Dissecting cellular processes using small molecules: identification of colchicine-like, taxol-like and other small molecules that perturb mitosis

Background: Understanding the molecular mechanisms of complex cellular proc esses requires unbiased means to identify and to alter conditionally gene p roducts that function in a pathway of interest. Although random mutagenesis and screening (forward genetics) provide a useful means to this end, the c omplexity of the genome, long generation time and redundancy of gene functi on have limited their use with mammalian systems. We sought to develop an a nalogous process using small molecules to modulate conditionally the functi on of proteins. We hoped to identify simultaneously small molecules that ma y serve as leads for the development of therapeutically useful agents. Results: We report the results of a high-throughput, phenotype-based screen for identifying cell-permeable small molecules that affect mitosis of mamm alian cells. The predominant class of compounds that emerged directly alter s the stability of microtubules in the mitotic spindle. Although many of th ese compounds show the colchicine-like property of destabilizing microtubul es, one member shows the taxol-like property of stabilizing microtubules. A nother class of compounds alters chromosome segregation by novel mechanisms that do not involve direct interactions with microtubules. Conclusions: The identification of structurally diverse small molecules tha t affect the mammalian mitotic machinery from a large library of synthetic compounds illustrates the use of chemical genetics in dissecting an essenti al cellular pathway. This screen identified five compounds that affect mito sis without directly targeting microtubules. Understanding the mechanism of action of these compounds, along with future screening efforts, promises t o help elucidate the molecular mechanisms involved in chromosome segregatio n during mitosis.