Function-Oriented Biosynthesis of β-Lactone Proteasome Inhibitors in Salinispora tropica

Abstract

The natural proteasome inhibitor salinosporamide A from the marine bacterium Salinispora tropica is a promising drug candidate for the treatment of multiple myeloma and mantle cell lymphoma. Using a comprehensive approach that combined chemical synthesis with metabolic engineering, we generated a series of salinosporamide analogues with altered proteasome binding affinity. One of the engineered compounds is equipotent to salinosporamide A in inhibition of the chymotrypsin-like activity of the proteasome, yet, exhibits superior activity in the cell-based HCT-116 assay.

Proteasome Inhibitors Prevent Caspase-1-Mediated Disease in Rodents Challenged with Anthrax Lethal Toxin

“…As an alternative approach, we focused on proteasome inhibitors, which efficiently block LT killing of murine macrophages, 7,15,36 and which have been used in vivo. [37][38][39][40] Consistent with findings in murine macrophages, we found that the proteasome inhibitor MG132 blocked LT killing of susceptible rat (F344) BMMs (Figure 1, B and C). The water-insoluble MG132, however, is like the general caspase-1 inhibitor Boc-d-cmk, not suitable for in vivo usage.…”

“…We therefore focused on the water-soluble proteasome inhibitors bortezomib and salinosporamide-A (NPI-0052), which have been widely used in animals and humans. [37][38][39][40] Bortezomib and NPI-0052 effectively blocked cytolysis in primary F344 BMMs at significantly lower concentrations than MG132 ( Figure 3A). NPI-0052 was particularly potent, protecting macrophages at concentrations 100 times lower than MG132 and approximately 20 times lower than bortezomib (Figure 3A).…”

Mining the Cinnabaramide Biosynthetic Pathway to Generate Novel Proteasome Inhibitors

“…Two salinosporamide derivatives with saturated cyclohexane or cyclopentane rings were prepared by mutasynthesis, through administration of derivatives and branched-chain amino acids to a culture of the S. tropica salX mutant strain. [29] To establish the function of cinQ in the salinosporamide gene cluster we inactivated the gene by insertion of an inactivation plasmid (pCN2) into the Streptomyces JS360 genome, leading to complete elimination of cinnabaramide biosynthesis in the mutant. When we attempted to restore product formation by feeding cyclopentyl-dl-alanine to the culture, new compounds exhibiting the expected masses were indeed detected.…”

Marine Compounds and Cancer

“…In the cell cycle of normal human fibroblasts, -carotene has a delaying effect on the G1 phase [87] which is related to the expression of p21 waf1/cip1 protein (an inhibitor of CDK) [88]; in colon cancer, the presence of -carotene has been associated to a reduced expression of cyclin A (regulator of G2/M progression) [89]; in leukemia cells, the inhibition of cell cycle progression is attributed to the up-regulation of PPAR signaling pathway and the expression of Nrf2, an important transcription factor in Keap 1-Nnf2/EpRE/ARE signaling pathway [90]; therefore, the in vitro effect of -carotene on the cell cycle depends on the studied cell line. On the other hand, -carotene influences and enhances cellular apoptosis by modulating the expression of regulatory genes in cancer cell lines such as colon [89], leukemia [91], melanoma [92], and breast [93].…”

“…The apoptosis mechanism in hepatoma cell cancer has been attributed to depletion of GSH levels [94], and in leukemia cells to down-regulation of Bcl-2 protein [96]. The inhibition of cell cycle progression and apoptosis mechanisms are attributed to the up-regulation of PPAR signaling pathway and the expression of Nrf2, an important transcription factor in Keap 1-Nnf2/EpRE/ARE signaling pathway [90].…”