Adrenocortical carcinoma (ACC) is a rare cancer with poor prognosis. Its rarity results in a lack of screening program and patients present with advanced disease. Five-year survival, all stages, approaches 35%. Accepted current therapies include surgery with chemotherapy and mitotane. The first international RCT of chemotherapy and mitotane regimens for advanced ACC showed no increase in overall survival. There is a need for novel treatments for ACC. MicroRNAs (miRNAs) are small non coding RNAs functioning in RNA silencing and post-transcriptional gene regulation. They are implicated in tumourigenesis and cancers’ susceptibility and response to chemotherapy and radiation.
AIMS AND HYPOTHESIS
There has recently been a focus of interest on unexpected clinical response of cancer “super responders” to treatment and the underlying molecular mechanisms. Further to this, we aimed to identify differentially expressed miRNAs between “responsive” and “non-responsive” Stage 4 ACC patients to adjuvant treatment. We speculate that these miRNAs may play a tumour suppressive and chemosensitising role in ACC.
Frozen stage 4 ACC tissue obtained from the Kolling Institute of Medical Research Tumour Bank were stratified into “responsive” and “non-responsive” groups based on clinical survival and treatment response. Tumour miRNA profiling was performed with Taqman Low Density Array Cards (ThermoFisher Scientific). Differentially expressed miRNAs between the groups were selected. The candidate miRNA mimic was transfected onto the ACC H295R cell line (Lipofectamine RNAiMax,ThermoFisher Scientific). Transfected H295R cells were treated with chemotherapy drugs/mitotane at various concentrations. Cell proliferation/viability was assessed with MTS assays (Promega).
miR-431 was significantly underexpressed in the “non-response” group and confirmed via individual RT-qPCR in the cohort. Restoration of miR-431 in the ACC cell line reduced cell proliferation in ACC cells. There are some early results suggesting a chemosensitising effect, with a decrease in IC50 in the miR-431 transfected cells versus negative control transfected, for mitotane and doxorubicin.
In vitro data shows an miRNA therapeutic potential of increasing chemotherapy/mitotane responses in ACC treatment. Further work to ascertain underlying molecular mechanisms is required.