Targeting the Undruggable in Castration-Resistant Prostate Cancer with FTDR-Stapled Peptide Probes

Temple Univ Of The Commonwealth, Philadelphia PA

Investigators

Abstract

1 This proposal aims at solving the unmet biomedical needs in the treatment of castrate-resistant 2 prostate cancer (CRPC) which essentially develops to be drug-resistant with ligand-independent 3 androgen receptor (AR) signaling. CRPC cells constantly upregulate c-Myc which was believed 4 to drive the CRPC malignancy and progression. The c-Myc mediated transcription in CRPC also 5 promoted the expression of AR splice variants (AR-V) that were truncated and lacked ligand 6 binding domains thereby endowing CRPC cells resistance to common AR antagonist such as 7 enzalutamide. Thus, c-Myc appears to be an important target for elucidating the AR signaling in 8 CRPC and for novel therapeutic development. Yet, there is a lack of intracellular tools or chemical 9 probes available to effectively target c-Myc, as it belongs to a typical basic helix-loop-helix (HLH) 10 transcription factor family which consist of flat, hydrophilic, and extended surface areas with 11 limited small molecule binding pockets and is considered “undruggable”. Although there have 12 already been c-Myc bound peptide fragments that can effectively inhibit c-Myc-Max dimerization 13 in vitro, most peptides discovered to date suffer from limited biostability and membrane 14 permeability, thereby largely limiting their applications towards in vitro only. We recently invented 15 fluorine-thiol displacement reaction (FTDR) and applied this to staple a diverse set of peptide 16 mimetics, which later displayed significantly enhanced cellular and nuclear uptake. Based on this 17 observation, we hypothesize that application of the FTDR stapling strategy to rationally designed 18 and c-Myc targeted peptide mimetics will result in a class of chemical probes with efficient cellular 19 and nuclear uptake and will efficaciously inhibit c-Myc mediated transcriptional activity in CRPC 20 cells and in vivo mouse xenografts. The first aim seeks to utilize FTDR to staple a H1 peptide 21 sequence designed to target the helix-loop-helix region of c-Myc and will thoroughly evaluate its 22 inhibition of c-Myc-Max heterodimerization and the suppression of c-Myc-mediated transcription 23 in CRPC cells, as well as the associated AR signaling particularly related to AR-FL and AR-V7. 24 The lead hit peptide mimetic that potently blocked the proliferation of CRPC cells, but not regular 25 prostate tissue cells will be eventually assessed in mouse CRPC xenograft models. The second 26 aim will exploit targeting at the C-tail leucine zipper (LZ) domain of c-Myc to directly block the 27 MYC-Max dimerization and will also explore the tandem stapling on the peptide mimetics for both 28 H1 and LZ domains. Completion of these research goals will result in a toolbox of c-Myc targeted 29 cellular probes, which will systematically dissect c-Myc mediated drug resistance and will facilitate 30 future therapeutic development for CRPC treatment or as adjuvants of AR antagonist.