Cannabinoid-drug interactions vary across brain tumor cell lines

BACKGROUND: Glioblastoma is still the most aggressive primary brain tumor in adults. Recently, several advanced experimental treatment options have been proposed for glioblastoma patients, including the application of cannabinoids as an add-on therapy. METHODS: In the MTT, LDH, and BrdU assays, the anti-proliferative effects of arachidonyl-2'-chloroethylamide (ACEA - a potent selective cannabinoid CB1 receptor agonist) and WIN 55,212-2 mesylate (a non-selective cannabinoid CB1 and CB2 receptor agonist) on neuroblastoma and glioblastoma cell lines (CHP-134, KELLY, U-87MG, T98G, and C6) were determined. The interaction profiles of ACEA and WIN 55,212-2 mesylate in combinations with cisplatin and temozolomide (two chemotherapeutic drugs) in CHP-134, KELLY, U-87MG, T98G, and C6 were assessed isobolographically in the MTT test. Additionally, the impact of ACEA and WIN 55,212-2 mesylate on cannabinoid CB1 receptors expressed on all the tested cell lines was examined with the Western blot technique. Pre-incubation with a selective cannabinoid CB1 receptor antagonist/invert agonist (AM281) and consecutive exposure of the neuroblastoma CHP-134 and glioblastoma T98G cell lines to ACEA or WIN 55,212-2 mesylate at various treatment times (24, 48, and 72&#xa0;h) in the MTT assay was studied. Expression of Bax and Bcl-2 proteins in response to ACEA or WIN 55,212-2 mesylate treatment was examined with Western blot. RESULTS: ACEA and WIN 55,212-2 mesylate produced anti-proliferative effects on the tested cell lines. The selectivity index for ACEA ranged from 2.61 to 5.95, and that for WIN 55,212-2 mesylate ranged from 4.32 to 12.85. The combinations of ACEA with cisplatin (at the fixed ratio of 1:1) exerted additive interactions in all the tested cell lines. In contrast, WIN 55,212-2 mesylate, when combined with cisplatin, exerted a synergistic interaction in the CHP-134 cell line (p&#x2009;<&#x2009;0.05) and additive interactions in the remaining (KELLY, U-87MG, T98G, and C6) cell lines in the MTT test. The combinations of ACEA with temozolomide (at the fixed-ratio of 1:1) exerted antagonistic interactions in two (CHP-134 at p&#x2009;<&#x2009;0.05; and C6 at p&#x2009;<&#x2009;0.0001) cell lines and additive interactions in three (KELLY, U-87MG, T98G) cell lines in the MTT assay. In contrast, WIN 55,212-2 mesylate, when combined with temozolomide, produced antagonistic interactions in three (KELLY at p&#x2009;<&#x2009;0.05; T98G at p&#x2009;<&#x2009;0.01, and C6 at p&#x2009;<&#x2009;0.01) cell lines and additive interactions in the remaining (CHP-134 and U-87MG) cell lines in the MTT test. Western blot analysis confirmed that all the tested cell lines (CHP-134, KELLY, U-87MG, T98G, and C6) exposed to ACEA or WIN 55,212-2 mesylate changed the expression of cannabinoid CB1 receptors. Pre-incubation with AM281 and subsequent exposition of the CHP-134 and T98G cell lines to ACEA or WIN 55,212-2 mesylate revealed that the prior blockade of cannabinoid CB1 receptors reduced the anti-viability effects of the cannabinoid agonists in the MTT assay, confirming the involvement of cannabinoid CB1 receptors in this cellular response. Additionally, due to Western blot technique it was confirmed that neither Bax, nor Bcl-2 proteins were involved in the anti-proliferative effects of ACEA and WIN 55,212-2 mesylate in the tested CHP-134 and T98G cell lines. CONCLUSIONS: WIN 55,212-2 mesylate combined with cisplatin exerted the most desirable synergistic interaction in relation to the anti-proliferative effects in the neuroblastoma (CHP-134) cell line. In contrast, all the antagonistic interactions determined isobolographically for WIN 55,212-2 mesylate in combination with temozolomide in the KELLY, T98G, C6, and those of ACEA with temozolomide in the CHP-134, C6 cell lines in the MTT assay, should not be used clinically, due to the reduction of the anti-viability effects of the tested combinations.