Theranostic nanoparticles improve detection of pancreatic cancer

1336 Objectives Even with the increased funding in research, pancreatic cancer still claims the highest mortality rate of all major cancers with the 5-year survival rate at a dismal 6%. This can be directly correlated to the inability to detect the tumors before they reach stage III and IV. The tumors are very tiny and are located deep in the body making contemporary imaging modalities unable to spot them. The combination of Multispectral Optoacoustic Tomography (MSOT) and theranostic nanoparticles offers a possible solution by providing tumor targeting using fluorescent dyes and treatment through drug delivery. In order to combat the problems faced with pancreatic adenocarcinomas, we present a colloidal mesoporous silica nanoparticle (CMSN) utilizing a chitosan coating and the V7 peptide to provide pH specific dual targeting to deliver a contrast agent. Methods The nanoparticle was synthesized using a modified Stober method. Water, ethanol, cetyltrimethylammonium bromide (CTAB), triethanolamine (TEA), and tetraethyl orthosilicate (TEOS) were stirred under heat for 12 hours. This formed the main structure of the nanoparticle with the CTAB and silica forming the core and the TEA acting as a complexing agent limiting aggregation. Dialysis was utilized to remove the CTAB. Afterwards, the particles were coated with chitosan/GPTMS and then conjugated with APTES. Finally SMCC, an amine to sulfhydryl linker, joined the V7 pH low insertion peptide to the surface of the nanoparticle resulting in a dual acidic pH targeted system. Characterization was done using Transmission Electron Microscopy (TEM), UV-vis spectrophotometry (NanoDrop 200), and Zeta potential/DLS (Zetasizer Nano). To determine acidic pH specificity of V7-CMSN, Panc1 and S2VP10 cell lines were incubated in cell culture medium at either pH 7.4 or 6.6 followed by treatment with V7-CMSN. Particle uptake was determined using Near infrared fluorescence and tissue phantoms. Finally, for in vivo testing, the same CMSNs were injected into mice with S2VP10 pancreatic tumors. Visualization of the mice using the MSOT was performed 8 hours later. Results The UV-vis readings using the NanoDrop 2000 showed very similar absorption curves for the IR-780 dye alone and the CMSN+ IR-780 dye. V7-CMSN demonstrated acidic pH specificity in both S2VP10 and Panc 1 cells at pH 6.6 that is 8X and 5X times higher than pH 7.4, respectively. In tissue phantoms, increased pH specificity was observed, 20X and 4X, respectively, using multispectral optoacoustic tomography (MSOT). Eight hours post iv injection, V7-CMSN accumulated preferentially accumulated within orthotopic tumors as compared to untargeted nanoparticles (15.2 MSOT units vs 0.12 MSOT units p=0.00021). Conclusions The acidic pH specific dual targeting system using chitosan and the pHLIP V7 resulted in tumor specificity. Preferential binding and dye release was 20X higher in pH 6.6 as compared to pH 7.4 in tissue phantoms. Also, the MSOT was able to detect tumor specific accumulation of V7-CMSN in vivo. The general lack of V7-CMSN binding at pH 7.4 suggests that the particle would not accumulate in off-target organs and prevent systemic accumulation. Ordered silica nanoparticles are typically larger, the V7 targeted, smaller colloidal particles offer a substantial improvement in tumor uptake and specificity.