A MAO-A mRNA expression in benign and cancerous cryo tissue samples of 40 primary PCa specimens and MAO-A mRNA expression of 52 benign and 498 cancerous samples from the TCGA database (unpaired t-test; **, P < 0.01; ***, P < 0.001, Box Whisker Plot with 10–90 percentile). B Quantification of MAO-A IRS of 193 benign, 172 primary and 17 CRPC resection tissue samples as well as further stratification in low GS (≤6), intermediate GS , high GS (≥8) patients and in different tumor stages (Kruskal–Wallis test and correction for multiple testing using Dunn´s comparison test; *, P < 0.05;***, P < 0.001, Box Whisker Plot with 10–90 percentile). Representative microscopy images. Magnification: 20× (scale bar = 50 µm). C Kaplan–Maier analysis of progression-free survival (progression is defined as re-rising PSA levels (>0.2 ng/ml) within at least two consecutive measurements) of tumor relapse patients with low/intermediate (IRS ≥ 10) or strong (IRS < 10) MAO-A expression in tumor sections [Log Rank (Mantel Cox); P value: 0.028]. D Measurement of cell proliferation and cell viability as well as western blot analysis for cPARP and p21 protein expression after transient transfection with either 25 nM siMAO-A or scrambled neg.C for 9 d. Data represent mean + SE from three independent experiments (unpaired t-test; ***, P < 0.001). E Schematic illustration of tumor progression. Current treatment options for different progression steps and the combination with potential pharmacological MAO-A inhibition in LNCaP and corresponding resistant LNCaP cell sub-lines as representative preclinical in vitro treatment models. F Representative western blot analysis for AR, GR and MAO-A protein expression in hormone naïve parental and therapy resistant LNCaP cells.