Abstract
There is good evidence that compounds modulating the endocannabinoid (eCB) system, such as inhibitors of the synthetic and catabolic enzymes or the target CB receptors themselves, affect the proliferation and/or invasivity of prostate cancer cells (see e.g. Nithipatikom et al., Cancer Res 64 [2004] 8826-8830; Nomura et al. Chem Biol 18 [2011] 846-856). However, most studies utilise cells cultured under optimal conditions without consideration of the tumour microenvironment. In the present study, we investigated the effects of two factors known to be in the tumour environment, namely the cytokine interleukin-6 (IL-6) and lactic acid (Hammacher et al. Int J Biochem Cell Biol 37 [2005] 442-450; Sauvant et al. Int J Cancer 123 [2008] 2532-2542) upon the eCB system in prostate cancer cells.
Rat AT1 prostate cancer cells were cultured in 12 well plates. After 6 h, medium was replaced by serum-free medium and 12 h later, by Krebs-Ringer-HEPES bicarbonate buffer containing 0 or 40 mM lactic acid (set to pH 7.4 and 6.6, respectively, with KCl concentrations of 3.6 and 0 mM, respectively), and 0, 25 or 100 ng/ml IL-6. After 3 h, cells were collected for qPCR, with three housekeeper genes (RPL19, RPS12 and PSMC4) used to standardise the data. The lysates were shown to express Il6r at the mRNA level.
Eleven genes involved in eCB signaling were measured (Dgla, Dglb, Cnr1, Cnr2, Napepld, Faah, Naaa, Mgll, Abhd6, Abhd12 and Ptgs2). With the exception of Abhd6, where an approximately 30% reduction in mRNA was seen, none of the levels were significantly affected by the IL-6 treatment. Lactic acid treatment doubled the mRNA expression of Dgla and halved the expression of Cnr2.
It is concluded that under the influence of factors known to be in the tumour microenvironment, changes in the components of the eCB signaling system are seen at the mRNA level. This underlines the importance of investigating the therapeutic potential of compounds affecting this system using cells cultured under more "tumour-realistic" conditions.
