Update on non-viral delivery methods for cancer therapy: possibilities of a drug delivery system with anticancer activities beyond delivery as a new therapeutic tool

Importance of the field: Cancer is the most formidable human disease. Owing to the heterogeneity of cancer, a single-treatment modality is insufficient for the complete elimination of cancer cells. Therapeutic strategies from various aspects are needed for cancer therapy. These therapeutic agents should be carefully selected to enhance multiple therapeutic pathways. Non-viral delivery methods have been utilized to enhance the tumor-selective delivery of therapeutic molecules, including proteins, synthetic oligonucleotides, small compounds and genes.

Areas covered in this review: As non-viral delivery methods, liposomes and polymer-based delivery materials to target tumors mainly by systemic delivery, physical methods including electroporation, sonoporation, and so on, to locally inject therapeutic molecules, and virosomes to use the viral infectious machinery for the delivery of therapeutic molecules are summarized.

What the reader will gain: This article aims to provide an overview of the characteristic properties of each non-viral vector. It will be beneficial to utilize appropriately the vector for cancer treatment.

Take home message: Efficient and minimally invasive vectors are generally considered to be the ideal drug delivery system (DDS). However, against cancer, DDS equipped with antitumor activities may be a therapeutic choice. By combining therapeutic molecules with DDS having antitumor activities, enhancement of the multiple therapeutic pathways may be achieved.     

MicroRNA-204 plays a role as a tumor suppressor in Newcastle disease virus-induced oncolysis in lung cancer A549 cells

Tumor development and progression are closely associated with various microRNAs (miRNAs/miRs). We have previously shown that Newcastle disease virus (NDV) strain 7793 induces oncolysis in lung cancer. However, how NDV exerts its oncolytic effect on lung cancer remains to be investigated. The present study assessed the role of miR-204 in the NDV-induced oncolysis of lung cancer A549 cells by oncolysis induction in vitro. miR-204 was significantly upregulated in NDV-treated A549 cells. Overexpression or inhibition of miR-204 was significantly associated with NDV-induced oncolysis in A549 cells. Caspase-3 and Bax, major regulators of the apoptosis pathway, were regulated by miR-204, and the association between caspase-3-related apoptosis and miR-204 was identified in NDV-mediated oncolysis. These data demonstrated that miR-204 as a tumor suppressor played a role in NDV-induced oncolysis in lung cancer cells. The present study demonstrates the potential of strategies using miRs to improve oncolytic NDV potency, and highlights miR-204 as a tumor suppressor in NDV-induced oncolysis of lung cancer cells.     

Reovirus-based therapy for cancer

Reovirus is an oncolytic virus that is not associated with significant disease in humans, but is selectively able to replicate in cancer cells through exploitation of abnormal Ras signaling. Pre-clinical studies have demonstrated that treatment with reovirus is associated with significant anticancer activity across a range of tumor types. Reolysin is a proprietary formulation of the human reovirus developed by Oncolytics Biotech. Clinical evaluation of reovirus therapy has shown that it is well tolerated when administered locally or systemically. Encouraging anticancer efficacy has been observed with single-agent treatment and in combination with chemotherapy and radiotherapy. Phase II studies are currently evaluating reovirus alone and in combination with standard therapy in an array of tumor types. While immune sensitization hinders the anticancer efficacy of reovirus, it is important in preventing systemic toxicity. Immunosuppressive strategies are being developed that reduce immune neutralization of the virus to allow for improved tumor penetration, but retain sufficient antibody levels to protect normal tissues. The lack of toxicity and promising efficacy of reovirus has raised hopes that it will become an established anticancer agent.     

Glioma virus therapies between bench and bedside

Despite extensive research, current glioma therapies are still unsatisfactory, and novel approaches are pressingly needed. In recent years, both nonreplicative viral vectors and replicating oncolytic viruses have been developed for brain cancer treatment, and the mechanistic background of their cytotoxicity has been unveiled. A growing number of clinical trials have convincingly established viral therapies to be safe in glioma patients, and maximum tolerated doses have generally not been reached. However, evidence for therapeutic benefit has been limited: new generations of therapeutic vectors need to be developed in order to target not only tumor cells but also the complex surrounding microenvironment. Such therapies could also direct long-lasting immune responses toward the tumor while reducing early antiviral reactions. Furthermore, viral delivery methods are to be improved and viral spread within the tumor will have to be enhanced. Here, we will review the outcome of completed glioma virus therapy trials as well as highlight the ongoing clinical activities. On this basis, we will give an overview of the numerous strategies to enhance therapeutic efficacy of new-generation viruses and novel treatment regimens. Finally, we will conclude with approaches that may be crucial to the development of successful glioma therapies in the future.     

Virus-based therapies for colon cancer

Viral vectors are under development for anticancer therapy. As they can infect tumours and activate the immune system, viral vectors may directly destroy cancers (oncolysis), deliver genes with antitumour activity directly to the cancer cells, or act as cancer vaccines. Better insights into the biology of the various vectors in use (e.g., poxvectors, adenovirus, adeno-associated virus, reovirus, Newcastle disease virus) are making it possible to engineer viruses that are more tumour-specific, efficient at tumour infection, and which have enhanced safety due to incorporation of safeguards should dissemination occur. As considerable research has focused on therapy of colon cancer with viral vectors, this review will illustrate the major concepts of viral therapy of cancers with examples from studies targeting colorectal carcinoma.     

Friendly fire: redirecting herpes simplex virus-1 for therapeutic applications

Herpes simplex virus-1 (HSV-1) is a relatively large double-stranded DNA virus encoding at least 89 proteins with well characterized disease pathology. An understanding of the functions of viral proteins together with the ability to genetically engineer specific viral mutants has led to the development of attenuated HSV-1 for gene therapy. This review highlights the progress in creating attenuated genetically engineered HSV-1 mutants that are either replication competent (viral non-essential gene deleted) or replication defective (viral essential gene deleted). The choice between a replication-competent or -defective virus is based on the end-goal of the therapeutic intervention. Replication-competent HSV-1 mutants have primarily been employed as antitumor oncolytic viruses, with the lytic nature of the virus harnessed to destroy tumor cells selectively. In replacement gene therapy, replication-defective viruses have been utilized as delivery vectors. The advantages of HSV-1 vectors are that they infect quiescent and dividing cells efficiently and can encode for relatively large transgenes.     

5-Fluorouracil and gemcitabine potentiate the efficacy of oncolytic herpes viral gene therapy in the treatment of pancreatic cancer

Oncolytic herpes viruses are attenuated, replication-competent viruses that selectively infect, replicate within, and lyse cancer cells and are highly efficacious in the treatment of a wide variety of experimental cancers. The current study seeks to define the pharmacologic interactions between chemotherapeutic drugs and the oncolytic herpes viral strain NV1066 in the treatment of pancreatic cancer cell lines. The human pancreatic cancer cell lines Hs 700T, PANC-1, and MIA P_aC_a-2 were treated in vitro with NV1066 at multiplicities of infection (MOI; ratio of the number of viral particles per tumor cell) ranging from 0.01 to 1.0 with or without 5-fluorouracil (5-FU) or gemcitabine. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Viral replication was measured using a standard plaque assay. Six days after combination therapy, 76% of Hs 700T cells were killed compared with 43% with NV1066 infection alone (MOI = 0.1) or 0% with 5-FU alone (2 βmol/L) (P < .01). Isobologram and combination-index analyses confirmed a strongly synergistic pharmacologic interaction between the agents at all viral and drug combinations tested (LD5 to LD95) in the three cell lines. Dose reductions up to 6- and 78-fold may be achieved with combination therapy for NV1066 and 5-FU, respectively, without compromising cell kill. 5-FU increased viral replication up to 19-fold compared with cells treated with virus alone. Similar results were observed by combining gemcitabine and NV1066. We have demonstrated that 5-FU and gemcitabine potentiate oncolytic herpes viral replication and cytotoxicity across a range of clinically achievable doses in the treatment of human pancreatic cancer cell lines. The potential clinical implications of this synergistic interaction include improvements in efficacy, treatment-associated toxicity, tolerability of therapeutic regimens, and quality of life. These data provide the cellular basis for the clinical investigation of combined oncolytic herpes virus therapy and chemotherapy in the treatment of pancreatic cancer. Presented at the Forty-Sixth Annual Meeting of The Society for Surgery of the Alimentary Tract, Chicago, Illinois, May 141-18, 2005 (oral presentation). Supported in part by training grant T 32 CA09501 (D.P.E. and K.J.H.), AACR-AstraZeneca Cancer Research and Prevention fellowship (P.S.A), grants RO1 CA 76416 and RO1 CA/DK80982 (Y.F.) from the National Institutes of Health, grant BC024118 from the U.S. Army (Y.F.), grant IMG0402501 from the Susan G. Komen Foundation (Y.F.), and grant 032047 from Flight Attendant Medical Research Institute (Y.F.).     

Herpes oncolytic therapy of salivary gland carcinomas

Bcl-xL functions as a dominant regulator of apoptotic cell death and is implicated in chemotherapeutic resistance of malignant pleural mesothelioma (MPM). Mesothelioma cell lines demonstrate increasing levels of Bcl-xL as resistant clones are selected in vitro. Moreover, upon introduction of antisense oligonucleotides specific to Bcl-xL mRNA, MPM cells are sensitized to chemotherapeutic agents. Here we describe the therapeutic effects of a novel combination therapy, Bcl-xL antisense oligonucleotide (ASO 15999) and cisplatin, on mesothelioma cell lines in vitro and in vivo; in addition, efficacy of ASO 15999 in decreasing tumor load as well as its effect on survival in an animal model. Finally, we initiated preliminary toxicity studies involved with intraperitoneal (IP) injections of ASO 15999 into mice. This novel combination, with doses of cisplatin four times below established IC(50) levels, significantly decreased viability of MPM cell lines after 48 hr. The growth of established mouse flank human tumor xenografts was reduced with intra-tumor administration of ASO 15999. Local spread and development of IP xenografts was reduced with treatments of ASO alone, and survival of mice afflicted with these xenografts was prolonged after administration of ASO alone and ASO 15999 + cisplatin combination therapy. These findings suggest that ASO 15999 sensitizes MPM cell lines to the toxic effects of cisplatin. ASO 15999 induced reduction of Bcl-xL is effective in slowing the progression of human mesothelioma cell lines both in vitro and in vivo. More notably, the combination of Bcl-xL ASO and cisplatin extends survival in an orthotopic tumor xenograft model.