Cytotoxicity of momordin-folate conjugates in cultured human cells.
We have shown previously that macromolecules can be nondestructively delivered into cultured cells via folate receptor-mediated endocytosis if the macromolecules are conjugated to folic acid prior to addition to receptor-bearing cells (Leamon, C.P., and Low, P. S. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 5572-5576). Although an intracellular destination of the folate-linked proteins could be easily documented, the spatial resolution of the earlier data was insufficient to evaluate whether any endocytosed material was delivered into the cytosol. To resolve this issue, a folate-toxin conjugate was constructed using the impermeable ribosome-inactivating protein, momordin. Diminution of [3H]leucine incorporation into newly synthesized protein was then employed as a quantitative measure of the entry of the toxin into the cytosol. In studies with both HeLa and KB cells, cellular protein synthesis was found to be inhibited in a time- and concentration-dependent manner by the momordin-folate conjugate, but not by the underivatized toxin. IC50 values centered around 10(-9) M for the folate-linked samples. These observations provide direct evidence that folate conjugates not only reach the cytosol, but do so in a functionally active form.
Leamon
C P
CP
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393.
Low
P S
PS
D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects*; D002474:Cell-Free System; D004305:Dose-Response Relationship, Drug; D005492:Folic Acid / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007457:Iodine Radioisotopes; D007624:KB Cells; D007700:Kinetics; D009699:N-Glycosyl Hydrolases; D010940:Plant Proteins / Q000494:pharmacology*; D014176:Protein Biosynthesis; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D054790:Ribosome Inactivating Proteins, Type 2; D013763:Tetrahydrofolates / Q000494:pharmacology
D000963:Antimetabolites; D007457:Iodine Radioisotopes; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D013763:Tetrahydrofolates; D005492:Folic Acid; D009699:N-Glycosyl Hydrolases; C005984:5-methyltetrahydrofolate