Dose-Dependent Cytotoxic Effects of Boldine in HepG-2 Cells—Telomerase Inhibition and Apoptosis Induction

Abstract

Plant metabolites are valuable sources of novel therapeutic compounds. In an anti-telomerase screening study of plant secondary metabolites, the aporphine alkaloid boldine (1,10-dimethoxy-2,9-dihydroxyaporphine) exhibited a dose and time dependent cytotoxicity against hepatocarcinoma HepG-2 cells. Here we focus on the modes and mechanisms of the growth-limiting effects of this compound. Telomerase activity and expression level of some related genes were estimated by real-time PCR. Modes of cell death also were examined by microscopic inspection, staining methods and by evaluating the expression level of some critically relevant genes. The growth inhibition was correlated with down-regulation of the catalytic subunit of telomerase (hTERT) gene (p < 0.01) and the corresponding reduction of telomerase activity in sub-cytotoxic concentrations of boldine (p < 0.002). However, various modes of cell death were stimulated, depending on the concentration of boldine. Very low concentrations of boldine over a few passages resulted in an accumulation of senescent cells so that HepG-2 cells lost their immortality. Moreover, boldine induced apoptosis concomitantly with increasing the expression of bax/bcl2 (p < 0.02) and p21 (p < 0.01) genes. Boldine might thus be an interesting candidate as a potential natural compound that suppresses telomerase activity in non-toxic concentrations.

Short-term inhibition of TERT induces telomere length-independent cell cycle arrest and apoptotic response in EBV-immortalized and transformed B cells

“…In fact, TERT inhibition in different cellular backgrounds is associated with cell growth arrest, induction of apoptosis 7, 17, 18, 19 and increased sensitivity to ionizing radiation. 18 Our previous work has demonstrated that TERT inhibition by short hairpin RNA triggers the complete viral lytic cycle and cell death in EBV-positive cells.…”

Therapeutic strategies for targeting telomerase in cancer

“…Here, we collect natural telomerase inhibitors reported in the literature and summarize their telomerase inhibition effects, structures, possible mechanisms, and provide references for pharmaceutical chemists searching for suitable lead compounds. Table and Figures and show natural products and chemical structures that target the telomere elongation process …”

“…Boldine ( 48 ) is a natural opioid alkaloid with 1,10‐dimethoxy‐2,9‐dihydroxy aporphine moiety. Boldine exhibits cytotoxic effects against various tumor cell lines (HepG‐2, T24, U138‐MG, U87, and MGC6), and this cytotoxic effect is dose‐and time‐dependent . A decrease in telomerase activity can be observed in these cell lines; however, the specific mechanism behind inhibiting telomere elongation remains unclear.…”

“…Pristimerins ( 55 ) is a highly reversible monoacylglycerol lipase inhibitor that belongs to quinone methyl triterpenoids with broad biological activities. The studies found that it has antiproliferative effects on a variety of tumor cell lines (multiple myeloma, prostate cancer, lung cancer, cervical cancer, and breast cancer) . Deeb et al reported that it inhibits telomere elongation and induces apoptosis, which may be caused by the reduction in the transcription factors and nuclear factor κB associated with the expression of hTERT.…”

Telomerase Inhibitors from Natural Products and Their Anticancer Potential

“…It exhibits a dose- and time-dependent cytotoxic and anti-tumor effect against various cell lines, such as liver (HepG-2), bladder (T24), and brain (U138-MG, U87-MG, and C6). The treatment with boldine in these cell lines concomitantly reduces telomerase activity, induces apoptosis and down-regulates hTERT gene expression [ 24 , 219 , 220 , 221 ]. A study conducted by Paydar et al [ 222 ] in human invasive breast cancer cell lines (MDA-MB-231) and animal model shows that boldine induces cell cycle arrest at the G2/M phase and induces apoptosis, as indicated by a release of lactate dehydrogenase, membrane permeability, and DNA fragmentation.…”