Bafilomycin A1 triggers proliferative potential of senescent cancer cells in vitro and in NOD/SCID mice

// Halina Was 1, 2 , Kamila Barszcz 1, 2 , Joanna Czarnecka 1, 2 , Agata Kowalczyk 3 , Tytus Bernas 4 , Ewelina Uzarowska 5 , Paulina Koza 5, 6 , Agata Klejman 5 , Katarzyna Piwocka 3 , Bozena Kaminska 2 , Eva Sikora 1 1 Laboratory of Molecular Basis of Ageing, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland 2 Laboratory of Molecular Neurobiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland 3 Laboratory of Cytometry, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland 4 Laboratory of Imaging Tissue Structure and Function, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland 5 Laboratory of Animal Models, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland 6 Laboratory of Neurobiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland Correspondence to: Halina Was, email: h.was@nencki.gov.pl Keywords: colon cancer, chemotherapy, senescence, autophagy, angiogenesis Received: June 07, 2016      Accepted: December 12, 2016      Published: December 21, 2016 ABSTRACT Anticancer therapies that induce DNA damage tend to trigger senescence in cancer cells, a process known as therapy-induced senescence (TIS). Such cells may undergo atypical divisions, thus contributing to tumor re-growth. Accumulation of senescent cancer cells reduces survival of patients after chemotherapy. As senescence interplays with autophagy, a dynamic recycling process, we sought to study whether inhibition of autophagy interferes with divisions of TIS cells. We exposed human colon cancer HCT116 cells to repeated cycles of a chemotherapeutic agent – doxorubicin (doxo) and demonstrated induction of hallmarks of TIS (e.g. growth arrest, hypertrophy, poliploidization and secretory phenotype) and certain properties of cancer stem cells (increased NANOG expression, percentages of CD24+ cells and side population). Colonies of small and highly proliferative progeny appeared shortly after drug removal. Treatment with bafilomycin A1 (BAF A1), an autophagy inhibitor, postponed short term in vitro cell re-population. It was associated with reduction in the number of diploid and increase in the number of poliploid cells. In a long term, a pulse of BAF A1 resulted in reactivation of autophagy in a subpopulation of HCT116 cells and increased proliferation. Accordingly, the senescent HCT116 cells treated with BAF A1 when injected into NOD/SCID mice formed tumors, in contrast to the controls. Our results suggest that senescent cancer cells that appear during therapy, can be considered as dormant cells that contribute to cancer re-growth, when chemotherapeutic treatment is stopped. These data unveil new mechanisms of TIS-related cancer maintenance and re-population, triggered by a single pulse of BAF A1 treatment.