Benzodiazepines that bind at peripheral sites inhibit cell proliferation.

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Abstract
[3H]Ro5-4864 [7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one] binds to mouse thymoma cells in a specific, saturable, and reversible manner. Scatchard analysis shows a single class of binding sites with a Kd of 4.4 nM and a Bmax of 477 fmol/106 cells. This benzodiazepine binding site is of the peripheral type, based on the relative potencies of Ro5-4864 and clonazepam in competing for [3H]diazepam binding. Fifteen benzodiazepines that bind to this site with affinities ranging from 6 nM to 1 .mu.M also reversibly inhibit the proliferation of thymoma cells in culture at the micromolar dose range. There is a strong positive correlation (r = 0.85) between the binding constants of these compounds for the peripheral-type sites and their ED50 in inhibiting the uptake of [3H]thymidine into the cells. These sites may be involved in the regulation of thymoma cell proliferation.