| Autor: |
Goldmacher VS; Department of Cell Biology, ImmunoGen, Inc., Waltham, Massachusetts, United States of America., Audette CA; Department of Cell Biology, ImmunoGen, Inc., Waltham, Massachusetts, United States of America., Guan Y; Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America; Renal Division, Brigham and Women's Hospital, Boston, Massachusetts, United States of America., Sidhom EH; Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America; Renal Division, Brigham and Women's Hospital, Boston, Massachusetts, United States of America., Shah JV; Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America; Renal Division, Brigham and Women's Hospital, Boston, Massachusetts, United States of America., Whiteman KR; Department of Cell Biology, ImmunoGen, Inc., Waltham, Massachusetts, United States of America., Kovtun YV; Department of Cell Biology, ImmunoGen, Inc., Waltham, Massachusetts, United States of America. |
| Abstrakt: |
The microtubule-targeting maytansinoids accumulate in cells and induce mitotic arrest at 250- to 1000-fold lower concentrations than those required for their association with tubulin or microtubules. To identify the mechanisms of this intracellular accumulation and exceptional cytotoxicity of maytansinoids we studied interaction of a highly cytotoxic maytansinoid, S-methyl DM1 and several other maytansinoids with cells. S-methyl DM1 accumulated inside the cells with a markedly higher apparent affinity than to tubulin or microtubules. The apparent affinities of maytansinoids correlated with their cytotoxicities. The number of intracellular binding sites for S-methyl DM1 in MCF7 cells was comparable to the number of tubulin molecules per cell (~ 4-6 × 10(7) copies). Efflux of 3[H]-S-methyl DM1 from cells was enhanced in the presence of an excess of non-labeled S-methyl DM1, indicating that re-binding of 3 [H]-S-methyl DM1 to intracellular binding sites contributed to its intracellular retention. Liposomes loaded with non-polymerized tubulin recapitulated the apparent high-affinity association of S-methyl DM1 to cells. We propose a model for the intracellular accumulation of maytansinoids in which molecules of the compounds diffuse into a cell and associate with tubulin. Affinities of maytansinoids for individual tubulin molecules are weak, but the high intracellular concentration of tubulin favors, after dissociation of a compound-tubulin complex, their re-binding to a tubulin molecule, or to a tip of a microtubule in the same cell, over their efflux. As a result, a significant fraction of microtubule tips is occupied with a maytansinoid when added to cells at sub-nanomolar concentrations, inducing mitotic arrest and cell death. |
