Growth inhibition, drug load, and degradation studies of gelatin/methotrexate conjugates.
Macromolecular gelatin-methotrexate conjugates have potential therapeutic advantages over the free drug. Conjugates with MTX:gelatin molar ratios (MR) ranging from 1:1 to 27:1 were examined for cell growth inhibition, stability, degradation, and methotrexate (MTX) release. Conjugate growth inhibition was less than that of free MTX whose IC(50) value of 1.3 x 10(-8) M was about 10-fold less. Cell uptake of fluorescein labeled gelatin (145 kD) was observed by 24-30 h. Higher MR conjugates produced less growth inhibition, measurably greater stability at pH 7.4 based on MTX release, and had less gelatin degradation in the conjugate by the lysosomal enzyme Cathepsin B (Cat B) compared to low MR conjugates. Cat B conjugate degradation was greater at the in vitro lysosomal pH of 4.8 than the intra-tumor pH of 6.5. The presence of Cat B did not meaningfully affect MTX release, but less MTX was released at pH 4.8 than pH 6.5. The maximum MTX release was a relatively low 7% after 72 h at pH 6.5 for the low MR conjugate. Low molecular weight conjugate fragments were also produced and were also influenced by pH and MR. Reduced growth inhibition by high MR conjugates may be due to a hindered enzymatic degradation in the lysosomes. A strong peptide conjugate bond at lysosomal pH and a 24-30 h delayed gelatin uptake may contribute to reduced growth inhibition of the conjugate compared to free MTX. MTX release under these in vitro conditions occurs by aqueous hydrolysis, not by Cat B cleavage of the conjugate bond.
Ofner
Clyde M
CM
Department of Pharmaceutical Sciences, Philadelphia College of Pharmacy, University of the Sciences in Philadelphia, 600 South 43rd Street, PA 19104, USA. cofner@usip.edu
Pica
Karen
K
Bowman
Bill J
BJ
Chen
Chao-Sheng
CS
D000964:Antimetabolites, Antineoplastic / Q000737:chemistry / Q000494:pharmacology*; D002401:Cathepsin B; D049109:Cell Proliferation / Q000187:drug effects*; D017077:Culture Media, Conditioned; D004305:Dose-Response Relationship, Drug; D004337:Drug Carriers / Q000737:chemistry* / Q000378:metabolism; D004355:Drug Stability; D005780:Gelatin / Q000737:chemistry* / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008727:Methotrexate / Q000737:chemistry* / Q000494:pharmacology*; D012995:Solubility; D013997:Time Factors
D000964:Antimetabolites, Antineoplastic; D017077:Culture Media, Conditioned; D004337:Drug Carriers; D005780:Gelatin; D002401:Cathepsin B; D008727:Methotrexate