Raymond M. Doss

Programmable DNA binding oligomers for control of transcription.

Mapping and sequencing the genetic blueprint in human, mice, yeast and other model organisms has created challenges and opportunities for chemistry, biology and human medicine. An understanding of the function of each of the approximately 25,000 genes in humans, and the biological circuitry that controls these genes will be driven in part by new technologies from the world of chemistry. Many cellular events that lead to cancer and the progression of human disease represent aberrant gene expression. Small molecules that can be programmed to mimic transcription factors and bind a large repertoire of DNA sequences in the human genome would be useful tools in biology and potentially in human medicine. Polyamides are synthetic oligomers programmed to read the DNA double helix. They are cell permeable, bind chromatin and have been shown to downregulate endogenous genes in cell culture.

Shape selective recognition of T.A base pairs by hairpin polyamides containing N-terminal 3-methoxy (and 3-chloro) thiophene residues.

Hairpin polyamides selectively recognize predetermined DNA sequences with affinities comparable to naturally occurring proteins. Internal side-by-side pairs of unsymmetrical aromatic rings within the minor groove of DNA distinguish each of the four Watson-Crick base pairs. In contrast, N-terminal ring pairs exhibit less specificity, with the exception of Im/Py targeting G.C base pairs. In an effort to explore the sequence specificity of new ring pairs, a series of hairpin polyamides containing 3-substituted-thiophene-2-carboxamide residues at the N-terminus was synthesized. An N-terminal 3-methoxy (or 3-chloro) thiophene residue paired opposite Py displayed 6- (and 3-) fold selectivity for T.A relative to A.T base pair, while disfavoring G,C base pairs by >200-fold. Our data suggests shape selective recognition with projection of the 3-thiophene substituent (methoxy or chloro) to the floor of the minor groove.