Identification of kinetin riboside as a repressor of CCND1 and CCND2 with preclinical antimyeloma activity

Abstract

Knockout and transgenic studies in mice demonstrate that normal somatic tissues redundantly express 3 cyclin D proteins, whereas tumor cells seem dependent on a single overexpressed cyclin D. Thus, selective suppression of the individual cyclin D deregulated in a tumor represents a biologically valid approach to targeted cancer therapy. In multiple myeloma, overexpression of 1 of the cyclin D proteins is a ubiquitous feature, unifying at least 7 different initiating genetic events. We demonstrate here that RNAi of genes encoding cyclin D1 and cyclin D2 (CCND1 and CCND2, respectively) inhibits proliferation and is progressively cytotoxic in human myeloma cells. By screening a chemical library using a cell-based assay for inhibition of CCND2 trans-activation, we identified the plant cytokinin kinetin riboside as an inhibitor of CCND2 trans-activation. Kinetin riboside induced marked suppression of CCND2 transcription and rapidly suppressed cyclin D1 and D2 protein expression in primary myeloma cells and tumor lines, causing cell-cycle arrest, tumor cell-selective apoptosis, and inhibition of myeloma growth in xenografted mice. Mechanistically, kinetin riboside upregulated expression of transcription repressor isoforms of cAMP-response element modulator (CREM) and blocked both trans-activation of CCND2 by various myeloma oncogenes and cis-activation of translocated CCND1, suggesting induction of an overriding repressor activity that blocks multiple oncogenic pathways targeting cyclin D genes. These data support targeted repression of cyclin D genes as a therapeutic strategy for human malignancies. IntroductionMultiple myeloma (MM) is a postgerminal center B cell malignancy characterized by clonal plasma cell expansion. The disease manifests clinically with anemia, monoclonal immunoglobulin, renal insufficiency, and lytic bone lesions and currently affects 63,000 people in the United States alone (1); moreover, as it is currently incurable, MM causes a disproportionate 2% of all cancer deaths.Although myeloma tumors present with complex karyotypes and an assortment of structural and numerical chromosomal abnormalities, these tumors are unified in their ubiquitous targeting of cyclin D genes for overexpression. Of MM tumors, 54% overexpress cyclin D1 (CCND1), 48% overexpress cyclin D2 (CCND2), 3% overexpress cyclin D3 (CCND3), and 8% overexpress both CCND1 and CCND2 (2). Deregulated expression of single CCND genes in MM occurs as the result of selective cyclin D gene trans-activation by deregulated transcription factors or from translocation of a single

Cereblon expression is required for the antimyeloma activity of lenalidomide and pomalidomide

“…Apoptosis, using annexin V (BD Biosciences), and cell cycle assays were performed as previously described. 2 To confirm CRBN knockdown, real-time quantitative PCR analysis of CRBN level was performed in control and CRBN shRNA-expressing cells harvested at 72 hours after infection. GFP-positive cells were sorted and expanded at 3 weeks after infection, and quantitative PCR was performed in sorted cells to confirm the low CRBN expression level.…”

“…1 However, recent findings also demonstrate the efficacy of thalidomide and related immunomodulatory drugs (IMiDs) for the treatment of several hematologic malignancies, including multiple myeloma. [2][3][4][5][6] IMiDs, including lenalidomide (CC-5013) and pomalidomide (CC-4047), thus represent a novel class of small-molecule antitumor drugs. 7 Nevertheless, only 30% of patients respond to these drugs when used as single agents, and many patients will develop resistance.…”

The targeting of the sole cyclin D1 is not adequate for mantle cell lymphoma and myeloma therapies

“…This was achieved recently in MM cells by the plant cytokinin kinetin riboside. 6 Indeed, kinetin riboside causes cell cycle arrest of primary myeloma cells and tumor lines and tumor cells selective apoptosis, in vitro and in vivo. However, in MCL cell lines, the double knockdown of cyclins D1 and D2 had no synergistic effect.…”

Post-transcriptional Modifications Contribute to the Upregulation of Cyclin D2 in Multiple Myeloma

“…In addition, Dcyclins have been proposed as molecular therapeutic targets in multiple myeloma (2). Cyclin D2 belongs to the group of D-type cyclin proteins that are cyclically expressed during the cell cycle.…”