Induction of teratocarcinoma F9 cell differentiation with cis-diammine dichloroplatinum(II) (CDDP)

The cisplatin-irradiation combination suggests that apoptosis is not a major determinant of clonogenic death

It is commonly believed that tumor cells treated with anticancer agents, chemotherapy and/or radiation, die by apoptosis and that tumors which do not undergo apoptosis are resistant to treatment. In this study, we investigated the molecular basis underlying cisplatin cytotoxicity in the murine teratocarcinoma F9 cell line to see whether irradiation enhances cisplatin-induced cytotoxicity. We compared the apoptosis induced by chemo and/or radiotherapy with other cellular effects such as cell survival, clonogenic capability, cell cycle perturbation, expression of p53 and p53-related mRNAs, and necrosis. When combined with radiation, a clear additive cytotoxic effect of cisplatin was demonstrated. We found that both cisplatin and radiation induced cell death, but the level of induced apoptosis was low and there was no correlation with the results of the clonogenic assays: we noted a difference between cytotoxic effects in the clonogenic assay and the extent of apoptosis by fluorescence-activated cell sorter analysis, suggesting that cell killing reflected not only apoptosis but also cell cycle arrest, and that apoptosis, cell kinetics and clonogenicity suppression were independent processes.

Induction of instability of p34(cdc2) expression by treatment with cisplatin (CDDP) in mouse teratocarcinoma F9 cells

p34(cdc2) is a protein kinase that plays an important role in the control of the cell cycle and regulation of activity of the tumor suppressor gene. Previously, we demonstrated that cisplatin (CDDP) induced growth suppression resulting in differentiation of teratocarcinoma F9 cells. In the present study, we investigated the mechanism of cell cycle retardation by CDDP in F9 cells, focusing on p34(cdc2). After the induction of differentiation with CDDP, F9 cells were arrested at the late S+G2/M. After treatment with CDDP, the level of the expression of cdc2 mRNA did not change. However, the half-life of p34(cdc2) was greatly reduced, thus, the level of p34(cdc2) protein was decreased. These findings suggest that the cell cycle arrest by CDDP is due partly to the induced instability of p34(cdc2) in F9 cells.

Influence of cisplatin and doxorubicin on 125I-meta-iodobenzylguanidine uptake in human neuroblastoma cell lines

The combination of 131I-meta-iodobenzylguanidine (MIBG) with chemotherapy has recently been employed in the treatment of advanced stage neuroblastoma with encouraging results. However, the mechanisms underlying the interaction between these two different modalities of treatment have not yet been explored. In this study, human neuroblastoma cell lines pretreatment with cisplatin and doxorubicin increased cellular 125I-MIBG accumulation in a dose-dependent manner. Cell cycle analysis showed that increased 125I-MIBG accumulation correlated with the drug-induced G2/M phase block. Northern blot analysis demonstrated an increase in gene expression of the noradrenaline transporter induced by doxorubicin, but not by cisplatin treatment. Increased 125I-MIBG accumulation was also observed in murine xenografts of the human neuroblastoma cell line SK-N-DZ or BE(2)M17 treated intraperitoneally (i.p.) with cisplatin or doxorubicin, respectively. These results suggest that the combination of 131I-MIBG and these drugs could selectively increase radiation doses delivered to neuroblastomas.

Induction of apoptosis by hinokitiol, a potent iron chelator, in teratocarcinoma F9 cells is mediated through the activation of caspase-3

Hinokitiol, a potent iron chelator, has been reported to induce differentiation in teratocarcinoma F9 cells with a reduction of viable cells. In this study, we examined the steps leading to eventual cell death by hinokitiol during differentiation. Hinokitiol induced DNA fragmentation of F9 cells in a concentration- and time-dependent manner. This effect was also observed in a cell-free system using the nuclei from intact cells and the cytosols from hinokitiol-treated cells. In contrast, hinokitiol methyl ether and hinokitiol-Fe (III) complex, which are deficient in iron-chelating activity, showed no DNA fragmentation activity in both cell culture and cell-free systems. These results suggest that iron deprivation by hinokitiol may be involved in the induction of apoptosis of F9 cells. Caspase-3, one of the key enzymes in the apoptotic cascade, was specifically activated by hinokitiol treatment, but not by the other two derivatives. In addition, its specific inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone, strongly blocked hinokitiol-induced DNA fragmentation. These results indicate that iron deprivation by hinokitiol can induce apoptosis of F9 cells through the activation of caspase-3.

The effect of cisplatin pretreatment on the accumulation of MIBG by neuroblastoma cells in vitro

[131I]meta-iodobenzylguanidine ([131I]MIBG) provides a means of selectively delivering radiation to neuroblastoma cells and is a promising addition to the range of agents used to treat neuroblastoma. As MIBG is now being incorporated into multimodal approaches to therapy, important questions arise about the appropriate scheduling and sequencing of the various agents employed. As the ability of neuroblastoma cells to actively accumulate MIBG is crucial to the success of this therapy, the effect of chemotherapeutic agents on this uptake capacity needs to be investigated. We report here our initial findings on the effect of cisplatin pretreatment on the neuroblastoma cell line SK-N-BE (2c). After treating these cells with therapeutically relevant concentrations of cisplatin (2 microM and 20 microM), a stimulation in uptake of [131I]MIBG was observed. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that this effect was due to increased expression of the noradrenaline transporter. These results suggest that appropriate scheduling of cisplatin and [131I]MIBG may lead to an increase in tumour uptake of this radiopharmaceutical with consequent increases in radiation dose to the tumour.