|Ph.D Student||Binenbaum Yoav|
|Subject||Exosomes Secreted by Macrophages Facilitate Chemotherapy|
Resistance in Pancreatic Ductal Adenocarcinoma
|Department||Department of Medicine||Supervisor||Professor Ziv Gil|
|Full Thesis text|
Despite years or research, cure rates of Pancreatic Ductal Adenocarcinoma (PDAC) are disappointingly low, with 5-year survival rate that approximates a mere 5%. This dismal prognosis stems mainly from late detection of the disease and chemotherapy resistance. Gemcitabine, the drug of choice for the treatment of PDAC, is a cytidine analog that acts to inhibit cell growth by termination of DNA replication. Our group has previously demonstrated that tumor associated macrophages (TAMs), which are abundant in PDAC stroma, cause gemcitabine resistance by inducing expression of cytidine deaminase (CDA), the enzyme that metabolizes gemcitabine to its inactive form. The present thesis shows that TAMs communicate gemcitabine resistance to by secretion of exosomes, which are internalized by the PDAC cell. Macrophage-derived-exosomes (MDEs) were significantly enriched in PDAC cells relatively to their stromal companions, indicating selective affinity of exosomes towards cancer cells. Mice lacking exosomal secretion due to mutations in Rab27 a/b genes responded significantly better to gemcitabine than did wildtype mice and had lower intra-tumoral CDA expression.
Analysis of MDE
content suggested that shuttling of deoxycytidine and miR-365 by exosomes was responsible
for CDA induction and gemcitabine resistance. miR-365 increased the tri-phospho-nucleotide
pool in cancer cells, inducing CDA's expression and hastening the excretion of
chemotherapy out of the cell. To overcome drug resistance, adoptive transfer of
macrophages loaded with miR-365 antagonist was performed, which lowered CDA
expression and translated to better response to chemotherapy and overall survival.
These results identify macrophage-derived-exosomes as key regulators of gemcitabine resistance in pancreatic cancer, facilitating the transfer of miR-365 and rewiring of the intracellular drug metabolism.