The epothilones are naturally occurring antimitotic drugs that share with the taxanes a similar mechanism of action without apparent structural similarity. Although photoaffinity labeling and electron crystallographic studies have identified the taxanebinding site on -tubulin, similar data are not available for epothilones. To identify tubulin residues important for epothilone binding, we have isolated two epothilone-resistant human ovarian carcinoma sublines derived in a single-step selection with epothilone A or B. These epothilone-resistant sublines exhibit impaired epothilone-and taxane-driven tubulin polymerization caused by acquired -tubulin mutations (274 Thr3 Ile and 282 Arg3 Gln ) located in the atomic model of ␣-tubulin near the taxane-binding site. Using molecular modeling, we investigated the conformational behavior of epothilone, which led to the identification of a common pharmacophore shared by taxanes and epothilones. Although two binding modes for the epothilones were predicted, one mode was identified as the preferred epothilone conformation as indicated by the activity of a potent pyridine-epothilone analogue. In addition, the structure-activity relationships of multiple taxanes and epothilones in the tubulin mutant cells can be fully explained by the model presented here, verifying its predictive value. Finally, these pharmacophore and activity data from mutant cells were used to model the tubulin binding of sarcodictyins, a distinct class of microtubule stabilizers, which in contrast to taxanes and the epothilones interact preferentially with the mutant tubulins. The unification of taxane, epothilone, and sarcodictyin chemistries in a single pharmacophore provides a framework to study drug-tubulin interactions that should assist in the rational design of agents targeting tubulin.
The biological screening results in this study established the importance of the nitrogen atom at the ortho position as well as the beneficial effect of a methyl substituent at the 4- or 5-position of the pyridine ring. Two pyridine epothilone B analogs (i.e. compounds 3 and 4) possessing higher potencies against drug-resistant tumor cells than epothilone B, the most powerful of the naturally occurring epothilones, were identified.
Lymphocyte trafficking is critically regulated by the Sphingosine 1-phosphate receptor-1 (S1P(1)), a G protein-coupled receptor that has been highlighted as a promising therapeutic target in autoimmunity. Fingolimod (FTY720, Gilenya) is a S1P(1) receptor agonist that has recently been approved for the treatment of multiple sclerosis (MS). Here, we report the discovery of NIBR-0213, a potent and selective S1P(1) antagonist that induces long-lasting reduction of peripheral blood lymphocyte counts after oral dosing. NIBR-0213 showed comparable therapeutic efficacy to fingolimod in experimental autoimmune encephalomyelitis (EAE), a model of human MS. These data provide convincing evidence that S1P(1) antagonists are effective in EAE. In addition, the profile of NIBR-0213 makes it an attractive candidate to further study the consequences of S1P(1) receptor antagonism and to differentiate the effects from those of S1P(1) agonists.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.