Biomedical subjects

D Gary Gilliland

Publications and source records attributed to D Gary Gilliland.

At least 19 recordsLinked to original sources

PubMed2005

KIAA1509 is a novel PDGFRB fusion partner in imatinib-responsive myeloproliferative disease associated with a t(5;14)(q33;q32).

We report the cloning of a novel PDGFRB fusion gene partner in a patient with a chronic myeloproliferative disorder characterized by t(5;14)(q33;q32), who responded to treatment with imatinib mesylate. Fluorescence in situ hybridization demonstrated that PDGFRB was involved in the translocation. Long distance inversion PCR identified KIAA1509 as the PDGFRB fusion partner. KIAA1509 is an uncharacterized gene with a predicted coiled-coil oligomerization domain with homology to the HOOK family of proteins. The predicted KIAA1509-PDGFRbeta fusion protein contains the KIAA1509 coiled-coil domain fused to the cytoplasmic domain of PDGFRbeta that includes the tyrosine kinase domain. Imatinib therapy resulted in rapid normalization of the patient's blood counts, and subsequent bone marrow biopsies and karyotypic analysis were consistent with sustained complete remission.

Adult↗

PubMed2004

Global effects of BCR/ABL and TEL/PDGFRbeta expression on the proteome and phosphoproteome: identification of the Rho pathway as a target of BCR/ABL.

Many leukemic oncogenes form as a consequence of gene fusions or mutation that result in the activation or overexpression of a tyrosine kinase. To identify commonalities and differences in the action of two such kinases, breakpoint cluster region (BCR)/ABL and TEL/PDGFRbeta, two-dimensional gel electrophoresis was employed to characterize their effects on the proteome. While both oncogenes affected expression of specific proteins, few common effects were observed. A number of proteins whose expression is altered by BCR/ABL, including gelsolin and stathmin, are related to cytoskeletal function whereas no such changes were seen in TEL/PDGFRbeta-transfected cells. Treatment of cells with the kinase inhibitor STI571 for 4-h reversed changes in expression of some of these cytoskeletal proteins. Correspondingly, BCR/ABL-transfected cells were less responsive to chemotactic and chemokinetic stimuli than non-transfected cells and TEL/PDGFRbeta-transfected Ba/F3 cells. Decreased motile response was reversed by a 16-h treatment with STI571. A phosphoprotein-specific gel stain was used to identify TEL/PDGFRbeta and BCR/ABL-mediated changes in the phosphoproteome. These included changes on Crkl, Ras-GAP-binding protein 1, and for BCR/ABL, cytoskeletal proteins such as tubulin, and Nedd5. Decreased phosphorylation of Rho-GTPase dissociation inhibitor (Rho GDI) was also observed in BCR/ABL-transfected cells. This results in the activation of the Rho pathway, and treatment of cells with Y27632, an inhibitor of Rho kinase, inhibited DNA synthesis in BCR/ABL-transfected Ba/F3 cells but not TEL/PDGFRbeta-expressing cells. Expression of a dominant-negative RhoA inhibited both DNA synthesis and transwell migration, demonstrating the significance of this pathway in BCR/ABL-mediated transformation.

Animals↗

PubMed2004

PKC412 inhibits the zinc finger 198-fibroblast growth factor receptor 1 fusion tyrosine kinase and is active in treatment of stem cell myeloproliferative disorder.

Human stem cell leukemia-lymphoma syndrome usually presents itself as a myeloproliferative disorder (MPD) that evolves to acute myeloid leukemia and/or lymphoma. The syndrome associated with t(8;13)(p11;q12) results in expression of the ZNF198-fibroblast growth factor receptor (FGFR) 1 fusion tyrosine kinase. Current empirically derived cytotoxic chemotherapy is inadequate for treatment of this disease. We hypothesized that small-molecule inhibitors of the ZNF198-FGFR1 fusion would have therapeutic efficacy. We characterized the transforming activity of ZNF198-FGFR1 in hematopoietic cells in vitro and in vivo. Expression of ZNF198-FGFR1 in primary murine hematopoietic cells caused a myeloproliferative syndrome in mice that recapitulated the human MPD phenotype. Transformation in these assays, and activation of the downstream effector molecules PLC-gamma, STAT5, and phosphatidylinositol 3-kinase/AKT, required the proline-rich domains, but not the ZNF domains, of ZNF198. A small-molecule tyrosine kinase inhibitor, PKC412 (N-benzoyl-staurosporine) effectively inhibited ZNF198-FGFR1 tyrosine kinase activity and activation of downstream effector pathways, and inhibited proliferation of ZNF198-FGFR1 transformed Ba/F3 cells. Furthermore, treatment with PKC412 resulted in statistically significant prolongation of survival in the murine model of ZNF198-FGFR1-induced MPD. Based in part on these data, PKC412 was administered to a patient with t(8;13)(p11;q12) and was efficacious in treatment of progressive myeloproliferative disorder with organomegaly. Therefore, PKC412 may be a useful therapy for treatment of human stem cell leukemia-lymphoma syndrome.

Animals↗

PubMed2004

Prediction of resistance to small molecule FLT3 inhibitors: implications for molecularly targeted therapy of acute leukemia.

Mutations in the receptor tyrosine kinase FLT3 occur frequently in patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Small molecules that selectively inhibit FLT3 kinase activity induce apoptosis in blasts from AML patients with FLT3 mutations and prolong survival in animal models of FLT3-induced myeloproliferative disease. A spectrum of structurally different small molecules with activity against FLT3 have been described, and their efficacy for treatment of AML and ALL is now being investigated in clinical trials. Here, we describe the results of an in vitro screen designed to identify mutations in the ATP-binding pocket of FLT3 that confer resistance to tyrosine kinase inhibitors. Mutations at four different positions (Ala-627, Asn-676, Phe-691, and Gly-697) were identified that confer varying degrees of resistance to PKC412, SU5614, or K-252a. FLT3 proteins mutated at Ala-627, Asn-676, or Phe-691 remained sensitive to higher concentrations of the inhibitors, but the G697R mutation conferred high-level resistance to each of these inhibitors as well as to six additional experimental inhibitors. These data provide insights into potential mechanisms of acquired resistance of FLT3 to small molecule inhibitors and indicate that the G697R mutation may be a clinically problematic resistance mutation that warrants proactive screening for additional inhibitors.

Acute Disease↗

PubMed2004

Patients with acute myeloid leukemia and an activating mutation in FLT3 respond to a small-molecule FLT3 tyrosine kinase inhibitor, PKC412.

Leukemic cells from 30% of patients with acute myeloid leukemia (AML) have an activating mutation in the FLT3 (fms-like tyrosine kinase) gene, which represents a target for drug therapy. We treated 20 patients, each with mutant FLT3 relapsed/refractory AML or high-grade myelodysplastic syndrome and not believed to be candidates for chemotherapy, with an FLT3 tyrosine kinase inhibitor, PKC412 (N-benzoylstaurosporine), at a dose of 75 mg 3 times daily by mouth. The drug was generally well tolerated, although 2 patients developed fatal pulmonary events of unclear etiology. The peripheral blast count decreased by 50% in 14 patients (70%). Seven patients (35%) experienced a greater than 2-log reduction in peripheral blast count for at least 4 weeks (median response duration, 13 weeks; range, 9-47 weeks); PKC412 reduced bone marrow blast counts by 50% in 6 patients (2 of these to < 5%). FLT3 autophosphorylation was inhibited in most of the Corresponding patients, indicating in vivo target inhibition at the dose schedule used in this study. PKC412 is an oral tyrosine kinase inhibitor with clinical activity in patients with AML whose blasts have an activating mutation of FLT3, suggesting potential use in combination with active agents, such as chemotherapy.

Adult↗

PubMed2004

Mouse model of Noonan syndrome reveals cell type- and gene dosage-dependent effects of Ptpn11 mutation.

Noonan syndrome is a common human autosomal dominant birth defect, characterized by short stature, facial abnormalities, heart defects and possibly increased risk of leukemia. Mutations of Ptpn11 (also known as Shp2), which encodes the protein-tyrosine phosphatase Shp2, occur in approximately 50% of individuals with Noonan syndrome, but their molecular, cellular and developmental effects, and the relationship between Noonan syndrome and leukemia, are unclear. We generated mice expressing the Noonan syndrome-associated mutant D61G. When homozygous, the D61G mutant is embryonic lethal, whereas heterozygotes have decreased viability. Surviving Ptpn11(D61G/+) embryos ( approximately 50%) have short stature, craniofacial abnormalities similar to those in Noonan syndrome, and myeloproliferative disease. Severely affected Ptpn11(D61G/+) embryos ( approximately 50%) have multiple cardiac defects similar to those in mice lacking the Ras-GAP protein neurofibromin. Their endocardial cushions have increased Erk activation, but Erk hyperactivation is cell and pathway specific. Our results clarify the relationship between Noonan syndrome and leukemia and show that a single Ptpn11 gain-of-function mutation evokes all major features of Noonan syndrome by acting on multiple developmental lineages in a gene dosage-dependent and pathway-selective manner.

Animals↗

PubMed2004

Variable sensitivity of FLT3 activation loop mutations to the small molecule tyrosine kinase inhibitor MLN518.

FLT3 is constitutively activated by internal tandem duplications (ITDs) in the juxtamembrane domain or by activation loop mutations in acute myeloid leukemia (AML). We tested the sensitivity of 8 activation loop mutations to the small molecule FLT3 inhibitor, MLN518. Each FLT3 activation loop mutant, including D835Y, D835A, D835E, D835H, D835N, D835V, D835del, and I836del, transformed Ba/F3 cells to factor-independent proliferation and had constitutive tyrosine kinase activation, as assessed by FLT3 autophosphorylation and activation of downstream effectors, including STAT5 and ERK. MLN518 inhibited FLT3 autophosphorylation and phosphorylation of STAT5 and ERK in FLT3-ITD-transformed Ba/F3 cells with an IC(50) (50% inhibition of cell viability) of approximately 500 nM. However, there was a broad spectrum of sensitivity among the 8 activation loop mutants, with IC(50) ranging from approximately 500 nM to more than 10 microM for the inhibition of phosphorylation of FLT3, STAT5, and ERK. The relative sensitivity of the mutants to MLN518 in biochemical assays correlated with the cellular IC(50) for cytokine-independent proliferation of FLT3-transformed Ba/F3 cells in the presence of MLN518. Thus, certain activation loop mutations in FLT3 simultaneously confer resistance to small molecule inhibitors. These findings have implications for the evaluation of responses in clinical trials with FLT3 inhibitors and provide a strategy to screen for compounds that can overcome resistance.

Animals↗

PubMed2004

Identifying and characterizing a novel activating mutation of the FLT3 tyrosine kinase in AML.

The FLT3 receptor is activated by juxtamembrane insertion mutations and by activation loop point mutations in patients with acute myeloid leukemia (AML). In a systematic tyrosine kinase gene exon resequencing study, 21 of 24 FLT3 exons were sequenced in samples from 53 patients with AML, 9 patients with acute lymphoblastic leukemia (ALL), and 3 patients with myelodysplasia samples. Three patients had novel point mutations at residue N841 that resulted in a change to isoleucine in 2 samples and to tyrosine in 1 sample. Introduction of FLT3-N841I cDNA into Ba/F3 cells led to interleukin-3 (IL-3)-independent proliferation, receptor phosphorylation, and constitutive activation of signal transducer and activator of transcription 5 (STAT5) and extracellular regulatory kinase (ERK), suggesting that the N841I mutation confers constitutive activity to the receptor. An FLT3 inhibitor (PKC412) inhibited the growth of Ba/F3-FLT3N841I cells (IC(50) 10 nM), but not of wild-type Ba/F3 cells cultured with IL-3. PKC412 also reduced tyrosine phosphorylation of the mutant receptor and inhibited STAT5 phosphorylation. Examination of the FLT3 autoinhibited structure showed that N841 is the key residue in a hydrogen-bonding network that likely stabilizes the activation loop. These results suggest that mutations at N841 represent a significant new activating mutation in patients with AML and that patients with such mutations may respond to small-molecule FLT3 inhibitors such as PKC412.

Adult↗

PubMed2004

Oncogenic K-ras in mouse models of myeloproliferative disease and acute myeloid leukemia.

Oncogenic N-RAS and K-RAS mutations are among the most frequently detected genetic alterations in patients with acute myeloid leukemia (AML). Recently, the role of oncogenic K-ras in leukemogenesis was investigated in a novel mouse model utilizing interferon (IFN)-inducible, Cre-mediated expression of oncogenic K-ras from its endogenous promoter. Conditional expression of oncogenic K-ras from its endogenous promoter in the hematopoietic system induces a lethal myeloproliferative disease in mice, but not AML, indicating that additional mutations are required for AML development. These results are consistent with a model in which the AML phenotype requires at least two cooperating mutations in the hematopoietic progenitor cells: one promoting proliferation and enhanced cell survival (such as oncogenic ras or a constitutively activated receptor tyrosine kinase) and one associated with impaired differentiation and enhanced immortalization (such as loss-of-function mutations in hematopoietic transcription factors). The model system with oncogenic K-ras provides a versatile platform to test the contribution of cooperating mutations in AML, and the efficacy of Ras pathway inhibitors in vivo.

Animals↗

PubMed2004

Positive and negative regulatory roles of the WW-like domain in TEL-PDGFbetaR transformation.

TEL-platelet-derived growth factor-beta receptor (TEL-PDGFbetaR) is expressed in chronic myelomonocytic leukemias associated with t(5;12)(q33;p13), and the fusion tyrosine kinase retains a conserved WW-like domain in the PDGFbetaR autoinhibitory juxtamembrane region. Here we report that mutation of the 2 conserved tryptophan residues of the WW-like domain has opposing effects on TELPDGFbetaR kinase activation. Alanine substitution of W593, essential for protein-protein interaction in the context of other WW domains, impaired TEL-PDGFbetaR-mediated transformation of hematopoietic cells due to inhibition of TEL-PDGFbetaR kinase activity. In contrast, alanine substitution of W566, essential for structural integrity of WW domain in other contexts, had no effect on TEL-PDGFbetaR activation and oncogenic activity. Surprisingly, however, the W566A mutation suppressed the W593A phenotype. Double mutant W566A/W593A was indistinguishable from the wild-type fusion protein with regard to kinase activity, ability to confer factor-independent growth to Ba/F3 cells, or ability to induce a myeloproliferative disease in mice. Additional mutational analysis identified other substitutions within the WW-like domain in addition to W566A that could also suppress the W593A phenotype, including mutations predicted to diminish the autoinhibitory function of the juxtamembrane region. Therefore, the WW-like domain in the context of TELPDGFbetaR may have both positive and negative regulatory roles in kinase activation.

Amino Acid Sequence↗

PubMed2004

Combination of rapamycin and protein tyrosine kinase (PTK) inhibitors for the treatment of leukemias caused by oncogenic PTKs.

Abnormal protein tyrosine kinases (PTKs) cause many human leukemias. For example, BCR/ABL causes chronic myelogenous leukemia (CML), whereas FLT3 mutations contribute to the pathogenesis of acute myelogenous leukemia. The ABL inhibitor Imatinib (Gleevec, STI571) has remarkable efficacy for treating chronic phase CML, and FLT3 inhibitors (e.g., PKC412) show similar promise in preclinical studies. However, resistance to PTK inhibitors is a major emerging problem that may limit long-term therapeutic efficacy. Development of rational combination therapies will probably be required to effect cures of these and other neoplastic disorders. Here, we report that the mTOR inhibitor rapamycin synergizes with Imatinib against BCR/ABL-transformed myeloid and lymphoid cells and increases survival in a murine CML model. Rapamycin/Imatinib combinations also inhibit Imatinib-resistant mutants of BCR/ABL, and rapamycin plus PKC412 synergistically inhibits cells expressing PKC412-sensitive or -resistant leukemogenic FLT3 mutants. Biochemical analyses raise the possibility that inhibition of 4E-BP1 phosphorylation may be particularly important for the synergistic effects of PTK inhibitor/rapamycin combinations. Addition of a mitogen-activated protein kinase kinase inhibitor to rapamycin or rapamycin plus PTK inhibitor further increases efficacy. Our results suggest that simultaneous targeting of more than one signaling pathway required by leukemogenic PTKs may improve the treatment of primary and relapsed CML and/or acute myelogenous leukemia caused by FLT3 mutations. Similar strategies may be useful for treating solid tumors associated with mutant and/or overexpressed PTKs.

Antibiotics, Antineoplastic↗

PubMed2004

NPM-ALK fusion kinase of anaplastic large-cell lymphoma regulates survival and proliferative signaling through modulation of FOXO3a.

Between 30% and 50% of patients with advanced-stage anaplastic large-cell lymphoma (ALCL) harbor the balanced chromosomal rearrangement t(2;5)(p23;q35), which results in the generation of the fusion protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). To further study survival signaling by NPMALK, we generated Ba/F3 cell lines with either inducible or constitutive expression of NPM-ALK and examined the regulation of the AKT target FOXO3a. We hypothesized that NPM-ALK signaling through phosphoinositol 3-kinase (PI 3-kinase) and AKT would regulate FOXO3a, a member of the forkhead family of transcription factors, thereby stimulating proliferation and blocking programmed cell death in NPM-ALK-transformed cells. In Ba/F3 cells with induced or constitutive expression of NPM-ALK, concomitant AKT activation and phosphorylation of its substrate, FOXO3a, was observed. In addition, transient expression of NPM-ALK in U-20S cells inhibited FOXO3a-mediated transactivation of reporter gene expression. Furthermore, NPM-ALK-induced FOXO3a phosphorylation in Ba/F3 cells resulted in nuclear exclusion of this transcriptional regulator, up-regulation of cyclin D2 expression, and down-regulation of p27(kip1) and Bim-1 expression. NPMALK reversal of proliferation arrest and of p27(kip1) induction was dependent on the phosphorylation of FOXO3a. Thus, FOXO3a is a barrier to hematopoietic transformation that is overcome by phosphorylation and cytoplasmic relocalization induced by the expression of NPM-ALK.

Cell Division↗

PubMed2004

The role of signal transducer and activator of transcription factors in leukemogenesis.

Human leukemias are frequently associated with the aberrant expression of activated fusion tyrosine kinases or activated protein tyrosine kinases carrying insertional or point mutations. The activated kinase enzymes typically phosphorylate one or more signal transducer and activator of transcription (STAT) factors, which translocate to the cell nucleus and regulate the expression of genes associated with survival and proliferation. The phosphorylation and activation of STAT family members has been described in a wide range of human leukemias. Furthermore, animal models of leukemia have demonstrated the pivotal contribution of STAT activation to leukemic pathogenesis. This review discusses evidence for the functional importance of STAT activation in the biology of leukemia and current opportunities for modulating STAT proteins in the therapy of this group of diseases.

Animals↗

PubMed2004

Blasts from the past: new lessons in stem cell biology from chronic myelogenous leukemia.

Cancer can be viewed as a hierarchical system that is dependent on a small population of "cancer stem cells" with unlimited self-renewal potential for continued growth and propagation of tumors. The identity and nature of these cells remains enigmatic, but an improved understanding of their biology may allow for selective therapeutic targeting. A recent report by sheds new light on leukemia stem cells by identifying the cells with in vitro self-renewing properties in various phases of chronic myelogenous leukemia, and linking the self-renewal properties of this population to activation of beta-catenin, a major effector of the canonical Wnt signaling pathway.

Cell Division↗

PubMed2004

MOZ-TIF2, but not BCR-ABL, confers properties of leukemic stem cells to committed murine hematopoietic progenitors.

To better understand the origin of leukemic stem cells, we tested the hypothesis that all leukemia oncogenes could transform committed myeloid progenitor cells lacking the capacity for self-renewal, as has recently been reported for MLL-ENL. Flow-sorted populations of common myeloid progenitors and granulocyte-monocyte progenitors were transduced with the oncogenes MOZ-TIF2 and BCR-ABL, respectively. MOZ-TIF2-transduced progenitors could be serially replated in methylcellulose cultures and continuously propagated in liquid culture, and resulted in an acute myeloid leukemia in vivo that could be serially transplanted. In contrast, BCR-ABL transduction conferred none of these properties to hematopoietic progenitors. These data demonstrate that some, but not all, leukemia oncogenes can confer properties of leukemic stem cells to hematopoietic progenitors destined to undergo apoptotic cell death.

Acute Disease↗

PubMed2004

Platelet-derived growth factor receptor inhibition to treat idiopathic hypereosinophilic syndrome.

Hypereosinophilic syndrome (HES) is a heterogeneous group of rare disorders characterized by peripheral blood and tissue eosinophilia leading to end-organ damage. Hypereosinophilic syndrome can be fatal, particularly in patients with endomyocardial fibrosis, and treatment has traditionally been palliative or preventive. The disease shares features with myeloproliferative disorders, such as chronic myeloid leukemia, including responsiveness to hydroxyurea and interferon. The tyrosine kinase inhibitor imatinib, a highly effective treatment for chronic myeloid leukemia, has shown efficacy in normalizing eosinophil counts and resolving signs and symptoms in some HES patients. Fusion of the Fip1-like 1 gene (FIP1L1) and the platelet-derived growth factor receptor alpha gene (PDGFRA) was discovered in the majority of patients with imatinib-sensitive HES, and all patients with the fusion responded to imatinib. The product of this fusion gene, FIP1L1-PDGFRalpha, is a constitutively active protein-tyrosine kinase capable of transforming hematopoietic cells. The efficacy of relatively low imatinib concentrations in HES, mediated by inhibition of FIP1L1-PDGFRalpha kinase activity, causally implicates FIP1L1-PDGFRA in the pathogenesis in certain HES patients.

Benzamides↗

PubMed2004

The FIP1L1-PDGFRalpha kinase in hypereosinophilic syndrome and chronic eosinophilic leukemia.

PURPOSE OF REVIEW: The idiopathic hypereosinophilic syndrome is a rare hematologic disorder characterized by sustained unexplained eosinophilia with associated end-organ damage and by a striking male predominance. The first insights into the molecular etiology of this heterogeneous disease were obtained from a "bedside-to-bench" approach. Successful empiric treatment of patients with the hypereosinophilic syndrome with the selective tyrosine kinase inhibitor imatinib mesylate (Gleevec, Novartis) ultimately led to the discovery of the FIP1L1-PDGFRalpha fusion kinase in about half of the hypereosinophilic syndrome cases. RECENT FINDINGS: The FIP1L1-PDGFRA fusion gene is generated by a cryptic interstitial chromosomal deletion, del(4)(q12q12), which indicates that these cases are clonal hematopoietic malignancies and should be reclassified as chronic eosinophilic leukemias based on current World Health Organization recommendations. In addition, the FIP1L1-PDGFRA fusion gene was also identified in cases with systemic mast cell disease. In vitro and in vivo studies confirmed that FIP1L1-PDGFRalpha is a therapeutic target of imatinib, forming a rational basis for the treatment of FIP1L1-PDGFRA positive chronic eosinophilic leukemia and mastocytosis with imatinib. Similar to BCR-ABL-positive leukemias, resistance to imatinib due to point mutations in the PDGFRalpha kinase domain may develop. We have explored strategies to circumvent resistance to imatinib using alternative tyrosine kinase inhibitors such as PKC412. SUMMARY: The discovery of the FIP1L1-PDGFRA fusion gene in the hypereosinophilic syndrome is an example of the power of clinical translational research and identifies interstitial chromosomal deletion as a novel mechanism to generate oncogenic tyrosine kinase fusion genes.

Amino Acid Sequence↗

PubMed2004

Conditional expression of oncogenic K-ras from its endogenous promoter induces a myeloproliferative disease.

Oncogenic ras alleles are among the most common mutations found in patients with acute myeloid leukemia (AML). Previously, the role of oncogenic ras in cancer was assessed in model systems overexpressing oncogenic ras from heterologous promoters. However, there is increasing evidence that subtle differences in gene dosage and regulation of gene expression from endogenous promoters play critical roles in cancer pathogenesis. We characterized the role of oncogenic K-ras expressed from its endogenous promoter in the hematopoietic system using a conditional allele and IFN-inducible, Cre-mediated recombination. Mice developed a completely penetrant myeloproliferative syndrome characterized by leukocytosis with normal maturation of myeloid lineage cells; myeloid hyperplasia in bone marrow; and extramedullary hematopoiesis in the spleen and liver. Flow cytometry confirmed the myeloproliferative phenotype. Genotypic and Western blot analysis demonstrated Cre-mediated excision and expression, respectively, of the oncogenic K-ras allele. Bone marrow cells formed growth factor-independent colonies in methylcellulose cultures, but the myeloproliferative disease was not transplantable into secondary recipients. Thus, oncogenic K-ras induces a myeloproliferative disorder but not AML, indicating that additional mutations are required for AML development. This model system will be useful for assessing the contribution of cooperating mutations in AML and testing ras inhibitors in vivo.

Adenoma↗