For example, in SK-N-SH neuroblastoma cells exactly caspase-3 was not activated by CB-64D [11], nor did caspase inhibitors afford protection against cell death in MCF-7 breast cancer cells [12]. Caspase-3 is however activated in MCF-7 [13] and in murine pancreatic adenocarcinoma Panc02cells [10] bysiramesine, though caspase-3 inhibitor did not rescue viability in either case. With another compound, PB28, no caspase-3 activity was observed in MCF-7 [14] or SK-N-SH cells [15]. Thus, while various sigma-2 receptor ligands are capable of inducing apoptosis in tumor cells, the activation of caspase-3 and upstream signaling events leading to this appear to be specific to particular ligand and cell type.

In this study, we sought to more closely study the apoptotic pathway induced by a number of structurally distinct sigma-2 receptor ligands in pancreatic cancer, which have proven efficacious in preclincal models. With knowledge of chemotherapy resistance to apoptotic stimuli depending on different mechanisms, we may more appopriately choose effective therapies. Results Structurally distinct sigma-2 receptor ligands inhibit growth of pancreatic cancer Multiple structurally distinct compounds (Figure (Figure1)1) with high affinity for sigma-2 receptors were tested for cytotoxicity against multiple pancreatic cancer cell lines in vitro (Table1) and screened for efficacy in a mouse model of pancreatic cancer with Panc02 cells (Additional file 1: figure S1). Compounds were further tested in athymic nude mice bearing human Bxpc3 subcutaneous tumorsand treated daily with equimolar doses of these sigma-2 receptor ligands.

These mice with established tumors were treated for eleven days and compared to vehicle, SV119, SW43, PB28, and PB282 each significantly decreased tumor volume (Figure (Figure22). Figure 1 Structures. Sigma-2 receptor ligands SW43 and SW120, derivatives of N-(9-(6-aminohexyl)-9-azabicyclo[3.3.1]nonan-3��-yl)-N-(2-methoxy-5-methylphenyl) carbamate hydrochloride (SV119), and PB282 and PB385, derivatives of 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydro-naphthalen-1-yl)propyl]-piperazine … Figure 2 In vivo efficacy of sigma-2 receptor ligands. Athymic nude mice inoculated subcutaneously with 1×106 Bxpc3 cells were treated daily with sigma-2 receptor ligands SV119, SW43, PB28, or PB282 when tumors reached an average of 5mm in diameter. …

Distinct sigma-2 receptor ligands induce lysosomal membrane permeabilization (LMP) Recently characterized fluorescent sigma-2 receptor ligands SW120 (derivative of SW43) [16] and PB385 (derivative of PB282) [17], colocalize with LysoTracker Red in Bxpc3 pancreatic cancer cells by confocal microscopy (Figure (Figure3),3), Anacetrapib and also appreciated by fluorescent microscopy in Bxpc3 and Aspc1 (Additional file 2 figure S2A).