Martin H Johansson

Galiellalactone is a novel therapeutic candidate against hormone-refractory prostate cancer expressing activated Stat3.

Signal transducer and activator of transcription 3 (Stat3) is constitutively active (phosphorylated) in several forms of cancer, including prostate cancer (PCa). Stat3 signaling may be an interesting target for cancer therapy since inhibition of this pathway mediates growth inhibition and apoptosis of these cells. In this study we investigated the in vitro and in vivo effects of the fungal metabolite galiellalactone, a direct inhibitor of Stat3, on PCa cells.

Galiellalactone is a Direct Inhibitor of STAT3 in Prostate Cancer Cells.

Background: STAT3 is constitutively active in castration-resistant prostate cancer and the fungal metabolite galiellalactone inhibits STAT3 signaling. Results: Galiellalactone binds covalently to one or more cysteines in STAT3 and prevents STAT3 binding to DNA. Conclusion: Galiellalactone inhibits STAT3 signaling by binding directly to STAT3. Significance: Galiellalactone is a promising direct STAT3 inhibitor for treatment of castration-resistant prostate cancer. The transcription factor STAT3 is constitutively active in several malignancies including castration-resistant prostate cancer and has been identified as a promising therapeutic target. The fungal metabolite galiellalactone, a STAT3 signaling inhibitor, inhibits the growth, both in vitro and in vivo, of prostate cancer cells expressing active STAT3 and induces apoptosis of prostate cancer stem cell-like cells expressing phosphorylated STAT3 (pSTAT3). However, the molecular mechanism of this STAT3-inhibiting effect by galiellalactone has not been clarified. A biotinylated analogue of galiellalactone (GL-biot) was synthesized to be used for identification of galiellalactone target proteins. By adding streptavidin-Sepharose beads to GL-biot-treated DU145 cell lysates, STAT3 was isolated and identified as a target protein. Confocal microscopy revealed GL-biot in both the cytoplasm and the nucleus of DU145 cells treated with GL-biot, appearing to co-localize with STAT3 in the nucleus. Galiellalactone inhibited STAT3 binding to DNA in DU145 cell lysates without affecting phosphorylation status of STAT3. Mass spectrometry analysis of recombinant STAT3 protein pretreated with galiellalactone revealed three modified cysteines (Cys-367, Cys-468, and Cys-542). Here we demonstrate with chemical and molecular pharmacological methods that galiellalactone is a cysteine reactive inhibitor that covalently binds to one or more cysteines in STAT3 and that this leads to inhibition of STAT3 binding to DNA and thus blocks STAT3 signaling without affecting phosphorylation. This further validates galiellalactone as a promising direct STAT3 inhibitor for treatment of castration-resistant prostate cancer.

Reversible Michael additions: Covalent inhibitors and prodrugs.

Covalent inhibition is an efficient molecular mechanism for inhibiting enzymes or modulating the function of proteins and is found in the action of many drugs and biologically active natural products. However, it is has been less appreciated that the formation of covalent bonds can be reversible or irreversible. This review focuses on biologically active compounds that are Michael acceptors and how the reversible nature of the Michael addition reaction influences biological activity and how this can be exploited in designing prodrugs.

Tandem Pd-Catalyzed Carbonylation and Intramolecular Vinyl Allene Diels−Alder Reaction toward Galiellalactone Analogues

A novel route toward new galiellalactone analogues via a tandem palladium-catalyzed carbonylation and intramolecular Diels-Alder reaction of a dienyne carbonate is presented.

Biomimetic Synthesis toward the Transtaganolides/Basiliolides.

A concise biomimetic approach toward transtaganolides C and D involving an Ireland-Claisen rearrangement/intramolecular Diels-Alder reaction sequence suggesting the involvement of pericyclic reactions in the biosynthesis of these biologically active plant metabolites is presented. A final coupling reaction establishes the carbon framework of the transtaganolides.

Synthesis of (-)-pregaliellalactone, conversion of (-)-pregaliellalactone to (-)-galiellalactone by mycelia of Galiella rufa

An enantioselective synthesis of (-)-pregaliellalactone (1), a biosynthetic precursor of the potent fungal metabolite ( -)-galiellalactone (3) produced by several ascomycetes, is reported. When fed to a culture of Galiella rufa, 1 was efficiently converted to 3

The fungal metabolite galiellalactone interferes with the nuclear import of NF-κB and inhibits HIV-1 replication

Galiellalactone (GL) is a metabolite produced by the fungus Galiella rufa that presents antitumor and immunomodulatory activities. GL interferes with the binding to DNA of signal transducer and activator of transcription (STAT)-3 and also inhibits other signal pathways such as NF-κB, but the mechanism of action in this pathway remains unknown. In this study we report that GL inhibits vesicular stomatitis virus-recombinant HIV-1 infection and the NF-κB-dependent transcriptional activity of the HIV-LTR promoter. We found that GL prevents the binding of NF-κB to DNA but neither affects the phosphorylation and degradation of NF-κB inhibitory protein, IκBα, nor the phosphorylation and acetylation of the NF-κB p65 subunit. However, GL prevents the association of p65 with the importin α3 impairing the nuclear translocation of this transcription factor. Using a biotinylated probe we found that GL binds to p65 but not to importin α3. Therefore, GL is a dual NF-κB/STAT3 inhibitor that could serve as a lead compound for the development of novel drugs against HIV-1, cancer and inflammatory diseases.

Preclinical Characterization of 3β-(N-Acetyl l-cysteine methyl ester)-2aβ,3-dihydrogaliellalactone (GPA512), a Prodrug of a Direct STAT3 Inhibitor for the Treatment of Prostate Cancer

The transcription factor STAT3 is a potential target for the treatment of castration-resistant prostate cancer. Galiellalactone (1), a direct inhibitor of STAT3, prevents the transcription of STAT3 regulated genes. In this study we characterized 6 (GPA512, Johansson , M. ; Sterner , O. Patent WO 2015/132396 A1, 2015 ), a prodrug of 1. In vitro studies showed that 6 is rapidly converted to 1 in plasma and is stable in a buffer solution. The pharmacokinetics of 6 following a single oral dose indicated that the prodrug was rapidly absorbed and converted to 1 with a tmax of 15 min. Oral administration of 6 in mice increased the plasma exposure of the active parent compound 20-fold compared to when 1 was dosed orally. 6 treated mice bearing DU145 xenograft tumors had significantly reduced tumor growth compared to untreated mice. The favorable druglike properties and safety profile of 6 warrant further studies of 6 for the treatment of castration-resistant prostate cancer.

Mild Microwave-Assisted Hydrolysis of Acetals Under Solvent-Free Conditions

Abstract Acetals are efficiently hydrolyzed with silica gel‐supported pyridinium tosylate moistened with water in solvent‐free conditions under microwave irradiation. The method is efficient and mild, with acid‐sensitive 3‐hydroxyacetals and 3‐methoxyacetals being hydrolyzed in minutes in good yields.

Synthesis of podoscyphic acid

Podoscyphic acid 1, a fungal metabolite inhibiting RNA-directed DNA polymerases, was synthesised in four steps starting from dodecanal. The concluding ester hydrolysis of 4 was not feasible with chemical reagents, only enzymatic hydrolysis was mild enough to release the highly reactive natural product in good yields.