Abstract
Inhibition of the heat shock protein 90 (Hsp90) chaperone is a promising therapeutic strategy to target expression of the androgen receptor (AR) and other oncogenic drivers in prostate cancer cells. However, identification of clinically-relevant responses and predictive biomarkers is essential to maximize efficacy and treatment personalization. Here, we combined mass spectrometry (MS)-based proteomic analyses with a unique patient-derived explant (PDE) model that retains the complex microenvironment of primary prostate tumors. Independent discovery and validation cohorts of PDEs (n = 16 and 30, respectively) were cultured in the absence or presence of Hsp90 inhibitors AUY922 or 17-AAG. PDEs were analyzed by LC-MS/MS with a hyper-reaction monitoring data independent acquisition (HRM-DIA) workflow, and differentially expressed proteins identified using repeated measure analysis of variance (ANOVA; raw p value <0.01). Using gene set enrichment, we found striking conservation of the most significantly AUY922-altered gene pathways between the discovery and validation cohorts, indicating that our experimental and analysis workflows were robust. Eight proteins were selectively altered across both cohorts by the most potent inhibitor, AUY922, including TIMP1, SERPINA3 and CYP51A (adjusted p < 0.01). The AUY922-mediated decrease in secretory TIMP1 was validated by ELISA of the PDE culture medium. We next exploited the heterogeneous response of PDEs to 17-AAG in order to detect predictive biomarkers of response and identified PCBP3 as a marker with increased expression in PDEs that had no response or increased in proliferation. Also, 17-AAG treatment led to increased expression of DNAJA1 in PDEs that exhibited a cytostatic response, revealing potential drug resistance mechanisms. This selective regulation of DNAJA1 was validated by Western blot analysis. Our study establishes "proof-of-principle" that proteomic profiling of drug-treated PDEs represents an effective and clinically-relevant strategy for identification of biomarkers that associate with certain tumor-specific responses.
Highlights
Inhibition of the heat shock protein 90 (Hsp90) chaperone is a promising therapeutic strategy to target expression of the androgen receptor (AR) and other oncogenic drivers in prostate cancer cells
AUY922 is Significantly More Efficacious in patient-derived explant (PDE) Tissues Than 17-AAG—Human PDEs cultured in the absence or presence of two Hsp90 inhibitors, 17-AAG (500 nM) or AUY922 (500 nM) for 48 h (Fig. 1A), were assessed for the biological response to these agents
Principal component analysis of protein expression variability of these differential proteins segregated patient PDE samples based on Hsp90 inhibitor treatment (Fig. 2)
Summary
Inhibition of the heat shock protein 90 (Hsp90) chaperone is a promising therapeutic strategy to target expression of the androgen receptor (AR) and other oncogenic drivers in prostate cancer cells. Despite robust preclinical data demonstrating anti-tumor activity of first-generation ansamycin-derived Hsp inhibitors (e.g. 17-AAG) in prostate cancer [9], poor clinical responses in prostate cancer trials initially cast doubt over this class of agent [10]. This lack of efficacy has been attributed to poor solubility and pharmacokinetics, hepatotoxicity and multidrug resistance mechanisms that prevented adequate therapeutic doses from being achieved [11]. There is substantial variation and a lack of conservation of results from these cell line studies emphasizing the need for a more clinically-relevant model system
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