Abstract
Based on a molecular classification of prostate cancer using gene expression pathway signatures, we derived a set of 48 genes in critical pathways that significantly predicts clinical outcome in all tested patient cohorts. We tested these genes in a functional genomics screen in a panel of three prostate cancer cell lines (LNCaP, PC3, DU145), using RNA interference. The screen revealed several genes whose knockdown caused strong growth inhibition in all cell lines. Additionally, we tested the gene set in the presence of docetaxel to see whether any gene exhibited additive or synergistic effects with the drug. We observed a strong synergistic effect between DLGAP5 knockdown and docetaxel in the androgen-sensitive line LNCaP, but not in the two other androgen-independent lines. We then tested whether this effect was connected to androgen pathways and found that knockdown of the androgen receptor by si-RNA attenuated the synergy significantly. Similarly, androgen desensitized LNCaP-AI cells had a higher IC50 to docetaxel and did not exhibit the synergistic interaction. Short-term exposure to enzalutamide did not significantly alter the behaviour of parental LNCaP cells. An immunofluorescence analysis in LNCaP cells suggests that under the double insult of DLGAP5 knockdown and docetaxel, cells predominantly arrest in metaphase. In contrast, the knockdown of the androgen receptor by siRNA appears to assist cells to progress through metaphase in to anaphase, even in the presence of docetaxel. Our data suggest that DLGAP5 has a unique function in stabilizing spindle formation and surviving microtubule assault from docetaxel, in an androgen-regulated cell cycle system.
Highlights
Prostate cancer is a common disease—the third most common cancer in males—that is characterized clinically by a wide diversity of outcomes
The gene set was expressed at significantly higher levels in castration resistant prostate cancer (CRPCa) (Fig. 1c, upper left), and metastatic disease compared to primary PCa (Fig. 1c, upper right, Supp Fig. 1A, left), in distant metastatic samples compared to prostate recurrent disease (Fig. 1c, lower right, Supp Fig. 1A, right) and in high Gleason grade tumours (Fig. 1c, lower left), overall supporting the idea that these genes might contribute to metastatic potential, as well as treatment resistance
Recent large-scale clinical trials (STAMPEDE, CHAARTED) have shown that advanced prostate cancers respond better to a first-line combination of chemotherapy (DCT) and androgen deprivation therapy (ADT) than to the sequential treatment where ADT is given first and chemotherapy is given upon recurrence
Summary
Prostate cancer is a common disease—the third most common cancer in males—that is characterized clinically by a wide diversity of outcomes. We aim to explore further options to target the aggressive, lethal form of prostate cancer To this end, we make use of a molecular classification of prostate cancer based on gene expression data that we established previously[2]. We make use of a molecular classification of prostate cancer based on gene expression data that we established previously[2] This classification system identifies a subtype of highly aggressive tumours with poor outcomes, characterized by gene expression signatures for embryonic and induced pluripotent stem cells (ESC, iPSC), and for loss of function of the tumour suppressors PTEN and p53. We selected genes highly enriched in the ESC|PTEN-|p53- subgroup relative to the normal-like subgroup across several patient data sets From these we curated a small set of 48 genes that were associated with p53 function, cell cycle mechanics or stemness. Data analysis aimed to identify genes whose knockdown would either significantly inhibit the growth of the cell lines in general, or whose knockdown would be synergistic with DCT
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