Results of a Prospective Non-Interventional Post-Authorization Safety Study of Idelalisib in Germany.

BACKGROUND: In pivotal studies, idelalisib demonstrated remarkable efficacy and manageable tolerability in patients with chronic lymphocytic leukemia (CLL) and follicular lymphoma (FL). This prospective, multicenter, non-interventional post-authorization study assessed the characteristics, clinical management, and outcome of CLL and FL patients receiving idelalisib in routine clinical practice in Germany. PATIENTS: Observational study in CLL and FL patients treated with idelalisib between September 2015 and December 2020. RESULTS: A total of 147 patients with CLL and FL were included with a median age of 75 and 71 years, respectively. More than 80% of patients presented with comorbidity and many CLL patients with documented high-risk genetic features, including del(17p)/TP53 mutation or unmutated IGHV. The median progression-free survival (PFS) and overall survival (OS) were not reached in the CLL cohort irrespective of del(17p)/TP53 or unmutated IGHV. The estimated 6-month PFS and OS rates in CLL were 82% and 92%. The estimated 6-month PFS and OS rates for FL were 32.2% and 77.2%. Overall response rates in the CLL and FL cohorts were 70.4% and 36.4%, with the presence of high-risk genetics having no negative impact. No unexpected adverse events were observed. Most frequently reported adverse drug reactions (ADRs) were diarrhea, nausea, pneumonia, rash, and fatigue. CONCLUSION: This real-world study shows that idelalisib is an effective therapy for CLL and FL, regardless of age and high-risk genetic features, consistent with results from previous clinical trials. Collected safety data and the pattern of ADRs reflect those from previous studies.

Quiescence-induced LncRNAs trigger H4K20 trimethylation and transcriptional silencing.

A complex network of regulatory pathways links transcription to cell growth and proliferation. Here we show that cellular quiescence alters chromatin structure by promoting trimethylation of histone H4 at lysine 20 (H4K20me3). In contrast to pericentric or telomeric regions, recruitment of the H4K20 methyltransferase Suv4-20h2 to rRNA genes and IAP elements requires neither trimethylation of H3K9 nor interaction with HP1 proteins but depends on long noncoding RNAs (lncRNAs) that interact with Suv4-20h2. Growth factor deprivation and terminal differentiation lead to upregulation of these lncRNAs, increase in H4K20me3, and chromatin compaction. The results uncover a lncRNA-mediated mechanism that guides Suv4-20h2 to specific genomic loci to establish a more compact chromatin structure in growth-arrested cells.

Dynamic changes of the epigenetic landscape during cellular differentiation.

Epigenetic mechanisms are crucial to stabilize cell type-specific gene-expression programs. However, during differentiation, these programs need to be modified - a complex process that requires dynamic but tightly controlled rearrangements in the epigenetic landscape. During recent years, the major epigenetic machineries for gene activation and repression have been extensively characterized. Snapshots of the epigenetic landscape in pluripotent versus differentiated cells have further revealed how chromatin can change during cellular differentiation. Although transcription factors are the key drivers of developmental transitions, it became clear that their function is greatly influenced by the chromatin environment. Better insight into the tight interplay between transcription factor networks and the epigenetic landscape is therefore necessary to improve our understanding of cellular differentiation mechanisms. These systems can then be challenged and modified for the development of regenerative therapies.

Suv4-20h2 mediates chromatin compaction and is important for cohesin recruitment to heterochromatin.

Cohesin plays an important role in chromatid cohesion and has additional functions in higher-order chromatin organization and in transcriptional regulation. The binding of cohesin to euchromatic regions is largely mediated by CTCF or the mediator complex. However, it is currently unknown how cohesin is recruited to pericentric heterochromatin in mammalian cells. Here we define the histone methyltransferase Suv4-20h2 as a major structural constituent of heterochromatin that mediates chromatin compaction and cohesin recruitment. Suv4-20h2 stably associates with pericentric heterochromatin through synergistic interactions with multiple heterochromatin protein 1 (HP1) molecules, resulting in compaction of heterochromatic regions. Suv4-20h mutant cells display an overall reduced chromatin compaction and an altered chromocenter organization in interphase referred to as "chromocenter scattering." We found that Suv4-20h-deficient cells display chromosome segregation defects during mitosis that coincide with reduced sister chromatid cohesion. Notably, cohesin subunits interact with Suv4-20h2 both in vitro and in vivo. This interaction is necessary for cohesin binding to heterochromatin, as Suv4-20h mutant cells display substantially reduced cohesin levels at pericentric heterochromatin. This defect is most prominent in G0-phase cells, where cohesin is virtually lost from heterochromatin, suggesting that Suv4-20h2 is involved in the initial loading or maintenance of cohesion subunits. In summary, our data provide the first compelling evidence that Suv4-20h2 plays essential roles in regulating nuclear architecture and ensuring proper chromosome segregation.

CENP-C facilitates the recruitment of M18BP1 to centromeric chromatin.

Centromeres are important structural constituents of chromosomes that ensure proper chromosome segregation during mitosis by providing defined sites for kinetochore attachment. In higher eukaryotes, centromeres have no specific DNA sequence and thus, they are rather determined through epigenetic mechanisms. A fundamental process in centromere establishment is the incorporation of the histone variant CENP-A into centromeric chromatin, which provides a binding platform for the other centromeric proteins. The Mis18 complex, and, in particular, its member M18BP1 was shown to be essential for both incorporation and maintenance of CENP-A. Here we show that M18BP1 displays a cell cycle-regulated association with centromeric chromatin in mouse embryonic stem cells. M18BP1 is highly enriched at centromeric regions from late anaphase through to G1 phase. An interaction screen against 16 core centromeric proteins revealed a novel interaction of M18BP1 with CENP-C. We mapped the interaction domain in M18BP1 to a central region containing a conserved SANT domain and in CENP-C to the C-terminus. Knock-down of CENP-C leads to reduced M18BP1 association and lower CENP-A levels at centromeres, suggesting that CENP-C works as an important factor for centromeric M18BP1 recruitment and thus for maintaining centromeric CENP-A.

Heterochromatin dysregulation in human diseases.

Heterochromatin is a repressive chromatin state that is characterized by densely packed DNA and low transcriptional activity. Heterochromatin-induced gene silencing is important for mediating developmental transitions, and in addition, it has more global functions in ensuring chromosome segregation and genomic integrity. Here we discuss how altered heterochromatic states can impair normal gene expression patterns, leading to the development of different diseases. Over the last years, therapeutic strategies that aim toward resetting the epigenetic state of dysregulated genes have been tested. However, due to the complexity of epigenetic gene regulation, the "first-generation drugs" that function globally by inhibiting epigenetic machineries might also introduce severe side effects. Thus detailed understanding of how repressive chromatin states are established and maintained at specific loci will be fundamental for the development of more selective epigenetic treatment strategies in the future.

A yeast two-hybrid system reconstituting substrate recognition of the von Hippel-Lindau tumor suppressor protein.

The von Hippel-Lindau tumor suppressor protein (pVHL) is inactivated in the hereditary cancer syndrome von Hippel-Lindau disease and in the majority of sporadic renal carcinomas. pVHL is the substrate-binding subunit of the CBC(VHL) ubiquitin ligase complex that negatively regulates cell growth by promoting the degradation of hypoxia-inducible transcription factor subunits (HIF1/2alpha). Proteomics-based identification of novel pVHL substrates is hampered by their short half-life and low abundancy in mammalian cells. The usefulness of yeast two-hybrid (Y2H) approaches, on the other hand, has been limited by the failure of pVHL to adopt its native structure and by the absence of prolylhydroxylase activity critical for pVHL substrate recognition. Therefore, we modified the Y2H system to faithfully reconstitute the physical interaction between pVHL and its substrates. Our approach relies on the coexpression of pVHL with the cofactors Elongin B and Elongin C and with HIF1/2alpha prolylhydroxylases. In a proof-of-principle Y2H screen, we identified the known substrates HIF1/2alpha and new candidate substrates including diacylglycerol kinase iota, demonstrating that our strategy allows detection of stable interactions between pVHL and otherwise elusive cellular targets. Additional future applications may include structure/function analyses of pVHL-HIF1/2alpha binding and screens for therapeutically relevant compounds that either stabilize or disrupt this interaction.