Granulosa cell tumours (GCT) are uncommon ovarian cancers that are characterised by an indolent clinical course and significant rates of late recurrence. Furthermore, these tumours are unique from other ovarian cancers with a majority secreting estrogen and inhibin. Aside from invasive surgery, there are limited therapeutic options. Chemotherapy is not effective and associated with severe adverse effects, highlighting the need for targeted therapies in GCT.
Our laboratory has previously shown that the X-linked Inhibitor of Apoptosis protein (XIAP) inhibitors, Smac-mimetics, are an effective combination agent in GCT. XIAP inhibition sensitises cancer cells to anti-cancer therapies through regulating key pro-survival pathways, namely NFkB.
We hypothesised that XIAP inhibition using Smac-mimetics (SM) combined with established drugs targeting additional pathogenic pathways will provide a novel therapeutic strategy for GCT. To determine the most effective combination agents, we performed a high-throughput drug screen (HTS) using both an FDA-approved and an anti-cancer compound library (1μM each compound) +/- SM (500nM). We used two cell lines, KGN (GCT-derived) and hGrC1 (transformed normal granulosa cells). Cell viability was determined using an alamarBlue assay following 72 hours of treatment. We selected two compounds, YM155 (survivin inhibitor), and Panobinostat (HDAC inhibitor) for further investigation. We demonstrated using cell proliferation and viability assays, that YM155 is highly effective as a single agent at 50nM. Additionally, 100nM Panobinostat acted synergistically with 500nM SM. The use of both agents led to an increase in apoptosis at these same concentrations, as demonstrated by increased caspase 3/7 activity. We are currently validating these results by assessing apoptosis using flow cytometry. Further aims will be to determine the mechanism of action of these compounds by investigating the expression of key components of the NFkB signalling pathway. These results represent two different promising therapeutic strategies for GCT, leading to potential clinical translation.