Gold Nanoshells Coated5-Aminolevulinic Liposomes For Photothermal-Photodynamic Antitumor Therapy

Photodynamic therapy(PDT)was founded in the 1970 s.With the continuous development and progress of photosensitizers in recent years,PDT has gradually become one of the basic means of cancer treatment.5-aminolevulinic acid is an endogenous biochemical substance that can produce a strong photosensitizer(PpIX)via ALA dehydratase and a series of enzymatic actions.The low activity of ferrochelatase in cancer cells can induce PpIX to reach high level.Light can transfer energy to oxygen and water to form free radicals,and these free radicals can cause a series of chain reactions of biomolecules,leading to death of cancer cells.Chitosan acts as heterogeneous nucleation places for further formation of gold nanoshells,with which liposomes tend to aggregate at the site of tumors.The strong NIR absorption and high photothermal conductivity of gold nanoshells can enhance light-heat conversion more efficiently and induce the gel-to-liquid phase transition of biological membranes.This leads to instability of liposome membranes and release of drugs at the same time,thereby enhancing the synergistic effect of the combination therapy.First,5-aminolevulinic liposomes(5-ALA-Lips)was made based on ethanol injection method and pH-gradient method.Methods orthogonal experiment was carried out to optimize the formulation.Chitosan-coated liposomes was synthesised as templates to prepare gold nanoshells coated Iiposomes(GNALs).Finally,the direct reduction method was used to prepare GNALs.Results showed that GNALs exhibit a uniform-sized spherical shape of 185.8±0.9 nm,with a zeta potential of 33.0±1.6 mV.TEM and SEM images showed globular shapes of GNALs with smooth surfaces.Good stability of GNALs was displayed at 4°C.GNALs also showed pH sensitivity and controlled-release of 5-ALA by drug release experiments.Photothermal experiments verified good photothermal conversion efficiency(0.32).In addition,NIR light-excited nanosystems significantly promoted antitumor effects in this study compared to single photodynamic therapy.It was also found that the increased temperature promoted inhibition rate of SKOV3 cells.The long-circulating CuS NDs/liposomes(CuS@lips)was designed to diagnose tumors during treatment.CuS nanodots were first prepared and characterized by DLS and TEM.Subsequently,a long-circulating CuS NDs/liposomes(CuS@lips)was prepared by thin film hydration method.CuS NDs showed good shape and uniform dispersion,and the mean particle size was 2.7 nm.The particle size and PDI of CuS@lips were 188.9 nm and 0.186.CuS@lips also showed good ability to enhance photoacoustic imaging and magnetic resonance imaging.CuS@lips with long circulation life time in vivo could be attributed to DSPE-PEG2000,which further enhanced in vivo contrast ability of CuS@lips.The successful preparation of gold nanoshells coated 5-ALA liposomes(GNALs)enabled superior antitumor property through combination of near-infrared photothermal therapy and photodynamic therapy.Gold nanoshells coated 5-ALA liposomes was firstly prepared as a novel multifunctional drug delivery system with excellent performance.GNALs prepared with mean size less than 200 nm could accumulate into tumor tissues by the enhanced permeability and retention(EPR)effect.Long-circulating CuS@lips was used to analyze the therapeutic effect by photoacoustic imaging and magnetic resonance imaging.Effective combination of GNALs and CuS@lips can achieve both tumor treatment and diagnosis in the future.