Autophagy (A) inhibition to enhance combined immunotherapy (I) and anti-EGFR treatment (E) in colorectal cancer (CRC).

e14554 Background: Resistance to E impairs survival of metastatic CRC (mCRC) patients. The aim of this study is to assess the preclinical activity of triple inhibition of E, I and A in CRC. Methods: RKO and Colo-205 cell lines were treated with E [cetuximab (C) / panitamumab (P)] and/or I [pembrolizumab (PE) or nivolumab (NI) with/without ipilimumab (IPI)] and/or autophagy inhibitor 3-Methyladenine (3-MA). Phosphorylated EGFR (pEGFR), p62 (SQSTM1), MAP1LC3 (LC3B) and PARP protein levels were detected by Western blotting. Cell viability was determined by MTT Assay. Tumor volumes were determined from 3D cell culture on Corning Matrigel Matrix as well as the apoptotic cell death. Results: E+I combination compared to E alone decreased pEGFR and increased A activation through p62 downregulation and LC3II activation. Similar results were shown for cell viability/apoptosis. Cells were also treated with C or P combined with I plus 3-MA. Triple inhibition suppresses EGFR and blocks A. Compared to E+I, triple inhibition reduced more cell growth/viability. Caspase-3 activity was increased as well as proportion of apoptotic cells (Table). Conclusions: Τhese results indicate that the combinatorial inhibition of A, E and I represents a promising treatment strategy in mCRC that needs further testing. [Table: see text]

Mre11 is expressed in mammalian mitochondria where it binds to mitochondrial DNA

Mre11 is a critical participant in upkeep of nuclear DNA, its repair, replication, meiosis, and maintenance of telomeres. The upkeep of mitochondrial DNA (mtDNA) is less well characterized, and whether Mre11 participates has been unknown. We previously found that high NaCl causes some of the Mre11 to leave the nucleus, but we did not then attempt to localize it within the cytoplasm. In the present studies, we find Mre11 in mitochondria isolated from primary renal cells and show that the amount of Mre11 in mitochondria increases with elevation of extracellular NaCl. We confirm the presence of Mre11 in the mitochondria of cells by confocal microscopy and show that some of the Mre11 colocalizes with mtDNA. Furthermore, crosslinking of Mre11 to DNA followed by Mre11 immunoprecipitation directly demonstrates that some Mre11 binds to mtDNA. Abundant Mre11 is also present in tissue sections from normal mouse kidneys, colocalized with mitochondria of proximal tubule and thick ascending limb cells. To explore whether distribution of Mre11 changes with cell differentiation, we used an experimental model of tubule formation by culturing primary kidney cells in Matrigel matrix. In nondifferentiated cells, Mre11 is mostly in the nucleus, but it becomes mostly cytoplasmic upon cell differentiation. We conclude that Mre11 is present in mitochondria where it binds to mtDNA and that the amount in mitochondria varies depending on cellular stress and differentiation. Our results suggest a role for Mre11 in the maintenance of genome integrity in mitochondria in addition to its previously known role in maintenance of nuclear DNA.