Background: The Androgen receptor (AR) is the central driver of prostate cancer and AR signaling is intact across all stages of disease. The interaction of AR with protein cofactors is critical for its signaling: targeted disruption of these interactions may enable shutdown of AR signaling.
Methods: Using known crystal structure, modeled structure and imputed structure based models, peptide agents were rationally designed to block the interface between AR and critical cofactors in its interactome and tested for physiologic activity using prostate cancer cell lines, xenografts and primary tumor explants.
Results: Knowledge of the protein cofactors, their interacting motifs and structure of the interface are needed for optimal targeting of protein-protein interactions. Using an iterative rational design approach, we have been able to successfully disrupt three classes of the AR interactome:
1. Interactions where the protein cofactor, the motifs and the structure of the interface is known, (targeting AR-PELP1 interface through a helical LxxLL motif)
2. Interactions where the protein cofactor is known but the motifs and the structure of the interface is not known, (targeting AR-FoxA1 interaction) and
3. Interactions where the motif is known, but neither the protein cofactor nor the structure of the interface are known (only known is a critical motif on AR).
The design of initial compounds targeting the interactions in Class 1 was based on crystal structures, while those for Class 2 and Class 3 were based on either predicted or imputed (motif in different context) structures. The interaction between AR and proteins in each of these classes is disrupted by a targeted agent as evidenced by co-immunoprecipitation of endogenous protein cofactors and AR. The functional utility of these agents blocking the AR interactome on AR driven gene expression and proliferation has been validated for agents in Class 1, but is being validated for agents in Classes 2 and 3. In each case, using significant structural modeling, active agents were synthesized with a minimal use of synthesis of analogues.
Conclusions: The rational targeting of the AR interactome is feasible and may be a useful complement to traditional screening campaigns. We have demonstrated the utility of this approach to blocking the interface in three distinct classes of protein-protein interactions. Further validation/optimization of these drugs is needed prior to their clinical implementation.
Funding: Department of Defense, PCF, Thompson Foundation, Wood Foundation.