Characterisation of a novel phage-guided gene delivery vector and investigation of its gene therapy efficacy against metastatic cancer.

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The majority of cancer patients die because of metastases which are established after cancer cells leave their initial site or primary tumour in order to spread and form secondary tumours or metastases in other tissues. Failure of conventional therapies (surgery, radiotherapy and chemotherapy) to treat metastases is associated with the high number of metastases located in various tissues, requiring systemic treatment to reach all these metastases. Conventional systemic chemotherapeutic agents have been used but often ineffective, mostly because they are not selective, resulting in their accumulation in healthy tissues, which comes with sever side effects limiting the chemotherapeutic dose to be injected to patients. Gene therapy, or therapy using genes, is a promising treatment approach against metastatic cancer. Gene therapy requires a vector (vehicle or delivery system) to carry the therapeutic gene and achieve its delivery at the tumour site. Human viruses have mostly been used to design vectors of gene therapy because they can enter human cells and deliver therapeutic genes as part of their natural infection process. Gene therapy for cancer has been attempted for more than 26 years. However, like chemotherapy, gene therapy has faced a major challenge that has also been inefficacy after systemic administration, limiting its effectiveness against metastases since real clinical benefit against metastatic cancer can only happen with systemic gene therapy. These challenges are associated with vectors of gene therapy, since the vectors accumulate in various healthy tissues and get neutralized by the body immune response against these viral vectors. Our previous work shows that the harmless and non-pathogenic bacteriophage or phage, viruses that infect bacteria only, can deliver genes to human cells if they are engineered to display ligands on their capsid. These ligands allow the bacteriophage to bind to receptors on human cells resulting in their entry into the cells and expression of the therapeutic genes. If the target receptor is specific in cancer, then the phage vector becomes targeted after systemic administration to deliver therapeutic genes to cancer while sparing the healthy tissues. Our first generation of these phage vectors showed safety and anti-tumour efficacy in preclinical models of cancer after intravenous administration. We have spent the last 10 years to improve these vectors and generate systems that can overcome their limitations since bacteriophages have evolved to infect bacteria only with no developed strategies to express genes in human cells. Indeed efficacy of gene therapy depends on the ability of vectors to express genes at therapeutic levels in tumours. Importantly, very recently our efforts have yielded a bacteriophage vector that could make a breakthrough in systemic gene therapy of metastatic cancer. It is important to undertake this work because the vector shows ability to overcome major limitations that cancer gene therapy has faced and could bring to fruition the promise of gene therapy to save the lives of patients with deadly metastatic cancers.