PPARγ ligand sensitizes prostate cancer cells to the oxaliplatin treatment

Peroxisome proliferator activated receptors (PPARs) are members of the large group of nuclear receptors. These transcriptional factors can regulate metabolic processes, inflammation, proliferation and differentiation of the cells. Thiazolidinediones are synthetic ligands of PPARγ, which were used for the treatment of diabetes mellitus type 2. One of the most mutated gene in the tumors is tumour suppressor p53. In addition, amplification of MDM genes or changed protein expression are also often observed in many tumours. Protein MDM2 represents a member of the family of E3 ligases. It is well known that MDM2 is able to inhibit p53 transcriptional activity. MDMX is a homolog of MDM2 and it supports MDM2 negative regulation of p53. Platinum-based drugs are broadly used for the cancer treatment, but they are often inefficient and have serious side effects. That is why new platinum-based drugs are developed and their combinations with other compounds are studied.

In our experiments PPARγ ligand – rosiglitazone (RGZ ) and platinum derivate – oxaliplatin (L-OHP) were used. Analyses were performed on prostate cancer cell line BPH-1 CAFTD 03 and on samples from prostate cancer patients. We suggest that combination of the drugs may be more effective than the drugs used alone. Thus, the aim of our study was to analyze the effects of combined application of RGZ and L-OHP in prostate cancer cell lines and to detect changes of selected protein expression in samples of prostate cancer patients. Our results indicated that pretreatment of cancer cells with RGZ sensitizes BPH-1 CAFTD 03 cell line to the effects of L-OHP. We detected increased inhibition of proliferation and block in G2/M phase of the cell cycle together with changes in cyclin expressions after this type of treatment. Cell death was detected by Annexin V assay and Western blot analysis. After combination of RGZ and L-OHP we observed increased percentage of the dead cells by Annexin V staining, but decreased activity of caspases. It could indicate another form of cell death in addition to apoptosis. Combined drug treatment decreased PPARγ and MDMX protein expression which imply important correlation of these two proteins in in vitro conditions. Moreover, this correlation was also confirmed in prostate patient samples. Thus, our data suggest a possible link between PPARγ and MDMX. Expression of MDM2 protein showed an opposite pattern than expression of its partner MDMX and p53 expression was not changed. Tumour suppressor p53 is stabilized but nonfunctional in BPH-1 CAFTD 03 cell line. The role of PPARγ in RGZ and L-OHP combined effects was verified also by silencing of PPARγ using siRNA .

This work was supported by grant of Czech Science Foundation No. 13-09766S, grant Internal Grant Agency of Ministry of Health of the Czech Republic No. NT11201-5/2010, grant CZ.1.07/2.4.00/31.0155 and project MUNI/A/0927/2013