A Novel Versipelostatin Analogue, Versipelostatin F Isolated from Streptomyces versipellis 4083-SVS6

Abstract

A novel versipelostatin (1) analogue, versipelostatin F (2) was isolated from Streptomyces versipellis 4083-SVS6. The structure of 2 was determined by the analyses of the spectroscopic data. Compound 2 inhibited the expression of GRP78 induced by 2-deoxyglucose with an IC 50 value of 0.3 mM, which is 10-times more potent compared with that of 1. Keywords Streptomyces versipellis, versipelostatin, molecular chaperone, GRP78GRP78 is a molecular chaperone in the endoplasmic reticulum (ER) induced by ER stress that promotes protein folding and plays an important role as a survival factor in solid tumors by providing resistance to both chemotherapy and hypoglycemic stress [1]. Therefore, specific downregulators of GRP78 transcription can reasonably be expected to become promising drugs in cancer chemotherapy. In the course of our screening program for down-regulators of GRP78 molecular chaperone expression, we have isolated versipelostatin (1) Compound 1 is the first compound which has been found to down-regulate GRP78 expression induced by ER stress. Although the biological activities of 1, namely its inhibitory effects against GRP78 expression, were investigated in detail [9], its target is still unknown. Further investigation for congeners of 1 resulted in the isolation of a novel derivative, versipelostatin F (2), which showed stronger inhibitory activity against GRP78 expression than that of 1. In this paper, we report herein the isolation, structure elucidation and its brief biological activity of 2.The versipelostatin-producing strain, S. versipellis 4083-SVS6 was cultured at 27°C for 5 days in 50-liter jar fermentors containing 30 liters of a medium consisting of 2.5% starch, 1.5% soy bean meal, 0.2% dry yeast and 0.4% CaCO 3 (pH 6.2 before sterilization). The fermentation broth (60 liters) was centrifuged and the supernatant was extracted with EtOAc. The organic layer was dried over Na 2 SO 4 , and concentrated in vacuo. The dried residue was subjected to normal-phase MPLC (Purif-Pack SI-60, Moritex) by stepwise elution with a CHCl 3 -MeOH (5.0%, 10%, 20% MeOH, successively) solvent system. The 10% MeOH eluate (210 mg) was separated by reversed-phase MPLC (Purif-Pack ODS-100, Moritex) with a H 2 O -MeOH linear gradient system and further purified by preparative reversed-phase HPLC using a XBridge Prep C18 column (5.0 mm OBD, 19 i.d.ϫ150 mm, Waters) with 60% aqueous MeOH containing 0.4% diethylamine (flow rate, 10 ml/minute) to yield versipelostatin F (2, 31 mg; Rt, 23.2 minutes). The structure of 2 (Fig. 1) was mainly elucidated by NMR spectral analysis as follows.The physico-chemical properties of 2 are summarized in Table 1. Compound 2 was obtained as a colorless amorphous solid and its molecular formula was determined

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“…158–160 Genome screening efforts by the Kuzuyama laboratory led to the discovery of the putative biosynthetic gene cluster vst , which was then confirmed when the authors transformed a nonproducing strain of Streptomyces albus into a producer via integration of the vst cluster into the S. albus genome. 220 By comparing the vst cluster with previously reported spirotetronate biosynthetic gene clusters, these investigators went on to identify a small, highly conserved open reading frame of unknown function dubbed vstJ .…”

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“…mM in the inhibition of GRP78 expression, tenfold more potent than the originally isolated derivative. 143 When the cytotoxic effects of versipelostatin were investigated in more detail, it was shown that versipelostatin was signicantly more toxic to glucose-deprived cells. 144 Since cancer cells in a number of solid tumors live under low-glucose conditions, the selective killing of cancer cells over healthy cells by versipelostatin could thus be explained.…”

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“…The Shin‐ya group has further investigated the secondary metabolites isolated from S. versipellis 4083‐SVS6. As a result, they reported the isolation and characterization of a novel analogue of 1 designated as versipelostatin F ( 2 ), as shown in Figure . Compound 2 is an analogue in terms of the trisaccharide unit.…”