Design and synthesis of peptidomimetic estrogen receptor modulators (PERMs)

Estrogen receptor (ER), a member of the nuclear receptor superfamily, is a versatile transcriptional regulator. Coactivator (CoA) proteins have a significant role in regulating ER's transcriptional activity. Association between estrogen receptor and its coactivators represents an example of a crucial protein-protein interaction that can be exploited for developing lead molecules against diseases such as breast cancer. We synthesized and assayed forty different cyclic and linear peptidomimetic estrogen receptor modulators (PERMS). We have utilized unnatural cysteine and leucine surrogates to modify the disulfide ring and the NR box (LXXLL), respectively. The most potent peptide discovered during this effort contains an i, i+3 spaced cystathionine, which binds to the ERα with a Ki of 6.9 nM. The most selective PERM came in the form of D-Pen, L-Pen; i, i+3, disulfide-bridged peptide. This bis-penicillamine peptide was 50-fold more selective towards the ERα over ERβ. Surprisingly, unconstrained monocysteine linear peptides also showed low nanomolar Ki values. The most potent peptide in this series showed a Ki of 13 nM.; During the synthesis of cyclic PERMS, we observed facile sulfur extrusion from our disulfide-bridged peptides, under mild alkaline conditions. We carried out mechanistic and stereochemical analyses of this novel reaction of ‘base-assisted desulfurization’. The desulfurization reaction is compatible with disulfide bridges formed through homocysteines and penicillamines, yielding unusual amino acids such as lanthionine and cystathionine in a peptide chain. Our studies support a β-elimination/Michael-addition mechanism for this transformation. Amino acid configuration, disulfide ring size, position of the disulfide bridge, amino acids adjacent to and incorporated into the disulfide bridge, and peptide conformation are among the factors determining the stereoselectivity and the facility of this reaction.; ER-CoA interactions apparently occur within the nucleus of a cell. Hence cell permeable versions of a few selected PERMs were designed and synthesized. We successfully synthesized ten cell permeable PERMs using amide, disulfide, ester, and thioester chemistries for conjugating cell permeable moieties (CPMs). We utilized heptaarginine peptide as a hydrophilic CPM and decanoic acid as a lipophilic CPM for bioconjugation. Cellular uptake studies on these peptides confirmed their ability to cross the membrane barrier.