No abstract

Mantle cell lymphoma (MCL) is characterized by the chromosomal translocation t(11;14)(q13;q32), resulting in overexpression of CCND1 in the vast majority of cases. In addition, alterations of other cell-cycle-regulating signal pathways (CDKN2B/CDKN2A-CCND1 and ARF-MDM2-TP53) are frequently observed. However, the hierarchy of promoter methylations and genomic alterations as well as the interaction with other cell-cycle regulator CDKN1A is poorly understood. A complete methylation-specific PCR coupled with direct sequencing of 71 MCL patient samples previously characterized for TP53 alterations, Ki67 expression by immunohistochemistry, and other genomic alterations was performed. In contrast to rare p16(INK4a) promoter methylation (9%), frequent p15(INK4b) (62%) and p14(ARF) (70%) promoter methylation was detectable in MCL. In an additional 16% of MCL cases, LOH for p16(INK4a) was detected. However, MCL cases with p15(INK4b) methylation tended to have lower proliferation (73% vs. 57%), and p15(INK4b) and p14(ARF) promoter methylation was also detected in normal stem cells. Therefore, epigenetic changes of those genes seem not to represent primary oncogenic mechanisms but physiological mechanisms of cell regulation. The rare p16(INK4a) promoter methylation and p16(INK4a) genetic alterations were directly correlated to cell proliferation and therefore are regarded as additional molecular alterations involved in the cell-cycle dysregulation of MCL.

Deletions in the short arm of chromosome 17 (17p) involving the tumor suppressor TP53 occur in up to 20% of diffuse large B-cell lymphomas (DLBCLs). Although inactivation of both alleles of a tumor suppressor gene is usually required for tumor development, the overlap between TP53 deletions and mutations is poorly understood in DLBCLs, suggesting the possible existence of additional tumor suppressor genes in 17p. Using a bacterial artificial chromosome (BAC) and Phage 1 artificial chromosome (PAC) contig, we here define a minimally deleted region in DLBCLs encompassing approximately 0.8 MB telomeric to the TP53 locus. This genomic region harbors the tumor suppressor Hypermethylated in Cancer 1 (HIC1). Methylation-specific PCR demonstrated hypermethylation of HIC1 exon 1a in a substantial subset of DLBCLs, which is accompanied by simultaneous HIC1 deletion of the second allele in 90% of cases. In contrast, HIC1 inactivation by hypermethylation was rarely encountered in DLBCLs without concomitant loss of the second allele. DLBCL patients with complete inactivation of both HIC1 and TP53 may be characterized by an even inferior clinical course than patients with inactivation of TP53 alone, suggesting a functional cooperation between these two proteins. These findings strongly imply HIC1 as a novel tumor suppressor in a subset of DLBCLs.

Mantle cell lymphoma (MCL) is a distinct subtype of malignant lymphoma characterized by the chromosomal translocation t(11;14)(q13;q32), resulting in constitutional overexpression of cyclin D1 and cell cycle dysregulation in virtually all cases. Clinically, MCL displays an aggressive course, with a continuous relapse pattern and a median survival of only 3-7 years. However, a subset of up to 15% long-term survivors has recently been identified with a rather indolent clinical course. In general, conventional chemotherapy is only palliative and the median duration of remissions is only 1-2 years. In 2000, the European MCL Network (http://www.european-mcl.net) was founded, which consists of 15 national lymphoma study groups supplemented by experts in hematopathology, cytogenetics and molecular genetics. During the last decade, the European consortium has successfully initiated the largest phase III trials in MCL worldwide. In the current study generation, the addition of high dose cytosine arabinoside (Ara-C) to an R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone)-like regimen followed by myeloablative consolidation achieved a significant improvement of progression-free survival. Similarly, in elderly patients, rituximab maintenance until progression led to a marked prolongation of remission duration. Emerging strategies include proteasome inhibitors, immune modulatory drugs (IMiDs), mammalian target of rapamycin (mTOR) inhibitors and others, all based on the dysregulated cell cycle machinery and impairment of several signaling transduction and apoptotic pathways. Future strategies will apply individualized approaches according to the molecular risk profile of the patient. At the annual conference in Lisbon, recent results of molecular pathogenesis, analyses of current clinical trials and new study concepts were discussed.

Single-agent bortezomib, a potent, selective, and reversible inhibitor of the 26S proteasome, has demonstrated clinical efficacy in relapsed and refractory mantle cell lymphoma (MCL). Objective response is achieved in up to 45% of the MCL patients; however, complete remission rates are low and duration of response proved to be relatively short. These limitations may be overcome by combining proteasome inhibition with conventional chemotherapy. Rational combination treatment and schedules require profound knowledge of underlying molecular mechanisms. Here we show that single-agent bortezomib treatment of MCL cell lines leads to G2/M arrest and induction of apoptosis accompanied by downregulation of EIF4E and CCND1 mRNA but upregulation of p15(INK4B) and p21 mRNA. We further present synergistic efficacy of bortezomib combined with cytarabine in MCL cell lines. Interestingly this sequence-dependent synergistic effect was seen almost exclusively in combination with AraC, indicating that pretreatment with cytarabine, followed by proteasome inhibition, may be the preferred approach.