Clinical biology of OPCML and its potential therapeutic applications in ovarian and breast cancers

Abstract

Opioid binding protein cell adhesion molecule like (OPCML), is a glycosyl phosphatidylinositol (GPI) anchored cell adhesion molecule, that was discovered by our lab to be somatically methylated with its expression silenced in over 80% of epithelial ovarian cancers (EOCs) (Sellar, Watt et al. 2003). This was subsequently confirmed and further expanded by other groups to include many other tumours (Czekierdowski, Czekierdowska et al. 2006, Yao, Li et al. 2006, Zhang, Ye et al. 2006, Chen, Ye et al. 2007). OPCML exhibited the functional characteristics of a tumour suppressor gene (TSG) both in vitro and in vivo (Sellar, Watt et al. 2003). Our lab has defined the function of OPCML, acting on a disparate set of RTKs (EphA2, FGFR1, FGFR3, HER2, HER4) by being a systems level regulator that ultimately leads to phospho ERK (pERK) and phospho AKT (pAKT) down-regulation, inducing apoptosis and growth inhibition in cancer but not normal cells (McKie, Vaughan et al. 2012). The overall aim of this PhD was to investigate the use of OPCML as a targeted therapy in ovarian cancer. The key finding of this thesis is the evidence of potential therapeutic effects of OPCML along with other targeted therapies. Here, I report on in vitro sensitising effects of OPCML to anti-HER2 but not anti-EGFR therapy in ovarian and breast cancer cell lines, thus further confirming earlier group findings regarding OPCML selectivity with HER2 but not EGFR. I have also explored the association of OPCML and different angiogenic factors; namely VEGFA and the VEGFR family, with evidence that OPCML expression decreases levels of VEGFR3 as demonstrated by western blotting under different stimulation conditions, FACS and pull down experiments. Another part of this thesis explores further characterisation of OPCML at the cellular protein level via the use of reverse phase protein microarray (RPPA), and further western blots to validate some of the results as well as proliferation assays confirming the growth inhibition properties of OPCML transiently transfected into a biologically varied group of ovarian cancer cell lines. The final part shows attempts to further develop a recombinant OPCML (rOPCML) that mimic the function of the original gene in prokaryotic and later in HEK293 mammalian cell vector which proved challenging. A ‘sandwich’ ELISA plate to measure the generated His-tagged rOPCML protein was developed en route. In conclusion, this PhD thesis progressed our understanding of OPCML biology and its potential future use as targeted therapy in cancer.