Synergism between 5-fluorouracil and N-methylformamide in HT29 human colon cancer line

Abstract

Summary In HT29 cells 5-fluorouracil (5FU) cytotoxicity is enhanced by subsequent incubation of cells in medium containing 1% N-methylformamide (NMF). This enhancement does not appear to be related to differences in the repair of 5FU-induced DNA damage. It is proposed that the inhibition of DNA synthesis by NMF (that is reversible and does not result in any detectable toxicity) becomes a lethal event in a cell in which DNA synthesis has already been altered by 5FU exposure. The synergism is sequence dependent (i.e. it does not occur when NMF is given before 5FU) and specific for some cell types as shown by the fact that no synergism was found in L1210 mouse leukaemia cells. In nude mice transplanted s.c. with HT29 cells daily 5FU treatment (for 5 days) followed by daily NMF treatment (for 10 days) caused much greater inhibition of tumour growth than either drug alone or the same combination given in the opposite order (NMF then 5FU). These results, if confirmed on other human colon tumours, could be of clinical interest as a means of increasing the therapeutic efficacy of 5FU in patients with colon cancer.The polar solvent N-methylformamide (NMF) has recently been reported to induce the expression of a better differentiated or less malignant phenotype in both rodent and human tumour cells (Langdon & Hickman, 1987). Cellular alterations associated with NMF-mediated induction of differentiation include changes in morphology, clonogenicity, tumorigenicity and cell culture doubling time (Zupi et al., 1988), which ultimately result in a lower tumour aggressiveness. NMF-treated cells revert to the original phenotype upon removal of the inducer, but the maturational treatment has been associated with increased tumour cell sensitivity to certain cytotoxic agents, such as X-rays, cisplatinum and bleomycin (Dexter et al., 1984;Harpur et al., 1986;Langdon et al., 1985;Leith et al., 1985Leith et al., , 1986. It has been proposed that the sequential use of cytotoxic and differentiating agents might improve anti-cancer therapy by preventing or slowing tumour cell proliferation and phenotypic diversification (Lotan & Nicolson, 1988).In the human colon cancer cell line HT29 we have already studied the lethal effects of the combination of NMF and 5-fluorouracil (5FU) (Zupi et al., 1988). 5FU cytotoxicity was potentiated by subsequent exposure of cells to a nontoxic dose of NMF (1%), but when the two compounds were given in the opposite sequence there was no synergism. The enhanced cytotoxicity of the sequence 5FU to NMF could be related to the NMF-treated cells being less able to recover from the sublethal damage produced by the anti-metabolite.In order to shed some light on the mechanism of this potentiation we designed a study to assess the DNA damage and alteration of macromolecule synthesis caused by 5FU alone or SFU followed by NMF on HT29 cells. Materials and methods Cell culturesThe HT29 colon adenocarcinoma cell line was maintained as monolayer culture in RPMI 1640 medium supplemented with 10% FCS, L-glutamine and antibi...

Therapeutic potential of differentiating agents in colon cancer treatment

“…This finding has been confirmed in the in vivo model [7]. The association in which 5-FU administration follows NMF proves to exert a powerful inhibiting effect on the growth of HT29 xenografts.…”

“…The enhanced cytotoxicity of the sequence 5-FU-NMF could be related to the NMF-treated cells being less able to recover from the sublethal damage induced by the antimetabolite. The NMF-induced inhibition of DNA synthesis, normally reversed without any cytotoxicity upon NMF removal, could thus be lethal in a cell whose DNA synthesis capacity has already been impaired by 5-FU [7].…”

Telomere damage induced by the G-quadruplex ligand RHPS4 has an antitumor effect

“…Transformed BJ fibroblasts expressing hTERT and SV40 early region (BJ-EHLT) were maintained as previously described (20). Human M14 melanoma, CG5 breast carcinoma, and HT29 colon carcinoma lines were previously described (45)(46)(47). Human non-small cell lung carcinoma and PC3 prostate cancer cells were obtained from ATCC and maintained in RPMI-1640 supplemented with 10% FCS, 2 mM l-glutamine and antibiotics (Invitrogen).…”

Pre‐Treatment of human osteosarcoma cells with N‐methylformamide enhances P‐glycoprotein expression and resistance to doxorubicin

“…NMF exerts a wide spectrum of biological and antineoplastic effects, including enhanced differentiation in leukemic and colorectal tumor cell lines, decreased proliferation not associated with cytotoxicity in different neoplastic cells and in vivo anti-tumor activity against experimental primary and metastatic tumors (Iwakawa et al, 1987;Langdon et al, 1988;Clagett-Carr et al, 1988;Greco et al, 1990). Although NMF failed to demonstrate significant effects in patients with carcinoma, leukemia or melanoma (McGuire et al, 1990;Murphy et al, 1987;Planting et al, 1987;Eton et al, 1991), recent studies have renewed interest in using NMF in sequential combination with chemotherapeutic agents (Zupi et al, 1988;Iwakawa et al, 1989;Laudonio et al, 1990;Cucco et al, 1991). In particular, NMF improves the lethal effects of doxorubicin (DXR) and 5-fluorouracil (5-FU), this effect being strictly dependent on the timing of exposure to drug.…”