Searching for Novel HDAC6/Hsp90 Dual Inhibitors with Anti-Prostate Cancer Activity: In Silico Screening and In Vitro Evaluation

Abstract

Prostate cancer (PCA) is one of the most prevalent types of male cancers. While current treatments for early-stage PCA are available, their efficacy is limited in advanced PCA, mainly due to drug resistance or low efficacy. In this context, novel valuable therapeutic opportunities may arise from the combined inhibition of histone deacetylase 6 (HDAC6) and heat shock protein 90 (Hsp90). These targets are mutually involved in the regulation of several processes in cancer cells, and their inhibition is demonstrated to provide synergistic effects against PCA. On these premises, we performed an extensive in silico virtual screening campaign on commercial compounds in search of dual inhibitors of HDAC6 and Hsp90. In vitro tests against recombinant enzymes and PCA cells with different levels of aggressiveness allowed the identification of a subset of compounds with inhibitory activity against HDAC6 and antiproliferative effects towards LNCaP and PC-3 cells. None of the candidates showed appreciable Hsp90 inhibition. However, the discovered compounds have low molecular weight and a chemical structure similar to that of potent Hsp90 blockers. This provides an opportunity for structural and medicinal chemistry optimization in order to obtain HDAC6/Hsp90 dual modulators with antiproliferative effects against prostate cancer. These findings were discussed in detail in the study.

Keywords: HDAC6; Hsp90; drug design; prostate cancer; virtual screening.

Figure 1

Chemical structures of the 18 commercially available compounds selected from the virtual screening campaign.

Figure 2

Western blot analysis and relative quantification of the expression levels of acetylated-Tubulin (Ac-TUB), acetylated H3 (Ac-H3), and HSP70 in LNCaP (A,B) and PC-3 (C,D) cells treated for 24 h at GI₅₀ concentration. Tubastatin-A was used as HDAC6-specific positive control, Geldanamycin (GELDA) as HSP90-specific positive control, and SAHA as pan-HDAC inhibitor. Protein expression was normalized with Tubulin levels (Ac-TUB and HSP70) or total H3 (Ac-H3). Quantification is reported as fold change in treated cells versus DMSO control (CTR), arbitrarily set at 1 (one sample t-test p-values: * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001; n = 3).

Figure 3

Binding mode predicted for compounds 4, 8, 11, and 18 into HDAC6. In particular, (A) reports the docking pose of compound 11 into HDAC6 (PDB code: 5WGI) [57]. (B) reports the docking pose of compound 18 into HDAC6 (PDB code: 6DVL) [58]. (C) reports the docking pose of compound 4 into HDAC6 (PDB code: 6DVL). (D) reports the docking pose of compound 8 into HDAC6 (PDB code: 6DVL).