2 research outputs found
Structural Elucidation and Synthesis of Eudistidine A: An Unusual Polycyclic Marine Alkaloid that Blocks Interaction of the Protein Binding Domains of p300 and HIF-1α
Low oxygen environments
are a hallmark of solid tumors, and transcription
of many hypoxia-responsive genes needed for survival under these conditions
is regulated by the transcription factor HIF-1 (hypoxia-inducible
factor 1). Activation of HIF-1 requires binding of its α-subunit
(HIF-1α) to the transcriptional coactivator protein p300. Inhibition
of the p300/HIF-1α interaction can suppress HIF-1 activity.
A screen for inhibitors of the protein binding domains of p300 (CH1)
and HIF-1α (C-TAD) identified an extract of the marine ascidian <i>Eudistoma</i> sp. as active. Novel heterocyclic alkaloids eudistidines
A (<b>1</b>) and B (<b>2</b>) were isolated from the extract,
and their structures assigned by spectroscopic analyses. They contain
an unprecedented tetracyclic core composed of two pyrimidine rings
fused with an imidazole ring. Eudistidine A (<b>1</b>) was synthesized
in a concise four-step sequence featuring a condensation/cyclization
reaction cascade between 4-(2-aminophenyl)Âpyrimidin-2-amine (<b>3</b>) and 4-methoxy-phenylglyoxal (<b>4</b>), while eudistidine
B (<b>2</b>) was synthesized in a similar fashion with glyoxylic
acid (<b>5</b>) in place of <b>4</b>. Naturally occurring
eudistidine A (<b>1</b>) effectively inhibited CH1/C-TAD binding
with an IC<sub>50</sub> of 75 μM, and synthetic <b>1</b> had similar activity. The eudistidine A (<b>1</b>) scaffold,
which can be synthesized in a concise, scalable manner, may provide
potential therapeutic lead compounds or molecular probes to study
p300/HIF-1α interactions and the role these proteins play in
tumor response to low oxygen conditions. The unique structural scaffolds
and functional group arrays often found in natural products make these
secondary metabolites a rich source of new compounds that can disrupt
critical protein–protein binding events
Screening and Biological Effects of Marine Pyrroloiminoquinone Alkaloids: Potential Inhibitors of the HIF-1α/p300 Interaction
Inhibition of the hypoxia-inducible
factor 1α (HIF-1α) pathway by disrupting its association
with the transcriptional coactivator p300 inhibits angiogenesis and
tumor development. Development of HIF-1α/p300 inhibitors has
been hampered by preclinical toxicity; therefore, we aimed to identify
novel HIF-1α/p300 inhibitors. Using a cell-free assay designed
to test compounds that block HIF-1α/p300 binding, 170 298
crude natural product extracts and prefractionated samples were screened,
identifying 25 active extracts. One of these extracts, originating
from the marine sponge <i>Latrunculia</i> sp., afforded
six pyrroloiminoquinone alkaloids that were identified as positive
hits (IC<sub>50</sub> values: 1–35 μM). Luciferase assays
confirmed inhibition of HIF-1α transcriptional activity by discorhabdin
B (<b>1</b>) and its dimer (<b>2</b>), 3-dihydrodiscorhabdin
C (<b>3</b>), makaluvamine F (<b>5</b>), discorhabdin
H (<b>8</b>), discorhabdin L (<b>9</b>), and discorhabdin
W (<b>11</b>) in HCT 116 colon cancer cells (0.1–10 μM, <i>p</i> < 0.05). Except for <b>11</b>, all of these compounds
also reduced HIF-1α transcriptional activity in LNCaP prostate
cancer cells (0.1–10 μM, <i>p</i> < 0.05).
These effects occurred at noncytotoxic concentrations (<50% cell
death) under hypoxic conditions. At the downstream HIF-1α target
level, compound <b>8</b> (0.5 μM) significantly decreased
VEGF secretion in LNCaP cells (<i>p</i> < 0.05). In COLO
205 colon cancer cells no activity was shown in the luciferase or
cytotoxicity assays. Pyrroloiminoquinone alkaloids are a novel class
of HIF-1α inhibitors, which interrupt the protein–protein
interaction between HIF-1α and p300 and consequently reduce
HIF-related transcription