Demonstration of Cl- requirement for inhibition of vacuolar acidification by cycloprodigiosin in situ

Cycloprodigiosin hydrochloride activates the Ras-PI3K-Akt pathway and suppresses protein synthesis inhibition-induced apoptosis in PC12 cells

Cycloprodigiosin hydrochloride (cPrG-HCl), a member of the prodigiosin family of compounds, has been reported to act as an H(+)/Cl(-) symporter. This compound induces apoptosis in several cancer cells and acts as an antitumor drug in animal models. In this study, we found a novel function of cPrG-HCl; to suppress cell death in PC12 cells, which is caused by protein synthesis inhibitors cycloheximide and actinomycin D. cPrG-HCl activated Akt and suppressed apoptosis, and this was accompanied by inhibition of caspase-3 activity and DNA fragmentation independently of its H(+)/Cl(-) symporter activity. Wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, and dominant-negative Ras attenuated the anti-apoptotic activity of cPrG-HCl, which indicates that cPrG-HCl activated the Ras-PI3K-Akt pathway suppressing apoptosis. On the other hand, serum-deprivation-induced apoptosis was not suppressed by cPrG-HCl.

Anticancer and immunosuppressive properties of bacterial prodiginines

Bacterial prodiginines are a family of red-pigmented, tripyrrolic compounds that display numerous biological activities, including antibacterial, antifungal, antiprotozoal, antimalarial, immunosuppressive and anticancer properties. Recently, significant progress has been made in understanding the biosynthesis and regulation of bacterial prodiginines. An understanding of the biosynthesis of prodiginines will allow engineering of bacterial strains capable of synthesizing novel prodiginines through rational design and mutasynthesis experiments. Bacterial prodiginines and synthetic derivatives are effective proapoptotic agents with multiple cellular targets, and they are active against numerous cancer cell lines, including multidrug-resistant cells, with little or no toxicity towards normal cell lines. A synthetic derivative, GX15-070 (Obatoclax), developed through structure-activity relationship studies of the pyrrolic ring A of GX15, is in multiple Phase I and II clinical trials in both single and dual-agent studies to treat different types of cancer. Therefore, prodiginines have real therapeutic potential in the clinic.

Suppression of AP-1 Activity by Cycloprodigiosin Hydrochloride

Cycloprodigiosin hydrochloride (cPrG.HCl), a compound isolated from a marine bacterium, acts as an immunosuppressant and an anti-cancer drug. We have previously reported that cPrG.HCl suppressed the transcriptional activation of nuclear factor (NF)-kappaB. Here we studied the effect of cPrG.HCl on activation of another transcription factor, activator protein 1 (AP-1). cPrG.HCl potently suppressed AP-1 activity induced by tumor necrosis factor (TNF) alpha and phorbol myristate acetate (PMA). cPrG.HCl did not inhibit any of the mitogen-activated protein kinase (MAPK) families, whereas it did suppress transcriptional activation of AP-1 induced by constitutively activated mutants of MEKK1 or Ras. cPrG.HCl inhibited neither TNFalpha- or PMA-induced DNA-binding of AP-1 nor co-activator p300-induced activation of AP-1. Taken together, cPrG.HCl suppresses AP-1-dependent gene expression downstream of MAPK group through the inhibition of the transcription activation step of the AP-1 promoter complex.

The prodigiosins, proapoptotic drugs with anticancer properties

The family of natural red pigments, called prodigiosins (PGs), characterised by a common pyrrolylpyrromethene skeleton, are produced by various bacteria. Some members have immunosuppressive properties and apoptotic effects in vitro and they have also displayed antitumour activity in vivo. Understanding the mechanism of action of PGs is essential for drug development and will require the identification and characterisation of their still unidentified cell target. Four possible mechanisms of action have been suggested for these molecules: (i) PGs as pH modulators; (ii) PGs as cell cycle inhibitors; (iii) PGs as DNA cleavage agents; (iv) PGs as mitogen-activated protein kinase regulators. Here, we review the pharmacological activity of PG and related compounds, including novel synthetic PG derivatives with lower toxicity and discuss the mechanisms of action and the molecular targets of those molecules. The results reported in this review suggest that PGs are a new class of anticancer drugs, which hold out considerable promise for the Pharmacological Industry.

cPrG-HCl a potential H+/Cl- symporter prevents acidification of storage vacuoles in aleurone cells and inhibits GA-dependent hydrolysis of storage protein and phytate

The putative H+/Cl- symporter cycloprodigiosin-HCl (cPrG-HCl) was used to investigate the role of vacuole acidification in cereal aleurone cell function. The protein storage vacuole (PSV) becomes acidified rapidly when aleurone cells are treated with gibberellic acid (GA) but not abscisic acid (ABA). We show that cPrG prevents PSV acidification in aleurone layers and prevents synthesis of secretory proteins such as alpha-amylase. Our data support the hypothesis that decreased hydrolase synthesis is a consequence of decreased hydrolysis of storage proteins in PSV. Support for this hypothesis comes from experiments showing that breakdown of barley 7S globulins and phytate is inhibited by cPrG in GA-treated aleurone layers. Decreased mobilization of PSV reserves is accompanied by reductions in the free amino acid pool size and in the amount of ions released from the aleurone layer. Vacuolation of the aleurone cell is a diagnostic feature of the response to GA, and vacuolation is also inhibited by cPrG. Evidence that cPrG acts as a potential H+/Cl- symporter in aleurone is presented. We show that cPrG does not inhibit the synthesis and secretion of alpha-amylase when Cl- ions are omitted from the incubation medium. Although cPrG blocks many GA-induced responses of aleurone layers, it does not affect early steps in GA signaling. The SLN1 protein, a negative regulator of GA signaling, is turned over in GA-treated cells in the presence and absence of cPrG. Similarly, synthesis of the transcriptional activator GAMYB is unaffected by the presence of cPrG in GA-treated cells.

Cycloprodigiosin hydrocloride suppresses tumor necrosis factor (TNF) alpha-induced transcriptional activation by NF-kappaB

Cycloprodigiosin hydrochloride (cPrG.HCl) obtained from a marine bacterium Pseudoalteromonas denitrificans induces apoptotic cell death in various cancerous cell lines. cPrG.HCl alone caused a little cytotoxicity in HeLa cells, but it enhanced the apoptotic process progressively when co-administered with tumor necrosis factor (TNF)alpha. Here we studied the effect of cPrG.HCl on TNFalpha-induced activation of the transcription factor nuclear factor kappaB (NF-kappaB). Luciferase gene reporter assays revealed that cPrG.HCl potently suppressed the TNFalpha- and the phorbol myristate acetate-induced activation of NF-kappaB. The suppression occurred in the presence of imidazole, indicating that it was not related to the intracellular acidification resulting from the intrinsic H(+)/Cl(-) symporter activity of cPrG.HCl. cPrG.HCl inhibited neither the TNFalpha-induced phosphorylation and degradation of inhibitor of nuclear factor-kappaB, nor the subsequent nuclear translocation and DNA binding of NF-kappaB. cPrG.HCl also suppressed NF-kappaB-enhanced gene expression induced by Rac1, Cdc42, MEKK1, inhibitor of nuclear factor-kappaalpha (IKKalpha), IKKbeta, and a subunit of NF-kappaB, p65. These results indicate that cPrG.HCl suppresses NF-kappaB-dependent gene expression through the inhibition of transcriptional activation.