Identification of kinetin riboside as a repressor of CCND1 and CCND2 with preclinical antimyeloma activity
Rodger E. Tiedemann, … , Aaron D. Schimmer, A. Keith Stewart
Rodger E. Tiedemann, … , Aaron D. Schimmer, A. Keith Stewart
Published April 22, 2008
Citation Information: J Clin Invest. 2008;118(5):1750-1764. https://doi.org/10.1172/JCI34149.
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Research Article Oncology

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.

Authors

Rodger E. Tiedemann, Xinliang Mao, Chang-Xin Shi, Yuan Xiao Zhu, Stephen E. Palmer, Michael Sebag, Ron Marler, Marta Chesi, Rafael Fonseca, P. Leif Bergsagel, Aaron D. Schimmer, A. Keith Stewart

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Figure 5

Kinetin riboside induces growth arrest and apoptosis in HMCL and primary myeloma cells and shows synergistic cytotoxicity with corticosteroids.

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Kinetin riboside induces growth arrest and apoptosis in HMCL and primary...
(A) HMCL viability following kinetin riboside (1–20 μM) in the presence or absence of MM growth cytokines IL-6 (10 ng/ml), IGF-1 (100 ng/ml), and BAFF (25 ng/ml) by MTT assay at 72 hours. The Burkitt lymphoma line RAMOS is also shown. *MTT on day 0 without drug. (B) Induction of apoptosis in HMCL by vehicle or kinetin riboside at 96 hours, assessed by annexin V and propidium iodide uptake. (C) Synergistic cytotoxicity induced by kinetin riboside (5 μM) and dexamethasone (10 nM) in JJN3, MM1S, and MY5 HMCL, assessed by MTT assay at 48 hours; graph shows the mean of triplicates ± SEM. (D) Two examples of flow cytometric analyses of MM patient bone marrow samples treated with vehicle or kinetin riboside (10 μM), showing preferential loss of viable primary CD138+ tumor cells (left upper quadrants) versus CD138– hematopoietic cells (left lower quadrants) with kinetin riboside at 72 hours. Following kinetin riboside treatment, CD138+ plasma cells became annexin V positive and CD138 negative, consistent with apoptosis. (E) Effects of kinetin riboside on CD138+ and CD138– compartments in 10 MM patient bone marrow samples at 72 hours. CD138+ and CD138– viability responses are compared by Mann-Whitney test. CD138+ (primary tumor) cells are preferentially killed.