Antitumor effects of tyropeptin-boronic acid derivatives: New proteasome inhibitors.
Bottom Line: Here we report the antitumor effects of two new tyropeptin-boronic acid derivatives, AS-06 and AS-29.We show that these derivatives also suppress the degradation of the NF-κB inhibitor IκB-α and the nuclear translocation of NF-κB p65 in multiple myeloma cells, resulting in the inhibition of NF-κB activation.Our results indicate that tyropeptin-boronic acid derivatives could be lead therapeutic agents against human multiple myeloma.
Affiliation: Institute of Microbial Chemistry, Numazu, Japan.Show MeSH
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Mentions: We investigated whether tyropeptin-boronic acid derivatives induce apoptosis in RPMI8226 cells. Using annexin V and propidium iodide double staining and a flow cytometer (Fig. 3a), AS-06 and AS-29 significantly increased the number of late-apoptotic cells (annexin V-positive/propidium iodide-positive). We examined the effect of tyropeptin-boronic acid derivatives on the activation of caspases, a family of cysteine proteases playing a central role in apoptosis (Fig. 3b). AS-06 and AS-29 induced the degradation of full-length caspase-8 and full-length caspase-9, and cleaved fragments are detected. In addition, bortezomib was reported to activate ER-resident caspase-12 in multiple myeloma cells.(30) Although bortezomib induced the degradation of full-length caspase-12, neither AS-06 nor AS-29 induced the decrease of full-length caspase-12 (Fig. 3b). Caspase-3, a critical executioner of apoptosis, interacts with caspase-8 and caspase-9. AS-06 and AS-29 also stimulated the degradation of full-length caspase-3 and the appearance of cleaved forms, resulting in the cleavage of poly (ADP-ribose) polymerase (PARP), one of the main cleavage targets of caspase-3. In RPMI8226 cells, we found that AS-06 and AS-29 enhance caspase-3 activity in a dose-dependent manner (Fig. 3c). Furthermore, we performed gene expression analysis to compare the effects of tyropeptin-boronic acid derivatives and bortezomib on global gene transcription in RPMI8226 cells (Fig. 3d). We used whole human genome microarrays covering over 41 000 genes and transcripts. The transcription of 757, 744 and 2707 genes was altered over threefold in response to AS-06, AS-29 and bortezomib, respectively. The hierarchical clustering analysis for a total 2803 genes showed that the global gene expression signatures of AS-06 and AS-29 highly correlated with that of bortezomib. In summary, our data demonstrate that tyropeptin-boronic acid derivatives induce apoptosis through the caspase-8 and caspase-9 cascades, and that these derivatives and bortezomib have a similar effect on genome-wide transcriptional expression.