Transient antagonism of anti-CD20 monoclonal antibodies and PI3K inhibitor idelalisib in DLBCL cell lines.

INTRODUCTION: PI3K inhibitors are evaluated for relapsed and refractory Diffuse large B-cell lymphoma (DLBCL) patients. OBJECTIVE: As rituximab has shown to influence B-cell receptor (BCR) signaling, we investigated the interaction of anti-CD20 antibody rituximab and the new type II glycoengineered anti-CD20 antibody obinutuzumab in combination with the PI3K delta inhibitor idelalisib. METHODS: Established DLBCL cell lines were treated with either rituximab or obinutuzumab alone or in combination with PI3K delta inhibitor idelalisib. RESULTS: Rituximab and to a lesser extent obinutuzumab monotherapy resulted in a temporary upregulation of p-Akt, p42/44, and p38 signaling pathways. Idelalisib reduced p-Akt expression. Rituximab antagonized the p-Akt downregulation at early time points, while obinutuzumab did not interfere with idelalisib's effects. In cell growth analysis, early antagonism could also be detected. CONCLUSION: The combination of idelalisib with CD antibodies shows an initial antagonism of rituximab but not obinutuzumab in downregulation of PI3K-signaling targets.

The Emerging Role of PI3K Inhibitors in the Treatment of Hematological Malignancies: Preclinical Data and Clinical Progress to Date.

The phosphoinositide 3-kinase (PI3K)/Akt/mTOR pathway is implicated in the pathogenesis of lymphoma. Deeper understanding of the diversity and biological impact of this pathway has led to the development of specific inhibitors to this pathway. Preclinical data in cell lines, patient samples and disease models have broadened our understanding of PI3K inhibition. Several PI3K inhibitors are currently in advanced stages of clinical development. Idelalisib is the first agent of this new substance class to be approved in chronic lymphocytic leukemia and follicular lymphoma. Other agents specifically target different PI3K isoforms and show promising clinical efficacy.

Temsirolimus acts as additive with bendamustine in aggressive lymphoma.

The mammalian target of rapamycin (mTOR) is a protein kinase involved in the phosphatidylinositol 3-kinase (PI3K)/AKT signalling pathway. It plays a pivotal role in the control of cell proliferation, survival, and angiogenesis with multiple and frequent dysregulations of this pathway in human tumors. Temsirolimus is an intravenous drug, specifically inhibiting the mTOR pathway. Bendamustine is well known for its clinical activity in indolent non-Hodgkin-lymphoma (NHL) and has lately shown clinical activity in mantle cell lymphoma (MCL). Here, we present a case report of temsirolimus in combination with bendamustine and rituximab leading to a CR in a pretreated male. In addition, our in vitro data underlines the additive and synergistic efficacy in cell growth reduction of temsirolimus combined with bendamustine in MCL cell lines and in DLBCL cell lines. Furthermore, as an underlying mechanism of this additive, effects on cell cycle inhibition and apoptosis induction could be identified.

Temsirolimus inhibits cell growth in combination with inhibitors of the B-cell receptor pathway.

Lately, mTOR inhibitors have gained clinical relevance in malignant lymphoma. Still, rapamycin derivatives may activate a pro-survival feedback loop through PI3K-Akt. In this current study, temsirolimus effectively reduced cell growth in GCB and ABC diffuse large cell B-cell lymphoma (GCB=30-66%, ABC=45-57%). Combination treatment with the PI3K-δ inhibitor idelalisib additively effected ABC and GCB lymphoma (GCB=16-38%, ABC=25-50%). Since Bruton's Tyrosine Kinase (BTK) plays a significant role for the survival of ABC lymphoma, this study also combined the BTK inhibitor ibrutinib with temsirolimus, which resulted in additive cell growth reduction (ibrutinib 50%, temsirolimus 44%, combination 25%) in ABC lymphoma. In contrast, bortezomib, which has been shown previously to be efficient in ABC lymphoma, revealed an antagonistic effect with temsirolimus in some GCB lymphoma (temsirolimus 53%, temsirolimus+bortezomib 63%). Western blot analysis identified the increase of phosphorylated pro-survival kinases Akt and PDK as a possible underlying mechanism of this interaction.

Update on the molecular pathogenesis and clinical treatment of mantle cell lymphoma: report of the 11th annual conference of the European Mantle Cell Lymphoma Network.

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.

The proteasome inhibitor bortezomib targets cell cycle and apoptosis and acts synergistically in a sequence-dependent way with chemotherapeutic agents in mantle cell lymphoma.

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.

Update on the molecular pathogenesis and clinical treatment of mantle cell lymphoma: report of the 10th annual conference of the European Mantle Cell Lymphoma Network.

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 shows an aggressive clinical course with a continuous relapse pattern and a median survival of only 3-5 years. However, recently a subset of up to 15% long-term survivors has been identified with a rather indolent clinical course. Advanced stage disease is usually apparent already at first clinical manifestation; in general, conventional chemotherapy is only palliative and 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 Ara-C to a rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP)-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 control of cell cycle machinery and impairment of several apoptotic pathways. Combination strategies are currently being investigated in numerous trials, but their introduction into clinical practice and current treatment algorithms remains a challenge. Future strategies will apply individualized approaches according to the molecular risk profile of the patient. At the annual conference in Warsaw, recent results of molecular pathogenesis, analyses of current clinical trials and new study concepts were discussed.

Update on the molecular pathogenesis and clinical treatment of Mantle Cell Lymphoma (MCL): minutes of the 9th European MCL Network conference.

Mantle cell lymphoma (MCL) is a distinct subtype of malignant lymphoma which is 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 shows an aggressive clinical course with a continuous relapse pattern and a median survival of only 3-5 years. However, recently a subset of 15% long-term survivors has been identified with a rather indolent clinical course, even after conventional treatment strategies only. Advanced stage disease is usually apparent already at first clinical manifestation; thus, conventional chemotherapy is only palliative, and the median duration of remissions is only 1-2 years. Emerging strategies including proteasome inhibitors, immune modulatory drugs (IMiDs), mTOR inhibitors, and others are based on the dysregulated control of cell cycle machinery and impaired apoptotic pathways. Monotherapy of these compounds achieves efficacy comparable to conventional chemotherapy in relapsed MCL, and combination strategies are currently being investigated in numerous trials; however, their introduction into clinical practice and current treatment algorithms remain a challenge. In 2000 the European MCL Network ( http://www.european-mcl.net ) was founded, consisting of 15 national lymphoma study groups supplemented by experts in histopathology and molecular genetics. During the past decade, the European consortium has successfully initiated the largest phase III trials in MCL worldwide, with a current annual recruitment of almost 200 patients per year in first-line studies. In detail, in prospective randomized studies, the addition of a B-lymphocyte specific antibody doubled the median progression-free survival from 14 to 28 months, and a dose-intensified consolidation with high-dose radiochemotherapy and subsequent autologous stem cell transplant resulted in superior response duration (3.7 vs. 1.6 years) and even improved overall survival in a recent analysis. Future strategies will apply individualized approaches according to the molecular risk profile of the patient. At the recent annual conference in Jerusalem, recent results of molecular pathogenesis, analyses of current clinical trials, and new study concepts were discussed.

Combined RNA-expression and 2D-PAGE-screening identifies comprehensive interaction networks affected after bortezomib or enzastaurin exposure of mantle cell lymphoma.

Despite recent advances in treatment, mantle cell lymphoma (MCL) still represents a disease with dismal prognosis due to its progressive clinical course, high rate of therapy refractory cases and frequent relapses. During recent years, the proteasome inhibitor bortezomib and enzastaurin, an inhibitor of protein kinase c have been explored in MCL. In relapsed disease enzastaurin achieved disease stabilization in a subset of patients. Bortezomib in relapsed and refractory MCL achieves response rates of 30-40%. To identify signal pathways and manifold interactions regulating cellular response to molecular targeted approaches several high throughput screening methods were applied. A combined network analysis of the identified target molecules based on both RNA array expression data and a survey of cellular protein levels resulted in a unified interaction network more comprehensive (bortezomib: 394 and enzastaurin: 174 molecules) than the networks of the individual screening techniques (329/44 and 117/36 molecules respectively). Interestingly, although none of the target molecules were matched in both RNA-expression and protein level analysis they were mapped nonetheless to common pathways. Additionally, the ranking of identified pathways allowed an improved characterization of the observed induction of cell apoptosis.

3'UTR mediated regulation of the cyclin D1 proto-oncogene.

In mantle cell lymphoma (MCL), overexpression of cyclin D1 is the hallmark of malignant transformation and results from it's juxtaposition to the immunoglobulin heavy chain enhancer. In addition, genomic deletions or point mutations leading to premature truncation of the cyclin D1 3' untranslated region (UTR) have been reported in a several MCL patients as well as in cell lines isolated from various tumors types. We demonstrate that the expression of cyclin D1 with or without the 3'UTR has different phenotypic consequences in stably transduced fibroblasts, with the hyper-proliferative phenotype of cyclin D1 closely linked to the deletion of its 3'UTR. In our study, the loss of the cyclin D1 3'UTR led to a significant upregulation of the protein. However, the loss of AU-rich elements (AREs) from the cyclin D1 3'UTR results in a significant decrease in cyclin D1 protein and UTR-tagged reporter expression. In contrast, the levels of cyclin D1 protein can be significantly reduced by microRNAs of the miR-15/16 family and the miR17-92 cluster that directly target the cyclin D1 3'UTR. Most importantly, these microRNAs regulated the levels of the endogenous cyclin D1 protein encoded by an mRNA with a full 3'UTR but not with 3' UTR deletions. Taken together, our data highlight the regulatory role of the cyclin D1 3'UTR in the expression and phenotype of cyclin D1 and suggest that in MCL and solid tumors with cyclin D1 3'UTR mutations, the loss of microRNA target sites, rather than ARE elements contribute to the pathogenic overexpression of the cyclin D1 protein.

2-D PAGE-based comparison of proteasome inhibitor bortezomib in sensitive and resistant mantle cell lymphoma.

Although gene expression following bortezomib treatment has been previously explored, direct effects of bortezomib-induced proteasome inhibition on protein level has not been analyzed so far. Using 2-D PAGE in five mantle cell lymphoma cell lines, we screened for cellular protein level alterations following treatment with 25 nM bortezomib for up to 4 h. Using MS, we identified 38 of the 41 most prominent reliably detected protein spots. Twenty-one were affected in all cell lines, whereas the remaining 20 protein spots were exclusively altered in sensitive cell lines. Western blot analysis was performed for 17 of the 38 identified proteins and 70.6% of the observed protein level alterations in 2-D gels was verified. All cell lines exhibited alterations of the cellular protein levels of heat shock-induced protein species (HSPA9, HSP7C, HSPA5, HSPD1), whereas sensitive cell lines also displayed altered cellular protein levels of energy metabolism (ATP5B, AK5, TPI1, ENO-1, ALDOC, GAPDH), RNA and transcriptional regulation (HNRPL, SFRS12) and cell division (NEBL, ACTB, SMC1A, C20orf23) as well as tumor suppressor genes (ENO-1, FH). These proteins clustered in a tight interaction network centered on the major cellular checkpoints TP53. The results were confirmed in primary mantle cell lymphoma, thus confirming the critical role of these candidate proteins of proteasome inhibition.

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.

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

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.

Promoter methylation and expression of DNA repair genes hMLH1 and MGMT in acute myeloid leukemia.

Gene silencing of DNA repair genes hMLH1 and MGMT caused by aberrant promoter methylation has been detected in various solid tumors. However, in acute myeloid leukemia (AML) the frequency of hMLH1 and MGMT promoter methylation is not yet fully elucidated. To determine the methylation status and expression of hMLH1 and MGMT, we investigated 22 AML cases by methylation-specific polymerase chain reaction (MS-PCR) and reverse transcription PCR (RT-PCR). To exclude unspecific PCR amplifications DNA sequencing was performed. hMLH1 promoter methylation was detectable in 4 of 20 AML cases. However, DNA sequencing could only confirm a methylated hMLH1 promoter in one case. mRNA expression was absent in one case and reduced in another. However, these cases did not display aberrant promoter methylation. In contrast, MGMT promoter methylation was not detectable in the investigated AML patient samples. Accordingly, MGMT mRNA expression was found to be normal in all but one case. Aberrant promoter methylation of hMLH1 was detectable only in a small number of AML cases. Additionally, in two cases the promoter methylation detected by MS-PCR could not be confirmed by sequencing, clearly indicating the importance of controlling MS-PCR results by the more specific sequence analysis. Surprisingly, hMLH1 promoter methylation was not associated with gene silencing, suggesting monoallelic methylation or promoter methylation only in a small subpopulation of malignant cells. The reduced mRNA expression in additional samples may indicate an involvement of hMLH1 in the malignant transformation in a small subset of cases. In contrast, MGMT does not seem to be involved in the pathogenesis of AML.

Use of polymorphisms in the noncoding region of the human mitochondrial genome to identify potential contamination of human leukemia-lymphoma cell lines.

The availability of the complete sequence of human mitochondrial DNA (mtDNA) has proven extremely useful in phylogenetic studies, forensic science and the determination of chimerism after allogeneic stem cell transplantation. In this study, we could demonstrate that the analysis of mtDNA polymorphisms is a quick and reliable method to identify contamination of human hematopoietic cell lines. This assay is based on PCR-sequencing of three hypervariable segments of the control region of mtDNA (hypervariable region (HRV) 1, 2 and 3). All three regions contain a large number of single-base polymorphisms. mtDNA was isolated according to standard laboratory procedures and amplified by PCR. Subsequently products were sequenced and evaluated with a semiautomated DNA sequencer system. So far, 21 human leukemia-lymphoma (LL) cell lines and nine other human cell lines were screened for contamination by other cell lines applying this method. We conclude that analysis of mtDNA polymorphisms is a quick, reliable and inexpensive method to detect intra - and interspecies cross-contamination and for the authentication of human LL cell lines. In comparison to other methods (cytogenetics, fluorescence in situ hybridization or immunophenotyping), this technique is less laborious and time consuming.