Stuart Schreiber

Schreiber also contributed to more conventional small molecule discovery projects. He collaborated with Tim Mitchison to discover monastrol – the first small-molecule inhibitor of mitosis that does not target tubulin. Monastrol was shown to inhibit kinesin-5, a motor protein and was used to gain new insights into the functions of kinesin-5. This work led pharmaceutical company Merck, among others, to pursue anti-cancer drugs that target human kinesin-5.

Schreiber applied small molecules to biology through the development of diversity-oriented synthesis (DOS), chemical genetics, and ChemBank. Schreiber has shown that DOS can produce small molecules distributed in defined ways in chemical space by virtue of their different skeletons and stereochemistry, and that it can provide chemical handles on products anticipating the need for follow-up chemistry using, for example, combinatorial synthesis and the so-called Build/Couple/Pair strategy of modular chemical synthesis. DOS pathways and new techniques for small-molecule screening provided many new, potentially disruptive insights into biology. Small-molecule probes of histone and tubulin deacetylases, transcription factors, cytoplasmic anchoring proteins, developmental signaling proteins (e.g., histacin, tubacin, haptamide, uretupamine, concentramide, and calmodulophilin), among many others, have been uncovered in the Schreiber lab using diversity-oriented synthesis and chemical genetics. Multidimensional screening was introduced in 2002 and has provided insights into tumorigenesis, cell polarity, and chemical space, among others.

In 1996, Schreiber and co-workers used the small molecules trapoxin and depudecin to investigate the histone deacetylases (HDACs). Prior to Schreiber's work in this area, the HDAC proteins had not been isolated. Coincident with the HDAC work, David Allis and colleagues reported work on the histone acetyltransferases (HATs). These two contributions catalyzed much research in this area, eventually leading to the characterization of numerous histone-modifying enzymes, their resulting histone “marks”, and numerous proteins that bind to these marks. By taking a global approach to understanding chromatin function, Schreiber proposed a “signaling network model” of chromatin and compared it to an alternative view, the “histone code hypothesis” presented by Strahl and Allis. These studies shined a bright light on chromatin as a key gene expression regulatory element rather than simply a structural element used for DNA compaction.

In 1995, Schreiber and co-workers found that the small molecule lactacystin binds and inhibits specific catalytic subunits of the proteasome, a protein complex responsible for the bulk of proteolysis in the cell, as well as proteolytic activation of certain protein substrates. As a non-peptidic proteasome inhibitor lactacysin has proven useful in the study of proteasome function. Lactacystin modifies the amino-terminal threonine of specific proteasome subunits. This work helped to establish the proteasome as a mechanistically novel class of protease: an amino-terminal threonine protease. The work led to the use of bortezomib to treat multiple myeloma.

In 1994, Schreiber and co-workers investigated (independently with David Sabitini) the master regulator of nutrient sensing, mTOR. They found that the small molecule rapamycin simultaneously binds FKBP12 and mTOR (originally named FKBP12-rapamycin binding protein, FRAP). Using diversity-oriented synthesis and small-molecule screening, Schreiber illuminate the nutrient-response signaling network involving TOR proteins in yeast and mTOR in mammalian cells. Small molecules such as uretupamine and rapamycin were shown to be particularly effective in revealing the ability of proteins such as mTOR, Tor1p, Tor2p, and Ure2p to receive multiple inputs and to process them appropriately towards multiple outputs (in analogy to multi-channel processors). Several pharmaceutical companies are now targeting the nutrient-signaling network for the treatment of several forms of cancer, including solid tumors.

In 1993, Schreiber and Crabtree developed "small-molecule dimerizers", which provide small-molecule activation over numerous signaling molecules and pathways (e.g., the Fas, insulin, TGFβ and T-cell receptors) through proximity effects. Schreiber and Crabtree demonstrated that small molecules could activate a signaling pathway in an animal with temporal and spatial control. Dimerizer kits have been distributed freely resulting in many peer-reviewed publications. Its promise in gene therapy has been highlighted by the ability of a small molecule to activate a small-molecule regulated EPO receptor and to induce erythropoiesis (Ariad Pharmaceuticals, Inc.), and more recently in human clinical trials for treatment of graft-vs-host disease.

Following his work on the FK506-binding protein FKBP12 in 1988, Schreiber reported that the small molecules FK506 and cyclosporin inhibit the activity of the phosphatase calcineurin by forming the ternary complexes FKBP12-FK506-calcineurin and cyclophilin-ciclosporin-calcineurin. This work, together with work by Gerald Crabtree at Stanford University concerning the NFAT proteins, led to the elucidation of the calcium-calcineurin-NFAT signaling pathway. The Ras-Raf-MAPK pathway was not elucidated for another year.

Schreiber obtained a Bachelor of Science degree in chemistry from the University of Virginia in 1977, after which he entered Harvard University as a graduate student in Chemistry. He joined the research group of Robert B. Woodward and after Woodward's death continued his studies under the supervision of Yoshito Kishi. In 1980, he joined the faculty of Yale University as an assistant professor in Chemistry, and in 1988 he moved to Harvard University as the Morris Loeb Professor.

Stuart L. Schreiber (born 6 February 1956) is a scientist at Harvard University and co-Founder of the Broad Institute. He has been active in chemical biology, especially the use of small molecules as probes of biology and medicine. Small molecules are the molecules of life most associated with dynamic information flow; these work in concert with the macromolecules (DNA, RNA, proteins) that are the basis for inherited information flow.