Anita Gandhi

Cereblon is a direct protein target for immunomodulatory and antiproliferative activities of lenalidomide and pomalidomide

Thalidomide and the immunomodulatory drug, lenalidomide, are therapeutically active in hematological malignancies. The ubiquitously expressed E3 ligase protein cereblon (CRBN) has been identified as the primary teratogenic target of thalidomide. Our studies demonstrate that thalidomide, lenalidomide and another immunomodulatory drug, pomalidomide, bound endogenous CRBN and recombinant CRBN–DNA damage binding protein-1 (DDB1) complexes. CRBN mediated antiproliferative activities of lenalidomide and pomalidomide in myeloma cells, as well as lenalidomide- and pomalidomide-induced cytokine production in T cells. Lenalidomide and pomalidomide inhibited autoubiquitination of CRBN in HEK293T cells expressing thalidomide-binding competent wild-type CRBN, but not thalidomide-binding defective CRBNYW/AA. Overexpression of CRBN wild-type protein, but not CRBNYW/AA mutant protein, in KMS12 myeloma cells, amplified pomalidomide-mediated reductions in c-myc and IRF4 expression and increases in p21WAF-1 expression. Long-term selection for lenalidomide resistance in H929 myeloma cell lines was accompanied by a reduction in CRBN, while in DF15R myeloma cells resistant to both pomalidomide and lenalidomide, CRBN protein was undetectable. Our biophysical, biochemical and gene silencing studies show that CRBN is a proximate, therapeutically important molecular target of lenalidomide and pomalidomide.

Apremilast, a cAMP phosphodiesterase-4 inhibitor, demonstrates anti-inflammatory activity in vitro and in a model of psoriasis

Background and purpose:  Apremilast is an orally administered phosphodiesterase‐4 inhibitor, currently in phase 2 clinical studies of psoriasis and other chronic inflammatory diseases. The inhibitory effects of apremilast on pro‐inflammatory responses of human primary peripheral blood mononuclear cells (PBMC), polymorphonuclear cells, natural killer (NK) cells and epidermal keratinocytes were explored in vitro, and in a preclinical model of psoriasis.

Lenalidomide induces ubiquitination and degradation of CK1α in del(5q) MDS.

Lenalidomide is a highly effective treatment for myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)). Here, we demonstrate that lenalidomide induces the ubiquitination of casein kinase 1A1 (CK1α) by the E3 ubiquitin ligase CUL4–RBX1–DDB1–CRBN (known as CRL4CRBN), resulting in CK1α degradation. CK1α is encoded by a gene within the common deleted region for del(5q) MDS and haploinsufficient expression sensitizes cells to lenalidomide therapy, providing a mechanistic basis for the therapeutic window of lenalidomide in del(5q) MDS. We found that mouse cells are resistant to lenalidomide but that changing a single amino acid in mouse Crbn to the corresponding human residue enables lenalidomide-dependent degradation of CK1α. We further demonstrate that minor side chain modifications in thalidomide and a novel analogue, CC-122, can modulate the spectrum of substrates targeted by CRL4CRBN. These findings have implications for the clinical activity of lenalidomide and related compounds, and demonstrate the therapeutic potential of novel modulators of E3 ubiquitin ligases.

Immunomodulatory agents lenalidomide and pomalidomide co-stimulate T cells by inducing degradation of T cell repressors Ikaros and Aiolos via modulation of the E3 ubiquitin ligase complex CRL4CRBN

Cereblon (CRBN), the molecular target of lenalidomide and pomalidomide, is a substrate receptor of the cullin ring E3 ubiquitin ligase complex, CRL4CRBN. T cell co‐stimulation by lenalidomide or pomalidomide is cereblon dependent: however, the CRL4CRBN substrates responsible for T cell co‐stimulation have yet to be identified. Here we demonstrate that interaction of the transcription factors Ikaros (IKZF1, encoded by the IKZF1 gene) and Aiolos (IKZF3, encoded by the IKZF3 gene) with CRL4CRBN is induced by lenalidomide or pomalidomide. Each agent promotes Aiolos and Ikaros binding to CRL4CRBN with enhanced ubiquitination leading to cereblon‐dependent proteosomal degradation in T lymphocytes. We confirm that Aiolos and Ikaros are transcriptional repressors of interleukin‐2 expression. The findings link lenalidomide‐ or pomalidomide‐induced degradation of these transcriptional suppressors to well documented T cell activation. Importantly, Aiolos could serve as a proximal pharmacodynamic marker for lenalidomide and pomalidomide, as healthy human subjects administered lenalidomide demonstrated Aiolos degradation in their peripheral T cells. In conclusion, we present a molecular model in which drug binding to cereblon results in the interaction of Ikaros and Aiolos to CRL4CRBN, leading to their ubiquitination, subsequent proteasomal degradation and T cell activation.

Pomalidomide and Lenalidomide Induce p21WAF-1 Expression in Both Lymphoma and Multiple Myeloma through a LSD1-Mediated Epigenetic Mechanism

Lenalidomide and pomalidomide have both been evaluated clinically for their properties as anticancer agents, with lenalidomide being available commercially. We previously reported that both compounds cause cell cycle arrest in Burkitts lymphoma and multiple myeloma cell lines by increasing the level of p21(WAF-1) expression. In the present study, we unravel the molecular mechanism responsible for p21(WAF-1) up-regulation using Namalwa cells as a human lymphoma model. We show that the increase of p21(WAF-1) expression is regulated at the transcriptional level through a mechanism independent of p53. Using a combination of approaches, we show that several GC-rich binding transcription factors are involved in pomalidomide-mediated up-regulation of p21(WAF-1). Furthermore, we report that p21(WAF-1) up-regulation is associated with a switch from methylated to acetylated histone H3 on p21(WAF-1) promoter. Interestingly, lysine-specific demethylase-1 (LSD1) silencing reduced both pomalidomide and lenalidomide up-regulation of p21(WAF-1), suggesting that this histone demethylase is involved in the priming of the p21(WAF-1) promoter. Based on our findings, we propose a model in which pomalidomide and lenalidomide modify the chromatin structure of the p21(WAF-1) promoter through demethylation and acetylation of H3K9. This effect, mediated via LSD1, provides GC-rich binding transcription factors better access to DNA, followed by recruitment of RNA polymerase II and transcription activation. Taken together, our results provide new insights on the mechanism of action of pomalidomide and lenalidomide in the regulation of gene transcription, imply possible efficacy in p53 mutated and deleted cancer, and suggest new potential clinical uses as an epigenetic therapy.

Measuring cereblon as a biomarker of response or resistance to lenalidomide and pomalidomide requires use of standardized reagents and understanding of gene complexity.

Cereblon, a member of the cullin 4 ring ligase complex (CRL4), is the molecular target of the immunomodulatory drugs (IMiDs) lenalidomide and pomalidomide and is required for the antiproliferative activity of these agents in multiple myeloma (MM) and immunomodulatory activity in T cells. Cereblons central role as a target of lenalidomide and pomalidomide suggests potential utility as a predictive biomarker of response or resistance to IMiD therapy. Our studies characterized a cereblon monoclonal antibody CRBN65, with high sensitivity and specificity in Western analysis and immunohistochemistry that is superior to commercially available antibodies. We identified multiple cereblon splice variants in both MM cell lines and primary cells, highlighting challenges with conventional gene expression assays given this gene complexity. Using CRBN65 antibody and TaqMan quantitative reverse transcription polymerase chain reaction assays, we showed lack of correlation between cereblon protein and mRNA levels. Furthermore, lack of correlation between cereblon expression in MM cell lines and sensitivity to lenalidomide was shown. In cell lines made resistant to lenalidomide and pomalidomide, cereblon protein is greatly reduced. These studies show limitations to the current approaches of cereblon measurement that rely on commercial reagents and assays. Standardized reagents and validated assays are needed to accurately assess the role of cereblon as a predictive biomarker.

CC-122, a pleiotropic pathway modifier, mimics an interferon response and has antitumor activity in DLBCL

Cereblon (CRBN), a substrate receptor of the Cullin 4 RING E3 ubiquitin ligase complex, is the target of the immunomodulatory drugs lenalidomide and pomalidomide. Recently, it was demonstrated that binding of these drugs to CRBN promotes the ubiquitination and subsequent degradation of 2 common substrates, transcription factors Aiolos and Ikaros. Here we report that CC-122, a new chemical entity termed pleiotropic pathway modifier, binds CRBN and promotes degradation of Aiolos and Ikaros in diffuse large B-cell lymphoma (DLBCL) and T cells in vitro, in vivo, and in patients, resulting in both cell autonomous as well as immunostimulatory effects. In DLBCL cell lines, CC-122-induced degradation or short hairpin RNA-mediated knockdown of Aiolos and Ikaros correlates with increased transcription of interferon (IFN)-stimulated genes independent of IFN-α, -β, and -γ production and/or secretion and results in apoptosis in both activated B-cell (ABC) and germinal center B-cell DLBCL cell lines. Our results provide mechanistic insight into the cell-of-origin independent antilymphoma activity of CC-122, in contrast to the ABC subtype selective activity of lenalidomide.

Circulating Tumor Cells in a Phase 3 Study of Docetaxel and Prednisone with or without Lenalidomide in Metastatic Castration-resistant Prostate Cancer.

Elevated circulating tumor cell (CTC) blood levels (≥5 cells/7.5ml) convey a negative prognosis in metastatic castration-resistant prostate cancer but their prognostic significance in patients receiving chemotherapy is uncertain. The association between CTC counts (at baseline or after treatment), overall survival (OS), and response to docetaxel with lenalidomide was evaluated in a 208-patient subset from the MAINSAIL trial, which compared docetaxel-prednisone-lenalidomide and docetaxel-prednisone-placebo in metastatic castration-resistant prostate cancer patients. Baseline CTCs were <5 cells/7.5ml blood in 87 (42%) patients and ≥5 cells/7.5ml in 121 (58%) patients. Neither tumor response nor prostate-specific antigen response correlated with baseline CTCs. However, CTC count ≥5 cells/7.5ml was significantly associated with lower OS (hazard ratio: 3.23, p = 0.0028). Increases in CTCs from <5 cells/7.5ml to ≥5 cells/7.5ml after three cycles were associated with significantly shorter OS (hazard ratio: 5.24, p=0.025), whereas CTC reductions from ≥5 cells/7.5ml to <5 cells/7.5ml were associated with the best prognosis (p=0.003). PATIENT SUMMARY Our study in metastatic castration-resistant prostate cancer patients treated with docetaxel chemotherapy, with or without lenalidomide, showed that patient survival was best predicted by circulating tumor cell count at the start of treatment. A rising circulating tumor cell count after three cycles of therapy predicted poor survival, while a decline predicted good survival.

Absence of mutations in cereblon ( CRBN ) and DNA damage-binding protein 1 ( DDB1 ) genes and significance for IMiD therapy

Thalidomide and the IMiD immunomodulatory drugs, lenalidomide and pomalidomide, are widely used in the treatment of multiple myeloma (MM), del(5q) myelodysplastic syndromes and other hematologic malignancies, including mantle cell lymphoma. Ito et al.1 recently identified cereblon as a key target of thalidomide. Subsequent studies confirmed cereblon to be a common target for lenalidomide and pomalidomide, and established its essential role in mediating anticancer and immunomodulatory effects of these drugs.2, 3 Cereblon is encoded by the CRBN gene on chromosome 3 containing 11 exons, and the fully spliced transcript produces a 51-kDa protein. Cereblon is a component of the cullin ring E3 ubiquitin ligase complex (CRL4CRBN) that also contains DNA damage-binding protein 1 (DDB1), cullin (Cul) 4a and regulator of cullins (Roc) 1.1 E3 ligases attach ubiquitin moieties to specific substrate proteins in the cell that can mark them for proteasomal degradation. The putative role of cereblon within the E3 ligase complex is that of a substrate receptor.

Immunomodulatory effects in a phase II study of lenalidomide combined with cetuximab in refractory KRAS-mutant metastatic colorectal cancer patients.

This study assessed the immunomodulatory effects in previously treated KRAS-mutant metastatic colorectal cancer patients participating in a phase II multicenter, open-label clinical trial receiving lenalidomide alone or lenalidomide plus cetuximab. The main findings show the T cell immunostimulatory properties of lenalidomide as the drug induced a decrease in the percentage CD45RA+ naïve T cells 3-fold while increasing the percentage HLA-DR+ activated T helper cells and percentage total CD45RO+ CD8+ memory T cytotoxic cells, 2.6- and 2.1-fold respectively (p<0.0001). In addition, lenalidomide decreased the percentage of circulating CD19+ B cells 2.6-fold (p<0.0001). Lenalidomide increased a modest, yet significant, 1.4-fold change in the percentage of circulating natural killer cells. Our findings indicate that lenalidomide significantly activates T cells, suggestive of an immunotherapeutic role for this drug in settings of maintenance therapy and tumor immunity. Furthermore, reported for the first time is the effect of lenalidomide in combination with cetuximab on T cell function, including increases in circulating naïve and central memory T cells. In summary, lenalidomide and cetuximab have significant effects on circulating immune cells in patients with colorectal carcinoma. Trial Registration ClinicalTrials.gov NCT01032291