinib failure.

The novel tyrosine kinase inhibitor EXEL-0862 induces apoptosis in human FIP1L1-PDGFR-α-expressing cells through caspase-3-mediated cleavage of Mcl-1

The FIP1-like-1 (FIP1L1)-platelet-derived growth factor receptor-alpha (FIP1L1-PDGFR-alpha) fusion kinase causes hypereosinophilic syndrome (HES) in a defined subset of patients. Imatinib mesylate is a potent inhibitor of ABL but also of PDGFR-alpha, and has been associated with durable hematologic responses in patients with HES. However, development of mutations in the tyrosine kinase domain may hamper the activity of tyrosine kinase inhibitors (TKIs), which suggests that novel agents are warranted to prevent or overcome resistance. We evaluated the efficacy of the novel TKI EXEL-0862 in FIP1L1-PDGFR-alpha-expressing cell lines and in cells from a patient with HES harboring the FIP1L1-PDGFR-alpha gene. EXEL-0862 inhibited the proliferation of EOL-1 and imatinib-resistant T674I FIP1L1-PDGFR-alpha-expressing cells and resulted in potent inhibition of the phosphorylation of PDGFR-alpha and downstream proteins STAT3 and Erk1/2, both in vitro and ex vivo. Moreover, EXEL-0862 induced apoptotic death in EOL-1 cells and imatinib-resistant T674I FIP1L1-PDGFR-alpha-expressing cells, and resulted in significant downregulation of the antiapoptotic protein Mcl-1 through a caspase-dependent mechanism. Our data establish EXEL-0862 as a solid candidate for the targeted treatment of patients with FIP1L1-PDGFR-alpha-positive HES.

A critical appraisal of conventional and investigational drug therapy in patients with hypereosinophilic syndrome and clonal eosinophilia

Hypereosinophilic syndrome (HES) is a rare disorder characterized by persistent and marked eosinophilia, leading to end-organ damage. Over the last decade, great progress has been made in unraveling the molecular basis of HES that has resulted in the characterization of specific genetic alterations linked to clonal eosinophilia. The most frequently encountered genetic aberrancy is the cryptic FIP1-like 1/platelet-derived growth factor receptor alpha (FIP1L1-PDGFRA) fusion transcript, which results in an eosinophilic, myeloproliferative disorder. In addition, in a subset of patients with HES, a population of aberrant T cells that secretes interleukin-5 can be identified, indicating the existence of lymphocyte-mediated hypereosinophilia. These new insights have led to both a genetically based (re)classification of eosinophilic blood disorders and to effective therapies with targeted agents, such as small-molecule tyrosine kinase inhibitors (eg, imatinib, nilotinib, PKC412) and, more recently, monoclonal antibodies (eg, mepolizumab, alemtuzumab). These targeted therapies hold great promise for improving the clinical outcomes of patients with HES and clonal eosinophilia, and they have exhibited relatively safe toxicity profiles.