Interestingly, caspase-3 activity was not observed in Aspc1 cells (Additional file 3 figure S3C), a cell line with less sensitivity to PB282 (Additional file 3 figure S3D). Figure 7 Caspase-3 inhibition by lipophilic antioxidant correlates with caspase dependence. (A) Caspase-3 inhibition by the hydrophobic antioxidant α-tocopherol

(α-toco), hydrophilic antioxidant N-acetylcyteine (NAC), or caspase-3 inhibitor DEVD-FMK (1 μM) in Bxpc3 cells following 24 hour treatment with SW43 (30 μM), PB282 (90 μM), or HCQ (90 μM). Data represents normalized inhibition compared to this website caspase-3 inducing treatment, n = 3, p < 0.05. (B) Cell viability following 24 hour treatment with SW43 or PB282 in the presence of α-toco or NAC. Data represents percent viability compared to DMSO

treated cells, n = 3, * p < 0.05. Discussion Recent synthesis of fluorescently labeled analogs of SV119 (SW120) and PB28 (PB385), allowing live cell imaging, has MK-1775 in vitro shown sigma-2 receptor ligand subcellular localization to the membrane components of the cell ultrastructure [16, 17]. In various pancreatic cancer cell lines we have observed similar results, and hypothesized that strong uptake into the endo-lysosomal compartment induces lysosomal membrane permeabilization (LMP). In addition, weakly basic amines as a class of drugs have N-acetylglucosamine-1-phosphate transferase been shown to induce LMP [24] and cell death [25], and the amine groups present on sigma-2 receptor ligands suggest they can induce LMP. We examined here whether this could influence the caspase-3 activation in pancreatic cancer we observed earlier [8–10] and found that LMP occurs shortly following treatment with a variety of structurally diverse

sigma-2 receptor ligands, verified by both AO and LysoTracker release from the lysosome. Uptake of fluorescently labeled compounds was inhibited by blocking the lysosomal pH gradient with concanamycin A (CMA), a specific inhibitor of the V-Type ATPase [26, 27], and translated into significant viability protection following treatment. SW43 was a stronger inducer of LMP, with greater protection from CMA pretreatment than for PB282. This that some sigma-2 receptor ligands have a greater propensity to influence the lysosomal death pathway Chemical structure differences may be responsible for this difference. For instance, the structure of the N-(9-(6-Aminohexyl)-9-azabicyclo[3.3.1]-nonan-3α-yl)-N-(2-methoxy-5-methylphenyl) carbamate hydrochloride (SV119) derivatives contain an alkyl extension with terminal amine group that is not present in the 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydro-naphthalen-1-yl)-propyl]-piperazine dihydrochloride (PB28) derivatives, a moiety that increases lysosomal membrane insertion and permeabilization [28].