6-Nitrobenzo[b]thiophene 1,1-dioxide
(Stattic)
is a potent signal transducer and activator of the transcription 3
(STAT3) inhibitor developed originally for anticancer therapy. However,
Stattic harbors several STAT3 inhibition-independent biological effects.
To improve the properties of Stattic, we prepared a series of analogues
derived from 6-aminobenzo[b]thiophene 1,1-dioxide,
a compound directly obtained from the reduction of Stattic, that includes
a methoxybenzylamino derivative (K2071) with optimized physicochemical
characteristics, including the ability to cross the blood–brain
barrier. Besides inhibiting the interleukin-6-stimulated activity
of STAT3 mediated by tyrosine 705 phosphorylation, K2071 also showed
cytotoxicity against a set of human glioblastoma-derived cell lines.
In contrast to the core compound, a part of K2071 cytotoxicity reflected
a STAT3 inhibition-independent block of mitotic progression in the
prophase, affecting mitotic spindle formation, indicating that K2071
also acts as a mitotic poison. Compared to Stattic, K2071 was significantly
less thiol-reactive. In addition, K2071 affected cell migration, suppressed
cell proliferation in tumor spheroids, exerted cytotoxicity for glioblastoma
temozolomide-induced senescent cells, and inhibited the secretion
of the proinflammatory cytokine monocyte chemoattractant protein 1
(MCP-1) in senescent cells. Importantly, K2071 was well tolerated
in mice, lacking manifestations of acute toxicity. The structure–activity
relationship analysis of the K2071 molecule revealed the necessity
of the para-substituted methoxyphenyl motif for antimitotic
but not overall cytotoxic activity of its derivatives. Altogether,
these results indicate that compound K2071 is a novel Stattic-derived
STAT3 inhibitor and a mitotic poison with anticancer and senotherapeutic
properties that is effective on glioblastoma cells and may be further
developed as an agent for glioblastoma therapy.