Study of the molecular mechanisms by which non-coding RNAs (IncH19 and miR-675) control tumor progression and resistance to drug therapy in colorectal cancer

Colorectal cancer (CRC) is one of the most common malignant tumors of the human gastrointestinal system, the third most frequently diagnosed cancer and the second most deadly worldwide, with almost one million deaths annually. The high mortality rate ismainly due to the increasing events of primary or acquired resistance to conventionalchemotherapy.Nowadays, advances in understanding the pathophysiology of CRC have increased thevariety of therapeutic options for both local and metastatic diseases, leading to targetedpersonalised medicine approaches. New therapeutic options are increasingly emerging, suchas immunotherapy, non-coding RNA-based anti-tumor therapies or epigenetic therapiesbased on the use of anti-cancer epigenetic compounds, such as Histone Deacetylase Inhibitors(HDACis).Accumulating evidence strongly indicates that non-coding RNAs (ncRNAs) are aberrantlyexpressed in different cancer types and play a crucial role in numerous key biologicalprocesses, including drug resistance.A more precise understanding of the molecular mechanisms of action of the ncRNAs andtheir specific downstream targets could be advantageous in order to improve therapeuticstrategies and overcome chemoresistance events.This PhD project aims to investigate the role of long non-coding RNA H19 (lncH19) and itsintragenic microRNA, miR-675, on the control of tumor progression and chemoresistancein CRC cells, with the ultimate goal of identifying new targets and therapeutic strategiesto enhance conventional therapy.Interestingly, for the first time to our knowledge, our data reveal a dual role of the lncRNAH19 and its miRNA, as both therapeutic targets and as putative prognostic biomarkers.Indeed, our data demonstrated that lncH19 enforces CRC cell resistance to 5-Fluorouracil(5-FU) especially under chronic hypoxic conditions, through its intragenic miRNA; on theother hand, its expression seems to be functional for the anti-tumor activity of the epi-drugas for the HDACi ITF2357.Specifically, in the first part of this project we demonstrate that under hypoxic stimulation,lncH19 gives rise to miR-675 which, in turn, inhibits caspase-3 expression. The inhibitionof miR-675-5p in combination with 5-FU treatment, enhances the pro-apoptotic effects ofthe chemotherapeutic drug and overcomes the hypoxia-induced drug resistance. Our datasuggest the use of AntagomiR-675-5p as an adjuvant to drug treatment.In the second part of the project, we found that lncH19 can contribute to the antitumoractivity of the HDACi ITF2357. Our data demonstrated that H19, after ITF2357 administrationpromotes TP53 stabilization by acting as an endogenous competitive sponge(ceRNA) for miRNAs targeting pro-apoptotic genes. Furthermore, we provided evidencethat ITF2357 is efficacious in colon cancer model overexpressing the lncH19, and it canovercome the 5-FU resistance.Overall, the data obtained from the following PhD project unveiled new mechanisms ofaction by which the lncH19 affects CRC and suggested the use of lncH19 as a putativebiomarker to assess the outcome of therapy in patients with 5-FU-resistant CRC.