Systemic delivery of modified mRNA encoding herpes simplex virus 1 thymidine kinase for targeted cancer gene therapy

Abstract

Failure of clinical trials of nonviral vector-mediated gene therapy arises primarily from either an insufficient transgene expression level or immunostimulation concerns caused by the genetic information carrier (e.g., bacteria-generated, double-stranded DNA (dsDNA)). Neither of these issues could be addressed through engineering-sophisticated gene delivery vehicles. Therefore, we propose a systemic delivery of chemically modified messenger RNA (mRNA) as an alternative to plasmid DNA (pDNA) in cancer gene therapy. Modified mRNA evaded recognition by the innate immune system and was less immunostimulating than dsDNA or regular mRNA. Moreover, the cytoplasmic delivery of mRNA circumvented the nuclear envelope, which resulted in a higher gene expression level. When formulated in the nanoparticle formulation liposome-protamine-RNA (LPR), modified mRNA showed increased nuclease tolerance and was more effectively taken up by tumor cells after systemic administration. The use of LPR resulted in a substantial increase of the gene expression level compared with the equivalent pDNA in the human lung cancer NCI-H460 carcinoma. In a therapeutic model, when modified mRNA encoding herpes simplex virus 1-thymidine kinase (HSV1-tk) was systemically delivered to H460 xenograft-bearing nude mice, it was significantly more effective in suppressing tumor growth than pDNA.

Figure 1

Preparation and characterizations of the LPR. (a) Illustration of formulating-modified mRNA into LPR. Anionic mRNA was mixed with different amounts of protamine and DOTAP/cholesterol liposome to form the core/membrane structure complex. The nanoparticles were then PEGylated by post-insertion. (b) Representative histogram showing the size distribution and zeta potential of nanoparticle formulated with formulation 6. (c) Nanoparticles observed with transmission electron microscope (TEM). Bar: 0.2 µm. Inset bar: 50 nm. DOTAP, 1,2-dioleoyl-3-trimethylammonium-propane; DSPE, 1,2-distearoyl-phosphatidylethanolamine; LPR, lipid/protamine/mRNA; mRNA, messenger RNA; PEG, polyethylene glycol.

Figure 2

In vitro transfection studies of the LPR. (a) Microscopic observation of cellular uptake and expression efficiency after administration of LPR or LPD. Nucleic acids (mRNA or pDNA) were labeled with Cy3 and the expression of transgene could be visualized by green fluorescent protein. (b) Quantification of cellular uptake and expression level with flow cytometry analysis. Percent of cells that took up nanoparticles and percent of cells that expressed transgenes were compared. The data were reported as mean ± SD. (c) Quantification of mean fluorescence intensity (MFI) with flow cytometry analysis. Expression level of each transfected cell, which was reflected by MFI, was compared for the H460 cells transfected with LPR. The data were reported as mean ± SD. (d) Epifluorescence microscopic photographs of transfected H460 cells in the presence of different concentrations of haloperidol. (e) Validation of targeting ability of anisamide ligand by transfecting H460 cells in the presence of sigma receptor ligand, haloperidol. Total green fluorescent protein and percent of transfected cells for the H460 cells transfected with LPR with and without targeting ligand, or in the presence of different concentration of haloperidol, was determined by flow cytometry analysis. The data were reported as mean ± SD. (f) Expression duration study with LPR loaded with luciferase mRNA. H460 cells were transfected with LPR or LPD loaded with equivalent amount of chemically modified mRNA, conventional mRNA, and pDNA that express firefly luciferase. Samples were assayed at different timepoints for luciferase expression level. The data were reported as mean ± SD. (g) Dose-response study and dose-toxicity study for LPR nanoparticle. H460 cells were transfected with various doses of LPR nanoparticle. Toxicity was monitored with 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay while transfection level was monitored by flow cytometry analysis. GFP, green fluorescent protein; LPR, lipid/protamine/mRNA; mRNA, messenger RNA; pDNA, plasmid DNA.

Figure 3

In vivo biodistribution and transfection studies of the LPR. (a) Biodistribution of Texas red-labeled LPR in the major organs of H460 xenograft-bearing nude mice 4 hours post-administration. (b) Expression profile of mcherry RFP in major organs of H460 xenograft-bearing nude mice 24 hours post-administration. Modified mRNA encoding mcherry RFP was formulated in LPR nanoparticle and intravenously administered to H460 xenograft-bearing nude mice. The transgene expression in major organs was determined with Kodak in vivo imaging system. (c) Confocal microscopic image of cryosection from RFP-expressing tumor tissue after in vivo transfection. (d) Quantification of luciferase activity in major organs and tumor tissue 24 hours post-administration of LPR loaded with modified mRNA encoding luciferase. Animals were killed 24 hours after intravenous injection of LPR. Tissue lysate was subjected to luciferase assay to quantify the expression level of transgene. (e) Serum cytokine levels of LPR-treated CD-1 mice were examined by ELISA assay. Sera were collected from CD-1 mice that received single dose injection of LPR 4 hours post-injection. The cytokine levels were assayed with ELISA kits, respectively. The data were reported as mean ± SD. IFN, interferon; IL, interleukin; LPR, lipid/protamine/mRNA; mRNA, messenger RNA; PBS, phosphate-buffered saline; pDNA, plasmid DNA; RFP, red fluorescent protein; TNF, tumor necrosis factor.

Figure 4

Systemic delivery of modified mRNA encoding HSV-tk in the LPR coupled with GCV for cancer gene therapy. (a) MTS cell proliferation assay used to determine the killing efficiency of LPR (HSV-tk)/GCV in vitro. The data were reported as mean ± SD. (b) Flow cytometry analysis of H460 cells treated with LPR (HSV-tk)/GCV followed by PI/annexin V staining. Cells were transfected with LPR (HSV-tk) nanoparticles in combination with GCV. Timeline of cell apoptosis was determined by PI/annexin-V double staining followed by flow cytometry analysis. (c) Proliferation capacity for the survival cells after HSV-tk/GCV therapy determined by clonogenic assay. The number was normalized against untreated group. The data were reported as mean ± SD. (d) Tumor growth inhibition study on H460 tumor xenograft. Tumor size was monitored every 3 days during the drug treatment. Tumor volumes were calculated as ½ × length × width × height. The data were reported as mean ± SEM (n = 4–6). (e) Tumor volumes from animals at end point of the experiment. Each symbol represents an individual mouse. Horizontal lines indicate mean values. (f) TUNEL assay showing the apoptosis degree of tumors harvested from end point of the tumor growth inhibition experiment. Con, control; GCV, ganciclovir; HSV-tk, herpes simplex virus-thymidine kinase; LPR, lipid/protamine/mRNA; mRNA, messenger RNA; PI, propidium iodide; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling.