LKB1 phosphorylation and deactivation in lung cancer by NNAL, a metabolite of tobacco-specific carcinogen, in an isomer-dependent manner.

LKB1 loss of function is one key oncogenic event in lung cancer. Clinical data suggest that LKB1 loss of function is associated with patients' smoking status. The responsible ingredients and molecular mechanisms in tobacco for LKB1 loss of function, however, are not defined. In this study, we reported that NNAL, a major metabolite of a tobacco-specific carcinogen NNK, induces LKB1 phosphorylation and its loss of function via the ß-AR/PKA signaling pathway in an isomer-dependent manner in human lung cancer cells. NNAL exposure also resulted in enhanced lung cancer cell migration and chemoresistance in an LKB1-dependent manner. A 120-day NNAL exposure in lung cancer cells, mimicking its chronic exposure among smokers, resulted in more prominent LKB1 phosphorylation, cell migration, and chemoresistance even in the absence of NNAL, indicating the long-lasting LKB1 loss of function although such an effect eventually disappeared after NNAL was removed for two months. These observations were confirmed in a lung cancer xenograft model. More importantly, human lung cancer tissues revealed elevated LKB1 phosphorylation in comparison to the paired normal lung tissues. These results suggest that LKB1 loss of function in human lung cancer could be extended to its phosphorylation, which may be mediated by NNAL from tobacco smoke in an isomer-dependent manner via the ß-AR/PKA signaling pathway.

Design, synthesis, and enzymatic characterization of quinazoline-based CYP1A2 inhibitors.

Cytochrome P450 isozyme 1A2 (CYP1A2) is one main xenobiotic metabolizing enzyme in humans. It has been associated with the bioactivation of procarcinogens, including 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco specific and potent pulmonary carcinogen. This work describes the computational design and in-silico screening of potential CYP1A2 inhibitors, their chemical synthesis, and enzymatic characterization with the ultimate aim of assessing their potential as cancer chemopreventive agents. To achieve this, a combined classifiers model was used to screen a library of quinazoline-based molecules against known CYP1A2 inhibitors, non-inhibitors, and substrates to predict which quinazoline candidates had a better probability as an inhibitor. Compounds with high probability of CYP1A2 inhibition were further computationally evaluated via Glide docking. Candidates predicted to have selectivity and high binding affinity for CYP1A2 were synthesized and assayed for their enzymatic inhibition of CYP1A2, leading to the discovery of novel and potent quinazoline-based CYP1A2 inhibitors.

Kava and its Kavalactones Inhibit Norepinephrine-induced Intracellular Calcium Influx in Lung Cancer Cells.

Kava, the extract of the roots of Piper methysticum, has been traditionally consumed in the South Pacific islands for its natural relaxing property. Epidemiological data suggests that kava consumption may reduce human cancer risk, and in vitro and in vivo models suggest chemopreventive potential against carcinogen-induced tumorigenesis. Therefore, knowledge about its molecular mechanisms and responsible ingredient(s) for these beneficial properties will better guide kava's use for the management of these disorders. Psychological stress typically results in increased production of stress hormones, such as norepinephrine (NE), which activate adrenergic receptors (ARs). Psychological stress has also been associated with increased cancer incidence and poor clinical outcomes in cancer patients. Mechanistically, binding of NE to ARs induces intracellular calcium influx, which activates downstream signaling pathways involved in both stress and cancer development. In this study, we characterized the effect of kava and its components, 3 fractions and 6 major kavalactones, on NE-induced intracellular calcium influx in H1299, a human non-small cell lung carcinoma cell line. Results show that kava extract effectively inhibits NE-mediated intracellular calcium influx in H1299 cells, potentially through antagonizing ß-AR signaling. This inhibitory activity is recapitulated by the major kavalactones in kava. Among the 6 major kavalactones, DHK demonstrated the best potency. Taken together, our study suggests a novel mechanism through which kava and its ingredients potentially offer the anxiolytic and cancer-preventive activity.