Hirsutinolide Series Inhibit Stat3 Activity, Alter GCN1, MAP1B, Hsp105, G6PD, Vimentin, TrxR1, and Importin α‑2 Expression, and Induce Antitumor Effects against Human Glioma

We
report that hirsutinolide series, 6, 7, 10, 11, 20, and 22,
and the semisynthetic analogues, 30, 31, 33, and 36, inhibit constitutively active
signal transducer and activator of transcription (Stat)­3 and malignant
glioma phenotype. A position 13 lipophilic ester group is required
for activity. Molecular modeling and nuclear magnetic resonance structural
analyses reveal direct hirsutinolide:Stat3 binding. One-hour treatment
of cells with 6 and 22 also upregulated
importin subunit α-2 levels and repressed translational activator
GCN1, microtubule-associated protein (MAP)­1B, thioredoxin reductase
(TrxR)­1 cytoplasmic isoform 3, glucose-6-phosphate 1-dehydrogenase
isoform a, Hsp105, vimentin, and tumor necrosis factor α-induced
protein (TNAP)­2 expression. Active hirsutinolides inhibited anchorage-dependent
and three-dimensional spheroid growth, survival, and migration of
human glioma lines and glioma patients’ tumor-derived xenograft
cells harboring constitutively active Stat3. Oral gavage delivery
of 6 or 22 inhibited human glioma tumor
growth in subcutaneous mouse xenografts. The inhibition of Stat3 signaling
represents part of the hirsutinolide-mediated mechanisms to induce
antitumor effects.