Apoptosis induced by isoliquiritigenin in human gastric cancer MGC-803 cells.

Isoliquiritigenin, which is possibly a principal anti-tumor constituent of licorice, a traditional Chinese herb, was examined for apoptosis-inducing activity in human gastric cancer MGC-803 cells. Typical morphological and biochemical features of apoptosis including cell shrinkage, chromatin condensation, DNA ladder formation, and appearance of apoptotic peaks (subG(1)) were observed in MGC-803 cells with isoliquiritigenin treatment. Using Fluo-3 and Rh123 as fluorescent probes, respectively, it was found that the intracellular free calcium concentration increased and the mitochondrial transmembrane potential (Deltapsi(m)) decreased in a dose-dependent manner in apoptotic cells. These results suggest that isoliquiritigenin induced apoptosis of MGC-803 cells through calcium- and Deltapsi(m)-dependent pathways, indicating that it is potentially useful as a natural anti-cancer agent.

[Mitochondrial permeability transition pore regulates the apoptosis in MGC-803 induced by the extract of glycyrrhiza uralensis Fisch].

In our previous studies, we have discovered that the extract of glycyrrhiza uralensis Fisch (EGUF) can induce obvious apoptosis in gastric cancer cell Line MGC-803. Here, further investigation was carried on about the time-lapse changes of mitochondria transmembrane potential, intracellular free calcium ions, DNA electrophoresis, plasma membrane permeability and chromatin condensation during the apoptotic process of MGC-803 induced by EGUF and the influences of MPT-specific inhibitor Cyclosporin A(CsA) on these changes. Enhancement of plasma membrane permeability with PI staining, increase of intracellular free calcium ion and decrease of mitochondria transmembrane potential are early events in apoptotic cascades, prior to the appearances of apoptotic peak, chromatin condensation and DNA ladder. CsA significantly inhibited enhancement of plasma membrane permeability, change of intracellular free calcium ions and decrease of mitochondria transmembrane potential, also greatly delayed the progress of apoptosis. Thus, our results suggest that calcium and CsA-sensitive MPT is involved in the apoptosis of MGC-803 induced by EGUF.

Resistance to apoptosis of harringtonine-resistant HL60 cells induced by tetrandrine.

AIM: To study the mechanism of resistance to apoptosis in the harringtonine (Har)-resistant HL60 cells with tetrandrine (Tet). METHODS: Growth inhibition, flow cytometry, DNA agarose gel electrophoresis, protein phosphorylation, and RNA dot hybridization. RESULTS: The resistant cells had no cross resistance to Tet. Tet induced the sensitive but not the Har-resistant HL60 cells to apoptosis. The high phosphorylation of protein < 30 kDa occurred when the resistant cells were treated with Tet. Tet and Har increased the expression of c-myc mRNA in the sensitive HL60 cells. The expression of c-myc mRNA in the resistant cells was obviously decreased and almost not changed in treatment with Tet and Har. CONCLUSION: Tet induced the sensitive but not the Har-resistant HL60 cells to apoptosis, and the resistance to apoptosis induced by Tet was associated with the high protein phosphorylation and reduction of the expression of c-myc mRNA.

[Retardation of human drug-resistant HL-60 cell in G1 phase and induction of sensitive cell to apoptosis by cyclosporine A].

To further study the relationship between resistance to apoptosis and drug resistance in harringtonine-resistant HL-60 cells (HR20), cyclosporine A (CsA) 20, 10 micrograms.ml-1 was shown to induce the sensitive HL-60 cells to apoptosis, showing a typical DNA "ladder" band. But the same concentrations of CsA retarded the HR20 cells in G1 phase and could not induce the cells to apoptosis. The cellular daunorubicin accumulation increased when HR20 cells were treated with low concentration of CsA and the reversal of drug resistance by CsA was unrelated to the retardation of cell cycle progression. High phosphorylation of about 50 kDa protein occured when HR20 cells were treated with CsA 10 micrograms.ml-1. The results domonstrate that cyclosporine A retarded the harringtonine-resistant HL-60 cells in G1 phase but induced HL-60 cells to apoptosis, and the retardation was unrelated to drug resistance.

[Induction of expression of MDR 1 gene by retinoic acid and DMSO and effects on rhodamine-123 efflux in HL-60 cell lines and resistant sublines].

Using dot blot hybridization and flowcytometry, the effects of differentiation inducers retinoic acid (RA) and dimethyl sulfoxide (DMSO) on the resistant level of HL-60 cells and its resistant subline cells were studied. When the cells were treated with RA 1 mumol.L-1 for 24 h, the expression of MDR 1 mRNA evidently increased in both HL-60 and its multidrug resistant subline cells. The efflux of Rho-123 in the multidrug resistant subline cells was slightly decreased. But, when the cells were treated with 2% DMSO for 24 h the efflux of Rho-123 increased obviously. The results suggest that RA can induce the expression of MDR1 gene but perhaps inhibit the function of pump glycoprotein 170 (Pgp-170) through phosphorylation/dephosphorylation pathway. However, DMSO could induce the expression of full function of Pgp.

[Apoptosis resistance and its reversal in harringtonine resistant cell line].

Harringtonine (HT), a domestic antitumor drug extracted from Cephalotaxus hainanensis Li showed high chemotherapeutic efficacy on human acute granulocytic leukemia and acute myelocytic leukemia in clinics. Apoptosis of HL-60 cells can be induced by HT effectively; but for cells resistant to harringtonine, apoptosis can not be induced, even if the drug (HT) concentration is over 100 times of IC50 value. Although apoptosis occurred when its multidrugs resistance had been reversed by verapamil, compared with sensitive HL-60 cells, the time at which apoptosis happened delayed and the drug dosage increased. All these suggest that apoptotic resistance might be one of the marks of drug resistance in tumor cells, and apoptosis related factors could play a role in the formation of multidrug resistance.