Differential effect of epigenetic alterations and genomic deletions of CDK inhibitors [p16(INK4a), p15(INK4b), p14(ARF)] in mantle cell lymphoma

First Report of FARSA in the Regulation of Cell Cycle and Survival in Mantle Cell Lymphoma Cells via PI3K-AKT and FOXO1-RAG1 Axes

Cancer-associated factors have been largely identified in the understanding of tumorigenesis and progression. However, aminoacyl-transfer RNA (tRNA) synthetases (aaRSs) have so far been neglected in cancer research due to their canonical activities in protein translation and synthesis. FARSA, the alpha subunit of the phenylalanyl-tRNA synthetase is elevated across many cancer types, but its function in mantle cell lymphoma (MCL) remains undetermined. Herein, we found the lowest levels of FARSA in patients with MCL compared with other subtypes of lymphomas, and the same lower levels of FARSA were observed in chemoresistant MCL cell lines. Unexpectedly, despite the essential catalytic roles of FARSA, knockdown of FARSA in MCL cells did not lead to cell death but resulted in accelerated cell proliferation and cell cycle, whereas overexpression of FARSA induced remarkable cell-cycle arrest and overwhelming apoptosis. Further RNA sequencing (RNA-seq) analysis and validation experiments confirmed a strong connection between FARSA and cell cycle in MCL cells. Importantly, FARSA leads to the alteration of cell cycle and survival via both PI3K-AKT and FOXO1-RAG1 axes, highlighting a FARSA-mediated regulatory network in MCL cells. Our findings, for the first time, reveal the noncanonical roles of FARSA in MCL cells, and provide novel insights into understanding the pathogenesis and progression of B-cell malignancies.

Effect of 5'-fluoro-2'-deoxycytidine, 5-azacytidine, and 5-aza-2'–deoxycytidine on DNA Methyltransferase 1, CIP/KIP Family, and INK4a/ARF in Colon Cancer HCT-116 Cell Line

Background: Cyclin-dependent kinase inhibitors (CKIs) are the negative regulator of cell cycle progression, which inhibits cyclin-cdk complexes, resulting in cell cycle arrest. Recently, we evaluated the effect of 5-Aza-CdR on DNMT1 gene expression in the WCH-17 hepatocellular carcinoma (HCC) cell line. Objectives: The current study was designed to analyze the effects of 5-aza-2'–deoxycytidine (5-Aza-CdR, decitabine), 5-azacytidine (5-AzaC, vidaza), and 5'-fluoro-2'-deoxycytidine (FdCyd) on INK4a/ARF, CIP/KIP, and DNA methyltransferase 1 gene expression, apoptosis induction, and cell growth inhibition in colon cancer HCT-116 cell line. Methods: The colon cancer HCT-116 cell line was treated with 5-azaC, 5-Aza-CdR, and FdCyd at 24 and 48h. To determine colon cancer HCT-116 cell viability, cell apoptosis, and the relative expression level of the INK4a/ARF, CIP/KIP, and DNA methyltransferase 1 genes, MTT assay, flow cytometry, and qRT-PCR were done, respectively. Results: 5-azaC, 5-Aza-CdR, and FdCyd significantly inhibited colon cancer HCT-116 cell growth and induced apoptosis. Besides, they significantly increased CIP/KIP (p21CIP1, p27KIP1, and p57KIP2) and INK4 (p14ARF, p15INK4b, and p16INK4a) and decreased DNMT1 gene expression. Besides, minimal and maximal apoptosis were seen in the groups treated with FdCyd and 5-Aza-CdR, respectively. The IC50 for CAF for FdCyd was 1.72 ± 0.23 and 1.63 ± 0.21μM at 24 and 48h, respectively. The IC50 for CAF for 5-AzaC was 2.18 ± 0.33 and 1.98 ± 0.29 μM at 24 and 48h, respectively. The IC50 for CAF for 5-Aza-CdR was 4.08 ± 0.61 and 3.18 ± 0.50 μM at 24 and 48h, respectively. Conclusions: The 5-azac, 5-Aza-CdR, and FdCyd can reactivate the INK4a/ARF and CIP/KIP families through inhibition of DNMT1 activity.

Long noncoding RNA LINC01296 plays an oncogenic role in colorectal cancer by suppressing p15 expression

OBJECTIVE

To examine the role of the long noncoding RNA LINC01296 in colorectal carcinoma (CRC) and to explore the underlying mechanism.

METHODS

We detected LINC01296 expression levels in a cohort of 51 paired CRC and normal tissues. We also assessed the effects of LINC01296 on cell proliferation and apoptosis in CRC cells in vitro, and measured its effect on tumor growth in an in vivo mouse model. We identified the potential downstream targets of LINC01296 and assessed its regulatory effects.

RESULTS

Expression levels of LINC01296 were elevated in 37/51 CRC tissues compared with the corresponding normal tissues and were significantly associated with tumor stage, lymph node metastasis, and distant metastasis. Knockdown of LINC01296 using antisense oligonucleotides inhibited cell proliferation and promoted apoptosis of colon cancer cells in vitro and inhibited tumor growth in vivo. Knockdown of LINC01296 also significantly increased the gene expression of p15 in colon cancer cells. LINC01296-specific suppression of p15 was validated by the interaction between enhancer of zeste homolog 2 and LINC01296.

CONCLUSION

Overexpression of LINC01296 suppressed the expression of p15 leading to CRC carcinogenesis. These findings may provide the basis for novel future CRC-targeted therapies.

Deregulation of Polycomb Repressive Complex-2 in Mantle Cell Lymphoma Confers Growth Advantage by Epigenetic Suppression of cdkn2b

The polycomb repressive complex 2 (PRC2) maintains the transcriptional repression of target genes through its catalytic component enhancer of zeste homolog 2 (EZH2). Through modulating critical gene expression, EZH2 also plays a role in cancer development and progression by promoting cancer cell survival and invasion. Mutations in EZH2 are prevalent in certain B-cell lymphoma subtypes such as diffuse large cell lymphoma and follicular lymphoma; while no EZH2 mutation has been reported in the mantle cell lymphoma (MCL). Here we demonstrate that the PRC2 components EZH2, EED and SUZ12 are upregulated in the MCL cells as compared to normal B-cells. Moreover, stably transfected cells with wild-type EZH2 or-EED showed increased cell growth and H3K27-trimehtylation. However, unlike wild-type EZH2, ectopic expression of a deletion construct of EZH2 (EZH2^Δ550−738 lacking SET domain) had no growth advantage over control cells. Pharmacological inhibition of EZH2 suppressed H3K27me3 and had significant inhibitory effect on cell growth and colony forming capacity (p < 0.05) of MCL cells, and this effect was more or less comparable to the anti-proliferative effects of EZH2 inhibition in cells harboring EZH2-mutation. Mechanistically, EZH2 appears to downregulate expression of cdkn2b gene via enhanced H3K27me3, a well-known suppressive epigenetic mark, at the cdkn2b promoter region. Overall, these results highlight that deregulation of PRC2/EZH2 is associated with epigenetic suppression of cdkn2b in MCL, and in part responsible for increased cell growth, thus the EZH2 inhibitors may have therapeutic potential in the patients with MCL.

Management of Drug Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a rare but aggressive B-cell hemopathy characterized by the translocation t(11;14)(q13;q32) that leads to the overexpression of the cell cycle regulatory protein cyclin D1. This translocation is the initial event of the lymphomagenesis, but tumor cells can acquire additional alterations allowing the progression of the disease with a more aggressive phenotype and a tight dependency on microenvironment signaling. To date, the chemotherapeutic-based standard care is largely inefficient and despite the recent advent of different targeted therapies including proteasome inhibitors, immunomodulatory drugs, tyrosine kinase inhibitors, relapses are frequent and are generally related to a dismal prognosis. As a result, MCL remains an incurable disease. In this review, we will present the molecular mechanisms of drug resistance learned from both preclinical and clinical experiences in MCL, detailing the main tumor intrinsic processes and signaling pathways associated to therapeutic drug escape. We will also discuss the possibility to counteract the acquisition of drug refractoriness through the design of more efficient strategies, with an emphasis on the most recent combination approaches.

Risk factors for etiology and prognosis of mantle cell lymphoma

Non-Hodgkin lymphomas (NHLs) include any kind of lymphoma except Hodgkin's lymphoma. Mantle cell lymphoma (MCL) is a B-cell NHL and it accounts for about 6% of all NHL cases. Its epidemiologic and clinical features, as well as biomarkers, can differ from those of other NHL subtypes. This article first provides a very brief description of MCL's epidemiology and clinical features. For etiology and prognosis separately, we review clinical, environmental, and molecular risk factors that have been suggested in the literature. Among a large number of potential risk factors, only a few have been independently validated, and their clinical utilization has been limited. More data need to be accumulated and effectively analyzed before clinically useful risk factors can be identified and used for prevention, diagnosis, prediction of prognosis path, and treatment selection.

A key role for EZH2 in epigenetic silencing of HOX genes in mantle cell lymphoma

The chromatin modifier EZH2 is overexpressed and associated with inferior outcome in mantle cell lymphoma (MCL). Recently, we demonstrated preferential DNA methylation of HOX genes in MCL compared with chronic lymphocytic leukemia (CLL), despite these genes not being expressed in either entity. Since EZH2 has been shown to regulate HOX gene expression, to gain further insight into its possible role in differential silencing of HOX genes in MCL vs. CLL, we performed detailed epigenetic characterization using representative cell lines and primary samples. We observed significant overexpression of EZH2 in MCL vs. CLL. Chromatin immune precipitation (ChIP) assays revealed that EZH2 catalyzed repressive H3 lysine 27 trimethylation (H3K27me3), which was sufficient to silence HOX genes in CLL, whereas in MCL H3K27me3 is accompanied by DNA methylation for a more stable repression. More importantly, hypermethylation of the HOX genes in MCL resulted from EZH2 overexpression and subsequent recruitment of the DNA methylation machinery onto HOX gene promoters. The importance of EZH2 upregulation in this process was further underscored by siRNA transfection and EZH2 inhibitor experiments. Altogether, these observations implicate EZH2 in the long-term silencing of HOX genes in MCL, and allude to its potential as a therapeutic target with clinical impact.

Genetic methylation and lymphoid malignancies: biomarkers of tumor progression and targeted therapy

Lymphoid malignancies, mainly including lymphocytic leukemia and lymphoma, are a group of heterogeneous diseases. Although the clinical outcome of patients has been significantly improved with current immuno-chemotherapy, definitive biomarkers remain to be investigated, particularly those reflecting the malignant behavior of tumor cells and those helpful for developing optimal targeted therapy. Recently, genome-wide analysis reveals that altered genetic methylations play an important role in tumor progression through regulation of multiple cellular transduction pathways. This review describes the pathogenetic effect of the aberrant genetic methylation in lymphoid malignancies, with special emphasis on potential therapeutic strategies targeting key signaling networks.

Genome-wide methylation analyses identify a subset of mantle cell lymphoma with a high number of methylated CpGs and aggressive clinicopathological features

Mantle cell lymphoma (MCL) is a B-cell neoplasm with an aggressive clinical behavior characterized by the t(11;14)(q13;q32) and cyclin D1 overexpression. To clarify the potential contribution of altered DNA methylation in the development and/or progression of MCL, we performed genome-wide methylation profiling of a large cohort of primary MCL tumors (n = 132), MCL cell lines (n = 6) and normal lymphoid tissue samples (n = 31), using the Infinium HumanMethylation27 BeadChip. DNA methylation was compared to gene expression, chromosomal alterations and clinicopathological parameters. Primary MCL displayed a heterogeneous methylation pattern dominated by DNA hypomethylation when compared to normal lymphoid samples. A total of 454 hypermethylated and 875 hypomethylated genes were identified as differentially methylated in at least 10% of primary MCL. Annotation analysis of hypermethylated genes recognized WNT pathway inhibitors and several tumor suppressor genes as frequently methylated, and a substantial fraction of these genes (22%) showed a significant downregulation of their transcriptional levels. Furthermore, we identified a subset of tumors with extensive CpG methylation that had an increased proliferation signature, higher number of chromosomal alterations and poor prognosis. Our results suggest that a subset of MCL displays a dysregulation of DNA methylation characterized by the accumulation of CpG hypermethylation highly associated with increased proliferation that may influence the clinical behavior of the tumors.

The use of microarray technologies in mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterized by adverse prognosis and the development of novel therapeutic approaches is essential to improve outcome. The introduction of gene expression profiling using DNA microarrays has significantly enhanced our understanding of the molecular pathogenesis of MCL, which is a prerequisite to the development of novel treatment strategies. Gene expression profiling can furthermore be applied to predict treatment response at diagnosis and thus can be used to assess a patient's individual risk profile. This review summarizes our current knowledge on the use of microarray technology in MCL.

Carfilzomib interacts synergistically with histone deacetylase inhibitors in mantle cell lymphoma cells in vitro and in vivo

Interactions between the proteasome inhibitor carfilzomib and the histone deacetylase (HDAC) inhibitors vorinostat and SNDX-275 were examined in mantle cell lymphoma (MCL) cells in vitro and in vivo. Coadministration of very low, marginally toxic carfilzomib concentrations (e.g., 3-4 nmol/L) with minimally lethal vorinostat or SNDX-275 concentrations induced sharp increases in mitochondrial injury and apoptosis in multiple MCL cell lines and primary MCL cells. Enhanced lethality was associated with c-jun-NH,-kinase (JNK) 1/2 activation, increased DNA damage (induction of λH2A.X), and ERK1/2 and AKT1/2 inactivation. Coadministration of carfilzomib and histone deacetylase inhibitors (HDACI) induced a marked increase in reactive oxygen species (ROS) generation and G(2)-M arrest. Significantly, the free radical scavenger tetrakis(4-benzoic acid) porphyrin (TBAP) blocked carfilzomib/HDACI-mediated ROS generation, λH2A.X formation, JNK1/2 activation, and lethality. Genetic (short hairpin RNA) knockdown of JNK1/2 significantly attenuated carfilzomib/HDACI-induced apoptosis, but did not prevent ROS generation or DNA damage. Carfilzomib/HDACI regimens were also active against bortezomib-resistant MCL cells. Finally, carfilzomib/vorinostat coadministration resulted in a pronounced reduction in tumor growth compared with single agent treatment in an MCL xenograft model associated with enhanced apoptosis, λH2A.X formation, and JNK activation. Collectively, these findings suggest that carfilzomib/HDACI regimens warrant attention in MCL.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

Quantitative evaluation of p16(INK4a) promoter methylation using pyrosequencing in de novo diffuse large B-cell lymphoma

The p16(INK4a) tumor suppressor gene can be inactivated by a variety of events including promoter hypermethylation. In diffuse large B-cell lymphoma (DLBCL), p16(INK4a) methylation has been associated with advanced disease stage and higher IPI. The prognostic impact of p16(INK4a) methylation in DLBCL remains unclear; however, it has been suggested to correlate with inferior outcome. To further investigate the clinical impact of p16(INK4a) methylation in DLBCL, promoter methylation of this gene was assessed quantitatively by pyrosequencing. Forty-two of 113 (37%) DLBCL patients with methylation level above 5% were categorized as methylated and subsequently divided into low, intermediate and high methylation categories. Overall, no association was shown between the extent of p16(INK4a) methylation and patients' clinical characteristics, except disease stage (P=0.049). Moreover, we could not reveal any impact of p16(INK4a) methylation on lymphoma-specific survival. Although >25% of p16(INK4a) methylation correlated with a better progression-free survival (P=0.048) in patients <65 years old, the significance of this finding, if any, needs to be further investigated. In conclusion, our finding questions the role of p16(INK4a) promoter methylation as a negative prognostic factor in DLBCL.

Mantle cell lymphoma: biology, pathogenesis, and the molecular basis of treatment in the genomic era

Mantle cell lymphoma (MCL) is a B-cell non-Hodgkin lymphoma of which at least a subset arises from antigen-experienced B cells. However, what role antigen stimulation plays in its pathogenesis remains ill defined. The genetic hallmark is the chromosomal translocation t(11;14) resulting in aberrant expression of cyclin D1. Secondary genetic events increase the oncogenic potential of cyclin D1 and frequently inactivate DNA damage response pathways. In combination these changes drive cell-cycle progression and give rise to pronounced genetic instability. Several signaling pathways contribute to MCL pathogenesis, including the often constitutively activated PI3K/AKT/mTOR pathway, which promotes tumor proliferation and survival. WNT, Hedgehog, and NF-κB pathways also appear to be important. Although MCL typically responds to frontline chemotherapy, it remains incurable with standard approaches. Proteasome inhibitors (bortezomib), mTOR inhibitors (temsirolimus), and immunomodulatory drugs (lenalidomide) have recently been added to the treatment options in MCL. The molecular basis for the antitumor activity of these agents is an area of intense study that hopefully will lead to further improvements in the near future. Given its unique biology, relative rarity, and the difficulty in achieving long-lasting remissions with conventional approaches, patients with MCL should be encouraged to participate in clinical trials.

Genomewide DNA methylation analysis reveals novel targets for drug development in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a mostly incurable malignancy arising from naive B cells (NBCs) in the mantle zone of lymph nodes. We analyzed genomewide methylation in MCL patients with the HELP (HpaII tiny fragment Enrichment by Ligation-mediated PCR) assay and found significant aberrancy in promoter methylation patterns compared with normal NBCs. Using biologic and statistical criteria, we further identified 4 hypermethylated genes CDKN2B, MLF-1, PCDH8, and HOXD8 and 4 hypomethylated genes CD37, HDAC1, NOTCH1, and CDK5 when aberrant methylation was associated with inverse changes in mRNA levels. Immunohistochemical analysis of an independent cohort of MCL patient samples confirmed CD37 surface expression in 93% of patients, validating its selection as a target for MCL therapy. Treatment of MCL cell lines with a small modular immunopharmaceutical (CD37-SMIP) resulted in significant loss of viability in cell lines with intense surface CD37 expression. Treatment of MCL cell lines with the DNA methyltransferase inhibitor decitabine resulted in reversal of aberrant hypermethylation and synergized with the histone deacetylase inhibitor suberoylanilide hydroxamic acid in induction of the hypermethylated genes and anti-MCL cytotoxicity. Our data show prominent and aberrant promoter methylation in MCL and suggest that differentially methylated genes can be targeted for therapeutic benefit in MCL.

Co-treatment with heat shock protein 90 inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin (DMAG) and vorinostat: a highly active combination against human mantle cell lymphoma (MCL) cells

Heat shock protein (hsp) 90 inhibitors promote proteasomal degradation of pro-growth and pro-survival hsp90 client proteins, including CDK4, c-RAF and AKT, and induce apoptosis of human lymphoma cells. The pan-histone deacetylase inhibitor vorinostat has also been shown to induce growth arrest and apoptosis of lymphoma cells. Here, we determined the effects of the more soluble, orally bio-available, geldanamycin analogue 17-NN-dimethyl ethylenediamine geldanamycin (DMAG, Kosan Biosciences Inc.) and/or vorinostat in cultured and primary human MCL cells. While vorinostat induced accumulation in the G(1) phase, treatment with DMAG arrested MCL cells in the G(2)/M phase of the cell cycle. Both agents dose-dependently induced apoptosis of MCL cells. Vorinostat also induced hyperacetylation of hsp90 and disrupted the association of hsp90 with its co-chaperones p23 and cdc37, as well as with its client proteins CDK4 and c-RAF. Treatment of MCL cells with vorinostat or 17-DMAG was associated with the inductionof p21 and p27, as well as with depletion of c-Myc, c-RAF, AKT and CDK4. Compared to treatment with either agent alone, co-treatment with DMAG and vorinostat markedly attenuated the levels of cyclin D1 and CDK4, as well as of c-Myc, c-RAF and AKT. Combined treatment with DMAG and vorinostat synergistically induced apoptosis of the cultured MCL cells, as well as induced more apoptosis of primary MCL cells than either agent alone. Therefore, these findings support the rationale to determine the in vivo efficacy of co-treatment with vorinostat and DMAG against human MCL cells.

Characterization of genetic changes in MCL by interphase FISH on tissue sections

Mantle cell lymphoma is a clinically heterogeneous disease, where further elucidation of pathogenetic mechanisms and better prognostic information is required. We evaluated genetic aberrations by interphase FISH on tissue sections or cytological material in 38 samples from 30 MCL patients, including 5 cases with cyclin D1 3'UTR low, which previously has been associated to unfavourable prognosis. The findings have been related to proliferation and clinical outcome. All but one of MCL showed t(11:14) translocation and in 22/30 samples taken at diagnosis or first relapse, one or several cytogenetic changes were detected; 11 deletions of ATM, 13 p53 deletions, 8 numerical c-myc-aberrations and 6 delp16. All but one MCL with low cyclin D1 3'UTR had additional cytogenetic changes, however no particular genetic change was strictly associated with this MCL variant. One fourth of MCL had none of the investigated additional aberrations and these tumours were in general less proliferative and some of these patients had a very long survival.

Identified hidden genomic changes in mantle cell lymphoma using high-resolution single nucleotide polymorphism genomic array

OBJECTIVE

Mantle cell lymphoma (MCL) is a lymphoma characterized by aberrant activation of CCND1/cyclin D1 followed by sequential genetic abnormalities. Genomic abnormalities in MCL have been extensively examined by classical cytogenetics and microarray-based comparative genomic hybridization techniques, pointing out a number of alterations in genomic regions that correlate with the neoplastic phenotype and survival. Recently, single nucleotide polymorphism genomic microarrays (SNP-chip) have been developed and used for analysis of cancer genomics. This technique allows detection of genomic changes with higher resolution, including loss of heterozygosity without changes of gene dosage, so-called acquired uniparental disomy (aUPD).

MATERIALS AND METHODS

We have examined 33 samples of MCL (28 primary MCL and 5 cell lines) using the 250,000 SNP-chip from Affymetrix.

RESULTS

Known alterations were confirmed by SNP arrays, including deletion of INK4A/ARF, duplication/amplification of MYC, deletion of ATM, and deletion of TP53. We also identified a duplication/amplification that occurred at 13q involving oncogenic microRNA, miR17-92. We found other genomic abnormalities, including duplication/amplification of cyclin D1, del(1p), del(6q), dup(3q) and dup(18q). Our SNP-chip analysis detected these abnormalities at high resolution, allowing us to narrow the size of the commonly deleted regions, including 1p and 6q. Our SNP-chip analysis detected a number of aUPD sites, including whole chromosome 9 aUPD and 9p aUPD. We also found an MCL case with 19p, leading to homozygous deletion of TNFSF genes.

CONCLUSION

SNP-chip analysis detected in MCL very small genomic gains/losses, as well as aUPDs, which could not be detected by more conventional methods.

Genomic deletion and promoter methylation status of Hypermethylated in Cancer 1 (HIC1) in mantle cell lymphoma

Mantle cell lymphomas (MCL), characterized by the t(11;14)(q13;q32), frequently carry secondary genetic alterations such as deletions in chromosome 17p involving the TP53 locus. Given that the association between TP53-deletions and concurrent mutations of the remaining allele is weak and based on our recent report that the Hypermethylated in Cancer 1 (HIC1) gene, that is located telomeric to the TP53 gene, may be targeted by deletions in 17p in diffuse large B-cell lymphoma (DLBCL), we investigated whether HIC1 inactivations might also occur in MCL. Monoallelic deletions of the TP53 locus were detected in 18 out of 59 MCL (31%), while overexpression of p53 protein occurred in only 8 out of 18 of these MCL (44%). In TP53-deleted MCL, the HIC1 gene locus was co-deleted in 11 out of 18 cases (61%). However, neither TP53 nor HIC1 deletions did affect survival of MCL patients. In most analyzed cases, no hypermethylation of the HIC1 exon 1A promoter was observed (17 out of 20, 85%). However, in MCL cell lines without HIC1-hypermethylation, the mRNA expression levels of HIC1 were nevertheless significantly reduced, when compared to reactive lymph node specimens, pointing to the occurrence of mechanisms other than epigenetic or genetic events for the inactivation of HIC1 in this entity.

Advances in the understanding of mantle cell lymphoma

Mantle cell lymphoma (MCL) is a well-defined lymphoid neoplasm characterized by a proliferation of mature B lymphocytes expressing CD5 that may show a spectrum of morphological and phenotypic features broader than initially described. Although some patients may follow an indolent clinical evolution, in most of them the tumour has an aggressive behaviour with poor response to conventional chemotherapy. The genetic hallmark is the t(11;14)(q13;q32) translocation leading to the overexpression of cyclin D1, which is considered the initial oncogenic event. In addition to this translocation, MCL may carry a high number of secondary chromosomal and molecular alterations that target regulatory elements of the cell cycle machinery and senescence (BMI1/INK4/ARF/CDK4/RB1), DNA damage response pathways (ATM/CHK2/p53), and cell survival signals. The knowledge of these mechanisms and their influence on the behaviour of the tumour are facilitating the development of prognostic models with a more precise prediction of the clinical evolution of the patients. This information coupled with the availability of a new generation of innovative drugs targeting basic molecular process of the tumour cells, should facilitate the design of new therapeutic protocols able to overcome the resistance of this aggressive lymphoma to conventional treatments and improve the life expectancy of the patients.

Frequent epigenetic inactivation of Rb1 in addition to p15 and p16 in mantle cell and follicular lymphoma

Dysregulation of cell cycle control is an important mechanism in carcinogenesis. Gene promoter hypermethylation is an alternative mechanism of gene inactivation. We analyzed the methylation status of the tumor suppressor components of the INK4/Rb pathway in mantle cell lymphoma and follicular lymphoma by methylation-specific polymerase chain reaction for p15, p16, p18, and Rb1 in 23 mantle cell lymphoma and 30 follicular lymphoma cases and lymphoma cell lines. The methylation-specific polymerase chain reaction results showed that in mantle cell lymphoma, frequent p16 (82%) but infrequent p15 (8.7%) or Rb1 (17.4%) hypermethylation occurred, with p16 and Rb1 hypermethylation being mutually exclusive (P=.01). In follicular lymphoma, frequent hypermethylation of p15 (36.7%), p16 (56.7%), and Rb1 (43.3%) occurred, with p15 and Rb1 hypermethylation being mutually exclusive (P=.05). Concurrent methylation of p15 and p16 occurred in 26.7% of patients with follicular lymphoma and 8.7% of patients with mantle cell lymphoma. Compared with mantle cell lymphoma, there was more frequent p15 (P=.025) hypermethylation but comparable Rb1 (P=.07) and p16 (P=.07) hypermethylation in follicular lymphoma. In a patient with follicular lymphoma with sequential biopsies, Rb1 was unmethylated and expressed at diagnosis but became methylated and down-regulated at relapse. Moreover, methylation analysis of these 4 genes in an additional 8 patients with grade I follicular lymphoma showed that Rb, but not the other genes, was preferentially methylated in grade II (P=.03). In summary, most patients with mantle cell lymphoma and follicular lymphoma had epigenetic aberrations targeting the INK4/Rb pathway. There is more frequent p16 hypermethylation in mantle cell lymphoma and p15 or Rb1 hypermethylation in follicular lymphoma. The role of Rb methylation in disease or histologic transformation in follicular lymphoma warrants further study.

Genetic and molecular pathogenesis of mantle cell lymphoma: perspectives for new targeted therapeutics

Mantle cell lymphoma (MCL) is a well-defined lymphoid malignancy characterized by a rapid clinical evolution and poor response to current therapeutic protocols. The genetic and molecular mechanisms involved in its pathogenesis combine the dysregulation of cell proliferation and survival pathways with a high level of chromosome instability that seems related to the disruption of the DNA damage response pathway. Understanding these mechanisms and how they affect tumour behaviour is providing the rationale for the identification of reliable predictors of clinical evolution and the design of innovative therapeutic strategies that could open new avenues for the treatment of patients with MCL.

Lack of methylthioadenosine phosphorylase expression in mantle cell lymphoma is associated with shorter survival: implications for a potential targeted therapy

PURPOSE

To determine the methylthioadenosine phosphorylase (MTAP) gene alterations in mantle cell lymphoma (MCL) and to investigate whether the targeted inactivation of the alternative de novo AMP synthesis pathway may be a useful therapeutic strategy in tumors with inactivation of this enzyme.

EXPERIMENTAL DESIGN

MTAP gene deletion and protein expression were studied in 64 and 52 primary MCL, respectively, and the results were correlated with clinical behavior. Five MCL cell lines were analyzed for MTAP expression and for the in vitro sensitivity to L-alanosine, an inhibitor of adenylosuccinate synthetase, and hence de novo AMP synthesis.

RESULTS

No protein expression was detected in 8 of 52 (15%) tumors and one cell line (Granta 519). Six of these MTAP negative tumors and Granta 519 cell line had a codeletion of MTAP and p16 genes; one case showed a deletion of MTAP, but not p16, and one tumor had no deletions in neither of these genes. Patients with MTAP deletions had a significant shorter overall survival (mean, 16.1 months) than patients with wild-type MTAP (mean, 63.6 months; P < 0.0001). L-Alanosine induced cytotoxicity and activation of the intrinsic mitochondrial-dependent apoptotic pathway in MCL cells. 9-beta-D-Erythrofuranosyladenine, an analogue of 5'-methylthioadenosine, selectively rescued MTAP-positive cells from L-alanosine toxicity.

CONCLUSIONS

MTAP gene deletion and lack of protein expression are associated with poor prognosis in MCL and might identify patients who might benefit from treatment with de novo AMP synthesis pathway-targeted therapies.