No abstract

A synthetic LDL (sLDL) has been prepared by combining a lipid microemulsion with amphipathic peptides containing the apoprotein B receptor domain. The biological properties of sLDL have been investigated using the U937 in vitro cell proliferation assay. sLDL exhibits a concentration dependent and saturable stimulation of U937 proliferation. By utilizing different amphipathic peptides, variable proliferation is achieved, indicating a specific interaction between sLDL and the U937 LDL receptor are possible. U937 proliferation is reduced by the addition of an anti-LDL receptor antibody, indicating that sLDL is assimilated via the LDL receptor pathway.The behavior of sLDL mimics that of native LDL, and this approach represents a viable technique for the production of an sLDL particle on a large scale for research and general application. -Baillie, G., M. D. Owens, and G. W. Halbert. A synthetic low density lipoprotein particle capable of supporting U937 proliferation in vitro.

Low density lipoprotein (LDL) is a normal plasma component, which is of interest in a number of research areas such as hypercholesterolaemia, drug targeting in cancer chemotherapy and as a lipid supplement in tissue culture systems. Currently, however, it can only be obtained by extraction from fresh plasma samples, which yields only small quantities. Synthetic LDL (sLDL) has been prepared using readily available lipid components coupled with a synthetic amphiphatic peptide molecule containing the apoprotein B receptor sequence. sLDL was capable of supporting the growth of Chinese Hamster Ovary (CHO) and fibroblast cells in serum-free culture media in a cholesterol-dependent manner that was related to the presence of the receptor peptide molecule. sLDL could be fluorescently labelled with 3,3'-dioctadecyloxalocarbocyanine perchlorate (DiO), and once labelled was assimilated by CHO and fibroblast cells in a time- and temperature-dependent manner that was dependent upon the presence of the receptor peptide. In addition, assimilation was reduced by an excess of unlabelled native LDL. The results indicated that the interaction of sLDL with CHO and fibroblast cells occurred via a receptor dependent system, most likely the LDL cellular receptor. sLDL is therefore a useful, easily obtained substitute for native LDL with potential applications in the areas of drug targeting to cells and serum-free tissue culture systems.

The s-triazine hexamethylmelamine (HMM) is perhaps the best known of the group of anti-tumour agents known as the methylmelamines. Despite its introduction into the clinic in a phase I trial some 30 years ago (Wilson and de la Garza, 1965), the role of HMM both in terms of its mechanism of action and as an anti-tumour agent has not been defined. As a single agent in advanced ovarian canccr, metastatic breast cancer, refractory lymphoma and metastatic small-cell lung cancer, HMM has been found to have significant activity comparable to that of classical alkylating agents. It has been employed in combination regimens, where an increased therapeutic effect has been demonstrated with cisplatin, doxorubicin and cyclophosphamide (HCAP) over cisplatin and cyclophosphamide therapy. However, clinical studies have indicated its dose-limiting toxicity to be gastrointestinal, involving nausea, vomiting, anorexia and diarrhoea (I-cgha el aL, 1976).The low aqueous solubility of HMM usually necessitates oral administration (p.0.). However, a formulation involving intralipid and HMM hydrochloride has been used for parenteral infusion (i.v.) in phase I clinical trial (Ames et al., 1990). Trimelamol (tris N-[ hydroxymethyl]trimethylmelamine; TM) was first synthesised in 1977 as a water-soluble derivative of IIMM, representing a third-generation analogue with potential advantages over the parent drug. As metabolism studies have indicated a requirement for HMM to be metabolised to cytotoxic N-( hydroxymrthyl) derivatives, TM, therefore, represents a bioactivated form of hexamethylmelamine. The importance of using such an analogue is highlighted by the ohservation of high levels of N-(hydroxymethyl) derivatives in HMMtreated mice but significantly lower levels in patients. In addition, a clinical study in ovarian cancer patients using HMM described wide interpatient variability in overall drug exposure ( A synthetic analogue programme has been set up in an effort to circumvent the aforementioned problems. A number of stabilised analogues have been made, including some tris N-( hydroxyme t hyl)-subst itu ted de rivat ivcs containing methyl groups replaced by electron-withdrawing substituents (Jarman et al., 1993). In addition, CB 7646, the bis N-(hydroxymethyl) derivative of TM, which possesses some important advantages over the parent compound, has been synthesised (Fig. 1).T M is typically prepared by the reaction of trimethylmelamine in concentrated aqueous formaldehyde, adjusted to pH 9.0. However, we now report that the reaction between 2,4,6-tris(niethylamino)-l,3,5-triazinc and dilute (3% w/v) aqueous formaldehyde in the presence of potassium carbonate afforded a mixture of mono-, his-and tris(hydroxymethy1)trimethyl melamines in which 2,4-his[(hydroxymcthyl)(methyl)-amino]-6-methylamino-1,3,5-triazinc, CB 7646, was the principal component. The concentration of formaldehyde was critical; when the reaction was conducted in 6% w/v formaldehyde under otherwise identical conditions, the product was TM of 97.5% purity.'To whom corr...