Background: Nitrogen containing bisphosphonates (N-BPs) are class of drugs used to prevent bone mass. On molecular level they act with inhibition of farnesyl pyrophosphate synthase (FPPS), which leads to accumulation of the isopenthenyl pyrophosphate (IPP) and its transformation by subsequent reaction in the cell cytotoxic ApppI.
Gamma delta T cells are subpopulation of cytotoxic T cells, which are able to recognise and be activated by phosphoantigens such as IPP. PC-3 cell line is an aggressive prostate cancer cell line which shows very low susceptibility to N-BP induced gdT cell cytotoxicity.
Methods: PC-3 cell lines were grown in FK-12 media, 5% CO2 at 370 C. Previously isolated and expanded dgT cells were maintained in RPMI-1640, 5% CO2 at 370 C. Cellular concentrations of IPP and ApppI were analysed with HPLC-ESI-MS and related to the amount of protein. Methyl beta cyclodextrin (mßCD) was used as cholesterol depletion agent. The statistical analysis of the data has been done with Graph Pad software.
Results and conclusions: Prolonged, but not pulse treatment of PC-3 cells with 50 μM zoledronic acid caused some Vg9Vd2T cell cytotoxicity. The addition of mßCD increased susceptibility of the PC-3 cells to gdT cell induced cytotoxicity significantly. Protein expression analysis confirmed that the low basal activity of the mevalonate pathway in PC-3 cells, highly elevated by the cholesterol depletion, is the most probable reason for the natural tolerance of PC-3 cells to N-BPs induced gdT cell cytotoxicity.
Disclosure: The authors declared no competing interests. The research leading to these results has received funding from the Seventh Framework Programme ([FP7/2007-2013]) under grant agreement n 264817 BONE-NET and by a research grant from the Academy of Finland (#132389).