In 2015 there were an estimated 2.5 million people living with cancer in the UK. This number will rise to 4 million by the year 2030. 1.1 million of these deaths will be due to colorectal cancer. For those patients who have progressive metastatic disease, that is not amenable to surgery, less than 10% of patients will survive 5 years. The standard regime for advanced or metastatic colorectal cancer is chemotherapy. This can take the form of mono-therapy with Capcitebine or oxaliplatin, in combination with 5-fluorocil (5-FU) and folinic acid. However, acquired drug resistance is a major issue and this can result in a decrease in therapeutic efficacies in cancer treatments.
Oncolytic viruses (OV) have been used to treat a variety of different cancers and are safe and well tolerated in cancer patients. They can be used independently or in conjunction with more traditional treatments such as chemotherapy and radiotherapy. Most notably, the US Food and Drug Administration (FDA) has licensed the OV, Talimogene Iaherparepvec (T-VEC), for patients with inoperable melanoma. OVs preferentially infect and kill cancer cells by two differential methods. Firstly, the cancer cells are destroyed by viral replication causing the release of viral progeny, which go on to destroy the additional tumour cells. Secondly, OV’s induce cell death by activating the human immune system, thereby acting as a cancer immunotherapy.
To date, 2-Dimensional (2D) cell cultures models have been utilised to test the efficacy of OV against CRC. However, 2D cell layers lack many features that are exhibited in human cancer cells, such as the complex cellular heterogeneity, or cell- to-cell interactions, that are present in clinical tumours. By contrast, 3-dimensional (3D) multicellular models are more likely to represent the complex tumour microenvironment (TME) as they develop cell-cell interactions, hypoxic areas, and from physical barriers for drug penetration. Therefore, 3D structures provide a more realistic pre-clinical model for testing of novel therapeutic agents.
MiRNAs are small, non-coding regulatory RNAs that bind to mRNA sequences and decrease mRNA stability prevent translation of specific target proteins. Significantly, miRNA aberrations have been associated with drug resistance in CRC. Dysregulation of miRNAs has been associated in a variety of solid tumours including gastric, breast and lung cancers. Pivotally, miRNA-145 is down regulated in CRC. If this miRNA can be re-introduced we can aim to restore chemo-sensitivity in CRC by normalizing gene expression. Evidence shows that over-expression of miR-145 can inhibit cell proliferation, migration and invasion.
As OV specifically target the TME, they can preferentially replicate in malignant cells and are also well tolerated in the patient population. Therefore, they are ideal vehicles to deliver miRNA species into malignant cells. Moreover, the ability of OV to synergise with chemotherapy is well established and therefore this approach would hopefully build on current studies and identify a novel approach to overcome drug resistance.
In this project we aim to develop and characterise superior 3D models of CRC, and test the efficacy of the OV, Maraba virus (MG-1), as a direct cytotoxic agent. We will also explore miRNA delivery using MG-1 and perform initial studies to investigate the ability miRNA-expressing MG-1 to potentiate the cytotoxic capabilities of the chemotherapy agent, 5-FU.
