Synthesis and Evaluation of D-Amino Acid Substituted Cyclic Peptide Inhibitors of Lysine Specific Demethylase 1

Lysine specific demethylase 1 (LSD1) is an enzyme that removes methyl groups from mono- and dimethylated histone 3 lysine 4 (H3K4), resulting in gene silencing. LSD1 became a valid cancer target because its overexpression has been observed in various human cancers and correlated with aberrant silencing of tumor suppressor genes. To date, a handful of small molecule—and peptide based—inhibitors mimicking the structure of the natural substrate (H3K4) displayed good in vitro inhibition activity toward LSD1. The present project has the aim of synthesizing, using the standard N-(9-Fluorenylmethoxycarbonyl-O-tert-butyl) (Fmoc/t-Bu) solid phase peptide synthesis procedure and evaluating the biological activity, using the Cell Titer 96® Aqueous One Cell Proliferation Assay, in which each L-amino acid is replaced by its stereoisomer D-amino acid. This approach is based on the fact that D-amino acids can stabilize certain reverse β-turns or destabilize α-helices, thus, providing insights about how a conformational constraint in the peptide affects the binding affinity toward the LSD1 enzyme. Specifically, the derivative is a cyclic peptide where the L-proline (Pro16 in the sequence) was replaced by D-proline. By replacing L-proline with D-proline, it is expected to identify the conformational features of the cyclic peptide that affect the in vitro LSD1 inhibition activity and the antitumor activity on cancer cell lines. The D-proline peptide showed a 38.1% growth inhibition on human anaplastic carcinoma cell lines at a concentration of 5mM, which indicated low antitumor activity. Future work include synthesis and evaluation of additional D-amino acid analogues along the peptide sequence