Targeting cyclin D1, a downstream effector of INI1/hSNF5, in rhabdoid tumors

Abstract

Rhabdoid tumors (RTs) are aggressive and currently incurable pediatric malignancies. INI1/hSNF5 is a tumor suppressor biallelically inactivated in RTs. Our previous studies have indicated that cyclin D1 is a key downstream target of INI1/hSNF5 and genesis and/or survival of RTs in vivo is critically dependent on the presence of cyclin D1. In this report, we have tested the hypothesis that therapeutic targeting of cyclin D1 is an effective means of treating RTs. We found that RNA interference of cyclin D1 in rhabdoid cells was sufficient to induce G1 arrest and apoptosis. Furthermore, we found that pharmacological intervention with low micromolar concentrations of N-(4-hydroxyphenyl)retinamide (4-HPR), which downmodulates cyclin D1, induced G1 arrest and apoptosis in rhabdoid cell lines. 4-HPR in combination with 4-hydroxy-tamoxifen (4OH-Tam), synergistically inhibited survival as well as anchorage-dependent and -independent growth of rhabdoid cells and caused synergistic induction of cell cycle arrest and apoptosis. 4-HPR and tamoxifen exhibited synergistic growth inhibition of RTs in xenograft models in vivo. The effects of combination of drugs were correlated to the depletion of cyclin D1 levels both in in vitro and in vivo tumor models. These results demonstrate that 4-HPR and tamoxifen are effective chemotherapeutic agents for RTs. We propose that downmodulation of cyclin D1 is a novel and effective therapeutic strategy for RTs.

SMARCB1/INI1 Genetic Inactivation Is Responsible for Tumorigenic Properties of Epithelioid Sarcoma Cell Line VAESBJ

“…Similar to MRTs cell lines (7,10), flavopiridol treatment in VAESBJ induced both CCND1 protein downmodulation and cell-cycle arrest. Unexpectedly, we observed a synergistic effect on cell-cycle block with combined Flavopiridol treatment and SMARCB1 ectopic reexpression, indicating that flavopiridol affects cell proliferation and viability through pathways at least in part independent of SMARCB1 tumor suppressor.…”

“…For comparison, selected experiments were conducted in parallel in G401 malignant rhabdoid tumor cell line ( Supplementary Fig. S3), which was previously reported to be affected by SMARCB1 restoration (7,8,20).…”

Rhabdoid Tumor Growth is Inhibited by Flavopiridol

“…Data was elaborated using CellQuest Pro software (BD Biosciences). Apoptosis was assessed by gating for a sub-G 1 population during FACS and by caspase 3/7 activation using the Caspase-Glo 3/7 Assay Kit (Promega), as previously described (9).…”

“…Rhabdoid tumors are dependent on cyclin D1 as shown both in vitro and in vivo; genetic ablation of cyclin D1 is sufficient to abrogate the formation of rhabdoid tumors in Ini1+/-mice (8) and downmodulation of cyclin D1 by RNA interference induces G 0 -G 1 arrest and apoptosis in rhabdoid tumor cell lines (9). Ini1 heterozygous mice develop a high frequency of spontaneous tumors that mimic the etiology, histopathology, and anatomic characteristics of atypical teratoid and rhabdoid tumors and extrarenal rhabdoid tumors (but not renal malignant rhabdoid tumor), as well as overexpress cyclin D1 (6,8).…”

Tumor Response to Temsirolimus for Epithelioid Angiomyolipoma and Novel Mutation of <i>SMARCB1/INI1</i> Tumor Suppressor Gene

“…In the mechanistic aspects, previous study have shown that SMARCB1/INI1 stimulate the p16/Rb tumor suppressor pathway by activation of CDKN2A and inhibition of CDK/cyclinD [25]. Of note, malignant rhabdoid tumor cell lines with SMARCB1/ INI1 inactivation showed responsiveness to Cdk/cyclin inhibitors (4-HPR, flavopiridol) [26] [27].…”