recombinant human tumor necrosis factor (γH-TNF0 and recombinant human interferon-γ (γH-IFN-γ) were tested using MTT asay to investigate the modificatin effects on the intrinsic and acquired resistance to cisplatin in human stomach cancer
cell
line
(MKN-450, lung cancer cell line 9PC-14) and their crisplatin-resistant cell lines established in vitro (MKN/CDDP and PC/CDDP). MKN/CDDP and PC/CDDDP were 5.8 and 46.3 fold resistant to cisplatin, respectively, compared to the respective parent
cell
line
in terms of IC50. MKN-45, PC, 14, MKN/CDDP and PC/CDDP were insenstive ot 12E2U/ml of rH-TNF. MKN/CDDP, PC-14, and PC/CDDP were not significantly inhibited by the doses up to 10E4U/ml of rH-IFN-.γ.RH-IFN-γ inhibited the survival of MKN-45
does-dependently, however, the maximum inhibition at the highest concentration tested (10E4U/ml) was less than 50%. Cisplatin inhibited the survival of these four cell lines dose-dependently. Cytotoxicity was significantly enhanced by the
simultaneous
comhbination of cisplatin with rH-TNF were 0.28 and 0.39μg/ml in MKN-45 and 0.12 and 0.13μg/ml in PC-14, respectively, while IC50s to cisplatin alone were 0.60 and 0.21μ/ml in MKN-45 and PC-14, respectively. IC50 to cisplatin of PC/CDDP at
10E2U/ml
of rH-TNF was 4.57μg/ml, which was significantly lower than that to cisplatin alone, 9.73μg/ml (p<0.01). RH-IFN-γ, even at the highest concentration tested (10E4U/ml), did not significantly modify the IC50s of PC-14, MKN/CDDP and PC/CDDP, but
IC50 in
MKN/CDDP decreased only at 10E4U/ml of rH-IFN-γ, RH-IFN-γ, however, significantly decreased in the IC50s to cisplatin in MKN-45 compared to the control (p<0.01) : IC50s in control, 10E3 and 10E4U/ml of rH-IFN-γwere 0.60, 0.34 and 0.24μg/ml,
respectively. The modification effects of rH-TNF and Rh-IFN-γ on the cytotoxicity to cisplatin were evaluated in terms of modification index (MI : the ratio of IC50 to cisplatin to IC50 to cisplatin plus rH-TNF or Rh-ifn-γ). RH-TNF
significantly
increased in MI values : MI at 10U/ml of rH-TNF were 2.41 and 1.75 in MKN-45 and PC-14, respectively : MI at 10E2U/ml were 1.54, 1.62 and 2.31 in MKN-45, PC-14, and PC/CDDP, resperctively. In MKN/CDDP, MI was not modified by rH-TNF. RH-IFN-γ
modified the cytotoxicity of cisplatin against MKN-45 : MI at 10E3 ant 10E4U/ml of rH-IFN-γ were 1.76 and 2.50, respectively. Modification of cytotoxicity was not observed in PC-14, PC/CDDP and MKN/CDDP, when evaluated in terms of MI, except
10E4U/ml
of rH-IFN-γ in MKN/CDDPD (MI : 1.31). The acquired resistance to cisplatin was not modified by the combination of cisplatin with rH-TNF or rH-IFN-γ. These results demonstrating that rH-TNF and rH-IFN-γ modified the cytotoxicity of cisplatin
suggest
that rH-TNF and rH-IFN-γhave some potential to overcome the intrinsic resistance to cisplatin.
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