Abstract

The ubiquitin-proteasome complex has recently been identified as a novel therapeutic target, particularly in hematological malignancies. An increased proteasome activity has been described in certain types of malignant cells including mantle cell lymphoma (MCL). The proteasome inhibitor bortezomib has shown in vitro activity in MCL cell lines and also clinical efficacy in patients with refractory or relapsed MCL. We previously described a novel tripeptide compound, BSc2118 which inhibits all three proteolytic activities of the 20S proteasome and has anti-tumor activity in melanoma and multiple myeloma (

Cancer Res
2006
;
66
:
7598
–7605
). We investigated the anti-tumor effects of BSc2118 in the MCL cell lines HBL-2, JeKo-1 and Granta-519 and studied its effects on cell cycle progression and the expression of the cell cycle regulatory proteins p21, p27 and cyclin D1. Furthermore the inhibition of intracellular proteasome and NF-kappa B activity was analyzed in MCL cells. In MCL cell lines HBL-2, JeKo-1 and Granta-519, BSc2118 caused a time- and dose-dependent growth inhibition, an induction of apoptosis and a dose-dependent inhibition of intracellular proteasome activity. After 24 and 48 hours of incubation with 40 – 260 nM BSc2118 we found a time- and dose-dependent cell cycle arrest in G2/M phase in all three MCL cell lines. Furthermore we could demonstrate a dose-dependent stabilization of p21 and a degradation of cyclin D1 in western blot analysis. No significant changes could be seen in p27 expression under proteasome inhibition with BSc2118. After TNF-alpha stimulation we found a low NF-kappa B activity also in untreated MCL cells, which could be partially inhibited by preincubation with BSc2118. In this study we show the effects of the novel proteasome inhibitor BSc2118 on cell cycle and growth inhibition in MCL cells lines and furthermore demonstrate that inhibition of proteasome activity, cyclin D1 degradation and p21 stabilization are crucial mechanisms of action for this compound in MCL. Since recent trials have shown a clinical efficacy of proteasome inhibition in MCL, our preclinical data suggest to consider BSc2118 as a novel agent in drug development against MCL.

Author notes

Disclosure: No relevant conflicts of interest to declare.