Pharmacological and therapeutic properties of carrier bound methotrexate against tumor confined to a third space body compartment.

The pharmacokinetics and therapeutic effectiveness of methotrexate (MTX) and MTX covalently bound to bovine serum albumin (MTX-BSA) and poly-l-lysine, MW 3,000 (MTX-PLL 3K) or MW 40,000 to 60,000 (MTX-PLL 40-60K) were compared when these drugs were injected directly into the pleural cavities of BDF1 mice containing the L1210 tumor. Simultaneous measurements od drug levels in both pleural fluid and blood after a single dose demonstrated that free MTX and MTX-PLL 3K were cleared from the pleural cavity and blood within 4 hr, MTX-PLL 40K-60K was cleared within 2 hr, and MTX-BSA was still present in the tumor compartment at 48 hr. The coupling of MTX to these carriers increased its toxicity by extending the half-life of MTX-BSA within the animal and by incorporating a toxic PLL derivative as a carrier. At equitoxic doses, a single dose of MTX-BSA gave a peak increase in lifespan (ILS) of 50% (at 35 mg/kg) compared with a peak ILS of 30 to 35% for both free drug (at 95 mg/kg) and the MTX-PLL derivatives (at 1.4-6 mg/kg). Systemic administration of sufficient leucovorin to provide partial marrow protection compromised the antitumor activity of both MTX and MTX-BSA in the pleural cavity, and although leucovorin permitted higher doses to be used, this resulted in only a small increase in peak ILS for MTX-BSA on a single dose schedule.