A new method for studying cell growth in suspension, and its use to show that indomethacin enhances cell killing by methotrexate

The effect of folate on the methotrexate/indomethacin interaction in a murine cancer cell line

1. The effect of folate on the interaction between methotrexate (a folate analogue) and indomethacin has been examined in murine NC carcinoma cells. 2. Conditioning of NC cells to a physiological (20 nM) folate concentration after culture in a high folate concentration increased the response to methotrexate. The sensitivity of these conditioned cells to methotrexate related inversely to the folate concentration. 3. At 20 nM and 2 microM folate, indomethacin 1 micrograms ml-1 potentiated the cytotoxicity of methotrexate 4 and 8 ng ml-1 (both P < 0.03). 4. When NC cells were incubated with [3H]-methotrexate at 20 nM and 2 microM folate, there was a trend for increased tritium accumulation with indomethacin 0.36 micrograms ml-1 (1 microM; P < 0.01). 5. We conclude that the folate concentration can affect the sensitivity of NC cells to methotrexate, although the degree of potentiation of cytotoxicity by indomethacin remains similar.

Interaction between methotrexate and indomethacin on a human normal haemopoietic cell line

1. The interaction between methotrexate and indomethacin has been examined, at a physiological folate concentration (20 nM), on a human normal lymphoblast-like cell line (RPMI 1788) in vitro. 2. Indomethacin (1 microgram ml-1) increased the reduction of lymphoblast growth caused by methotrexate (10-80 ng ml-1). 3. Indomethacin (0.1 and 1 microgram ml-1) potentiated the cytotoxicity of methotrexate (20 and 40 ng ml-1) after 4 days in culture. 4. Indomethacin (0.4 micrograms ml-1) reduced the accumulation of tritium in lymphoblasts incubated with [3H]-methotrexate after 30 min; therefore initial drug accumulation was not responsible for the potentiation seen after 4 days. 5. If indomethacin increases the killing of human cancer cells by methotrexate in vivo, with a smaller potentiation on lymphoblasts, this combination may be beneficial in treating human malignancy.

Effect of indomethacin on the pharmacokinetics of methotrexate in rabbits

The interaction between indomethacin (IND) and methotrexate (MTX) was investigated in rabbits. The study was designed so as to evaluate the effect of IND (1 mg h-1) during a continuous MTX infusion (1 x 2 mg kg-1) over 240 min. IND was injected i.v. at hourly intervals after a steady state MTX concentration had been established. Plasma MTX concentration before and after IND did not differ significantly (p greater than 0.05). The elimination half-life (t1/2 beta) calculated during the washout interval (mean +/- SD) was 47 x 4 +/- 21 x 5 min which is close to that calculated in a reference group of rabbits. This excludes the possibility of delayed elimination as responsible for this toxicity. The toxicity of this combination was confirmed despite the absence of significant pharmacokinetic changes. It is possible that the toxic interaction was caused by enhanced cytotoxic effect of MTX.

Changes in tissue fatty acid composition in murine malignancy and following anticancer therapy

We studied the mouse NC tumour, a subcutaneously transplanted adenocarcinoma originally of mammary origin. Measurements per g tissue were made of 17 fatty acids (FAs), the combined amounts of n-3, n-6, saturated, unsaturated, and total FAs, and of various FA ratios in the tumour, mammary tissue, spleen, liver and plasma. Compared with mammary tissue from normal mice, tumours of vehicle-treated controls had less of seven of the FAs and more of two FAs. Mice bearing the NC tumour often had changed (usually decreased) amounts of FAs in the 'normal' spleen, liver and plasma, but not in mammary tissue. Treatment with methotrexate (MTX) was studied alone and with indomethacin which can potentiate MTX cytotoxicity. Indomethacin 1.25 mg kg-1 (INDO) increased the amounts of 3/17 tumours FAs and the unsaturated FAs, but reduced 9/17 FAs, the saturated and the unsaturated FAs in 'normal' mammary tissue, and usually had no effect on the FAs of other tissues. MTX 2 or 4 mg kg-1 (MTX 2 or 4 mg) +/- INDO in general partly restored (increased) the amounts of tumour FAs, and reduced the saturated/unsaturated FA ratio. In the 'normal' spleen and plasma also, but not in the liver, MTX 2 mg generally somewhat restored the FA composition. However, as in the liver, the spleen 20:4 and 22:6 (which form prostaglandins and lipid peroxides) did not increase in the presence of INDO. With MTX 4 mg, some of the plasma and liver FAs decreased, in contrast to the tumour. There was generally no evidence of MTX potentiation by INDO. These results are discussed in relation to carcinogenesis, cachexia, and the response to treatment.

Methotrexate alters the fatty acid composition of NC adenocarcinoma cells in culture

The effects of methotrexate and indomethacin alone and in combination have been examined on the fatty acid (FA) composition of total cellular lipids in cultured NC adenocarcinoma cells. These studies show that methotrexate can alter the lipid content of cancer cells. Methotrexate 16 ng/ml incubated with NC cells for 2 days increased the content of various FAs. When used alone, indomethacin 1 microgram/ml or methotrexate 8 ng/ml had no significant effect, but in combination caused FA increases, usually to about the same extent as with the higher concentration of methotrexate alone. No FA changes were seen up to 3 h with these drug concentrations or with methotrexate up to 10 micrograms/ml alone or with INDO 1 microgram/ml. These effects may explain previous findings that indomethacin potentiates methotrexate, an interaction which may be important in cancer therapy.

The effect of nifedipine alone or combined with cytotoxic chemotherapy on the mouse NC carcinoma in-vitro and in-vivo

Effects of the calcium antagonist nifedipine on the response of the murine NC carcinoma has been examined alone and together with cytotoxic chemotherapy in-vitro and in-vivo. The cytotoxic drug combination of methotrexate and melphalan, or nifedipine alone (0.2-25 micrograms mL-1), caused a concentration-related reduction of NC cell growth in culture. At the lower concentrations, combination to the cytotoxic drugs with nifedipine resulted in an addition of the separate drug effects, but with drug concentrations that on their own approached maximal effectiveness the combined response was less than additive. NC tumours were excised from mice 14 days after inoculation s.c. with NC cells, weighed, and extracted for prostanoids. Mouse survival was determined up to day 121, and cancer spread was recorded postmortem. Nifedipine 1, 5 or 10 mg kg-1 had little or no effect on the tumour weight, tumour prostanoid content, metastasis to the lymph nodes or lungs, or on the increase of mouse longevity by the cytotoxic drugs.

The effects of dipyridamole and indomethacin on methotrexate cytotoxicity in LoVo human colon cancer cells

Dipyridamole and indomethacin were studied for their effects in the in-vitro response of LoVo colon cancer cells to methotrexate (MTX) using a dye elution method. Dipyridamole 0.5-5 micrograms mL-1 or indomethacin 1 microgram mL-1 alone had little or no effect on cell growth. The tumour cells were refractory to even high concentrations of MTX (2.5-10 micrograms mL-1) alone or with indomethacin 1 microgram mL-1. In contrast, dipyridamole 0.5-5 micrograms mL-1 sensitized the cells to MTX 5 micrograms mL-1 (their growth was reduced by 25 to 69%), possibly by inhibiting thymidine salvage.

Interactions between anticancer drugs and other clinically used pharmaceuticals. A review

Drug interactions are increasingly common, since clinical practice is getting more complex with the flood of new drugs. Simultaneously, the increased life expectancy of the population increases the number of individuals likely to receive multiple prescriptions. Cytotoxic drugs generally have a narrow therapeutic index, and are delivered at doses close to toxic levels. Consequently, a slight increase in biological activity caused by an interaction with other concomitantly administered drugs could be deleterious to the patient. Interactions between drugs can sometimes also be used in a positive way, i.e. to increase the therapeutic ratio and overcome drug resistance. Interactions between different cancer treatment modalities have attracted considerable interest. However, much less interest has been devoted to interactions between anticancer drugs and other pharmaceuticals. The purpose of this review is to summarize data about the interactions between anticancer drugs and other clinically used drugs with regard to effects on tumor and toxicity.

Studies on the mechanism by which indomethacin increases the anticancer effect of methotrexate

The effect of indomethacin on the response of the NC carcinoma to methotrexate has been examined in vivo and in vitro. Survival was prolonged in mice treated with indomethacin 1.25 mg kg-1 twice daily plus methotrexate 4 mg kg-1 daily, compared to mice given either drug alone or controls. Indomethacin 1 microgram ml-1 increased the killing of cultured NC cells by methotrexate. This was not due to displacement of methotrexate from binding sites on the serum proteins. Nor was it due (entirely) to inhibition of prostaglandin synthesis, since flurbiprofen did not mimic the effect. Inhibition of cyclic AMP phosphodiesterase seems unlikely to explain the effect of indomethacin since theophylline had little or no effect on NC cell killing by methotrexate. Indomethacin 1 microgram ml-1 increased the accumulation of tritium in NC cells incubated with [3H]-methotrexate. In contrast, with normal epithelial cells from human embryonic intestine, indomethacin 1 microgram ml-1 did not alter the cytotoxicity of methotrexate or the accumulation of tritium during incubation with [3H]-methotrexate. The beneficial interaction between indomethacin and methotrexate may have therapeutic potential in man.

Clinical and pharmacokinetic evidence of a life-threatening interaction between methotrexate and ketoprofen

Co-administration of ketoprofen was found in 4 of 118 cycles of high-dose methotrexate (MTX) analysed retrospectively in thirty-six patients. All 4 cycles were characterised by severe MTX toxicity, which was fatal in three cases. Simultaneous administration of ketoprofen was associated with prolonged and striking enhancement of serum MTX levels. There were no abnormalities in MTX kinetics or evidence of MTX toxicity when ketoprofen was given at least 12 h after completion of high-dose MTX infusion. The kidney may be the site of drug interaction. This high-risk association between MTX toxicity and ketoprofen may also apply to other non-steroidal anti-inflammatory drugs.