N-methylformamide: antitumour activity and metabolism in mice

Gas chromatography–mass spectrometry (GC–MS) analysis of ethyl acetate root bark extract of Strychnos innocua (Delile)

Background

Majority of phytochemicals have been known to bear valuable therapeutic activities such as insecticidal, antibacterial, antifungal, anticonstipative, spasmolytic, antiplasmodial and antioxidant activities. Strychnos innocua is straight-stemmed tree belonging to the family Loganiaceae and can grow up to 18 m tall. The plant is used for various pharmacological purposes. The aim of this study was to determine the chemical composition of the ethyl acetate extract of root bark of S. innocua using GC–MS analysis. The root bark was collected, air-dried and then crushed to powder. Standard extraction method (maceration) was used to obtain the ethyl acetate extract. The GC–MS was carried out on the extract using GC 7890B, MSD 5977A, Agilent Tech.

Results

Thirty-seven compounds were identified among which dibutyl benzene-1,2-dicarboxylate showed the highest peak area (31.03%) and monomethyl pimelate showed the lowest peak area (0.39%). The major compounds identified were cyclooctane (methoxymethoxy), 2,4-dimethylheptanedioic acid dimethyl ester, azelaic acid, 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester, dibutyl benzene-1,2-dicarboxylate, butyl 8-methylnonyl benzene-1,2-dicarboxylate, 9,15-octadecadienoic acid, methyl ester, cis-vaccenic acid, linoleic acid ethyl ester and ethyl oleate.

Conclusions

In conclusion, these phytoconstituents might be responsible for the medicinal efficacy of the root bark of S. innocua and can be used as a source therapeutic drug.

Enhancement of antitumor activity of the oxazaphosphorine cytostatic SUM-IAP by N-methylformamide

PURPOSE

SUM-IAP has been developed with the aim to optimize therapeutic response and minimize toxic reactions of oxazaphosphorine cytostatics. In therapy tests in mice, the primary tumor was successfully eradicated, but animals died due to formation of lethal metastases. We supposed that high activities of SUM-IAP detoxifying enzymes caused metastasis formation in the liver. Therefore, therapy tests with SUM-IAP in combination with cisplatin and N-methylformamide (NMF), which were not detoxified in the liver, were carried out.

METHOD

Antitumor activity was assayed in female CD2F1 mice with advanced subcutaneously growing P388 mice leukemia cells.

RESULT

The results of the therapy tests with SUM-IAP plus cisplatin were as expected: No formation of metastases and long-time survival of more than 100 days were observed; however, the toxicity was increased as measured by decrease in body weight and the number in leukocytes. The results of the tests in combination with NMF were surprising: Applying only half the dose of SUM-IAP used in the experiments with cisplatin, no metastases were found and long-time survivors did not show signs of additional toxicity.

CONCLUSION

NMF strongly enhances the antitumor activity of the oxazaphosphorine cytostatic SUM-IAP in mice with subcutaneously growing P388 mice leukemia cells by an unknown mechanism of action.

Metabolism and hepatotoxicity of N,N-dimethylformamide, N-hydroxymethyl-N-methylformamide, and N-methylformamide in the rat

The metabolism and hepatotoxicity of N,N-dimethylformamide (DMF) and two of its metabolites, N-hydroxymethyl-N-methylformamide (HMMF) and N-methylformamide (NMF) were evaluated over a 4-day period in rats. DMF toxicity was dose dependent and delayed toxicity after the administration of a high DMF dose (13.7 mmol/kg) in comparison to a lower dose (4.1 mmol/kg) was observed. Treatment of rats with 13.7 mmol/kg DMF, HMMF, or NMF showed i) that DMF is more toxic than HMMF or NMF, and ii) that hepatotoxicity occurs later for DMF than for HMMF or NMF. Analysis of serum and urine samples demonstrated that DMF is first metabolized to HMMF, which is then partially converted to NMF. After HMMF administration, NMF was found both in serum and in urine. The time course of DMF and HMMF toxicity in relation to NMF formation fitted the hypothesis that the hepatotoxicity of DMF and HMMF is mediated via NMF. The degree of hepatotoxicity after HMMF and NMF treatment is similar. However, the degree of DMF hepatotoxicity is much higher than in the case of NMF or HMMF. The role of NMF as an obligatory intermediate in DMF and HMMF hepatotoxicity is discussed.

Cytoskeleton-dependent surface blebbing induced by the polar solvent N-methylformamide

In vivo and in vitro studies performed on the polar solvent N-methylformamide (NMF), as well as on its association with chemotherapeutic agents or X rays, have clearly demonstrated that this compound is capable of inducing changes in biological characteristics of tumor cells, e.g., cell differentiation. However, the mechanism of action of NMF is far from being elucidated. Hence, in order to better clarify such a mechanism an in vitro study was carried out by using mouse fibroblasts in primary culture (MEF) and human melanoma cultured cells (M14). Results obtained by immunocytochemical and ultrastructural methods with doses of NMF ranging from 0.1 to 7% are reported here. As a general rule, a different sensitivity (in terms of cytopathologic changes induced by NMF) was found between the cell types considered. In fact, melanoma cells appeared to be highly susceptible to the action of the drug, undergoing severe morphological modifications represented mainly by a reversible dose and time-dependent cell rounding and surface blebbing. In contrast, NMF-induced injury in MEF cells was characterized mainly by a simple retraction of the cell body. A cytochemical analysis of the expression of certain membrane antigens (e.g., glycoproteins, epidermal growth factor receptor, B2 microglobulin) in NMF-treated M14 cells undergoing blebbing was also carried out. A randomly distributed labeling of such molecules was observed. Accordingly, freeze-fracturing electron microscopic analysis also displayed a random distribution of intramembrane particles over the plasma membrane. When subcellular changes induced by the drug were investigated, a remarkable modification of cytoskeletal components was detected in both cell types. In particular, cross-linked actin microfilament bundles were easily observed in NMF-exposed MEF cells. Finally, when different experimental conditions which perturb calcium ion homeostasis or restore protein thiol group reduced state were analyzed, a noticeable impairment of the blebbing phenomenon was observed. Thus, a target effect of NMF on the microfilament system, probably leading, in turn, to several subcellular changes and cell surface blebbing, can be hypothesized. Such a cytoskeletal element-dependent cytopathology appears to be related to changes of the oxidized state of such molecules as well as to calcium ion perturbations.

Different effects of sequential combinations of N-methylformamide with 5-fluorouracil on human colon carcinoma cells growing in nude mice

The effects of the combination of N-methylformamide (NMF) with 5-fluorouracil (5-FU) on tumor growth and morphological features of human colon carcinoma cells (HT29) implanted in nude mice were assessed. Both agents were administered i.p. at tolerable doses: 5-FU at 19 mg/kg for 5 days and NMF at 200 mg/kg for 12 days. Four main schedules were tested: 5-FU alone, NMF alone, NMF followed by 5-FU and 5-FU followed by NMF. The last sequence was the most effective, as compared with the other treatment regimens. In particular, the 5-FU----NMF combination induced a tumor inhibition of about 75% at the end of the treatments (17th day) versus an inhibition of 23%-43% in the other schedules. Morphological observations, carried out by light and electron microscopy, indicated a possible relationship between the presence of structural changes and tumor growth inhibition. The results of this study renew interest in the use of NMF in sequential combination confirming sequence as a critical factor for the optimal combination of NMF and 5-FU.

Importance of cell cycle perturbations on the effectiveness of N-methylformamide and anti-neoplastic drugs in combination

The effect of N-methylformamide (NMF) in combination with Adriamycin (ADM) and cis-diamminedichloroplatinum (DDP) on the cell survival and cell cycle kinetics of two human tumour lines was assessed: HT29 colon carcinoma and M14 melanoma cells were exposed to ADM and DDP alone or in combination with a non-cytotoxic dose of NMF, according to different schedules. The results demonstrate that NMF exposure sensitized both tumour cell lines to the lethal activity of ADM and DDP; however, reverse sequences had to be applied to reach an increase in the lethal activity of the two different drugs. The ADM-NMF combination determined a powerful decrease in the surviving fraction of the two cell lines when ADM was given as the first agent (ADM----NMF), while the reverse sequence did not increase the ADM cytotoxic effect. With respect to the DDP-NMF association, the sequence which accounted for a greater sensitizing effect was NMF administration followed by DDP treatment (NMF----DDP). This work demonstrates the importance of timing in combined treatments which involve NMF. A delay in cell proliferation elicited by NMF exposure could be responsible for the effectiveness of the combined treatment.

N-methylformamide affects spontaneous metastases of 3LL lines and increases natural killer activity of tumor-bearing mice

The antitumor activity of the polar solvent N-methylformamide (NMF) was evaluated on three lines derived from the Lewis lung carcinoma (3LL), endowed with different metastatic potential. Two administration schedules were tested, these being repeated regimens of NMF (200 mg/kg per dose) for 12 consecutive days, starting 24 h or 6-10 days after tumor implantation (early or late treatment, respectively). The results of the present work can be summarized as follows: (1) NMF regimens did not greatly affect tumor growth behavior of 3LL lines; conversely, they markedly influenced their spontaneous colonizing ability in the lungs, either by delaying early metastatic spread or by reducing the number and size of pulmonary metastases already implanted. (2) A significant increase of NK cell activity during and after early treatment with NMF was observed in the more-metastasizing lines, thus suggesting the possibility of an immunomodulating effect of NMF.

Assessment of N-methylformamide (NMF) administered orally on a three times weekly schedule: a phase I study

This phase I study was conducted to reevaluate the dose-limiting toxicities, maximum tolerated (MTD) and recommended phase II doses of oral NMF administered on a three times weekly schedule for 4 out of every 6 weeks. This schedule was based on the observation that prolonged administration of NMF was associated with the most efficacious antitumor activity in preclinical studies. Phase II trials that employed a starting dose of 800 mg/m2, determined in a previous phase I trial, were suspended because of frequent and severe toxicities. In the current study, a symptom complex characterized by nausea, vomiting, and malaise was the dose-limiting toxicity of oral NMF administered on this schedule. Other toxicities included hepatic enzyme elevations, mild myelosuppression, and worsening of preexistent toxic peripheral neuropathies. Of interest, three patients who were asymptomatic prior to treatment, rapidly developed symptoms of increased intracranial pressure after starting NMF; and, computerized tomographic brain scans revealed metastatic tumors with significant peritumoral edema. NMF was well tolerated at 600 mg/m2, however, an abrupt increase in toxicity resulted when the dose was increased to 700 mg/m2. Although NMF peak plasma concentrations (Cmax) and areas under the plasma disappearance curves (AUC) differed between the 600 and 700 mg/m2 dose levels, these differences were not striking, and similar NMF plasma concentrations and exposures were well tolerated during intravenous trials. Based on this study, the recommended phase II dose for oral NMF administered three times weekly for 4 of 6 weeks was 600 mg/m2.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences between rodents and humans in the metabolic toxification of N,N-dimethylformamide

The widely used industrial solvent N,N-dimethylformamide (DMF) causes liver damage in occupationally exposed persons and is suspected of involvement in the generation of certain occupational malignancies. Here the extent of the biotransformation of DMF to three urinary metabolites has been compared in humans and rodents. The metabolites, which were quantified by gas chromatography (GC) are N-(hydroxymethyl)-N-methylformamide (HMMF), which yielded N-methylformamide on GC analysis, a species which decomposed to formamide on GC analysis, and N-acetyl-S-(N-methylcarbamoyl) cysteine (AMCC), measured after derivatization with ethanol to give ethyl N-methylcarbamate. Ten volunteers who absorbed between 28 and 60 mumol/kg DMF during an 8-hr exposure to DMF in the air at 60 mg/m3 excreted in the urine within 72 hr between 16.1 and 48.7% of the dose as HMMF, between 8.3 and 23.9% as formamide, and between 9.7 and 22.8% as AMCC. AMCC, together with HMMF, was also detected in the urine of workers after occupational exposure to DMF. The portion of the dose (0.1, 0.7, or 7.0 mmol/kg given ip) which was metabolized in mice, rats, or hamsters to HMMF varied between 8.4 and 47.3% of the dose; between 7.9 and 37.5% were excreted as formamide and only between 1.1 and 5.2%, as AMCC. The results suggest that there is a quantitative difference between the metabolic pathway of DMF to AMCC in humans and rodents. It is argued that the hepatotoxic potential of DMF may be linked to the extent of its metabolic conversion to AMCC.

Cytotoxicity and metabolism of the hepatotoxin N-methylformamide and related formamides in mouse hepatocytes

Some N-alkylformamides such as N-methylformamide (NMF) possess hepatotoxic properties in vivo. To study the mechanism of this toxicity, suspensions of mouse hepatocytes were tested as an in vitro model system suitable for the study of the relationship between (i) the toxic potential of formamides, (ii) their metabolism to N-alkylcarbamoylating species, and (iii) their ability to deplete hepatic glutathione pools. The effects of NMF were compared with those of its analogs N-ethylformamide (NEF), N,N-dimethylformamide (DMF), formamide (F), N-methylacetamide (NMA), and N-methyldeuteroformamide ([2H]NMF). Only NEF and [2H]NMF share with NMF the ability to cause liver damage in vivo in mice. Hepatocellular toxicity was determined by measuring LDH leakage into the extracellular medium; metabolism to N-alkylcarbamoylating species was measured by GLC after derivatization with propanol to form propyl N-alkylcarbamate; glutathione concentrations were determined spectrophotometrically. Of the formamide analogs studied, only NMF and NEF caused cytotoxicity, being apparently equipotent. NMF, NEF, and [2H]NMF gave rise to the formation of detectable levels of N-alkylcarbamoylating metabolites and depleted glutathione pools. Toxicity, metabolism, and glutathione depletion were dependent on NMF concentration. [2H]NMF was markedly less cytotoxic than NMF, yielding only 35% of the amount of N-methylcarbamoylating metabolite compared to NMF and caused less depletion of glutathione than did NMF. These results parallel closely the in vivo hepatotoxic potential of NMF and its analogs, their metabolism to urinary S-(N-alkylcarbamoyl)mercapturates and their ability to deplete hepatic glutathione in mice. The results provide support for the contention that metabolism is involved with formamide-induced hepatotoxicity and suggest that suspensions of isolated mouse hepatocytes are an appropriate in vitro model for the further study of the mechanism by which formamides cause toxicity.

Comparative hepatotoxicity and metabolism of N-methylformamide in rats and mice

N-methylformamide (NMF) produced dose-dependent zone 3 haemorrhagic necrosis in mice; the threshold dose was 100-200 mg/kg. In rats a dose of 1000 mg/kg caused hepatic damage in some animals and slight elevations of plasma transaminases. A species difference in susceptibility to NMF-induced hepatotoxicity is clearly indicated. NMF depleted liver non-protein sulphydryl (NPSH) in a dose-dependent manner in mice, but not in rats. Depletion of liver glutathione by buthionine sulphoximine or diethylmaleate potentiated the hepatotoxicity of NMF in mice. [14C]-methyl NMF was metabolised by mice and rats and a number of urinary metabolites including an N-acetylcysteine conjugate, methylamine and N-hydroxymethylformamide were detected. There were no qualitative differences in the metabolites between rats and mice but mice metabolised NMF much faster and more extensively than rats.

Antitumor and antimetastatic activity of the differentiating agent N-methylformamide in murine tumor systems

N-Methylformamide (NMF), a cell-differentiating agent, was assessed for its antitumor activity against a fibrosarcoma (FSA), a hepatocarcinoma (HCA-I) and a mammary carcinoma (MCA-K), syngeneic to C3Hf/Kam mice. Tumors were grown as solitary tumors in the leg or as artificial or spontaneous micrometastases in the lung. NMF, at a dose of 300 mg/kg, was administered i.p. daily for 6 to 18 days. NMF slowed the growth of FSA and HCA-I tumors and totally inhibited the growth of the MCA-K tumor. However, the effect was transient; tumors resumed their pretreatment growth rate upon cessation of the treatment. Histologically, MCA-K tumors treated with NMF (300 mg/kg daily for six days) underwent considerable cell depopulation and reduction in mitotic activity. The number of artificial metastases, as well as the incidence and the number of spontaneous metastases, were markedly reduced by NMF. This resulted in a prolongation of the survival of mice that had artificial metastases of MCA-K tumor. The in vitro clonogenicity of MCA-K, but not of FSA or HCA-I cells, was reduced. However, in vivo reduction of MCA-K cell clonogenicity was minimal, if any. Thus, NMF is effective in restricting the growth of both solitary tumors and metastases, but the degree of response is highly dependent on tumor type.

N-methyl antitumour agents. A distinct class of anticancer drugs?

This article reviews the structure-activity characteristics, mode of action, pharmacokinetics and clinical utility of a group of chemically dissimilar antitumour agents which have as a common structural feature the N-methyl moiety. The importance of this feature is shown by the fact that molecules without a substituent on the nitrogen or compounds with N-alkyl groups other than methyl are usually inactive in experimental systems. This observation is supported by structure-activity studies with N-alkyl derivatives of s-triazines, triazenes, formamides, hydrazines and nitrosoureas. Representatives of these structural types which have found clinical application are, respectively, hexamethylmelamine, dacarbazine, N-methylformamide, procarbazine and streptozotocin. Mode of action studies have shown that dacarbazine, procarbazine and streptozotocin can give rise to species capable of methylating nucleic acid. This may be the lesion which produces antitumour activity. The mechanism of action of N-methylmelamines and N-methylformamide remains unclear. There is good evidence that, with the exception of N-methylnitrosoureas, host metabolism is prerequisite for activity with these agents. Although not pronounced, the clinical activity of N-methyl antitumour agents is useful, particularly as activity is not associated with severe haematological toxicity. Furthermore, responses may be observed in patients resistant to bifunctional alkylating agents. It is concluded that the drugs reviewed herein show a degree of coincidence in terms of their biological properties which may warrant a common classification. The term N-methyl antitumour agent is proposed.

Alkylformamides as inducers of tumour cell differentiation--a mini-review

The induction of terminal differentiation in tumour cells represents a possible therapeutic strategy for treating cancer. The alkylformamides are 1 group of experimental compounds which have been shown to induce terminal differentiation in human HL-60 leukemia and murine Friend erythroleukemia cells in vitro. Their mechanism of action is unknown. Dimethylformamide has been used as a model inducer in carcinoma and fibroblastic models. Analysis of the relationship between structure and inducing activity of the alkylformamides in vitro reveals that no specificity of structure exists and that their properties as inducers of terminal differentiation extend to related compounds, e.g. the alkylacetamides and alkylureas. This is in contrast to the marked specificity of N-methylformamide (NMF) as an in vivo antitumour agent. The potency of these compounds as inducers of differentiation is predictable and correlated with their molecular weight. High concentrations of NMF are required to induce differentiation in vitro and these concentrations are not achievable in vivo. However, while NMF is unlikely to be a useful inducer in vivo many of its higher MW analogues are very much more potent as inducers in vitro and yet no more toxic (to the host) in vivo. Some of these (e.g. tetramethylurea or 1,3-dimethylurea) may be capable of achieving inducing concentrations in vivo.

The effects of N-methylformamide on artificial and spontaneous metastases from a murine hepatocarcinoma

The effects of the differentiation-inducing polar solvent N-methylformamide (NMF) on artificially induced and spontaneous metastases from a murine hepatocarcinoma (HCA-1) in C3Hf/Kam mice were investigated. Exposure of HCA-1 cells in vitro for 6 days to 1.0% or 1.25% NMF resulted in an increase in the number of lung nodules formed in mice when these cells were injected into their tail veins. This in vitro NMF exposure increased cell volume and induced only a slight amount of cytotoxicity. Administration of NMF to mice 1 day before i.v. tumour cell inoculation resulted in a dose-dependent increase in the number of lung nodules formed, beginning at an NMF dose of 600 mg kg-1. NMF caused a similar magnitude of metastasis enhancement in immunosuppressed mice. However, when the maximum dose tested (1,800 mg kg-1) was administered as 6 daily fractions of 300 mg kg-1 each, no increase in artificial metastases was detected. Administration of NMF to mice one day after i.v. tumour cell injection resulted in a dose-dependent decrease in the number of lung nodules. In mice bearing 5-6 mm HCA-1 leg tumours, treatment with 6 daily fractions of NMF (300 mg kg-1 each) significantly reduced the number of spontaneous pulmonary metastases, yet had very little effect on the growth of the primary tumour. These data suggest that, in a clinically relevant treatment setting, NMF can reduce metastasis formation.

Hepatotoxicity of N-methylformamide in mice--II. Covalent binding of metabolites of [14C]-labelled N-methylformamide to hepatic proteins

Incubation of the hepatotoxin N-methylformamide (NMF) labelled either in the methyl group (OHCNH14CH3) or the formyl group (OH14CNHCH3) with mouse hepatic microsomes in the presence of NADPH, but not in its absence, led to covalent binding of metabolites to microsomal proteins. When [14C]NMF was injected into BALB/c mice radioactivity was found to be associated with liver and, to a much lesser extent, with kidney proteins. Association of radioactivity derived from OHCNH14CH3 with hepatic proteins was higher in BALB/c mice than in CBA/CA mice and in these it was higher than in BDF1 mice. Association of label derived from either isotopomer was significantly reduced but not abolished by pretreatment of mice with cycloheximide suggesting both covalent binding and metabolic incorporation of NMF metabolites. Depletion of hepatic glutathione by pretreatment of mice with buthionine sulfoximine or diethyl maleate prior to administration of OH14CNHCH3 enhanced the association of label with hepatic proteins measured 1 hr after drug injection. Covalent binding of [14C]NMF to hepatic microsomes in vitro was abolished in the presence of glutathione. It is argued that the generation of the toxic lesion and the association of NMF metabolites with hepatic proteins may be causally related even though certain mechanistic and enzymatic details of this link remain obscure.

Hepatotoxicity of N-methylformamide in mice--I. Relationship to glutathione status

In order to investigate the link between hepatotoxicity caused by N-methylformamide (NMF) and its ability to deplete hepatic glutathione experiments were conducted in three strains of mouse which differ in their susceptibility towards NMF-induced liver damage. NMF toxicity was measured by changes in plasma levels of sorbitol dehydrogenase and alanine and aspartate transaminases. In BALB/c mice, the most susceptible strain, a hepatotoxic dose of NMF (200 mg/kg) caused a depletion of hepatic glutathione to 21% of control levels 2 hr after drug administration. In CBA/CA and BDF1 mice the same dose of NMF depleted glutathione to 53% of control levels and did not cause hepatotoxicity. In BALB/c mice depletion of hepatic glutathione by pretreatment with buthionine sulfoximine decreased the hepatotoxic dose threshold of NMF from 150 mg/kg to 100 mg/kg. Conversely, pretreatment of mice with cysteine or N-acetylcysteine protected against both glutathione depletion and NMF-induced hepatotoxicity. The results are in accordance with the suggestion that the hepatotoxicity of NMF is associated with its metabolism to an intermediate which reacts with glutathione.

The influence of sodium ascorbate, menadione sodium bisulfite or pyridoxal hydrochloride on the toxic and antineoplastic action of N-methylformamide in P 388 leukemia or M 5076 sarcoma in mice

The toxicity of daily subcutaneously applied 500 mg/kg N-methylformamide (NMF) during a period of 8 days in female CD-mice was ameliorated when 100 mg/kg sodium ascorbate, 60 mg/kg menadione bisulfite or 80 mg/kg pyridoxal hydrochloride were applied simultaneously. The comparison of the daily s.c. application of 360 mg/kg NMF with the intermittent s.c. injection of 720 mg/kg NMF with an interval of 48 h in P 388 leukemia showed that the daily application of NMF induced an increase of life span of 82% whereas the intermittent schedule effected a 142% increase of life span. The simultaneous combination of 360 mg/kg NMF with 60 mg/kg sodium ascorbate applied daily caused a 133% increase of life span and the simultaneous combination of 360 mg/kg NMF with 30 mg/kg menadione sodium bisulfite lead to a 126% increase of life span. The combined daily s.c. application of 360 mg/kg NMF with 30 mg/kg pyridoxal hydrochloride induced only a minimal difference compared to the daily application of 360 mg/kg NMF alone. The combination of 720 mg/kg NMF with 120 mg/kg sodium ascorbate applied in intervals of 48 h showed a 164% increase of life span. In advanced M 5076 sarcoma the daily s.c. application of 360 mg/kg NMF effected a 82% increase of life span and the combination of 360 mg/kg NMF with 60 mg/kg sodium ascorbate effected a 135% increase of life span.

Phase II trial of N-methylformamide in advanced head and neck cancer

Eighteen patients with advanced epidermoid carcinoma of the head and neck were entered into a phase II trial of N-Methylformamide (NMF), 800 mg/M2 IV daily for 5 days every 4 weeks. Seventeen patients had received prior radiation therapy and 11 were previously treated with chemotherapy. No complete or partial responses were observed. The major toxicity was gastrointestinal. Fifty percent of patients experienced nausea and vomiting or reversible hepatotoxicity with greater than a 3-fold elevation of liver enzymes. Mild reversible myelosuppression occurred in 2 patients. NMF in this dose and schedule was not a useful agent to treat recurrent epidermoid carcinoma of the head and neck.

Modification of tumor and normal tissue radioresponse in mice by N-methylformamide

The effects of the differentiation-inducing agent N-methylformamide (NMF) on the in vivo response of the murine tumor FSA and its pulmonary metastases to ionizing radiation were investigated. In addition, the radioresponse of acutely responding normal tissues was determined in mice receiving systemic NMF. A dosage of 300 mg/kg administered for 8 days had little effect on the FSA tumor growth, yet enhanced the growth inhibitory actions of ionizing radiation with dose enhancement factors ranging from 1.5 to 1.7. Administration of NMF also enhanced the radiation response of FSA micrometastases. The response to irradiation of hematopoietic tissue, jejunum, and testes in mice receiving NMF was also investigated. NMF administered before or before and after radiation enhanced the formation of endogenous spleen colonies, yet did not influence the LD50/30 for radiation. Jejunal crypt cell survival after radiation was slightly increased in mice receiving NMF, but the survival of spermatogonia after radiation was not affected. These data indicate that NMF administration results in an increase in the radiosensitivity of the FSA tumor and its metastases with no concomitant increase in the radiation response of the normal tissue tested. Thus, at least in this model system, a therapeutic gain is achieved through the combination of NMF and ionizing radiation.

Potentiation of in vitro cytotoxic effects of misonidazole on human colon tumor cells by the differentiation-inducing agent N-methylformamide

Human colon tumor cells (clone A) were studied in vitro with regard to modification of dose-dependent cytotoxicity to misonidazole (MISO) treatment by pre-exposure growth in medium containing the differentiation-inducing agent N-methylformamide (NMF). Cells were grown as exponential cultures and were exposed for 2 passages to 170 mM NMF before exposure to graded doses of MISO (0-100 mM, 3 hours at 37 degrees C, oxic or hypoxic). Both oxic and hypoxic cells could be sensitized to MISO cell killing. Using the 10% level of survival for comparison, the calculated MISO doses (mM) were: 105, 37, 50, and 10 for oxic control cells, hypoxic control cells, oxic-NMF treated cells, and hypoxic-NMF treated cells, respectively. Therefore, for NMF treated oxic cells, cell killing was increased by a factor of about 2.1, while for NMF treated hypoxic cells, cell killing increased by a factor of about 3.7. These data indicate that NMF treatment, while potentiating effects on both oxic and hypoxic cells, appears to have selectivity towards hypoxic cells. NMF may therefore have use in combined modality radiation therapy of solid tumors with electron-affinic radiosensitizers.

Enhanced X ray sensitivity of human colon tumor cells by combination of N-methylformamide with chemotherapeutic agents

The responses of human colon tumor cells (clone A) to graded doses of x-irradiation were studied in combination with conventional chemotherapeutic drugs (bleomycin and 5-fluorouracil) after induction of commitment to differentiation by chronic exposure to N-methylformamide (NMF). NMF treated cells show increased radiation sensitivity, particularly in the low dose region of the survival curve. When doses of bleomycin (Bleo) and 5-fluorouracil (5-FU) were used that were subtoxic, both agents enhanced the cytotoxicity of x-irradiation by factors of about 1.25 and 1.10, respectively (at the 10% level of survival), and little sequence dependence was seen. However, in NMF treated cells, the combination of these drugs produced enhancement of X ray killing by factors of about 1.6 (x + bleo), 2.5 (bleo + x), 1.4 (x + 5-FU), and 1.6 (5-FU + x). Drug exposures were for 1 hr duration at 37 degrees C; 0.05 microgram/ml for Bleo, and 20 micrograms/ml for 5-FU. Since the X ray dose enhancement factor for NMF alone was about 1.3, the increased toxicity seen is probably additive in nature for the NMF + 5-FU + x experiments, but more than additive for the NMF + Bleo + x experiments. Also, complete removal of the shoulder was seen in the NMF + Bleo + X ray experiments. These data indicate that the use of differentiation-inducing agents in combination with other cytotoxic therapies might be important in yielding major decreases in the neoplastic cell burden, while avoiding the major morbidity seen in aggressive cancer therapy.

N-methylformamide-mediated enhancement of in vitro tumor cell chemosensitivity

The effects of the differentiation-inducing polar solvent N-methylformamide (NMF) on the in vitro response of murine hepatocarcinoma (HCa-1) cells to 1,3-bis(2-chloroethyl)-1-nitrosourea, cis-diamminedichloroplatinum (II), and melphalan were investigated using the sister chromatid exchange (SCE) and cell survival assays. When cells were exposed to 1.25% NMF, cell culture doubling time increased from 12 to 43 h and cell volume increased from 940 microns 3 to 1440 microns 3. Growth of HCa-1 cells in NMF for 96 h before drug treatment enhanced the SCEs induced by each of the three chemotherapeutic agents. For each drug, maximum enhancement occurred after 72 h of NMF pretreatment, and the enhancement was eliminated 48 h after NMF was removed. Pretreatment with 1.25% NMF for 96 h also enhanced the cell kill induced by each drug. NMF exposure modified primarily the low-dose shoulder region of each drug cell survival curve. The data indicate that NMF is an effective chemosensitizing agent for HCa-1 cells in vitro and suggest that NMF may provide clinical benefits when administered in combination with antineoplastic drugs.

The effects of diethyldithiocarbamate on the hepatotoxic action and antitumor activity of N-methylformamide in mice

The oral administration of diethyldithiocarbamate (DTC) prevented hepatic necrosis induced by N-methylformamide (NMF) in ddY-strain mice, in more susceptible BALB/c mice and in diethylmaleate-treated mice in which NMP-hepatotoxicity was potentiated, as evidenced by suppression of increases of plasma glutamic pyruvic transaminase activity and liver calcium content or by histological observations. Early depletion of liver glutathione following NMF administration was also prevented by DTC. DTC markedly delayed the in vivo metabolism of NMF as indicated by a prolonged retention of plasma and liver NMF levels and an enhancement of urinary excretion of NMF. These observations support a bioactivation mechanism for NMF hepatotoxicity, and the hepatoprotective action of DTC may be due to an inhibition of the metabolic activation of NMF. Hepatotoxic manifestations after repeated administration of NMF also tended to be ameliorated by simultaneous treatment with DTC. Cotreatment with DTC, however, decreased the antitumor activity of NMF against Ehrlich ascites tumors, and Sarcoma 180. This also implies the involvement of a bioactivation mechanism in the antitumor action of NMF, but further studies are necessary to confirm this point. The possible therapeutic value of DTC as a hepatoprotector may be diminished by the suppression of the antitumor activity of NMF.

Identification by proton NMR of N-(hydroxymethyl)-N-methylformamide as the major urinary metabolite of N,N-dimethylformamide in mice

Urine samples from mice which had received N,N-dimethylformamide were investigated by high field 1H-NMR spectroscopy. The most prominent signals in the N-CH3 region had chemical shifts identical with those of N,N-dimethylformamide (delta 2.85, 3.01) and N-(hydroxymethyl)-N-methylformamide (delta 2.91, 3.05). Resonances downfield of delta 7.5 (from formyl protons) also coincided with those of the reference formamides. When [14C]methyl-labelled N,N-dimethylformamide was injected and urine samples investigated by radio thin layer chromatography, the major area of radioactivity corresponded to the Rf of N-(hydroxymethyl)-N-methylformamide. Dimethylamine and methylamine were found to be minor metabolites of N,N-dimethylformamide.

Biological effects of acetamide, formamide, and their monomethyl and dimethyl derivatives

The industrial use of certain acetamides and formamides (particularly DMAC and DMF) for their solvent properties has resulted in rather extensive examination of their biological properties. Both DMAC and DMF are rapidly absorbed through biological membranes and are metabolized by demethylation first to monomethyl derivatives and then to the parent acetamide or formamide. Relatively high single doses to various species following oral, dermal, i.p., i.v., or inhalation exposures generally are required to produce mortality. The liver is the primary target following acute high level exposure, but massive doses can also produce damage to other organs and tissues. Repeated sublethal treatment by various routes also shows the liver to be the target organ with the degree of damage being proportional to the amount absorbed. With MMF, the potential usefulness as a cancer chemotherapeutic agent needs to be measured against the hepatotoxic effects produced in man. Acetamides and formamides are generally inactive in mutagenicity tests. Mammalian test systems do not appear to be genetically sensitive and DMF has been recommended for use as the vehicle in microbial assays designed to test for genetic activity of hard-to-dissolve chemicals. Embryotoxicity can be demonstrated at high doses; doses which generally show toxicity to the maternal animals. Structural abnormalities in sensitive species such as the rabbit are produced following exposure at near-lethal levels. The spectrum of abnormalities seen is broad and fails to show any time or site specificity in terms of developing organs/organ systems. Inhalation exposures to DMAC and DMF at levels producing some maternal toxicity in rats have produced no teratogenic response and only slight evidence of embryotoxicity. Long-term feeding of relatively high levels of acetamide produces liver cancer in rats. DMAC and DMF appear to be noncarcinogenic. The environmental toxicity of these chemicals is low. Liver damage can be produced by overexposure to these chemicals in man. Airborne concentrations need to be controlled and care should be taken to avoid excessive liquid contact as the chemicals are absorbed through the skin. A relationship exists between the amount of DMAC or DMF absorbed and the amount of MMAC or MMF excreted in the urine so that biomonitoring of the urinary metabolites can indicate situations in which total exposures, both dermal and inhalation, are excessive. An interaction between DMF and ethanol occurs such that signs, including severe facial flushing, appear when DMF-exposed individuals consume alcoholic beverages.

Enhancement of in vitro chemotherapeutic activity by dimethylsulfoxide

The effects of the differentiation-inducing polar solvent dimethylsulfoxide (DMSO) on the in vitro response of murine hepatocarcinoma cells to cisplatinum, BCNU, and melphalan were investigated using the sister chromatid exchange (SCE) and cell survival assays. Growth of cells in medium containing 2 per cent DMSO enhanced drug-induced SCEs and cell kill. In order for the enhancement to occur, cells had to be exposed to DMSO for at least 48 h prior to drug treatment. The presence of DMSO during drug treatment did not affect cell response to the three chemotherapeutic agents. The enhancement of chemosensitivity was eliminated within 24 h of DMSO removal. These data suggest that the differentiation-inducing polar solvents may provide antineoplastic benefits when administered in combination with standard chemotherapeutic agents.

Investigation of the mechanism of hepatotoxicity of N-methylformamide in mice: effects on calcium sequestration in hepatic microsomes and mitochondria and on hepatic plasma membrane potential

N-Methylformamide is an antitumour drug with hepatotoxic properties. Three potential targets for hepatocellular toxic lesions caused by N-methylformamide were investigated: the mitochondrial and microsomal Ca2+ pumps and the functional integrity of the plasma membrane. The administration of N-methylformamide to mice caused a dramatic decrease in the ability of the liver mitochondria to sequester [45Ca2+]. This effect was dose-dependent and was not caused by dimethylformamide, N-hydroxymethylformamide or formamide. The microsomal Ca2+ pump was not affected by N-methylformamide. Incubations of isolated mitochondria with N-methylformamide for 1 hr also led to the inhibition of the Ca2+ sequestration. Incubation of isolated mouse hepatocytes with N-methylformamide did not cause changes in plasma membrane potential as measured using the lipophilic cation triphenylmethylphosphonium. Of the three targets studied, the mitochondrial Ca2+ pump may be the one through which N-methylformamide triggers the events leading ultimately to hepatic necrosis.

In vivo metabolism of dimethylformamide and relationship to toxicity in the male rat

After in vivo administration of dimethylformamide (DMF) to male rats, about 50% of the dose is excreted in urine as N-hydroxymethyl-N-methylformamide (DMF-OH) and about 4% as N-methylformamide (NMF). NMF is not a product of DMF-OH biotransformation but is directly formed from DMF. Comparison of the acute toxicity of DMF, DMF-OH and NMF shows that NMF is more toxic than DMF-OH, which is itself more toxic than DMF. This study explains the different toxicity profile of DMF and NMF which until recently was believed to represent the main metabolite of DMF.

Reversal by L-cysteine of the growth inhibitory and glutathione-depleting effects of N-methylformamide and N,N-dimethylformamide

N-Methylformamide and N,N-dimethylformamide, which can induce differentiation in selected malignant cell lines, are known to increase doubling times, inhibit clonigenicity in agar, and to effect responses against particular human colon carcinomas in vivo. At concentrations which inhibit growth and clonigenicity, N-methylformamide (170 mM) and N,N-dimethylformamide (103 mM) deplete total intracellular glutathione levels of DLD-1 Clone A human colon carcinoma cells in a dose and time dependent manner. In the presence of 0.5 mM 1-cysteine, both the growth and glutathione levels of polar-solvent treated DLD-1 Clone A cells are restored. 1-Cysteine also reverses the inhibition of clonigenicity mediated by NMF. The mechanism of action of N-methylformamide and N,N-dimethylformamide against this cell line, at least in vitro, is therefore related to its effects on cysteine/glutathione metabolism. Furthermore, this evidence suggests that glutathione plays a key role in regulating the growth of these cells.

An investigation of the mechanism of hepatotoxicity of the antitumour agent N-methylformamide in mice

N-Methylformamide (NMF) has been reported to cause liver damage in animals and man. This hepatotoxicity was characterized in BALB/c mice by the release of liver enzymes into the plasma and by histopathological examination of livers after single and repeated administration of NMF. Whereas plasma levels of sorbitol dehydrogenase were elevated dramatically 24 hr after 400 mg/kg given as a single dose, the glutathione content of the livers was not different from controls even after repeated administration. Liver damage was apparent on gross inspection and was defined as periacinar necrosis on histopathology. A dose of 100 mg/kg did not cause damage even after repeated injections on five consecutive days. The hypothesis that NMF is metabolized to a chemically reactive species was tested. Incubation of mouse hepatocytes with 7 mM NMF for 80 min produced a decrease in intracellular glutathione. Exposure of hepatocytes to NMF for 240 min led to the production of breakdown products of lipid peroxides at levels significantly above controls. However, incubation of microsomes or mitochondria with NMF and NADPH did not lead to raised levels of lipid peroxides. The effects described were specific to NMF as incubation of N,N-dimethylformamide, N-hydroxymethylformamide or formamide with hepatocytes did not result in glutathione depletion or increased lipid peroxidation. NMF undergoes extensive metabolism in vivo and the results indicate that NMF forms a chemically reactive metabolite, even though incubation of the drug with liver fractions or hepatocytes did not lead to metabolites at levels which were analytically identifiable.

Study on in vivo and in vitro metabolism of dimethylformamide in male and female rats

The study of dimethylformamide (DMF) metabolism by rat tissues in vitro indicates that formaldehyde is not a metabolic product as previously reported [1]. Furthermore, no other monocarbon derivative (CO, CH3OH, HCOOH, CH4) was detected when DMF was incubated with a fortified liver preparation. One metabolic product is methylhydroxymethylformamide (DMF-OH) measured as N-methylformamide (NMF) due to the breakdown of the hydroxymethyl group during gas chromatography. It was usually believed that the main metabolite excreted in urine following administration of DMF to male and female rats was NMF. The results of this study indicate that DMF-OH constitutes the main metabolite in vivo. A quantitatively less important urinary metabolite, hydroxymethylformamide (NMF-OH), is determined as formamide (F) by gas chromatography. In male and female rats, partial hepatectomy reduces markedly the in vivo biotransformation of DMF. Following administration of DMF or NMF, the total amount of metabolites (DMF-OH and/or NMF-OH) excreted in urine is identical in both sexes, but female rats excrete more unchanged parent compound than male rats. The rate of NMF-OH excretion in urine following high doses of DMF supports the hypothesis that DMF may inhibit its own biotransformation.

The formation and metabolism of N-hydroxymethyl compounds--IV. Cytotoxicity and antitumour activity of N-hydroxymethylformamide, a putative metabolite of N-methylformamide (NSC 3051)

Experiments were conducted to test the hypothesis that N-hydroxymethylformamide (HMF) is the active metabolite of the antitumour agent N-methylformamide (NMF). In an in vitro bioassay against the TLX5 lymphoma HMF was more cytotoxic than NMF; this cytotoxicity was abolished by preincubating the TLX5 cells with semicarbazide, a formaldehyde trapping agent. Similarly, the inhibition of incorporation of radiolabelled thymidine, uridine, formate and leucine into TLX5 cells elicited by HMF was eliminated by preincubation of the cells with semicarbazide. HMF is considerably less toxic to tumour-bearing BDF1 mice than NMF and, unlike NMF, does not reduce hepatic glutathione levels in vivo. HMF has no inhibitory activity against the TLX5 lymphoma or the Sarcoma 180 in mice in vivo and only marginal activity against the M5076 reticulum cell sarcoma; these tumours are highly sensitive to NMF. However, like NMF, HMF inhibits growth of the human mammary tumour MX-1 implanted in the subrenal capsule of mice.

The formation and metabolism of N-hydroxymethyl compounds--III. The metabolic conversion of N-methyl and N,N,-dimethylbenzamides to N-hydroxymethyl compounds

The stability of metabolically-generated N-(hydroxymethyl) compounds was investigated using a series of N-methylbenzamides as model substrates. N-(Hydroxymethyl)-benzamide was characterized as a major metabolite of N-methylbenzamide in vitro, and was also identified as a urinary metabolite of N-methylbenzamide. N-(Hydroxymethyl) compounds were also found as metabolites of 4-chloro-N-methylbenzamide and 4-t-butyl-N-methylbenzamide in vitro. Thus substitution in the 4-position of the phenyl ring of derivatives of N-(hydroxymethyl)-benzamide did not affect their stability sufficiently to cause degradation to formaldehyde under the conditions used. N-(Hydroxymethyl)-N-methylbenzamide was identified as a metabolite of N,N-dimethylbenzamide in vitro. However, N-(hydroxymethyl)-N-methylbenzamide was less stable than N-(hydroxymethyl)-benzamide under alkaline conditions. Furthermore, N-(hydroxymethyl)-N-methylbenzamide, unlike N-(hydroxymethyl)-benzamide and its 4-substituted derivatives, was positive in the colorimetric assay for formaldehyde, presumably because of its degradation to produce formaldehyde. Thus substitution on the nitrogen atom which bears the methyl group in N-methylbenzamide markedly affected the stability of the N-methylol produced during oxidative metabolism. N-Formylbenzamide was identified as a metabolite of N-methylbenzamide in suspensions of mouse hepatocytes and also in vivo. The mechanism for its production probably involves the generation of N-(hydroxymethyl)-benzamide.