Prevention of Tobacco Carcinogen-Induced Lung Tumor Development by a Novel STAT3 Decoy Inhibitor

The STAT3 pathway is frequently overactive in non-small cell lung cancer (NSCLC), an often fatal disease with known risk factors including tobacco and chemical exposures. Whether STAT3 can be downmodulated to delay or prevent development of lung cancer resulting from an environmental exposure has not been previously tested. A circular oligonucleotide STAT3 decoy (CS3D) was used to treat mice previously exposed to the tobacco carcinogen nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. CS3D contains a double-stranded STAT3 DNA response element sequence and interrupts STAT3 signaling by binding to STAT3 dieters, rendering them unable to initiate transcription at native STAT3 DNA binding sites. An intermittent course of CS3D decreased the development of airway preneoplasias by 42% at 1 week posttreatment, reduced the progression of preneoplasia to adenomas by 54% at 8 weeks posttreatment, and reduced the size and number of resulting lung tumors by 49.7% and 29.5%, respectively, at 20 weeks posttreatment. No toxicity was detected. A mutant cyclic oligonucleotide with no STAT3 binding ability was used as a control. Chemopreventive effects were independent of the KRAS mutational status of the tumors. In lungs harvested during and after the treatment course with CS3D, airway preneoplasias had reduced STAT3 signaling. Chemopreventive effects were accompanied by decreased VEGFA expression, ablated IL6, COX-2, and p-NF-kappa B, and decreased pulmonary M2 macrophages and myeloid-derived suppressor cells. Thus, downmodulation of STAT3 activity using a decoy molecule both reduced oncogenic signaling in the airway epithelium and favored a lung microenvironment with reduced immunosuppression.