Curt Peterson

HYPOCHOLESTEROLAEMIA IN MALIGNANCY DUE TO ELEVATED LOW-DENSITY-LIPOPROTEIN-RECEPTOR ACTIVITY IN TUMOUR CELLS: EVIDENCE FROM STUDIES IN PATIENTS WITH LEUKAEMIA

59 patients with acute leukaemia were examined to see if hypocholesterolaemia, which is commonly found in acute leukaemia, was due to the high low-density-lipoprotein (LDL)-receptor activity of leukaemic cells. LDL-receptor activity was found to be inversely correlated with plasma-cholesterol concentration. Patients with both a high LDL-receptor activity per cell and a high white-blood-cell count had the lowest cholesterol concentrations. During chemotherapy, cholesterol levels rose concomitantly with the disappearance from the peripheral blood of leukaemic cells. Hypocholesterolaemia in leukaemia and other neoplastic disorders may be due to increased LDL-receptor activity in the malignant cells. This high uptake and degradation of LDL by malignant cells could be utilised to target neoplastic cells with LDL-bound chemotherapeutic agents.

Determination of daunorubicin and its main metabolites in plasma, urine and leukaemic cells in patients with acute myeloblastic leukaemia

The pharmacokinetics of daunorubicin were studied in 3 previously untreated patients with acute myeloblastic leukaemia by simultaneous monitoring of daunorubicin (DNR), daunorubicinol (DOL) and their aglycones in plasma, urine and leukaemic cells. The drug was given as an i.v. infusion in a dose of 1.5 mg/kg body wt. The plasma concentration of daunorubicin declined rapidly after the infusion. The concentration of daunorubicinol exceeded that of the parent compound only 5 min after the end of the infusion. Daunorubicin accumulated extensively in the leukaemic cells and reached concentrations there which exceeded the plasma concentration 400-4000 times. As compared to what was found in plasma, daunorubicinol appeared much slower in the leukaemic cells and the concentration ratio only reached 30-200. The concentration of aglycones was low in the leukaemic cells as well as in plasma. Only about 15% of the administered dose of daunorubicin could be recovered in the urine within 4 days, most of it as daunorubicinol. The results demonstrate that the plasma concentration of daunorubicin and its metabolites provides little information on the drug concentration in the leukaemic cells. Direct determinations of drug concentrations in the leukaemic cells might be of clinical value for optimization of the therapy in acute leukaemia.

Pharmacokinetic optimisation of anticancer therapy.

SummaryIt is obvious that there are great problems with pharmacokinetic individualisation of anti-cancer therapy. The strong relationship between dose intensity (total dose/unit time) and response revealed in clinical trials with some tumours provides a strong support for studies seeking relationships between the individual plasma pharmacokinetic profile and response to treatment. Unfortunately, studies that define a therapeutic window are sparse, and trials that prospectively test such models are even rarer. Thus, for most cancer drugs, it is not possible to give any definite advice on how to use pharmacokinetic determinations to establish individualised therapy, and there is therefore a definite need for such studies. It is important, however, that attempts to establish relationships between drug concentrations and therapeutic effects be founded on a sound theoretical base. When drugs, mainly antimetabolites, are extensively metabolised intracellularly and interact with intracellular processes about which there are data showing a strong interindividual heterogeneity, such data must be considered when designing pharmacokinetic investigations. Cytarabine and fluorouracil are good examples of this. The monitoring of intracellular drug/metabolite concentrations or of the direct biochemical events in the tumour cells seems to be a promising approach with such drugs. It also needs to be emphasised that pharmacokinetically guided individualisation cannot be achieved before a therapeutic window is established, i.e. a knowledge of the relationship between drug concentration and clinical effects. The investigators in this field accept a great responsibility when clinical studies are undertaken: a poorly designed study showing no benefit from pharmacokinetically guided individualisation can impair the possibilities of performing more adequate studies in the future.

Hypocholesterolemia in cancer patients may be caused by elevated LDL receptor activities in malignant cells

Several epidemiological studies indicate an inverse relation between plasma cholesterol and the occurrence of cancer. Since we in previous studies have found that certain malignant cell types have an elevated LDL receptor activity, the aim of the present study was to further explore the possibility that an elevated LDL consumption by tumor cells causes hypocholesterolemia. The plasma cholesterol concentrations in patients with acute leukemia were inversely correlated with the rate of receptor-mediated degradation of125I-LDL by the leukemic cells. During chemotherapy, the total plasma and the LDL cholesterol levels increased concomitantly with the reduction in the leukemic cell count in a patient whose leukemic cells exhibited a high rate at receptor-mediated degradation of125I-LDL. In certain patients with inoperable urinary bladder carcinoma, the plasma cholesterol concentration fell as the disease progressed. Studies in breast cancer patients indicate that the number of LDL receptors in the tumor tissue may have prognostic significance. The results are in agreement with the hypothesis that an elevated LDL receptor activity in malignant cells may lead to hypocholesterolemia.

A simple binding assay for the determination of low-density lipoprotein receptors in cell homogenates

A convenient binding assay has been developed for the determination of low-density lipoprotein (LDL) receptors in homogenates of cultured and freshly-isolated normal and malignant human cells. Cell homogenates were incubated with 125I-labeled LDL and the ligand bound to the homogenate particulates was separated from the unbound ligand by filtration. When the particulates of the homogenates were subsequently incubated with heparin, a fraction of the bound 125I-LDL was released. Previous studies on intact cells have shown that heparin exclusively releases LDL bound to its cell surface receptor. The heparin-sensitive binding of 125I-LDL to cell homogenate particulates represents LDL bound to its cell surface receptor as judged from the following criteria: (a) it was quantitatively similar to the heparin-sensitive binding of 125I-LDL to intact cells, (b) it showed a direct correlation to the receptor-mediated degradation of 125I-LDL by intact cells, (c) no heparin-sensitive binding could be detected in homogenates prepared from normal erythrocytes or from cultured fibroblasts from a patient with homozygous familial hypercholesterolemia (two types of cell lacking LDL receptors), (d) it was dependent on calcium and inhibited by EDTA, (e) it was susceptible to treatment with pronase, and (f) it was heat-labile. The assay developed should be of value in determining the number of LDL receptors in tissues, since it is far less time-consuming and requires less material than currently available methods.

LDL receptors in bovine tissues assayed as the heparin-sensitive binding of 125I-labeled LDL in homogenates: relation between liver LDL receptors and serum cholesterol in the fetus and post term.

The heparin-sensitive binding of 125I-labeled LDL in homogenates of bovine tissues was determined using a membrane filter assay. The binding fulfilled several criteria which have been established for the binding of LDL to its receptor, namely: saturability, dependence on Ca2+, sensitivity to proteolytic destruction and heat sensitivity. The adrenal cortex and the active corpus luteum exhibited the highest binding activity of the 22 different tissues assayed. Tissues from the central nervous system had low binding activity. Livers from fetal animals had higher binding than livers from young and adult animals and the binding of 125I-LDL to fetal liver homogenates showed an inverse correlation to the serum cholesterol levels, indicating that the LDL receptors in fetal liver may play a role in the regulation of the serum cholesterol level in the fetus during gestation. After birth, the binding of 125I-LDL to calf liver homogenates decreased to levels found in adult animals and this was paralleled by an increase of total serum cholesterol, suggesting that the rapid rise in serum cholesterol in mammals observed soon after birth may be caused by a decrease of the receptor-mediated catabolism of LDL in the liver.

Uptake of free and DNA-bound daunorubicin and doxorubicin into human leukemic cells

SummaryLeukemic cells from seven patients with acute nonlymphoblastic leukemia and granulocytes, and mononuclear cells from three healthy controls were isolated by centrifugation on metrozoate-dextran. The intracellular accumulation of both the free and DNA-bound forms of daunorubicin and doxorubicin was studied in vitro. The uptake of unbound daunorubicin was higher than that of doxorubicin. At drug concentrations of 1.75 μM and higher the uptake of the free drugs was greater than that of the bound forms, but at lower drug concentrations the uptake was about the same. This could at least partly be explained by a greater dissociation of the DNA-drug complexes at lower drug concentrations. The uptake into normal leukocytes was of the same order of magnitude as that into leukemic cells. There was a great interindividual variation in the accumulation of both free and DNA-bound drugs in the cells from leukemic patients. This variation might be of importance for the prediction of individual sensitivity to the different drugs.

Challenging Drug Resistance in Cancer Therapy: Review of the First Nordic Conference on Chemoresistance in Cancer Treatment, October 9th and 10th, 1997

The First Nordic Conference on Chemoresistance in Cancer Treatment was held in the Danish town of Helsingør on October 9th and 10th, 1997, under the auspices of the Nordic Cancer Chemoresistance Group (NCCG). The meeting focused on biochemical chemoresistance in a multidisciplinary approach. There were 19 oral and 15 poster presentations documenting recent advances in experimental and clinical research of drug transport mechanisms, DNA repair systems, detoxifying enzymes, drug target regulation, in vitro sensitivity tests, apoptosis inhibition, and strategies to circumvent chemoresistance. In the present paper we review the main issues that were addressed and discuss the findings with reference to the current literature in the field. The meeting demonstrated the plurality and the complexity of chemoresistance, which is a major obstacle to successful chemotherapy in cancer patients. The new insights to mechanisms of drug resistance and sensitization represent a useful basis for further development of strategies to circumvent chemoresistance in clinical practice.

Serum and tissue concentrations of doxorubicin after IV administration of doxorubicin or doxorubicin-DNA complex to patients with gastrointestinal cancer

SummaryBlood and tissue concentrations of doxorubicin (DOX) were assayed after an intraoperative IV test dose of either free DOX 10 mg or its DNA complex 10 mg to patients with gastrointestinal cancer. After administration of the free drug, blood DOX levels decreased in an at least biphasic way, while DOX-DNA gave higher blood concentrations, which decreased slowly with no clear inflexion point on the concentration-time curve within the first hour. Tissue concentrations of DOX did not differ significantly after the two forms of the drug, liver being the tissue with the highest levels, followed by lymph node metastases, tumor tissue, muscle, and normal intestinal mucosa. If skeletal muscle can be used as a substitute for myocardium, lower cardiotoxicity of DOX-DNA than of DOX is not likely to be due to a difference in tissue uptake and retention between the two forms of DOX.

Comparison of daunorubicin and daunorubicin-DNA complex in the treatment of acute nonlymphoblastic leukemia

SummarySixty consecutive patients, 15–60 years old, with ANLL were divided randomly into three groups for induction treatment with one of the following regimens: R1, daunorubicin (DNR) 1.5 mg/kg on day 1+ARA-C 2 mg/kg body weight on days 1–5; R2, DNR 1.5 mg/kg on days 1 and 2+ARA-C 2 mg/kg on days 4–8; R3, DNR-DNA complex 1.5 mg/kg on days 1 and 2+ARA-C 2 mg/kg on days 4–8. Maintenance treatment consisted of monthly courses of DNA 1.5 mg/kg (R1, R2) or DNR-DNA 1.5 mg/kg (R3) combined with ARA-C 1 mg/kg on days 1–5, alternating with thioguanine 2 mg/kg PO on days 1–5 combined with ARA-C 1 mg/kg IV on days 1–5. Fourteen patients of 20 went into complete remission with R1, 13 of 18 with R2, and 15 of 22 with R3. The overall remission frequency was 70% and there was no significant difference between the different groups. The median time in first remission and the median survival time were 300 and 510 days, respectively, with R1; 335 and 495 days with R2; and 295 and 677 days with R3. There was no statistically significant difference between the groups treated according to the different regimens concerning the time in first remission. Survival was slightly better with R3 than with R1. Treatment with the DNR-DNA complex caused less pronounced thrombocytopenia and fewer ‘minor’ cardiac abnormalities than treatment with free DNR in the same dosage schedule.