Research

Eloise Morecroft

Tumour suppressor protein OPCML as an anti-cancer drug: a potential biological therapeutic enabled through self-splicing GPI mimetics

Eloise Morecroft - 3rd year PhD

Abstract

Ovarian cancer remains the most deadly gynaecological malignancy today and little progress has been made in extending the overall survival or cure rates of patients. Targeted therapy in ovarian cancer holds much promise. We have identified a tumour suppressor gene, OPCML, which is silenced by methylation in 85% of ovarian cancer patients (Sellar et al, Nat Genet 2003). When re-expressed in tumour cells, OPCML prevents cell proliferation and tumorigenicity by binding to a subset of receptor tyrosine kinases (RTKs) and down-regulating their growth signalling pathways (McKie et al, Cancer Discov, 2012). More recently, we have also found that OPCML inhibits mesenchymal to epithelial transition, as evidenced by loss of the transcriptional regulator Slug and other EMT factors (unpublished data). OPCML is a GPI-anchored protein that is localised in the raft fraction of the outer surface of the plasma membrane. Since GPI anchored proteins are exceedingly challenging to express recombinantly and purify for therapeutic use, our aim is to develop a chemically lipidated form of OPCML bearing a GPI mimetic that inserts into the plasma membrane of ovarian cancer cells, and that can ultimately be pharmaceutically produced and used as tumour suppressor therapy in patients. For this, we will express recombinant soluble OPCML mutationally altered to site-specifically introduce C-terminal domains suitable for chemical coupling based on ligation technologies recently established in the ICB, and adding novel GPI mimetic motifs that target OPCML to lipid rafts. The diversity of functionality we can introduce in this mimetic will facilitate handling and also modulate the strength and stability of membrane attachment, as well as providing powerful functional handles for imaging and proteomic analysis. In order to study the function of the modified protein, we will apply single cell analysis using microfluidic antibody capture (MAC) chips to assay for the pharmacodynamic endpoints, these being the down-regulation of the RTKs with which it interacts and the depletion of the transcription factor Slug. This project will allow us to explore and optimise the production of a form of OPCML that would have the potential to become a new drug for ovarian cancer and, at the same time, to develop an accurate and novel assay to measure OPCML function in single cells.