Development of resistance to antiandrogens for treating advanced prostate cancer is a growing concern and extends to recently developed therapeutics, including enzalutamide. Therefore, new strategies to block androgen receptor (AR) function in prostate cancer are required. Here, we report the characterization of a multivalent conjugate presenting two bioactive ethisterone ligands arrayed as spatially defined pendant groups on a peptoid oligomer. The conjugate, named Multivalent Peptoid Conjugate 6 (MPC6), suppressed the proliferation of multiple AR-expressing prostate cancer cell lines including those that failed to respond to enzalutamide and ARN509. The structure–activity relationships of MPC6 variants were evaluated, revealing that increased spacing between ethisterone moieties and changes in peptoid topology eliminated its antiproliferative effect, suggesting that both ethisterone ligand presentation and scaffold characteristics contribute to MPC6 activity. Mechanistically, MPC6 blocked AR coactivator–peptide interaction and prevented AR intermolecular interactions. Protease sensitivity assays suggested that the MPC6-bound AR induced a receptor conformation distinct from that of dihydrotestosterone- or enzalutamide-bound AR. Pharmacologic studies revealed that MPC6 was
metabolically stable and displayed a low plasma clearance rate. Notably, MPC6 treatment reduced tumor growth and decreased Ki67 and AR expression in mouse xenograft models of enzalutamide-resistant LNCaP-abl cells. Thus, MPC6 represents a new class of compounds with the potential to combat treatment-resistant prostate cancer.
Multivalent peptoid conjugates which overcome enzalutamide resistance in prostate cancer cells
Yu Wang, Dilani C. Dehigaspitiya, Paul M. Levine, Adam A. Profit, Michael Haugbro, Keren Imberg-Kazdan, Susan K. Logan, Kent Kirshenbaum and Michael J. Garabedian
Cancer Res; 76(17); 5124 – 32.
Poly-proline type II (PPII) helical PXXP motifs are the recognition elements for a variety of protein–protein interactions that are critical for cellular signaling. Despite development of protocols for locking peptides into a-helical and b-strand conformations, there remains a lack of analogous methods for generating mimics of PPII helical structures. We describe herein a strategy to enforce PPII helical secondary structure in the 19-residue TrpPlexus miniature protein. Through sequence variation, we showed that a network of cation–pi interactions could drive the formation of PPII helical conformations for both peptide and N-substituted glycine peptoid residues. The achievement of chemically diverse PPII helical scaffolds provides a new route towards discovering peptidomimetic inhibitors of protein–protein interactions mediated by PXXP motifs.
PPII Helical Peptidomimetics Templated by Cation–π Interactions
TW Craven, R Bonneau, K Kirshenbaum
The design of folded miniature proteins is predicated on establishing noncovalent interactions that direct the self-assembly of discrete thermostable tertiary structures. In this work, we describe how a network of cation−π interactions present in proteins containing “WSXWS motifs” can be emulated to stabilize the core of a miniature protein. This 19-residue protein sequence recapitulates a set of interdigitated arginine and tryptophan residues that stabilize a distinctive β-strand:loop:PPII-helix topology. Validation of the compact fold determined by NMR was carried out by mutagenesis of the cation−π network and by comparison to the corresponding disulfide-bridged structure. These results support the involvement of a coordinated set of cation−π interactions that stabilize the tertiary structure.
Timothy W. Craven, Min-Kyu Cho, Nathaniel J. Traaseth, Richard Bonneau, and Kent Kirshenbaum. (2016), A Miniature Protein Stabilized by a Cation−π Interaction Network. J. Am. Chem. Soc. 138(5), 1543-1550 Link
Mallika Tatikola received the Dean’s Undergraduate Research award with a distinction of Arthur Noulas Research Scholar.
Antimicrobial peptides (AMPs) are critical components of the innate immune system and exhibit bactericidal activity against a broad spectrum of bacteria. We investigated the use of N-substituted glycine peptoid oligomers as AMP mimics with potent antimicrobial activity. The antimicrobial mechanism of action varies among different AMPs, but many of these peptides can penetrate bacterial cell membranes, causing cell lysis. We previously hypothesized that amphiphilic cyclic peptoids may act through a similar pore formation mechanism against methicillin-resistant Staphylococcus aureus (MRSA). Peptoid-induced membrane disruption is observed by scanning electron microscopy and results in a loss of membrane integrity. We demonstrate that the antimicrobial activity of the peptoids is attenuated with the addition of polyethylene glycol osmoprotectants, signifying protection from a loss of osmotic balance. This decrease in antimicrobial activity is more significant with larger osmoprotectants, indicating that peptoids form pores with initial diameters of ∼2.0–3.8 nm. The initial membrane pores formed by cyclic peptoid hexamers are comparable in diameter to those formed by larger and structurally distinct AMPs. After 24 h, the membrane pores expand to >200 nm in diameter. Together, these results indicate that cyclic peptoids exhibit a mechanism of action that includes effects manifested at the cell membrane of MRSA.
Smith, P. T., Huang, M. L., Kirshenbaum, K. (2015), Osmoprotective polymer additives attenuate the membrane pore-forming activity of antimicrobial peptoids. Biopolymers, 103: 227–236. Link