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Disrupting lung tumor growth via histone deacetylases (HDACs) inhibition is a strategy for cancer therapy or prevention. Targeting HDAC6 may disturb the maturation of heat shock protein 90 (Hsp90) mediated cell cycle regulation. In this study, we demonstrated the effects of semisynthesized NBM-T-BBX-OS01 (TBBX) from osthole on HDAC6-mediated growth arrest in lung cancer cells. The results exhibited that the anti-proliferative activity of TBBX in numerous lung cancer cells was more potent than suberoylanilide hydroxamic acid (SAHA), a clinically approved pan-HDAC inhibitor, and the growth inhibitory effect has been mediated through G1 growth arrest. Furthermore, the protein levels of cyclin D1, CDK2 and CDK4 were reduced while cyclin E and CDK inhibitor, p21Waf1/Cip1, were up-regulated in TBBX-treated H1299 cells. The results also displayed that TBBX inhibited HDAC6 activity via down-regulation HDAC6 protein expression. TBBX induced Hsp90 hyper-acetylation and led to the disruption of cyclin D1/Hsp90 and CDK4/Hsp90 association following the degradation of cyclin D1 and CDK4 proteins through proteasome. Ectopic expression of HDAC6 rescued TBBX-induced G1 arrest in H1299 cells. Conclusively, the data suggested that TBBX induced G1 growth arrest may mediate HDAC6-caused Hsp90 hyper-acetylation and consequently increased the degradation of cyclin D1 and CDK4.

Garcinol, a polyisoprenylated benzophenone, from Garcinia indica fruit rind has possessed anti-inflammatory, antioxidant, antiproliferation, and anticancer activities. However, the anticancer mechanisms of garcinol in lung cancer were still unclear. Therefore, we examine the effects of garcinol on antiproliferation in human lung cancer cells. Treatments with garcinol for 24 h exhibited morphological changes and inhibited the proliferation of H460 (p53-wild type) and H1299 (p53-null) cells in dose- and time-dependent manners. Furthermore, a significant G1 cell cycle arrest was observed in a dose-dependent treatment after H1299 cells were exposed in garcinol, whereas garcinol induced apoptosis rather than cell cycle arrest in H460 cells. Moreover, cyclin-dependent kinase 2 (CDK2), cyclin-dependent kinase 4 (CDK4), cyclin D1, and cyclin D3 were decreased, although cyclin E and cyclin-dependent kinase 6 (CDK6) were increased in garcinol-treated H1299 cells. Meanwhile, the protein levels of CDK inhibitors p21(Waf1/Cip1) and p27(KIP1) also exhibited upregulation after garcinol treatments. The enhanced protein-associated level between p21(Waf1/Cip1) and CDK4/2 rather than p27(KIP1) and CDK4/2 was demonstrated in garcinol-treated cells. Additionally, knock-down p21(Waf1/Cip1) by specific siRNA competently prevented garcinol-induced G1 arrest. Besides, garcinol also inhibited ERK and p38-MAPK activations in time-dependent mode. The pretreatment with p38-MAPK inhibitor but not ERK inhibitor raised garcinol-induced G1 population cells. Co-treatment with p38-MAPK inhibitor and garcinol synergistically elevated cyclin E, p21(Waf1/Cip1), and p27(Kip1) expressions. Meanwhile, overexpression dominant negative p38-MAPK also enhanced garcinol-induced p21(Waf1/Cip1) expression in H1299 cells. Accordingly, our data suggested that garcinol induced G1 cell cycle arrest and apoptosis in lung cancer cells under different p53 statuses. The p53-independent G1 cell cycle arrest induced by garcinol might be through upregulation of p21(Waf1/Cip1) triggered from p38-MAPK signaling inactivation.

Garcinol is a polyisoprenylated benzophenone derivative found in Garcinia indica fruit rind and other species. The potential antioxidative and neuroprotective effects of garcinol in rat cortical astrocyte were demonstrated in our laboratory recently. Here, the effects of garcinol on the neuritogenesis process in cultured cortical progenitor cells were investigated to understand the roles of garcinol in neuronal survival and differentiation. These cells, derived from embryonic day 17 rats, differentiated into EGF-responsive neural precursor cells, would further form neurospheres. Our data exhibited garcinol induced neurite outgrowth in early developing EGF-treated neurospheres and significantly enhanced the expression of neuronal proteins, microtubule-associated protein 2 (MAP-2), and glial fibrillary acidic protein (GFAP). Furthermore, the neuronal marker, high-molecular-weight subunit of neurofilaments (NFH), was highly expressed after 5 μM garcinol treatment in neural precursor cells for 20 days. To identify the extracellular mechanism, rat cortical progenitor cells were treated garcinol and accordingly mediated the sustained activation of extracellular signal-regulated kinase (ERK) for different periods up to 20 h. In this regard, NMDA receptor-mediated calcium influx led to excitotoxic death and activated tyrosine phosphatase which limited the duration of ERK in cultured neurons. MK801, the NMDA receptor antagonist, treatment also induced the sustained phosphorylation of ERK and therefore enhanced neuronal survival. In our observation, garcinol treatment reduced growth factor deprivation-mediated cell death and nuclear import of C/EBPβ levels. Noteworthy, garcinol could promote neurite outgrowth in EGF-responsive neural precursor cells and modulate the ERK pathway in the enhancement of neuronal survival.