Lenalidomide induces ubiquitination and degradation of CK1α in del(5q) MDS. Nature. 2015;523:183-188. [PMID: 26131937 PMCID: PMC4853910 DOI: 10.1038/nature14610]

A FRET-Based Assay for the Identification and Characterization of Cereblon Ligands

Cereblon serves as an ubiquitin ligase substrate receptor that can be tuned toward different target proteins by various cereblon-binding agents. This offers one of the most promising avenues for targeted protein degradation in cancer therapy, but cereblon binding can also mediate teratogenic effects. We present an effective assay that is suited for high-throughput screening of compound libraries for off-target cereblon interactions but also can guide lead optimization and rational design of novel cereblon effector molecules.

Myelodysplastic syndromes: Contemporary review and how we treat

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal stem cell disorders with an inherent tendency for leukemic transformation. Diagnosis is currently based on the presence of peripheral blood cytopenias, peripheral blood and bone marrow dysplasia/blasts, and clonal cytogenetic abnormalities. With the advent of next generation sequencing, recurrent somatic mutations in genes involved in epigenetic regulation (TET2, ASXL1, EZH2, DNMT3A, IDH1/2), RNA splicing (SF3B1, SRSF2, U2AF1, ZRSR2), DNA damage response (TP53), transcriptional regulation (RUNX1, BCOR, ETV6) and signal transduction (CBL, NRAS, JAK2) have been identified in MDS. Conventional prognostication is by the revised International prognostic scoring system (IPSS-R) with additional adverse prognosis conferred by presence of ASXL1, EZH2, or TP53 mutations. Currently Food and Drug administration (FDA)-approved drugs for the treatment of MDS are not curative and their effect on survival is limited; they include the hypomethylating agents (HMA) azacitidine and decitabine and lenalidomide for MDS with isolated del(5q). To date, allogeneic stem cell transplant (ASCT) remains the only treatment option for possible cure. Given the current lack of drugs with convincing evidence of favorable effect on survival, we consider ASCT as the treatment of choice for most patients with symptomatic disease, and especially for those with high-risk disease. For nontransplant candidates, participation in clinical trials is preferred over conventional therapy. There is not one right way of treatment for patients who are not candidates for either ASCT or clinical trials and palliative drugs of choice depend on the clinical problem, such as symptomatic anemia (ESAs, danazol, HMA), thrombocytopenia (HMA), or neutropenia (myeloid growth factors). Conversely, there is no controlled evidence to support the use of iron chelating agents in MDS. Going forward, we believe it is time to incorporate mutation information in clinically derived prognostic models in MDS and encourage development of novel drugs with disease-modifying activity.

Effect of lenalidomide treatment on clonal architecture of myelodysplastic syndromes without 5q deletion

Non-del(5q) transfusion-dependent low/intermediate-1 myelodysplastic syndrome (MDS) patients achieve an erythroid response with lenalidomide in 25% of cases. Addition of an erythropoiesis-stimulating agent could improve response rate. The impact of recurrent somatic mutations identified in the diseased clone in response to lenalidomide and the drug's effects on clonal evolution remain unknown. We investigated recurrent mutations by next-generation sequencing in 94 non-del(5q) MDS patients randomized in the GFM-Len-Epo-08 clinical trial to lenalidomide or lenalidomide plus epoetin β. Clonal evolution was analyzed after 4 cycles of treatment in 42 cases and reanalyzed at later time points in 18 cases. The fate of clonal architecture of single CD34(+)CD38(-) hematopoietic stem cells was also determined in 5 cases. Mutation frequency was >10%: SF3B1 (74.5%), TET2 (45.7%), DNMT3A (20.2%), and ASXL1 (19.1%). Analysis of variant allele frequencies indicated a decrease of major mutations in 15 of 20 responders compared with 10 of 22 nonresponders after 4 cycles. The decrease in the variant allele frequency of major mutations was more significant in responders than in nonresponders (P < .001). Genotyping of single CD34(+)CD38(-) cell-derived colonies showed that the decrease in the size of dominant subclones could be associated with the rise of founding clones or of hematopoietic stem cells devoid of recurrent mutations. These effects remained transient, and disease escape was associated with the re-emergence of the dominant subclones. In conclusion, we show that, although the drug initially modulates the distribution of subclones, loss of treatment efficacy coincides with the re-expansion of the dominant subclone. This trial was registered at www.clinicaltrials.gov as #NCT01718379.

The novel mechanism of lenalidomide activity

Lenalidomide acts by a novel drug mechanism-modulation of the substrate specificity of the CRL4(CRBN) E3 ubiquitin ligase. In multiple myeloma, lenalidomide induces the ubiquitination of IKZF1 and IKZF3 by CRL4(CRBN). Subsequent proteasomal degradation of these transcription factors kills multiple myeloma cells. In del(5q) myelodysplastic syndrome, lenalidomide induces the degradation of CK1α, which preferentially affects del(5q) cells because they express this gene at haploinsufficient levels. In the future, modulation of ubiquitin ligase function may enable us to target previously "undruggable" proteins.

F-box protein interactions with the hallmark pathways in cancer

F-box proteins (FBP) are the substrate specifying subunit of Skp1-Cul1-FBP (SCF)-type E3 ubiquitin ligases and are responsible for directing the ubiquitination of numerous proteins essential for cellular function. Due to their ability to regulate the expression and activity of oncogenes and tumour suppressor genes, FBPs themselves play important roles in cancer development and progression. In this review, we provide a comprehensive overview of FBPs and their targets in relation to their interaction with the hallmarks of cancer cell biology, including the regulation of proliferation, epigenetics, migration and invasion, metabolism, angiogenesis, cell death and DNA damage responses. Each cancer hallmark is revealed to have multiple FBPs which converge on common signalling hubs or response pathways. We also highlight the complex regulatory interplay between SCF-type ligases and other ubiquitin ligases. We suggest six highly interconnected FBPs affecting multiple cancer hallmarks, which may prove sensible candidates for therapeutic intervention.

New therapeutic approaches in myelodysplastic syndromes: Hypomethylating agents and lenalidomide

Recent advances in the treatment of myelodysplastic syndromes have come from the use of the hypomethylating agents decitabine and azacitidine as well as the immunomodulatory drug lenalidomide. Their clinical benefit has been demonstrated by randomized phase III clinical trials, mostly in high-risk and del(5q) myelodysplastic syndromes, respectively. Neither drug, however, appears to eradicate myelodysplastic stem cells, and thus they currently do not represent curative options. Here, we review data from both clinical and translational research on those drugs to identify their molecular and cellular mechanisms of action and to delineate paths for improved treatment allocation and further therapeutic advances in myelodysplastic syndromes.