Related Experiment Videos
Synergistic killing of virus-transformed human cells with interferon and N-methyl-N'-nitro-N-nitrosoguanidine
1Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD.
Abstract:
Interferons potentiate the cytotoxic effects of certain antineoplastic drugs on human tumor cells both in vitro and in vivo, although the mechanism of interferon's synergistic action is unknown. Interferon may act by modulating the expression of DNA repair activity in cells. To test this hypothesis, we maintained parallel cultures of normal O6-methylguanine repair-proficient human fibroblasts and tumor cells, or RSV-and SV40-transformed repair-deficient Mer- human fibroblasts in medium containing 0, 100, 500 or 680 U/ml human interferon alpha or beta; after 1-10 weeks, cultures were challenged with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, CAS: 70-25-7) and assayed for colony-forming ability. Based on the dose at 99% lethality, MNNG cytotoxicity was potentiated from 1.3- to 9-fold in interferon-treated cultures, compared with control cultures (no interferon). A significant potentiation was observed both with Mer+ normal fibroblasts (KD strain) and tumor cells (HOS) and with Mer- SV40-transformed fibroblasts (IMR90-830 and GM638) as well as with RSV-transformed cells (RHOS). However, the degree of potentiation was greater in Mer- virus-transformed cells than in Mer+ cells. The greatest effects were observed with Mer- IMR90-830 cells (5- to 9-fold reduction of dose at 99% lethality). Therefore, because the Mer+ phenotype is not required in order for HuIFNs to sensitize cells to killing by MNNG, interferon does not act by modulating O6-methylguanine repair. However, the effect of interferon on O6-methylguanine-DNA methyltransferase levels and on DNA excision repair should be examined in future experiments.
Insights
Interferons enhance cancer drug effectiveness by increasing cell sensitivity to MNNG. This potentiation occurs regardless of DNA repair capacity, suggesting interferons do not primarily act by modulating O6-methylguanine repair.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Interferons (IFNs) are known to potentiate the cytotoxic effects of antineoplastic drugs on human tumor cells.
- The precise mechanism underlying this synergistic action of interferons remains largely unknown.
- A hypothesis suggests interferons may modulate DNA repair activity within cells.
Purpose of the Study:
- To investigate whether interferons (IFNs) sensitize human cells to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) by modulating O6-methylguanine repair activity.
- To compare the potentiation effects of IFNs on both DNA repair-proficient and DNA repair-deficient human cell lines.
Main Methods:
- Cultured normal and transformed human fibroblasts, differing in O6-methylguanine repair proficiency (Mer+ and Mer-), were treated with human interferon alpha or beta.
- Treated and control cultures were subsequently challenged with MNNG, and their colony-forming ability was assayed.
- Cytotoxicity was quantified by determining the dose of MNNG required for 99% lethality.
Main Results:
- MNNG cytotoxicity was significantly potentiated (1.3- to 9-fold) in interferon-treated cultures compared to controls.
- Potentiation was observed in both Mer+ normal fibroblasts and tumor cells, as well as in Mer- transformed fibroblasts.
- The degree of MNNG sensitization was greater in Mer- virus-transformed cells than in Mer+ cells, with the most pronounced effect seen in Mer- IMR90-830 cells.
Conclusions:
- Interferons sensitize human cells to MNNG-induced cytotoxicity independently of the O6-methylguanine repair phenotype.
- The findings indicate that interferons do not exert their sensitizing effect by modulating O6-methylguanine repair.
- Future research should investigate the impact of interferons on O6-methylguanine-DNA methyltransferase levels and DNA excision repair.