Identification of potential oncogenes as novel therapeutic targets by RNAi screening

Every year, more than one million of people worldwide are diagnosed with colorectal cancer (CRC). Even though preventive screenings have been able to reduce incidence and mortality, nearly half of the patients die following the diagnosis and the treatment. In particular, a not negligible part is due to recurrences after treatment, probably caused by a limited efficacy of the current therapies. To improve the therapeutic success and options, repositioned or new drugs and novel therapeutic targets should be taken in consideration. Moreover, in the last years, large cancer genome analyses projects have shed new light on previously unknown genetic and biological makeup of this disease. Starting from a collection of amplified genes identified in CRC samples by The Cancer Genome Atlas (TCGA), the aim is to identify whether these genes have an oncogenic activity by using a RNAi screening, with a drug discovery perspective. Using colon cancer cell lines, we set up a functional RNAi screening, to address the impact of downregulation of the putative oncogenes on cell viability. The preliminary results have shown that among the genes, the silencing of only one could indeed significantly reduce cell viability, that was STARD3. Further validations confirmed STARD3 activity on cell viability, suggesting its possible involvement in cell cycle regulation. In fact, cell cycle analyses revealed an alteration of the phases, showing a decrease of G1 and S phases and concomitant increase of G2/M phase when STARD3 was knockdown. The effect of STARD3 downregulation, that was a block of G2/M transition, also increased the population of cells in sub-G1, a status often associated with apoptosis. Programmed cell death was indeed analysed, showing that the amount of apoptosis was higher after silencing among all cell lines. Moreover, we shown that STARD3 is necessary for cancer cell lines capability to grow regardless their interaction with solid substrate, hence substantiating the general concept that STARD3 could be considered a proper oncogene. Whereas further investigation should be carried out, STARD3 could represent a novel oncogene that play a supporting role in colorectal cancer oncogenesis and development. Finally, harboring a cholesterol binding domain, through which it exerts its function, STARD3 could represent a suitable pharmacological target of a novel class of inhibitors or nucleic acids.