Pharmacokinetics and toxicity of mitomycin C in rodents, given alone, in combination, or after induction of microsomal drug metabolism

Validation and use of microdialysis for determination of pharmacokinetic properties of the chemotherapeutic agent mitomycin C - an experimental study

BACKGROUND

Mitomycin C is a chemotherapeutic agent used in the treatment of peritoneal surface malignancies, administered as hyperthermic intraperitoneal chemotherapy after cytoreductive surgery. Pharmacokinetic studies have been based on analyses of blood, urine and abdominal perfusate, but actual tissue concentrations of the drug have never been determined. Microdialysis is an established method for continuous monitoring of low-molecular substances in tissues, and in the present study microdialysis of mitomycin C was studied in vitro and in vivo.

METHODS

Using in vitro microdialysis, relative recovery was determined when varying drug concentration, temperature and perfusion flow rate. In vivo microdialysis was performed in rats to verify long-term stability of relative recovery in four compartments (vein, peritoneum, extraperitoneal space and hind leg muscle). Subsequently, intravenous and intraperitoneal bolus infusion experiments were performed and pharmacokinetic parameters were calculated.

RESULTS

In vitro, compatibility of mitomycin C and microdialysis equipment was demonstrated, and relative recovery was stable over an adequate concentration range, moderately increased by raising medium temperature and increased when flow rate was reduced, all according to theory. In vivo, stable relative recovery was observed over seven hours. Mitomycin C exhibited fast and even distribution in rat tissues, and equal bioavailability was achieved by intravenous and intraperitoneal infusion. The half-life of mitomycin C calculated after intravenous infusion was 40 minutes.

CONCLUSIONS

Mitomycin C concentration can be reliable monitored in vivo using microdialysis, suggesting that this technique can be used in pharmacokinetic studies of this drug during hyperthermic intraperitoneal chemotherapy.

Variability in micronucleus induction with different mutagens applied to several species of fish

Fish are often used for screening genotoxicity of water. For such programs, a knowledge of the sensitivity to clastogens, spontaneous micronucleus frequency and cell cycle kinetics of the target tissue is necessary. To investigate the pattern of inter-specific sensitivity to micronucleus induction three species of fish, Tilapia rendalli, Oreochromis niloticus and Cyprinus carpio, were exposed to the clastogens bleomycin (BLM), cyclophosphamide (CP), 5-fluorouracil (5-FU), and mitomycin C (MMC). The binucleate/mononucleate ratio in peripheral erythrocytes exposed to cytochalasin B was also used to evaluate the time-dependent response of micronucleus formation during hematopoesis in the kidney and the micronucleus peak in peripheral erythrocytes. Micronucleus frequencies induced by CP were significantly greater than their respective controls for the three fish species throughout all treatment periods. During the whole evaluation period (30 days) CP was also the most effective clastogen. In general, until the 14th day of evaluation period T. rendalii was the most sensitive species to clastogens. No difference in micronucleus frequencies among species was observed in the 4th evaluation (at the 30th day). A micronucleus peak was observed at the 7th day after treatment. After the 14th day the frequencies were stabilized. The cytochalasin B experiment was carried out to demonstrate that micronuclei induced in the young kidney erythrocyte cells were detected in the circulating blood 2-4 days later.

Pharmacological determinants of the antitumour activity of mitomycin C

Recent investigations into bioreductive anticancer drugs have focused on profiling reductase enzymes and relating their expression to therapeutic activity in an approach referred to as enzyme directed drug development. However, few studies have attempted to validate this approach in vivo and even less is known about how the expression of reductases relates quantitatively and qualitatively to metabolic activation. In the present study, the antitumour activity, pharmacokinetics and metabolism of mitomycin C (MMC) has been determined in vivo in two murine adenocarcinomas of the colon, MAC 16 (high DT-diaphorase activity) and MAC 26 (low DT-diaphorase activity) after intra-tumoural injection of drug. Over a broad range of drug concentrations (50-250 microg), MAC 16 proved to be consistently the more sensitive tumour (e.g. 75 microg of MMC, T/C 11% for MAC 16 and 31% for MAC 26). Higher levels of parent drug (peak concentration 103 microg/tumour compared to 58 microg/tumour) were maintained over 45 min in MAC 16 after which time clearance was rapid from both tumours. Four metabolites were detected in both tumours characteristic of different pathways of metabolism. However, by far the major metabolite was 2,7-diaminomitosene (2,7-DM), an accurate indicator of metabolic activation of MMC. Despite higher reductase levels and greater sensitivity to the drug, there was 4-fold less production of 2,7-DM in MAC 16. These results indicate a lack of a simple relationship in vivo between reductase expression and metabolic activation and suggest factors other than pharmacological determinants being responsible for the chemosensitivity of the MAC tumours to MMC.

Differential effects of aneugens and clastogens on incidences of multinucleated cells and of micronucleate cells in Chinese hamster lung (V79) cell line in vitro

Two aneugens, vinblastine (0.025-0.4 microgram/ml) and colchicine (0.05-0.4 microgram/ml), and two clastogens, mitomycin C (0.05-0.4 microgram/ml) and cyclophosphamide (1-16 micrograms/ml) were applied respectively to the micronucleus test in Chinese hamster lung (V79) cells in vitro, and the frequency of multinucleated cells (Fmu) and that of micronucleate cells (Fmi) in each group were observed. The results showed that at relatively high concentrations, all four agents increased both Fmu and Fmi, but the ratios of Fmu to Fmi in groups of the two aneugens (average of 2.2, 2.8, respectively) were much (10-30 folds) higher than that in groups of the two clastogens (0.09, 0.20). The difference between aneugens and clastogens in the above ratio was much more remarkable than that in areas of micronuclei (only 1.6-2.5 folds for the latter). At relatively low concentrations, the two clastogens increased only Fmi (but not Fmu), while the two aneugens increased only Fmu (but not Fmi). This indicates that the induction of multinuclei by aneugens may be more sensitive than by clastogens, and the induction of micronuclei by clastogens may be more sensitive than by aneugens. So, it is possible for the ratio of Fmu to Fmi to become a simple and sensitive (though indirect) index for distinguishing aneugens from clastogens. Further studies with other mutagens and (or) other cell types will be needed to confirm the deduction. As no difference in frequency of polyploid cells was observed between control group and each treatment, the multinucleation does not seem related to endoreduplication of chromosomes.

An in vivo/in vitro method for assessing micronucleus and chromosome aberration induction in rat bone marrow and spleen. 2. Studies with chlorambucil and mitomycin C

An in vivo/in vitro system using rat bone marrow cells and spleen cells to assess micronucleus (MN) and structural chromosome aberrations (SCA) simultaneously (Moore et al., 1995) was further developed. In two separate experiments, two rats/dose/experiment were treated i.p. with 0, 5, 10 and 15 mg chlorambucil (CA)/kg or with mitomycin C (MMC) at 0, 1, 2, 4 mg/kg (experiment 1) or 0, 4, 6, and 8 mg/kg (experiment 2) and killed 6 h later. Cultures were then established in the presence of growth stimulants (interleukin-3 and granulocyte-macrophage colony stimulating factor for bone marrow; lipopolysaccharide and concanavalin A for spleen) and cytochalasin B, a cytokinesis inhibitor. Bone marrow cells were harvested 24 h after establishment of cultures, while spleen cells were harvested at 48 h. In addition, spleen cells were concurrently assayed for chromosome aberrations. With the MN endpoint, spleen cells appeared more sensitive than bone marrow cells to the effects of CA due both to a lower background and an increased response. For MMC, bone marrow cells exhibited both a higher background of MN and a greater numerical response than did spleen cells. However, on the basis of a fold-increase over control values, spleen cells were more sensitive than bone marrow cells. In general, the MN endpoint appeared more sensitive than the SCA in spleen cells after treatment with CA or MMC. Thus, the approach described here shows greater potential in detecting genotoxicity.

Conversion of mitomycin C to 2,7-diaminomitosene and 10-decarbamoyl 2,7-diaminomitosene in tumour tissue in vivo

The progress of mitomycin C (MMC) bioreduction was studied in vivo in the rat Sp 107 mammary carcinoma after intra-tumoural injection of either 100 micrograms or 1 mg. 2,7-Diaminomitosene (2,7-DM) was utilised as a primary bioreductive metabolite and 10-decarbamoyl 2,7-diaminomitosene (DC 2,7-DM) served as a secondary bioreductive metabolite, both of which were measured by high-performance liquid chromatography. 2,7-DM and DC 2,7-DM were produced rapidly, achieving close to their maximal concentrations at the earliest time point studied [5 min]. 2,7-DM was cleared rapidly from the tumour with apparent half-lives of 5 and 35 min after the low and high drug doses, respectively. DC 2,7-DM had a longer apparent half-life of 130 min at the higher dose but, as compared with 2,7-DM, was only a minor metabolite [the area under the curve (AUC) of 2,7-DM was 5.6-fold that of DC 2,7-DM]. At the lower drug dose, DC 2,7-DM was not detectable. Rapid formation and disappearance of bioreductive metabolites of MMC may account for the failure of previous studies to detect these products in vivo.

A comparative study of isolated liver perfusion versus hepatic artery infusion with mitomycin C in rats

Systemic toxicity is usually the dose-limiting factor in cancer chemotherapy. Regional chemotherapy is therefore an attractive strategy in the treatment of liver metastasis. Two ways of regional chemotherapy, hepatic artery infusion (HAI) and isolated liver perfusion (ILP), were compared investigating the difference in toxicity with tissue and biofluid concentrations of mitomycin C (MMC). In wistar derived WAG rats the maximally tolerated dose of mitomycin C via HAI was 1.2 mg kg-1. Body weight measurements after HAI with doses higher than 1.2 mg kg-1 suggest both an acute and delayed toxic effect of mitomycin C since the time weight curves were triphasic: a rapid weight loss, a steady state and a second fall in weight phase. These rats died due to systemic toxicity. ILP with 4.8 mg kg-1 was associated with no signs of systemic toxicity and only transient mild hepatotoxicity. ILP with 6.0 mg kg-1 was fatal mainly due to hepatic toxicity. The four times higher maximally tolerated dose in ILP resulted in a 4-5 times higher peak concentration of mitomycin C in liver tissue, while the plasma concentration remained significantly lower than in the HAI treated rats. In the tumour tissue a 500% higher concentration of mitomycin C was measured in the ILP with 4.8 mg kg-1 than in HAI with 1.2 mg kg-1 treated rats. We demonstrated that when mitomycin C was administered by ILP a 400% higher dose could be safely administered and resulted in a five times higher tumour tissue concentration. In view of the steep dose-response curve of this alkylating agent this opens new perspectives for the treatment of liver metastasis.

The difference in pharmacokinetics of mitomycin C, given either as a single agent or as a part of combination chemotherapy

In a previous report it was suggested that the total body clearance of mitomycin C (MMC) was different after single agent treatment compared to combination chemotherapy. This suggestion was based on recalculations to one dose level. In the present study a fixed dose of 10 mg/m2 was used. Seven patients on single agent MMC and eight on combination chemotherapy were studied. Terminal half-life varied from 25 to 78 mm, volume of distribution from 7 to 73 l/m2, total body clearance from 11 to 56 l/h per m2, and area under the plasma concentration-time curve (AUC) from 177 to 933 micrograms/h per l. Total body clearance was significantly higher and AUC significantly lower in patients on combination chemotherapy. The cause of this difference was not investigated.