Tumor treatment with complexes of cationic lipid and noncoding plasmid DNA results in the induction of cytotoxic T cells and systemic tumor elimination

Mechanisms of action underlying the immunotherapeutic activity of Allovectin in advanced melanoma

Allovectin (velimogene aliplasmid) is a cancer immunotherapeutic currently completing a pivotal phase 3 study for metastatic melanoma. Consisting of a bicistronic plasmid encoding both major histocompatibility complex (MHC) class I heavy and light chains (HLA-B7 and β2-microglobulin, respectively) formulated with a cationic lipid-based system, it is designed for direct intratumoral administration. Following injection into a single lesion, the product is intended to induce anti-tumor immune responses against both treated and distal lesions. Both the plasmid and lipid components of Allovectin contribute to the biological activity of the drug product, and its therapeutic activity is hypothesized to derive from multiple mechanisms of actions (MOAs). These include the induction of both cytotoxic T-cell and innate immune responses directed against allogeneic as well as tumor-derived targets, consequences of both an increased MHC class I expression on tumor cells and the induction of a localized immune/inflammatory response. In this paper, we review Allovectin's proposed MOAs, placing their contributions in the context of anti-tumor immunity and highlighting both preclinical and clinical supporting data.

Lipoplexes prepared from cationic liposomes and mammalian DNA induce CpG-independent, direct cytotoxic effects in cell cultures and in mice

BACKGROUND

Recent studies demonstrated the cytotoxic activity of bacterial DNA (pDNA) complexed with cationic lipids. This cytotoxicity is related to the ability of pDNA to induce potently the immune system, which is associated with release of inflammatory cytokines. Both activities seem to be related to the nonmethylated CpG sequences present in the pDNA. Here we study the cytotoxic activity of nonbacterial DNA complexed with cationic lipids against various tumor cell lines.

METHODS

Various nucleic acids complexed with cationic liposomes were prepared and their cytotoxic activity was studied in cell cultures and in tumor-bearing mice. Cell uptake of lipoplexes was evaluated, and mechanism of DNA cytotoxic activity was studied.

RESULTS

We found that nonbacterial (vertebrate) genomic DNA when complexed with cationic lipids is highly cytotoxic against C-26 and M-109 tumor cells. Cationic lipids alone were not toxic to these cells. The cytotoxic activity does not result from nonspecific acidification of the intracellular milieu, as substitution of DNA by poly-L-glutamate did not result in cytotoxicity, although the level of uptake of anionic charges per cell was similar to that of the nucleic acids, suggesting that this cytotoxic effect is specific to nucleic acids. By studying the nucleic acid fate using confocal microscopy, we found that cytotoxicity correlated with the release of DNA into the cytoplasm following uptake of lipoplexes. Injection of calf thymus DNA-based lipoplexes to mice with peritoneal C-26 metastases resulted in doubling of median survival time and long-term survival in 20% of the tumor-bearing mice. Judging by low levels of IFN-gamma, TNF-alpha and IL-6 in the treated mice, this effect cannot be ascribed to Th-1 inflammation, but rather to a direct cytotoxic effect on the tumor cells.

CONCLUSIONS

The above data provide a new insight into the mechanisms of lipoplex-mediated antitumor effects in vitro and in vivo and new perspectives in cancer therapy.

Liposome-DNA complexes infused intravenously inhibit tumor angiogenesis and elicit antitumor activity in dogs with soft tissue sarcoma

Intravenous gene delivery using liposome-DNA complexes (LDC) has previously been shown to elicit antitumor activity, but only in rodent tumor models. Therefore, we conducted a study to determine in a large animal spontaneous tumor model whether intravenous infusions of LDC could target gene expression to cutaneous tumor tissues and whether repeated treatments had an effect on tumor growth or angiogenesis. A total of 13 dogs with cutaneous soft tissue sarcomas were enrolled in the study and were randomized to receive a series of 6 weekly infusions of LDC containing either canine endostatin DNA or DNA encoding an irrelevant gene (luciferase). Serial tumor biopsies were obtained to assess transgene expression, tumor microvessel density (MVD), and intratumoral leukocyte inflammatory responses. We found that intravenous infusion of LDC did not result in detectable gene expression in cutaneous tumor tissues. However, two of 13 treated dogs had objective tumor responses and eight dogs had stable disease during the treatment period. In addition, a significant decrease in tumor MVD was noted in six of 12 treated dogs at the completion of six treatments. These results suggest that intravenous infusions of LDC may elicit nonspecific antitumor activity and inhibit tumor angiogenesis.

Liposome-mediated transient transfection reduces cholesterol-dependent coxsackievirus infectivity

Liposome-mediated gene delivery provides a powerful strategy for the study of gene function and for gene therapy. Coxsackievirus B3 is an important human pathogen associated with various diseases. Here we reported that liposome-mediated transient transfection of plasmid cDNA inhibited coxsackieviral replication at the levels of RNA, protein and viral progeny release. These inhibitory effects were observed in various cell types and by using different liposome reagents. We further showed that the inhibition was likely due to the lack of virus attachment. Moreover, we showed that addition of cholesterol restored, at least in part, the viral infectivity. Interestingly, we found that membrane cholesterol levels were unchanged during transfection, indicating that disruption rather than depletion of membrane cholesterol contributes to the inhibitory effects of transfection. Our data suggest that liposome-mediated cDNA transient transfection inhibits coxsackievirus infectivity via inhibition of viral attachment, which is likely occurring through the changes of membrane cholesterol integrity.

Systemic delivery of full-length C/EBP beta/liposome complex suppresses growth of human colon cancer in nude mice

C/EBP beta (CCAAT/enhancer-binding protein beta) is an important transcription factor involved in cellular proliferation and differentiation. Overexpression of the full-length C/EBP beta protein results in cellular growth arrest and apoptosis. Using a nonviral liposome as carrier, we delivered the full-length C/EBP beta expression plasmid, pCN, into nude mice bearing CW-2 human colon cancer tumors via tail vein. Southern blots revealed that the major organs and tumors were transfected. Experimental gene therapy showed that a strong suppression of tumor growth was observed in the pCN-treated mice, and such suppression was due to the overexpression of C/EBP beta, leading to the increased apoptosis in tumors of pCN-treated mice. No apparent toxic effects of pCN/liposome complex were observed in the animals. Thus, C/EBP beta has tumor suppression effect in vivo and may be used in gene therapy for cancers.

Phase I study of liposome-DNA complexes encoding the interleukin-2 gene in dogs with osteosarcoma lung metastases

Systemic gene delivery using cationic liposome-DNA complexes (LDCs) has been shown to elicit potent antitumor activity in mice with tumor metastases to the lungs. However, intravenous gene delivery for treatment of established cancer has not been evaluated previously in a spontaneous, large animal model. We therefore evaluated the safety, toxicity, and efficacy of intravenous gene delivery, using LDCs in dogs with established tumor metastases. Twenty dogs with chemotherapy-resistant osteosarcoma metastases to the lungs received a series of intravenous infusions of cationic liposomes and plasmid DNA encoding the canine interleukin-2 (IL-2) cDNA. Effects of intravenous gene delivery on immune activation, clinical and hematologic parameters, tumor responses, and survival times were assessed. We found that slow intravenous administration of IL-2 LDCs resulted in detectable IL-2 transgene expression in lung tissues of dogs. Repeated intravenous infusions of LDCs were well tolerated by dogs with lung tumor metastases and elicited systemic immune activation, as reflected by fever, leukogram changes, monocyte activation, and increased natural killer cell activity. Three of 20 dogs experienced partial or complete regression of lung metastases after infusion of IL-2 LDCs. Overall survival times were significantly increased in treated dogs compared with historical control animals with the same stage of disease. We conclude that repeated intravenous infusion of LDCs in cancerbearing dogs is safe and well tolerated at low doses and may be capable of eliciting antitumor activity in some animals with advanced tumor metastases.

Cytokine induction by a bacterial DNA-specific modified base

Unmethylated CpG dinucleotides in DNA contribute to a rapid inflammatory response in mammals. Here we show that N(6)-methyladenine (N(6)-MeA), a bacterium-specific modified base, also causes cytokine production. An oligodeoxyribonucleotide (ODN) containing N(6)-MeA induced cytokines when injected into mice. Co-injection of N(6)-MeA and CpG ODNs enhanced cytokines 2- to 3-fold, as compared with the injection of a CpG ODN alone. Plasmid DNA containing N(6)-MeA, complexed with cationic lipids, induced IL-12. These results indicate that the bacterium-specific base, in addition to the unmethylated CpG motif, triggers the mammalian immune response, and suggest that N(6)-MeA-containing DNA could be useful for cellular immunotherapy and DNA vaccine.

Intravenous Delivery of Liposome-mediated Nonviral DNA Is Less Toxic than Intraperitoneal Delivery in Mice

Suicide gene therapy has been shown to be an effective means of destroying pancreatic cancer cells. Liposomes have been described as having better efficacy in gene delivery, and an advantage of using liposomes as gene carriers is that they can be used repeatedly in vivo. The objective of this study is to compare the effect of gene delivery routes and to determine whether systemic delivery of the rat insulin promoter (RIP)-directed suicide gene construct would permit cell-specific gene delivery in vivo. Severe combined immunodeficient (SCID) mice were injected with liposome-RIP-TK (thymidine kinase) complex by either the intraperitoneal or the intravenous route. Twenty-four hours post gene delivery, mice received ganciclovir (GCV) treatment twice daily for 14 days. Mice were sacrificed at various time points. Complete necropsy and serum chemistry analysis were performed. Islet morphology was determined using hematoxylin and eosin (H&E) staining. Serum glucose and insulin levels were also determined. To determine the toxic effect on pancreatic islet cells, immunostaining of insulin-producing and glucagon-producing cells was carried out at each time point. H&E staining indicated that both intravenous and intraperitoneal liposome-RIP-TK gene expression had no effect in normal endocrine islet cells. Both gene-delivery routes in mice resulted in normal glycemia and serum insulin levels. The endocrine islets were intact, with a normal distribution pattern of insulin-producing beta cells and glucagon-secreting alpha cells. However, serum chemistry analysis revealed significantly elevated levels of liver enzymes; suggesting that possible liver damage had occurred with the intraperitoneal gene delivery of liposome-pRIP-TK. Intravenous liposome-mediated gene delivery had no effect on liver enzyme levels. Liposome-mediated gene delivery via intravenous injection was less toxic than intraperitoneal delivery. This gene-delivery route requires fewer liposome-DNA complexes and maintains normal liver function. Thus, intravenous delivery of gene therapy would be superior to intraperitoneal administration of gene therapy in mice.

Degradation kinetics of high molecular weight poly(L-lactide) microspheres and release mechanism of lipid:DNA complexes

Plasmid DNA encoding the green lantern protein was ion-paired with 1,2-dioleoyl, 3-trimethylammonium propane (DOTAP) at a (+/-) charge ratio of (1:1) to form a hydrophobic ion-pair (HIP) complex using the Bligh and Dyer method, and transferred into methylene chloride. Precipitation with a compressed antisolvent (PCA) was then employed to encapsulate plasmid DNA into poly(L-lactide) (PLLA) microspheres. The hydrophobicity of DOTAP:DNA complexes allowed consistently high encapsulation efficiencies (>70%) to be achieved. Release of the DOTAP:DNA complex from PLLA microspheres exhibited minimal burst and a short (ca. 1 week) lag phase, followed by sustained release over a 20 week period. Release kinetics were consistent with a simple Fickian diffusion model. No correlation was identified between release rate of soluble poly(L-lactide) species (< or =10 lactate units) from PLLA and the DNA release kinetics. Only approximately 12% of the polymer was degraded into soluble poly(L-lactide) over the time frame where approximately 90% of the plasmid load had been released.