Depsides isolated from the Sri Lankan lichen Parmotrema sp. exhibit selective Plk1 inhibitory activity.

CONTEXT: Mitotic kinase enzymes regulate critical stages of mitosis and are amenable to pharmacological inhibition. Since natural products have been a rich source of antimitotic inhibitors, we postulated that natural products would also provide effective inhibitors of mitotic kinases. OBJECTIVE: To explore unique marine and terrestrial natural product sources for new anticancer drug leads, we screened our natural product extract library for polo-like kinase-1 (Plk1) kinase inhibitors. MATERIALS AND METHODS: Extracts of the lichen Parmotrema sp. (Parmeliaceae) exhibited in vitro inhibitory activity. Bioassay-guided fractionation of the Parmotrema sp. extract led to the isolation of depside inhibitors. RESULTS: A new depside 1 has been isolated from the Sri Lankan lichen Parmotrema sp. along with the known metabolites 2 (ß-collatolic acid) and 3 (ß-alectoronic acid). The structure of depside 1 was elucidated by spectroscopic analysis. The three depsides 1-3 exhibited moderate inhibition of purified recombinant Plk1 kinase with IC50 of 2.8, 0.7, and 1.7 µM, respectively, at 1 µM ATP. Inhibitory activity was also observed at high concentrations of ATP, suggesting the potential for activity in a cellular environment. The depsides were also tested against a panel of 23 other recombinant kinases and were found to possess up to 30-fold selectivity toward Plk1. DISCUSSION AND CONCLUSION: These data suggest that the depsides 1-3 may serve as core structures that can be further explored as potential inhibitors of Plk1 and other kinases.

Pyranonaphthoquinone lactones: a new class of AKT selective kinase inhibitors alkylate a regulatory loop cysteine.

The naturally occurring pyranonaphthoquinone (PNQ) antibiotic lactoquinomycin and related aglycones were found to be selective inhibitors of the serine-threonine kinase AKT. A set of synthetic PNQs were prepared and a minimum active feature set and preliminary SAR were determined. PNQ lactones inhibit the proliferation of human tumor cell lines containing constitutively activated AKT and show expected effects on cellular biomarkers. Biochemical data are presented supporting a proposed bioreductive alkylation mechanism of action.

Discovery of lactoquinomycin and related pyranonaphthoquinones as potent and allosteric inhibitors of AKT/PKB: mechanistic involvement of AKT catalytic activation loop cysteines.

The serine/threonine kinase AKT/PKB plays a critical role in cancer and represents a rational target for therapy. Although efforts in targeting AKT pathway have accelerated in recent years, relatively few small molecule inhibitors of AKT have been reported. The development of selective AKT inhibitors is further challenged by the extensive conservation of the ATP-binding sites of the AGC kinase family. In this report, we have conducted a high-throughput screen for inhibitors of activated AKT1. We have identified lactoquinomycin as a potent inhibitor of AKT kinases (AKT1 IC(50), 0.149 +/- 0.045 micromol/L). Biochemical studies implicated a novel irreversible interaction of the inhibitor and AKT involving a critical cysteine residue(s). To examine the role of conserved cysteines in the activation loop (T-loop), we studied mutant AKT1 harboring C296A, C310A, and C296A/C310A. Whereas the ATP-pocket inhibitor, staurosporine, indiscriminately targeted the wild-type and all three mutant-enzymes, the inhibition by lactoquinomycin was drastically diminished in the single mutants C296A and C310A, and completely abolished in the double mutant C296A/C310A. These data strongly implicate the binding of lactoquinomycin to the T-loop cysteines as critical for abrogation of catalysis, and define an unprecedented mechanism of AKT inhibition by a small molecule. Lactoquinomycin inhibited cellular AKT substrate phosphorylation induced by growth factor, loss of PTEN, and myristoylated AKT. The inhibition was substantially attenuated by coexpression of C296A/C310A. Moreover, lactoquinomycin reduced cellular mammalian target of rapamycin signaling and cap-dependent mRNA translation initiation. Our results highlight T-loop targeting as a new strategy for the generation of selective AKT inhibitors.

07H239-A, a new cytotoxic eremophilane sesquiterpene from the marine-derived Xylariaceous fungus LL-07H239.

07H239-A (1), a new eremophilane sesquiterpene from a marine-derived xylariaceous fungus, was isolated, characterized, and shown to be cytotoxic toward a variety of cancer cell lines, with some selectivity for a CCRFCEM leukemia line (IC(50) = 0.9 microg/mL).

FTMS structure elucidation of natural products: application to muraymycin antibiotics using ESI multi-CHEF SORI-CID FTMS(n), the top-down/bottom-up approach, and HPLC ESI capillary-skimmer CID FTMS.

The molecular formulas for the structures and substructures of muraymycin antibiotics A1 (C52H90N14O19, MW 1214) and B1 (C49H83N11O18, MW 1113) were determined using electrospray ionization (ESI) Fourier transform mass spectrometry (FTMS). The muraymycin A1 and B1 structures were elucidated by utilizing capillary-skimmer fragmentation with up to five stages of mass spectrometry (MS5). Multi-CHEF, a multiple ion isolation method, was used at each stage of MS(n) to isolate a parent ion and up to four reference ions, for exact-mass calibration. The parent ions were fragmented by SORI-CID and the product ions internally calibrated with average absolute mass errors less than 1 ppm at each stage in the fragmentation processes. Using the top-down/bottom-up approach, the molecular formulas for the antibiotics were determined by summing the elemental formulas of the neutral losses, obtained by measuring the mass differences (<500 Da) between the genetically related sequential parent ion masses in the MS(n) spectra, with the unique elemental formula of the lowest parent ion mass (<500 Da). The structures of 12 additional compounds in the muraymycin complex were elucidated using HPLC ESI capillary-skimmer CID FTMS by correlating their fragmentation patterns with those of muraymycins A1 and B1. Sequential neutral losses of an aminosugar, a valine, a uridine, and an ester fatty acid from the muraymycin parent ions provided diagnostic fragments for characterization.

Muraymycins, novel peptidoglycan biosynthesis inhibitors: semisynthesis and SAR of their derivatives.

Sixteen muraymycin derivatives 2-17 were synthesized based on selective reactions of the primary and secondary amino groups of muraymycin C1 (1) with isocyanates and aldehydes. Disubstituted derivatives 3-9 demonstrated no activity against either MraY or MurG at