Abstract
Androgen receptor-negative (AR-) prostate tumours are observed in 11-24% of prostate cancer patients. To date, no treatments have been clinically approved for AR- prostate cancers. Histone deacetylases (HDACs) are overexpressed in late-stage prostate cancers and in AR- prostate cancer cell lines (PC3 and DU145). However, HDAC inhibitors, including suberanlihohydroxamic acid (SAHA), showed toxicity and lack of efficacy in clinical trials for prostate cancer. Novel HDAC inhibitors, N1-hydroxy-N8-(4-(pyridine-2-carbothioamido)phenyl)octanediamide) (Jazz90) and [chlorido(η5-pentamethylcyclopentadienyl)(N1-hydroxy-N8-(4-(pyridine-2-carbothioamido-κ2N,S)phenyl)octanediamide)rhodium(III)] chloride (Jazz167), were synthesised based on SAHA with the objective of making more efficacious and safer drugs. Jazz90 and rhodium-containing Jazz167 exhibited lesser toxicity towards non-cancerous (PNT1A and NIH 3T3) cells as compared to SAHA and were also non-toxic in BALB/c mice at the highest dose of 75 mg/kg. On comparing the selectivity of these compounds towards cancerous cells, Jazz90 was 2.9- and 2.5-fold more potent against PC3 and DU145 cells as compared to PNT1A cells, respectively, whereas Jazz167 was 3.5- and 1.3-fold more potent against PC3 and DU145 cells in contrast to PNT1A cells, respectively. As these drugs were effective at inhibiting the growth of PC3 and DU145 cells, they were also tested against PC3 and DU145 spheroids. Growth was inhibited by 78-89% in PC3 and DU145 spheroids, whereas branching was reduced in PC3 spheroids by ~95% following treatment. These compounds also reduced HDAC activity by 60% at 50 nM in PC3 nuclear lysates, whereas these drugs increased acetylation of histone-3 by 6- to 8-fold in PC3 cells. Although these compounds exhibited equipotent HDAC inhibition to SAHA, they were not as potent at inducing acetylation of histone-3 as compared to SAHA, which induced 14- and 3-fold acetylation in PC3 and DU145 cells in comparison to the control, respectively. Furthermore, the Jazz compounds exhibited a G0/G1 arrest and minimal apoptosis was recorded in AR- cells. Therefore, the drugs were concluded to be cytostatic and induced quiescence on their withdrawal. The mechanism of action by which these drugs induce cytostaticity remains unclear as different responses following drug treatment were observed on phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) and Ras/mitogen-activated protein kinase (Ras/MAPK) pathway in PC3 and DU145 cells. Although Jazz90 and Jazz167 did not induce cell death, they had anti-angiogenic effects, as they reduced vascular endothelial growth factor-A (VEGF-A) and vascular endothelial growth factor receptor-2 (VEGFR-2) levels by 67-72% and 71-93%, respectively, in PC3 cells and decreased human umbilical vein endothelial (HUVEC) cells from assembling into tubes. In conclusion, Jazz90 and Jazz167 function via cytostatic and anti-angiogenic mechanisms and are well-tolerated in BALB/c mice. However, as these compounds are not as potent at inducing acetylation of histone-3 in comparison to SAHA, they may have off-target cytostatic effects. Future studies should address their off-target effects on ribonucleotide reductase inhibition and outer dense fibre protein-2, as past studies suggest that the pyridine carbothioamide (PCA) and rhodium cyclopentadienyl complex PCA in these compounds have selectivity for these molecules. Furthermore, as these compounds contain an additional aromatic ring, their effects on pharmacokinetic profile need to be investigated.