Chloroacetaldehyde: mode of antitumor action of the ifosfamide metabolite

BACKGROUND

The ifosfamide metabolite chloroacetaldehyde had been made responsible for side effects only. We found in previous studies a strong cytotoxicity on human MX-1 tumor cells and xenografts in nude mice. Chloroacetaldehyde is supposed to act via alkylation or by inhibition of mitochondrial oxidative phosphorylation with decrease of ATP. The aim of this study was to further elucidate chloroacetaldehyde's mode of action.

METHODS

MX-1 breast carcinoma cells were measured for ATP-content after exposure to chloroacetaldehyde. Further, the effect of chloroacetaldehyde on DNA-synthesis and its potency of causing strand-breaks or cross-links were investigated by bromodeoxyuridine-incorporation, comet-assay and a DNA interstrand cross-linking-assay.

RESULTS

Chloroacetaldehyde in high concentrations induces a reduction of ATP-levels when anaerobic glycolysis is blocked by oxamate and reduces the bromodeoxyuridine-incorporation to 46.3% after 4 h when used in IC(50) concentrations (7.49 mumol/l). In addition we observed DNA single strand-breaks in MX-1 cells treated with chloroacetaldehyde visible in the Comet assay, but no DNA-cross-linking by comet assay and cross-linking assay.

CONCLUSION

In summary, our results show that chloroacetaldehyde influences the oxidative phosphorylation in mitochondria, however, this is observed only in high concentrations and is not of clinical relevance because the tumor cells regenerate ATP by anaerobic glycolysis. Nevertheless, chloroacetaldehyde causes DNA-strand-breaks and strong inhibition of DNA-synthesis.

Metabolism of ifosfamide to chloroacetaldehyde contributes to antitumor activity in vivo

Metabolic activation of ifosfamide (IFO) leads to the active 4-hydroxy-metabolite and to a substantial liberation of chloroacetaldehyde (CAA). CAA has been presumed responsible for side effects of IFO. We recently have shown cytotoxic effects of CAA against human tumor cells in vitro. The aim of this study was to demonstrate antitumor effects of CAA in vivo, and to compare its potency to 4-OH-IFO. Pharmacokinetics of IFO and metabolites were evaluated after infusion of 250 mg/kg IFO in mice. The area under the curve (AUC) for 4-hydroxyifosfamide (4-OH-IFO) and CAA were 138. 5 and 102.4 micromol. h/liter, respectively. To compare pharmacokinetics and antitumor effects, the mice received isolated infusion of 4-OH-IFO or CAA in equimolar doses to IFO. Administration of 4-OH-IFO yielded AUC values comparable with those obtained after administration of the parent drug. In contrast, infusion of isolated CAA via tail vein gave a low AUC value of 51.5 micromol. h/liter due to slow flow in the tail vein and rapid degradation. Administration of the parent drug gave highly cytotoxic intratumoral peak concentrations of 25 and 12 micromol/kg tumor weight for 4-OH-IFO and CAA in MX1 xenotransplanted nude mice. Both IFO and isolated 4-OH-IFO led to complete remissions. Administration of isolated CAA (75 mg/kg) delayed tumor growth significantly. The equitoxic dose of isolated 4-OH-IFO was 40 mg/kg. On a molar basis CAA was seven times less potent as 4-OH-IFO. However, on the basis of achieved AUC values, CAA seems to exhibit a similar antitumor activity to 4-OH-IFO.

[Subcutaneous manifestations of a centrocytic non-Hodgkin lymphoma at the injection site of a mistletoe preparation]

HISTORY AND CLINICAL FINDINGS

A 73-year-old man, first diagnosed as having centrocytic Non-Hodgkin lymphoma 5 years previously, presented with subcutaneous nodes of the abdominal wall at precisely the sites of previous regular injections of a mistletoe preparation. These nodes had first appeared 5 weeks after the first injection. Injections were stopped and he reported to the out-patient clinic. Except for the visible and easily nodes in the anterior wall no other subcutaneous nodes were palpated. Prominent cervical lymphomas and swelling of the epicranial aponeurosis and lower lip had, according to the patient, been present for some time.

INVESTIGATIONS

There was a T-lymphocytopenia, lactate dehydrogenase activity was raised to 255 U/l. The subcutaneous nodes in the anterior abdominal wall were also demonstrated by ultrasound. Computed tomography showed them as having the density of connective tissue and being up to 5 cm in diameter. The excised nodes histologically revealed to be infiltrations by the centrocytic lymphoma.

TREATMENT AND COURSE

Once the mistletoe injections had been discontinued no further subcutaneous infiltrates were seen despite the progression of the lymphoma. Six weeks later the patient died of bilateral pneumonia.

CONCLUSION

There are pointers that high concentrations of mistletoe preparations subcutaneously injected can have a growth-promoting action on cells of a centrocytic lymphoma. As part of a leukaemic "wash-out", these cells reach the subcutaneous tissue. This proliferative stimulus may have been mediated by a high local concentration of interleukin-6 liberated from the skin by mistletoe lectins.