Complexation in formulation of parenteral solutions: solubilization of the cytotoxic agent hexamethylmelamine by complexation with gentisic acid species

N-(Hydroxymethyl) melamines

1. The N-(hydroxymethyl) melamines are analogs of the antitumor agent hexamethylmelamine (HMM) which do not require bioactivation to exert their antitumor effects. 2. Trimelamol (N2,N4,N6-trihydroxymethyl-N2,N4,N6-trimethylmelamine; TM) was developed as a water-soluble antitumor agent for intravenous administration. 3. Phase I and II trials of TM showed promising activity versus platinum-refractory ovarian cancer, but unfortunately further clinical development was halted due to formulation difficulties. 4. Stable analogs of TM were synthesized in an effort to overcome this shortcoming and these were evaluated in a number of in vitro and in vivo studies. 5. While the stable analogs showed good in vitro cytotoxicity in tumor cell lines, only one analog, CB7646 [bis-N-(hydroxymethyl)trimethylmelamine], showed comparable in vivo antitumor activity to that seen for TM. 6. Both TM and CB7646 were curative in human ovarian and breast cancer xenograft models, including the HX110P ovarian cancer xenograft with acquired resistance to carboplatin. 7. As CB7646 possesses favorable formulation characteristics, relating to its superior stability over that for TM, it is currently being developed for phase I clinical trial. 8. The N-(hydroxymethyl) melamines are capable of overcoming many forms of drug resistance, based on data obtained in in vitro and in vivo studies, and thus show promise as agents in the treatment of heavily pretreated, refractive tumors.

Hexamethylmelamine: pharmacology and mechanism of action

Several conclusions can be drawn from a review of HMM preclinical and clinical pharmacology data. The drug is extensively metabolized by animals and by man. The drug is well absorbed following oral administration to animals, but oral bioavailability is low due to first pass metabolism. Based on limited human data and more complete animal data, absorption of HMM following oral administration may be quite high in man. We do not yet know the oral bioavailability of HMM in patients, but again based primarily on animal studies, oral bioavailability is most likely low and variable due to extensive first pass metabolism. Systemic exposure to HMM and demethylated metabolites following oral administration varies greatly from patient to patient and is sometimes quite low. Most patients are, however, exposed to a substantial fraction of the administered dose when determined by urinary recovery of the total dose (based on parent drug and metabolites or total radioactivity) or by the total plasma AUC of parent drug and all metabolites. Systemic exposure to HMM following intravenous administration is clearly greater and less variable than following oral administration. An unresolved question is whether the highly variable and often low systemic exposure after oral administration compromise antitumor activity when compared to intravenous administration. A key issue is whether or not one accepts the hypothesis that metabolism is a prerequisite for antitumor activity. The metabolic activation studies do not rule out other mechanisms of HMM antitumor activity. Modest activity of HMM was observed after prolonged exposure to cells which did not metabolize the drug. However, most of the accumulated data are consistent with the metabolic activation hypothesis. Certainly HMM has clinical activity when administered by mouth. If metabolism is required, then exposure to the total dose (parent drug and metabolites) could be of significance even when exposure to HMM is low, since every demethylated metabolite must have come ultimately from the initial HMM demethylation. We do not know whether the initial metabolic reaction (occurring in the liver rather than in the tumor) provides sufficient exposure of tumor to reactive species. Specifically, does the variable HMM plasma AUC seen after oral administration lead to variable delivery of potentially reactive species to tumor (by rapid breakdown and/or further metabolism of MPMM before it leaves the gut and/or liver) or are quantities of MPMM delivered to tumor comparable to those delivered following intravenous administration. The issue of rate of MPMM formation compared to rate of breakdown and ultimate delivery to tumor has been noted by Judson and Rutty.(ABSTRACT TRUNCATED AT 400 WORDS)

Hexamethylmelamine and hexamethylmelamine hydrochloride

Methods of analysis of the anticancer drug hexamethylmelamine, its physicochemical properties, its therapeutic uses and its fate in vivo upon oral administration, are described. The data are taken in part from the literature, in part from our own studies. The low solubility of hexamethylmelamine in water has prevented the parenteral administration of the drug to humans. The preparation of the water-soluble monohydrochloride of hexamethylmelamine, which may be suitable for this purpose, is reported, as well as its physicochemical characteristics and methods of analysis.

Determination of hexamethylmelamine and metabolites in plasma or serum by gas-liquid chromatography with a nitrogen-sensitive detector

A gas chromatographic method for the quantitative determination of hexamethylmelamine (HMM) and five of its metabolites in plasma (or serum) is described. After adjustment of the pH of the plasma sample to about 9.5, the compounds are extracted with chloroform containing 5% of isopropanol. Amyl alcohol is added to the extract, which is then evaporated until a small volume remains. An aliquot of this solution is injected into a gas chromatograph equipped with a nitrogen--phosphorus flame ionisation detector. Separation of the methylmelamines is achieved with a 10% Carbowax 20M--2% KOH column. By programming the oven temperature unnecessarily long retention times are avoided. Using 1 ml of plasma, concentrations as low as 5 ng/ml of HMM and its metabolites can be quantitated. The method has been applied to the determination of HMM and metabolites in plasma of patients who received oral doses of HMM.

Analogues of hexamethylmelamine. The anti-neoplastic activity of derivatives with enhanced water solubility

The preparation of some water soluble analogues of the tumour growth inhibitory hexamethylmelamine is described. The ultra-violet absorption characteristics, solubility and n-octanol/water partition coefficients of these new derivatives and some related compounds have been determined. Rates of demethylation by a liver microsomal preparation and anti-tumour assays against the ADJ/PC6A mouse plasma cell tumour and a human lung tumour xenograft are reported. Two of the derivatives, pentamethylmelamine and N2, N4, N6-trimethyl-N2, N4, N6-trimethylolmelamine, which have shown activity against the xenograft are potential candidates for clinical trials using the intravenous route of administration.