Dissecting Clonal Hematopoiesis in Tissues of Classical Hodgkin Lymphoma Patients.

Clonal hematopoiesis predisposes to hematological malignancies. However, clonal hematopoiesis is understudied in classical Hodgkin lymphoma (cHL), a mature B-cell neoplasm exhibiting the most abundant microenvironment. We analyzed clonal hematopoiesis in 40 cHL cases by sequencing microdissected tumor cells and matched normal cells from blood and/or lymph nodes. Five patients had blood and/or tissue clonal hematopoiesis. In three of five patients (all failing first-line therapy), clonal hematopoiesis spread through the tissue microenvironment extensively, and featured mutant DNMT3AR882H , KRASG60D and DNMT3AR882H +TET2Q1274 * in 33%, 92% and 60% of non-neoplastic cells, respectively. In the latter case, DNMT3A/TET2-mutant clonal hematopoiesis seeded the neoplastic clone, which was infected by the Epstein-Barr virus and showed almost no other somatic mutations exome-wide. In the former case, DNMT3A-mutant clonal hematopoiesis did not originate the neoplastic clone despite dominating the blood and B-cell lineage (~94% leukocytes; ~96% mature blood B cells), yet led to NPM1-mutated acute myeloid leukemia 6 years after therapy for cHL. Our results expand to cHL the spectrum of hematologic malignancies associated with clonal hematopoiesis.

Pervasive mutations of JAK-STAT pathway genes in classical Hodgkin lymphoma.

Dissecting the pathogenesis of classical Hodgkin lymphoma (cHL), a common cancer in young adults, remains challenging because of the rarity of tumor cells in involved tissues (usually <5%). Here, we analyzed the coding genome of cHL by microdissecting tumor and normal cells from 34 patient biopsies for a total of ∼50 000 singly isolated lymphoma cells. We uncovered several recurrently mutated genes, namely, STAT6 (32% of cases), GNA13 (24%), XPO1 (18%), and ITPKB (16%), and document the functional role of mutant STAT6 in sustaining tumor cell viability. Mutations of STAT6 genetically and functionally cooperated with disruption of SOCS1, a JAK-STAT pathway inhibitor, to promote cHL growth. Overall, 87% of cases showed dysregulation of the JAK-STAT pathway by genetic alterations in multiple genes (also including STAT3, STAT5B, JAK1, JAK2, and PTPN1), attesting to the pivotal role of this pathway in cHL pathogenesis and highlighting its potential as a new therapeutic target in this disease.

Genomics of Hairy Cell Leukemia.

Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with unique clinicopathologic features and an initial exquisite sensitivity to chemotherapy with purine analogs; however, the disease relapses, often repeatedly. The enigmatic pathogenesis of HCL was recently clarified by the discovery of its underlying genetic cause, the BRAF-V600E kinase-activating mutation, which is somatically and clonally present in almost all patients through the entire disease spectrum and clinical course. By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior. Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis. Conversely, BRAF-V600E is absent in other B-cell neoplasms, including mimickers of HCL that require different treatments (eg, HCL-variant and splenic marginal zone lymphoma). Thus, testing for BRAF-V600E allows for a genetics-based differential diagnosis between HCL and HCL-like tumors, even noninvasively in routine blood samples. BRAF-V600E also represents a new therapeutic target. Patients' leukemic cells exposed ex vivo to BRAF inhibitors are spoiled of their HCL identity and then undergo apoptosis. In clinical trials of patients with HCL who have experienced multiple relapses after purine analogs or who are refractory to purine analogs, a short course of the oral BRAF inhibitor vemurafenib produced an almost 100% response rate, including complete remission rates of 35% to 42%, without myelotoxicity. To further improve on these results, it will be important to clarify the mechanisms of incomplete leukemic cell eradication by vemurafenib and to explore chemotherapy-free combinations of a BRAF inhibitor with other targeted agents (eg, a MEK inhibitor and/or an anti-CD20 monoclonal antibody).

Arsenic trioxide and all-trans retinoic acid target NPM1 mutant oncoprotein levels and induce apoptosis in NPM1-mutated AML cells.

Nucleophosmin (NPM1) mutations represent an attractive therapeutic target in acute myeloid leukemia (AML) because they are common (∼30% AML), stable, and behave as a founder genetic lesion. Oncoprotein targeting can be a successful strategy to treat AML, as proved in acute promyelocytic leukemia by treatment with all-trans retinoic acid (ATRA) plus arsenic trioxide (ATO), which degrade the promyelocytic leukemia (PML)-retinoic acid receptor fusion protein. Adjunct of ATRA to chemotherapy was reported to be beneficial for NPM1-mutated AML patients. Leukemic cells with NPM1 mutation also showed sensibility to ATO in vitro. Here, we explore the mechanisms underlying these observations and show that ATO/ATRA induce proteasome-dependent degradation of NPM1 leukemic protein and apoptosis in NPM1-mutated AML cell lines and primary patients' cells. We also show that PML intracellular distribution is altered in NPM1-mutated AML cells and reverted by arsenic through oxidative stress induction. Interestingly, similarly to what was described for PML, oxidative stress also mediates ATO-induced degradation of the NPM1 mutant oncoprotein. Strikingly, NPM1 mutant downregulation by ATO/ATRA was shown to potentiate response to the anthracyclin daunorubicin. These findings provide experimental evidence for further exploring ATO/ATRA in preclinical NPM1-mutated AML in vivo models and a rationale for exploiting these compounds in chemotherapeutic regimens in clinics.

BRAF inhibitors reverse the unique molecular signature and phenotype of hairy cell leukemia and exert potent antileukemic activity.

Hairy cell leukemia (HCL) shows unique clinicopathological and biological features. HCL responds well to purine analogs but relapses are frequent and novel therapies are required. BRAF-V600E is the key driver mutation in HCL and distinguishes it from other B-cell lymphomas, including HCL-like leukemias/lymphomas (HCL-variant and splenic marginal zone lymphoma). The kinase-activating BRAF-V600E mutation also represents an ideal therapeutic target in HCL. Here, we investigated the biological and therapeutic importance of the activated BRAF-mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) pathway in HCL by exposing in vitro primary leukemic cells purified from 26 patients to clinically available BRAF (vemurafenib; dabrafenib) or MEK (trametinib) inhibitors. Results were validated in vivo in samples from vemurafenib-treated HCL patients within a phase 2 clinical trial. BRAF and MEK inhibitors caused, specifically in HCL (but not HCL-like) cells, marked MEK/ERK dephosphorylation, silencing of the BRAF-MEK-ERK pathway transcriptional output, loss of the HCL-specific gene expression signature, downregulation of the HCL markers CD25, tartrate-resistant acid phosphatase, and cyclin D1, smoothening of leukemic cells' hairy surface, and, eventually, apoptosis. Apoptosis was partially blunted by coculture with bone marrow stromal cells antagonizing MEK-ERK dephosphorylation. This protective effect could be counteracted by combined BRAF and MEK inhibition. Our results strongly support and inform the clinical use of BRAF and MEK inhibitors in HCL.

Constant activation of the RAF-MEK-ERK pathway as a diagnostic and therapeutic target in hairy cell leukemia.

The BRAF-V600E mutation defines genetically hairy cell leukemia among B-cell leukemias and lymphomas. In solid tumors, BRAF-V600E is known to aberrantly activate the oncogenic MEK-ERK pathway, and targeted BRAF and/or MEK inhibitors have shown remarkable efficacy in clinical trials in melanoma patients. However, the MEK-ERK pathway status in hairy cell leukemia has not been thoroughly investigated. We assessed phospho-ERK expression in 37 patients with hairy cell leukemia and 44 patients with neoplasms mimicking hairy cell leukemia (40 splenic marginal zone lymphoma, 2 hairy cell leukemia-variant and 2 splenic lymphoma/leukemia unclassifiable) using immunohistochemistry on routine biopsies and/or Western blotting on purified leukemic cells, and correlated the phospho-ERK status with the BRAF-V600E mutation status. Besides confirming the constant presence of BRAF-V600E in all patients with hairy cell leukemia, we observed ubiquitous phospho-ERK expression in this malignancy. Conversely, all 44 cases with neoplasms mimicking hairy cell leukemia were devoid of BRAF-V600E and none expressed phospho-ERK. Furthermore, the two exceptionally rare cases of non-hairy cell leukemia unclassifiable chronic B-cell neoplasms previously reported to be BRAF-V600E(+) on allele-specific polymerase chain reaction lacked phospho-ERK expression as well, suggesting the presence of the mutation in only a small part of the leukemic clone in these cases. In conclusion, our findings support the use of phospho-ERK immunohistochemistry in the differential diagnosis between hairy cell leukemia and its mimics, and establish the MEK-ERK pathway as a rational therapeutic target in this malignancy.

Acute myeloid leukemia with mutated nucleophosmin (NPM1): any hope for a targeted therapy?

Acute myeloid leukemia (AML) carrying nucleophosmin (NPM1) mutations displays distinct molecular and clinical-pathological features that led to its inclusion as provisional entity in 2008 WHO classification of myeloid neoplasms. Since NPM1 mutations behave as a founder genetic lesion in AML, they could be an attractive target for therapeutic intervention. Here, we discuss the potential for developing targeted therapies for NPM1-mutated AML with focus on: (i) interfering with the abnormal traffic of the NPM1 leukemic mutant, i.e., its cytoplasmic dislocation; (ii) disrupting the nucleolar structure/function by interfering with residual wild-type nucleophosmin and other nucleolar components acting as hub proteins; and (iii) evaluating the activity of epigenetic drugs (e.g., 5-azacytidine) or agents acting on differentiation and apoptosis. As quantitative assessment of NPM1 mutated transcript copies now provides the means to measure minimal residual disease, we also discuss the potential for intervening in NPM1-mutated AML before overt hematological relapse occurs (so-called pre-emptive therapy).

BRAF mutations in hairy-cell leukemia.

BACKGROUND: Hairy-cell leukemia (HCL) is a well-defined clinicopathological entity whose underlying genetic lesion is still obscure. METHODS: We searched for HCL-associated mutations by performing massively parallel sequencing of the whole exome of leukemic and matched normal cells purified from the peripheral blood of an index patient with HCL. Findings were validated by Sanger sequencing in 47 additional patients with HCL. RESULTS: Whole-exome sequencing identified five missense somatic clonal mutations that were confirmed on Sanger sequencing, including a heterozygous mutation in BRAF that results in the BRAF V600E variant protein. Since BRAF V600E is oncogenic in other tumors, further analyses were focused on this genetic lesion. The same BRAF mutation was noted in all the other 47 patients with HCL who were evaluated by means of Sanger sequencing. None of the 195 patients with other peripheral B-cell lymphomas or leukemias who were evaluated carried the BRAF V600E variant, including 38 patients with splenic marginal-zone lymphomas or unclassifiable splenic lymphomas or leukemias. In immunohistologic and Western blot studies, HCL cells expressed phosphorylated MEK and ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF-MEK-ERK mitogen-activated protein kinase pathway in HCL. In vitro incubation of BRAF-mutated primary leukemic hairy cells from 5 patients with PLX-4720, a specific inhibitor of active BRAF, led to a marked decrease in phosphorylated ERK and MEK. CONCLUSIONS; The BRAF V600E mutation was present in all patients with HCL who were evaluated. This finding may have implications for the pathogenesis, diagnosis, and targeted therapy of HCL. (Funded by Associazione Italiana per la Ricerca sul Cancro and others.).

CD34+ cells from AML with mutated NPM1 harbor cytoplasmic mutated nucleophosmin and generate leukemia in immunocompromised mice.

Acute myeloid leukemia (AML) with mutated NPM1 shows distinctive biologic and clinical features, including absent/low CD34 expression, the significance of which remains unclear. Therefore, we analyzed CD34(+) cells from 41 NPM1-mutated AML. At flow cytometry, 31 of 41 samples contained less than 10% cells showing low intensity CD34 positivity and variable expression of CD38. Mutational analysis and/or Western blotting of purified CD34(+) cells from 17 patients revealed NPM1-mutated gene and/or protein in all. Immunohistochemistry of trephine bone marrow biopsies and/or flow cytometry proved CD34(+) leukemia cells from NPM1-mutated AML had aberrant nucleophosmin expression in cytoplasm. NPM1-mutated gene and/or protein was also confirmed in a CD34(+) subfraction exhibiting the phenotype (CD34(+)/CD38(-)/CD123(+)/CD33(+)/CD90(-)) of leukemic stem cells. When transplanted into immunocompromised mice, CD34(+) cells generated a leukemia recapitulating, both morphologically and immunohistochemically (aberrant cytoplasmic nucleophosmin, CD34 negativity), the original patient's disease. These results indicate that the CD34(+) fraction in NPM1-mutated AML belongs to the leukemic clone and contains NPM1-mutated cells exhibiting properties typical of leukemia-initiating cells. CD34(-) cells from few cases (2/15) also showed significant leukemia-initiating cell potential in immunocompromised mice. This study provides further evidence that NPM1 mutation is a founder genetic lesion and has potential implications for the cell-of-origin and targeted therapy of NPM1-mutated AML.

The EML4-ALK transcript but not the fusion protein can be expressed in reactive and neoplastic lymphoid tissues.

Rearrangements involving the ALK gene define two distinct entities in the new 2008 WHO classification of lymphoid neoplasms, i.e. ALK+ anaplastic large cell lymphoma and a rare subset of ALK+ diffuse large B-cell lymphoma. Recently, rearrangements involving ALK and the echinoderm microtubule associated protein-like 4 (EML4) gene were described as a specific genetic alteration in about 6% of non-small cell lung cancer (NSCLC). We investigated the expression of EML4-ALK mRNA and protein in 51 reactive and 58 neoplastic lymphoid tissues. EML4-ALK transcripts were detected in 3/51 (5.9%) of reactive lymphoid tissues and 12/58 (20.7%) of lymphomas of different categories, including follicular lymphoma, diffuse large B-cell lymphoma and Hodgkin's disease. Notably, none of these cases expressed the EML4-ALK fusion protein at Western blotting samples and immunohistochemistry. These results indicate that EML4-ALK rearrangements are not specific of NSCLC and raise yet unsolved questions about their role in promoting human neoplasms.

EML4-ALK rearrangement in non-small cell lung cancer and non-tumor lung tissues.

A fusion gene, echinoderm microtubule associated protein like 4-anaplastic lymphoma kinase (EML4-ALK), with transforming activity has recently been identified in a subset of non-small cell lung cancer (NSCLC), but its pathogenetic, diagnostic, and therapeutic roles remain unclear. Both frequency and type of EML4-ALK transcripts were investigated by reverse transcription PCR in 120 frozen NSCLC specimens from Italy and Spain; non-neoplastic lung tissues taken far from the tumor were used as controls. In cases carrying the fusion transcript, we determined EML4-ALK gene and protein levels using fluorescence in situ hybridization, Western blotting, and immunoprecipitation. We also analyzed ALK protein levels in paraffin samples from 662 NSCLC specimens, including the 120 cases investigated in the molecular studies. EML4-ALK transcripts (variants 1 and 3) were detected in 9 of 120 NSCLC samples but were not specific for NSCLC since they were also found in non-cancerous lung tissues taken far from the tumor. Notably, no transcripts were detected in matching tumor samples from these patients. Fluorescence in situ hybridization analysis of cases expressing EML4-ALK transcripts showed that only a minority of cells harbored the EML4-ALK gene. None of these cases was found to express the EML4-ALK protein as examined by immunohistochemistry, Western blotting, and immunoprecipitation. The EML4-ALK transcript cannot be regarded as a specific diagnostic tool for NSCLC. Our results show therefore that the causal role and value of EML4-ALK as a therapeutic target remain to be defined.

HOPS: a novel cAMP-dependent shuttling protein involved in protein synthesis regulation.

The liver has the ability to autonomously regulate growth and mass. Following partial hepatectomy, hormones, growth factors, cytokines and their coupled signal transduction pathways have been implicated in hepatocyte proliferation. To understand the mechanisms responsible for the proliferative response, we studied liver regeneration by characterization of novel genes that are activated in residual hepatocytes. A regenerating liver cDNA library screening was performed with cDNA-subtracted probes derived from regenerating and normal liver. Here, we describe the biology of Hops (for hepatocyte odd protein shuttling). HOPS is a novel shuttling protein that contains an ubiquitin-like domain, a putative NES and a proline-rich region. HOPS is rapidly exported from the nucleus and is overexpressed during liver regeneration. Evidence shows that cAMP governs HOPS export in hepatocytes of normal and regenerating liver and is mediated via CRM-1. We demonstrate that HOPS binds to elongation factor eEF-1A and interferes in protein synthesis. HOPS overexpression in H-35-hepatoma and 3T3-NIH cells strongly reduces proliferation.

Cytoplasmic nucleophosmin in acute myelogenous leukemia with a normal karyotype.

BACKGROUND: Nucleophosmin (NPM), a nucleocytoplasmic shuttling protein with prominent nucleolar localization, regulates the ARF-p53 tumor-suppressor pathway. Translocations involving the NPM gene cause cytoplasmic dislocation of the NPM protein. METHODS: We used immunohistochemical methods to study the subcellular localization of NPM in bone marrow-biopsy specimens from 591 patients with primary acute myelogenous leukemia (AML). We then correlated the presence of cytoplasmic NPM with clinical and biologic features of the disease. RESULTS: Cytoplasmic NPM was detected in 208 (35.2 percent) of the 591 specimens from patients with primary AML but not in 135 secondary AML specimens or in 980 hematopoietic or extrahematopoietic neoplasms other than AML. It was associated with a wide spectrum of morphologic subtypes of the disease, a normal karyotype, and responsiveness to induction chemotherapy, but not with recurrent genetic abnormalities. There was a high frequency of FLT3 internal tandem duplications and absence of CD34 and CD133 in AML specimens with a normal karyotype and cytoplasmic dislocation of NPM, but not in those in which the protein was restricted to the nucleus. AML specimens with cytoplasmic NPM carried mutations of the NPM gene that were predicted to alter the protein at its C-terminal; this mutant gene caused cytoplasmic localization of NPM in transfected cells. CONCLUSIONS: Cytoplasmic NPM is a characteristic feature of a large subgroup of patients with AML who have a normal karyotype, NPM gene mutations, and responsiveness to induction chemotherapy.

Tumor protein D52 (TPD52): a novel B-cell/plasma-cell molecule with unique expression pattern and Ca(2+)-dependent association with annexin VI.

We generated a murine monoclonal antibody (B28p) detecting an antigenic determinant shared by the immunoglobulin superfamily receptor translocation-associated 1 (IRTA1) receptor (the immunogen used to raise B28p) and an unrelated 28-kDa protein that was subsequently subjected to extensive characterization. The expression of the 28-kDa protein in normal lymphohematopoietic tissues was restricted to B cells and plasma cells and clearly differed from that expected for IRTA1 (selectively expressed by mucosa-associated lymphoid tissue [MALT] marginal zone B cells). Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE)/mass-spectrometry analysis identified the 28-kDa protein as human tumor protein D52 (TPD52), whose expression had been previously described only in normal and neoplastic epithelia. Specific B28p reactivity with TPD52 was confirmed by immunostaining/immunoblotting of TPD52-transfected cells. TPD52 expression pattern in normal and neoplastic B cells was unique. In fact, unlike other B-cell molecules (paired box 5 [PAX5], CD19, CD79a, CD20, CD22), which are down-regulated during differentiation from B cells to plasma cells, TPD52 expression reached its maximum levels at the plasma cell stage. In the Thiel myeloma cell line, TPD52 bound to annexin VI in a Ca(2+)-dependent manner, suggesting that these molecules may act in concert to regulate secretory processes in plasma cells, similarly to what was observed in pancreatic acinar cells. Finally, the anti-TPD52 monoclonal antibody served as a valuable tool for the diagnosis of B-cell malignancies.

The neuron-specific Rai (ShcC) adaptor protein inhibits apoptosis by coupling Ret to the phosphatidylinositol 3-kinase/Akt signaling pathway.

Rai is a recently identified member of the family of Shc-like proteins, which are cytoplasmic signal transducers characterized by the unique PTB-CH1-SH2 modular organization. Rai expression is restricted to neuronal cells and regulates in vivo the number of postmitotic sympathetic neurons. We report here that Rai is not a common substrate of receptor tyrosine kinases under physiological conditions and that among the analyzed receptors (Ret, epidermal growth factor receptor, and TrkA) it is activated specifically by Ret. Overexpression of Rai in neuronal cell lines promoted survival by reducing apoptosis both under conditions of limited availability of the Ret ligand glial cell line-derived neurotrophic factor (GDNF) and in the absence of Ret activation. Overexpressed Rai resulted in the potentiation of the Ret-dependent activation of phosphatidylinositol 3-kinase (PI3K) and Akt. Notably, increased Akt phosphorylation and PI3K activity were also found under basal conditions, e.g., in serum-starved neuronal cells. Phosphorylated and hypophosphorylated Rai proteins form a constitutive complex with the p85 subunit of PI3K: upon Ret triggering, the Rai-PI3K complex is recruited to the tyrosine-phosphorylated Ret receptor through the binding of the Rai PTB domain to tyrosine 1062 of Ret. In neurons treated with low concentrations of GDNF, the prosurvival effect of Rai depends on Rai phosphorylation and Ret activation. In the absence of Ret activation, the prosurvival effect of Rai is, instead, phosphorylation independent. Finally, we showed that overexpression of Rai, at variance with Shc, had no effects on the early peak of mitogen-activated protein kinase (MAPK) activation, whereas it increased its activation at later time points. Phosphorylated Rai, however, was not found in complexes with Grb2. We propose that Rai potentiates the MAPK and PI3K signaling pathways and regulates Ret-dependent and -independent survival signals.