BERKELEY, CA (UroToday.com) - Chemotherapy in prostate cancer is usually the last line of defense. The typical drug that is used is docetaxel, which only provides minimal life extension. To improve chemotherapy options for prostate cancer we have to continue to test existing or novel drugs with defined mechanisms of action, and we must also reconsider the cell models in which we test them.
Palladium compounds are being considered as alternatives to platinum compounds such as cisplatin. The advantages of palladium compounds include greater or equal effectiveness to platinum compounds, the ability to kill cisplatin-resistant cell lines, a lower kidney toxicity, improved solubility, and the ability to bind to modifying ligands.
This study set out to test a novel palladium compound (with a saccharinate ligand attached) in a panel of normal, benign, and cancerous prostate cell lines, as well as in primary prostate epithelial cells cultured from patient samples.
We found that in the cell lines (normal - PNT1a, PNT2-C2, benign - BPH-1, localized early cancer - P4E6, metastatic cancer PC3, LNCaP) the drug reduced the viability of normal and benign cells more efficiently than cancer cells. Indeed, one of the cancer cell lines, PC3, showed very little sensitivity to this drug. However, when using the primary cells, we observed that it was equally effective at killing cells cultured from benign or low Gleason grade (Gl6/7) cancer samples. The IC50 values were generally higher for the primary cells than the cell lines. This is a typical observation; cell lines (with some exceptions) are considerably easier to kill than primary cell cultures. In addition, the IC50 for high-grade (Gl8/9) cancers was almost nine times higher than that for low-grade cancers.
Unfortunately, this is the opposite effect that you hope for when testing a new cancer drug. Nevertheless, we went on to investigate the cause of reduction of cell viability by assessing the cell proliferation and the expression of death markers by Western blot.
A dose-dependent increase in cell death was observed in all cell lines (except PC3) and all primary cells, with no other significant changes to the cell proliferation profile. Using Western blots, we observed that programmed cell death (apoptosis) was induced in all normal and benign cell lines but not in PC3 cells and only at the high dose in LNCaP cells. Dose-dependent apoptosis was not induced in the primary cells.
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| Prof. Norman Maitland, Prof. Engin Ulukaya, and Dr. Fiona M. Frame |
We also tested for autophagy using Western blots. Autophagy is a cell protective mechanism whereby the cell “eats itself,” ingesting non-essential components ensuring survival. However, it can also in certain circumstances lead to cell death. We saw a clear induction of the autophagy marker in all benign and normal cell lines but not in PC3 or LNCaP cells. Significantly, the palladium compound induced autophagy in all primary cells. It is worth considering the use of combination treatment first to inhibit autophagy, then promoting greater cell death. Interestingly, autophagy was not induced in PC3 and LNCaP cells (the standard prostate cancer lines) following palladium compound treatment. This is probably a result of their PTEN-deficient status. PTEN (phosphatase and tensin homolog) is part of the autophagy pathway, and so autophagy may not function in these cells. However, clearly, PC3 cells have alternate mechanisms to resist drug treatment.
Many studies in the literature have been carried out using one normal cell line versus one cancer cell line. Our study acts as a cautionary tale: using such different pairs of samples may provide you with very different conclusions. We expect that more studies like the one presented here will be carried out combining the expertise of medicinal chemists generating novel drugs with biologists, along with the cooperation of surgeons, who are using clinically relevant cell culture models. We think this is the way to elucidate drug response mechanisms, and, indeed, to minimise drug resistance and non-responses in close-to-patient samples. Such biologically relevant preclinical testing should be an additional step in the path from bench to bedside, following industry standard initial cell line panel testing and prior to early stage clinical trials.
Written by:
Fiona M. Frame,a Engin Ulukaya,b and Norman J. Maitlanda as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
a Department of Biology, YCR Cancer Research Unit, University of York, Heslington, York, North Yorkshire, United Kingdom
b Department of Medical Biochemistry, Medical School, Uludag University, Bursa, Turkey
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