HO-3867, a Safe STAT3 Inhibitor, Is Selectively Cytotoxic to Ovarian Cancer

Abstract

STAT3 is well corroborated preclinically as a cancer therapeutic target, but tractable translational strategies for its blockade by small molecule inhibitors have remained elusive. In this study, we report the development of a novel class of bifunctional STAT3 inhibitors, based on conjugation of a diarylidenyl-piperidone (DAP) backbone to an N-hydroxypyrroline (−NOH) group, which exhibits minimal toxicity against normal cells and good oral bioavailability. Molecular modeling studies of this class suggested direct interaction with the STAT3 DNA binding domain. In particular, the DAP compound HO-3867 selectively inhibited STAT3 phosphorylation, transcription, and DNA binding without affecting the expression of other active STATs. HO-3867 exhibited minimal toxicity toward noncancerous cells and tissues but induced apoptosis in ovarian cancer cells. Pharmacologic analysis revealed greater bioabsorption and bioavailability of the active (cytotoxic) metabolites in cancer cells compared with normal cells. The selective cytotoxicity of HO-3867 seemed to be multifaceted, eliciting differential activation of the Akt pathway in normal versus cancer cells. RNAi attenuation experiments confirmed the requirement of STAT3 for HO-3867–mediated apoptosis in ovarian cancer cells. In vivo testing showed that HO-3867 could block xenograft tumor growth without toxic side effects. Furthermore, in primary human ovarian cancer cells isolated from patient ascites, HO-3867 inhibited cell migration/invasion and survival. Our results offer preclinical proof-of-concept for HO-3867 as a selective STAT3 inhibitor to treat ovarian cancer and other solid tumors where STAT3 is widely upregulated.

MicroRNA-302b Suppresses Human Epithelial Ovarian Cancer Cell Growth by Targeting RUNX1

“…Furthermore, STAT3 activation is correlated with disease stage, lymph node metastasis, drug resistance and poor survival in ovarian cancer [27,28,29]. The expression of the phosphorylated form of STAT3, p-STAT3, is higher in ovarian cancer cell lines and in EOC tissues compared to benign ovarian tumors or normal ovarian tissues [27,30]. The nuclear localization of p-STAT3 has been detected in a significant proportion of ovarian cancer patients in association with poor prognosis [28,31].…”

Hypoxia-induced exosomes contribute to a more aggressive and chemoresistant ovarian cancer phenotype: a novel mechanism linking STAT3/Rab proteins

“…Samples were diluted in 11 ml 1× PBS and filtered through a 0.2 μm pore filter and then followed the same protocol as described above for the cell culture medium. The resulting exosome pellet was re-suspended in 100μl of cold PBS or lysis buffer according to the downstream applications such as NTA, TEM and Western blotting as we previously described 41, 42 .…”

“…The resultant STAT3 knockdown cells were called as OVCAR-8 KD cells. A negative scrambled shRNA was used as a control 41 .…”

An Integrated Computational and Experimental Binding Study Identifies the DNA Binding Domain as the Putative Binding Site of Novel Pyrimidinetrione Signal Transducer and Activator of Transcription 3 (STAT3) Inhibitors

“…Therefore, the traditional strategy of inhibiting STAT3 dimerization may not be an efficient strategy to eliminate functions in tumor cells. Recently, a curcumin-based STAT3 inhibitor HO-3867 was suggested to bind directly to the STAT3 DNA binding domain [44] unlike other STAT3 inhibitors. Meanwhile, only few studies have been accomplished in other STAT3 inhibition strategies or binding site verification, which all the more emphasizes the challenge to STAT3 inhibitor design.…”