EVALUATION OF PROTEIN-N-(2-HYDROXYPROPYL)METHACRYLAMIDE COPOLYMER CONJUGATES AS TARGETABLE DRUG-CARRIERS .2. BODY DISTRIBUTION OF CONJUGATES CONTAINING TRANSFERRIN, ANTITRANSFERRIN RECEPTOR ANTIBODY OR ANTI-THY 1.2 ANTIBODY AND EFFECTIVENESS OF TRANSFERRIN-CONTAINING DAUNOMYCIN CONJUGATES AGAINST MOUSE L1210 LEUKEMIA INVIVO

The body distribution (5 h) of protein-N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer conjugates (Mw congruent-to 15000) was evaluated in DBA2 Mice, using either the transferrin receptor, or the Thy-1.2 antigen as specific targets. Radioiodinated HPMA copolymer (25-mu-g), proteins (anti-Thy 1.2, monoclonal antibody B3/25 specific for the transferrin receptor, non-specific IgG, or diferric transferrin; 10-mu-g) and protein-HPMA copolymer conjugates (10-mu-g protein) were injected intraperitoneally (i.p.) or intravenously (i.v.). Administration of protein conjugates via either route resulted in an up to 4.7-fold increase in blood-associated radioactivity (compared with free protein) together with a 2-fold decrease in the rate of excretion via the kidney. However, the organ distribution of radioactivity following administration of protein-conjugates was essentially similar to that seen following administration of free protein, but generally greater than that of the parent copolymer. For example, a maximum 11-fold and 3.5-fold increase in thymus localisation of both the anti-Thy 1.2 conjugate and the transferrin conjugate was observed when compared with that of either free polymer or non-specific IgG, respectively. However, it should be noted that this thymus-localised radioactivity accounted only for a small proportion (approximately 1%) of the dose administered. Conjugates containing transferrin, B3/25 or anti-Thy 1.2 accumulated at sites of rapid cell division namely bone marrow, intestine and skin. In a preliminary experiment to assess anti-tumour activity of transferrin-containing conjugates, HPMA copolymers were synthesised to contain additionally daunomycin (DNM) bound to the copolymer via degradable (Gly-Phe-Leu-Gly) or non-degradable (Gly-Gly) peptide spacers. These were administered (DNM, 1 0 mg/kg) i.p. to DBA, mice bearing an i.p. L1210 ascites (5 X 10(5) cells). Untreated animals, and those treated with non-degradable polymer conjugate, had mean survival times of approximately 22 days, whereas those treated with free DNM (10 mg/kg) survived only until day 9. Administration of free apotransferrin (44.3 mg/kg) resulted in a marked delay in the onset of tumour appearance, but the mean survival time of these animals was increased only by 4 days. The biodegradable polymer-DNM conjugates greatly increased the mean survival time (to 31 days). However, HPMA copolymer conjugates containing both DNM and transferrin were less effective (no animals surviving at day 50) than the equivalent non-transferrin containing conjugate (2/5 long term survivors).