Chromatographic studies of mitomycin C degradation in albumin microspheres

Erythrocyte ghost cell-alkaline phosphatase: construction and characterization of a vesicular system for use in biomineralization studies

Alkaline phosphatase is required for the mineralization of bone and cartilage. This enzyme is localized in the matrix vesicle, which plays a role key in calcifying cartilage. In this paper we standardize a method to construction a resealed ghost cell-alkaline phosphatase system to mimic matrix vesicles and examine the kinetic behavior of the incorporated enzyme. Polidocanol-solubilized alkaline phosphatase, free of detergent, was incorporated into resealed ghost cells. This process was time-dependent and practically 50% of the enzyme was incorporated into the vesicles in 40 h of incubation, at 25 degrees C. Alkaline phosphatase-ghost cell systems were relatively homogeneous with diameters of about 300 nm and were more stable when stored at -20 degrees C. Alkaline phosphatase was completely released from the resealed ghost cell-system using only phospholipase C. These experiments confirm that the interaction between alkaline phosphatase and the lipid bilayer of resealed ghost cell is exclusively via glycosylphosphatidylinositol (GPI) anchor of the enzyme. An important point shown is that an enzyme bound to resealed ghost cell does not lose the ability to hydrolyze ATP, pyrophosphate and p-nitrophenyl phosphate (PNPP), but the presence of a ghost membrane, as a support of the enzyme, affects its kinetic properties. Moreover, calcium ions stimulate and phosphate ions inhibit the PNPPase activity of alkaline phosphatase present in resealed ghost cells.

Encapsulation of mitomycin C in albumin microspheres markedly alters pharmacokinetics, drug quinone reduction in tumour tissue and antitumour activity. Implications for the drugs' in vivo mechanism of action

Pharmacokinetics and metabolism of mitomycin C (MMC) have been studied in NMRI mice bearing MAC 16 colon adenocarcinoma after direct intratumoural injection of either 500 micrograms free MMC or the same dose incorporated in albumin microspheres. Microspheres produced a tumour pharmacokinetic profile of steady state drug levels, avoiding the much higher early peak (20.5 micrograms/tumour vs 98.9 micrograms/tumour) and lower trough of free MMC, and reducing significantly the levels of drug reaching the systemic circulation (AUC 1.8 micrograms/mL x hr for microspheres vs 6.8 micrograms/mL x hr for free drug). 2,7-Diaminomitosene (2,7-DM), a key intermediate in MMC quinone bioreduction, was used as an indicator of drug metabolic activation in tumour tissue. Peak levels were 10-fold higher (11.2 micrograms/tumour vs 1.1 micrograms/tumour) and area under the curve 5-fold higher after free drug. Even taking into account differences in tumour pharmacokinetic profiles of the parent drug, microspheres actively inhibited 2,7-DM formation 3-fold. However, the microspheres generated a completely different pattern of drug metabolism where four previously uncharacterized mitosane metabolites and elevated levels of cis and trans 1-hydroxy 2,7-diaminomitosene were detected. Despite similar parent drug exposure in tumours, free drug was significantly more active (P < 0.05, Student's t-test) against MAC 16. These results suggest that formation of 2,7-DM correlates more closely with antitumour activity than sustained parent drug levels or appearance of other key metabolites. Potentially, they provide the first direct evidence for an in vivo mechanism of action dependent on bioreductive activation and formation of 2,7-DM.

Incorporation and release of chemically intact mitomycin C from albumin microspheres: a high performance liquid chromatography evaluation

Preparation of mitomycin C-loaded human serum albumin (HSA) microspheres using a new technique that avoids the use of heat denaturation, which is known chemically to degrade incorporated drug, is described. This method is based on cross-linking of protein by glutaraldehyde (2.2%) during emulsification (W/O) at room temperature. The resultant particles have a mean (s.d.) diameter of 16.9 (0.34) microns (50% weight average), contain mean (s.d.) 1.15 (0.05%) mitomycin C (MMC) (w/w, n = 17) and maintain sustained release of drug over 20 h. High performance liquid chromatography (HPLC) with diode array detection was used to study the chemical integrity of the drug. Two classes of decomposition products were evaluated: chemical degradation products and drug/nucleophile covalent adducts. The HPLC separation was validated by a number of standards of proposed degradation products. To examine incorporated drug, a complete microsphere system was solubilized with 0.4% trypsin for 24 h, while to examine released drug, microspheres were immobilized on a flow-through glass wool column and fractions were collected. No evidence of significant chemical degradation or covalent coupling to protein was detected in microsphere digests. Two candidate decomposition products, representing approximately 10% of drug released from microspheres (assuming similar molar extinction coefficients to MMC), were identified in column fractions. One of these products appeared to be a covalent adduct, the other possibly an isomeric form of intact MMC. Thus, MMC is predominantly incorporated into and released (90%) chemically intact from HSA microspheres prepared by the technique described.

Chromatographic analysis of anticancer drugs

The present review on the methods for the analysis of anticancer drugs should be seen as an addition to the excellent work of Eksborg and Ehrsson published half a decade ago in this journal (Vol. 340, p.31). The style and format have been followed closely, with the focus again on chromatographic techniques. We felt it important to add a list of compound (group) structures as a service to the reader. Methods have been reviewed for alkylating agents, platinum compounds, antitumour antibiotics, antimetabolites, alkaloids, suramin, 1-hydroxy-3-amino-propylidene-1,1-bisphosphonate and tamoxifen.