Thesis, COLLÉGIALITÉ

Abstract

Small cell lung cancers (SCLCs) are highly aggressive neuroendocrine (NE) malignancies, accounting for 15% of all lung cancers. In addition to nearly universal loss of TP53 and RB1 tumour suppressor genes, 20-25% of SCLCs tumors carry loss-of-function (LOF) mutations within members of the NOTCH receptors family genes. Those mutations, drivers of SCLC, are often considered undruggable, there is therefore no effective targeted therapies for SCLC. Herein, we investigated selective vulnerabilities of SCLC carrying NOTCH LOF mutations, with an aim to lay a preclinical foundation to develop target therapies for SCLC tumors. We mainly worked in vitro with human and murine cells derived from SCLC tumors, which we genetically modified by CRISPR-Cas9- mediated knockouts (KO). We approached the subject from two angles of research : 1 NOTCH LOF mutation as a driver of the POU2F3-C11ORF53/COLCA2 complex First, we focused on the dependencies of non-neuroendocrine SCLC-P subtypes, expressing the key transcription factor POU2F3. SCLC-Ps are thought to depend on either transcriptional cofactors C11ORF53 or COLCA2. We studied the dependencies of different cell lines carrying or not NOTCH2 loss- of-function mutation. Finally, we hypothesized that C11ORF53 and POU2F3 formed a complex in all SCLC-Ps, regardless of their dependence on one cofactor or the other, since this complex would itself be dependent on C11ORF53. 2 NOTCH LOF mutations as a vulnerability synthetically lethal with TRIM28 Secondly, we validated a dTAG system applying to TRIM28 in vitro in neuroendocrine SCLC cells (SCLC- A) derived from genetically engineered mice (GEMMs). With this model we investigated the synthetic lethal interaction between NOTCH2 and TRIM28 in SCLC cells, previously described by Dr. Hong. In this context, we investigated how NOTCH participates in the repression of endogenous retroviruses (ERVs), as TRIM28 mainly function as a repressor of ERVs. We notably observed that the absence of TRIM28 decreased MYC-L expression, a key linage transcription factor of SCLC-A.