In vitro and in vivo antitumoral activity of alkylphosphonates

Hexadecylphosphocholine is a new antitumour agent with a highly selective activity in chemically induced mammary tumours. It was suggested, that hexadecylphosphocholine is a pro-drug, cleavable by phospholipases C and/or D, creating hexadecanol or hexadecylphosphate as the active principle. To test this hypothesis, the antineoplastic activity of three alkylphosphonates, cleavable either by phospholipase C or D, are compared with those of the parent compound, hexadecylphosphocholine. Cell culture experiments, in which radiolabelled alkylphosphonates were incubated with a neoplastic cell line, showed no metabolism even after 3 days of incubation. In in vivo experiments with dimethylbenzanthracene-induced rat mammary carcinomas, all three alkylphosphonates showed antineoplastic activity, although none of them reached the high activity of hexadecylphosphocholine. These results indicate that the antitumoral activity of alkylphosphocholines and alkyl lysophosphatidylcholines is due to direct toxicity and not dependent on metabolism by phospholipases C or D or related enzymes.

Distribution of hexadecylphosphocholine and octadecyl-methyl-glycero-3-phosphocholine in rat tissues during steady-state treatment

The distribution of the alkylphosphocholine hexadecylphosphocholine (He-PC) and the (alkyl)lysophospholipid 1-0-octadecyl-2-0-methyl-rac-glycero-3-phosphocholine (ET18-OCH3) was analyzed in rats. The compounds were given orally at a daily dose of 75 mumol/kg body weight. After 6, 11, and 18 days, three rats in each treatment group were killed and the drug concentration in various tissues and fluids was determined. With the exception of the kidney (He-PC) and brain (He-PC and ET18-OCH3), steady-state levels of the drugs could be achieved in all organs investigated and in serum. Maximal concentrations of He-PC were found in the kidney, adrenal glands, and spleen, whereas the highest concentrations of ET18-OCH3 were detected in the adrenal glands, spleen, and small intestine. The concentrations of He-PC exceeded those of ET18-OCH3 in most tissues by a factor of about 2-25. Since samples of urine and feces did not contain detectable amounts of the compounds, the absorption of both lipid analogues was assumed to be complete. The total amount of He-PC recovered after 6, 11, and 18 days was 15%, 12%, and 6%, respectively, and that of ET18-OCH3 was 1.3%, 0.8%, and 0.3%, respectively. This indicates that the bioavailability of He-PC and ET18-OCH3 is not controlled by differences in the uptake of the two drugs, but by differences in their metabolism. The results could explain the differing efficacy of these two compounds in their antitumor action in animal models.

Alkylphosphocholines: influence of structural variation on biodistribution at antineoplastically active concentrations

Hexadecylphosphocholine (HPC) and octadecylphosphocholine (OPC) show very potent antitumor activity against autochthonous methylnitrosourea-induced mammary carcinomas in rats. The longer-chain and unsaturated homologue erucylphosphocholine (EPC) forms lamellar structures rather than micelles, but nonetheless exhibits antineoplastic activity. Methylnitrosourea was used in the present study to induce autochthonous mammary carcinomas in virgin Sprague-Dawley rats. At 6 and 11 days following oral therapy, the biodistribution of HPC, OPC and EPC was analyzed in the serum, tumor, liver, kidney, lung, small intestine, brain and spleen of rats by high-performance thin-layer chromatography. In contrast to the almost identical tumor response noted, the distribution of the three homologues differed markedly. The serum levels of 50 nmol/ml obtained for OPC and EPC were much lower than the value of 120 nmol/ml measured for HPC. Nevertheless, the quite different serum levels resulted in similar tumor concentrations of about 200 nmol/g for all three of the compounds. Whereas HPC preferably accumulated in the kidney (1 mumol/g), OPC was found at increased concentrations (400 nmol/g) in the spleen, kidney and lung. In spite of the high daily dose of 120 mumol/kg EPC as compared with 51 mumol/kg HPC or OPC, EPC concentrations (100-200 nmol/g) were low in most tissues. High EPC concentrations were found in the small intestine (628 nmol/g). Values of 170 nmol/g were found for HPC and OPC in the brain, whereas the EPC concentration was 120 nmol/g. Obviously, structural modifications in the alkyl chain strongly influence the distribution pattern of alkylphosphocholines in animals. Since EPC yielded the highest tissue-to-serum concentration ratio in tumor tissue (5.1) and the lowest levels in other organs, we conclude that EPC is the most promising candidate for drug development in cancer therapy.

Hexadecylphosphocholine: preclinical and the first clinical results of a new antitumor drug

Dose-response studies on cytotoxic alkyl lysophospholipids with various chemical structures revealed that a long alkyl chain and a polar group are essential for antitumor activity. The combination of both the long alkyl chain and a phosphocholine group thus results in alkyl phosphocholines. Preclinical studies with hexadecylphosphocholine (He-PC) as a representative compound indicate distinct antineoplastic activity on leukemia cells of human origin. He-PC is highly effective in inhibiting the growth of chemically induced rat mammary carcinomas. Even more striking is the fact that a high percentage of the tumors regressed completely. In a clinical phase I trial on breast cancer patients with local recurrences, topically applied He-PC resulted in regression of skin metastases. A phase II trial for topical treatment and a phase I trial for orally applied He-PC have been initiated to further evaluate the antitumoral activity of this new compound.

Hexadecylphosphocholine: determination of serum concentrations in rats

A sensitive and quantitative determination of the concentration of hexadecylphosphocholine in serum is described. After HPLC separation, the concentration of hexadecylphosphocholine is determined by phosphate analysis. According to this method, the half-life of hexadecylphosphocholine in serum rats is about 96 h. A steady-state serum concentration of 110 microM is reached after 2 weeks of daily treatment with 10 mg/kg hexadecylphosphocholine. The described method has general application for other compounds with similar structures. For instance, serum levels of alkyllysophosphocholines such as 1-0-octadecyl-2-0-methyl- racglycero-3-phosphocholine can be determined using this method.

Distribution and metabolism of hexadecylphosphocholine in mice

Distribution and metabolic fate of radiolabeled hexadecylphosphocholine (He-PC) has been studied in mice. It is demonstrated that He-PC is well-absorbed from the intestinal tract, intravenous (IV) and oral administration lead to similar distributions throughout the body, the highest accumulation of radioactivity occurs in liver, lung and kidney, and the metabolic products are radioactive choline, phosphocholine and 1,2-diacylphosphatidylcholine. The occurrence of these metabolites indicates that phospholipases C and D may be involved in He-PC breakdown.