Senescence and immunotherapy in cancer mediated by Stat3 blockade

ELIANE PIAGGIO; MARÍA FLORENCIA CHERVO; MARA DE MARTINO; PATRICIA VIRGINIA ELIZALDE; MARIA FLORENCIA MERCOGLIANO; ROXANA SCHILLACI; CECILIA JAZMÍN PROIETTI; MERCEDES TKACH

París

Conferencia; International Cell Senescence Association Conference 2017; 2017

International Cell Senescence Association

Constitutiveactivation of Stat3 in diverse cancers is associated with tumor progression andimmune evasion. We described in murine breast cancer (BC) models that Stat3inhibition induces senescence and that immunization of mice with Stat3-blockedBC cells induces an antitumoral immune response that involves CD4+ Th and NKcells. Here, we studied the mechanism of senescence induced by Stat3inactivation and the use of the supernatant (SN) from Stat3-blocked cells toformulate an immunotherapy (IT). Knockdown of Stat3 with siRNA increased SA-β-gal staining in triple negative (4T1, MDA-MB-231and MDA-MB-468 cells) and ErbB2 positive (C4HD, JIMT-1 and KPL-4 cells) BCmodels, in colon cancer and melanoma. However, in cells that have low levels ofStat3 activation (BT-474, T47D and MCA101), the inhibition of Stat3 did notproduce changes in this marker. In senescent cells, we observed an increase intrimethylation of histone H3 at Lys9 and in cell cycle inhibitors expression(p16INK4a (p16) or p21CIP1). Interestingly, Stat3 inhibition in vivo increasedSA-β-gal staining and p16 expression in 4T1 tumor.Then, we embedded the SN of C4HD or 4T1 cells transfected with Control siRNA(SN-Control), Stat3 siRNA -senescent cells- (SN-Stat3) or the combination ofStat3 and p16 siRNAs -non senescent cells- (SN-Stat3+p16) in a slow deliverypellet. The IT protocol was to implant s.c. these pellets together with aninjection of irradiated wild-type tumor cells. Prophylactic IT with SN-Stat3and SN-Stat3+p16 using C4HD tumor model, decreased tumor growth (72% and 51%,respectively vs. SN-Control). Therapeutic IT with SNStat3 and SN-Stat3+p16 inmice bearing 4T1 tumor decreased tumor growth (51% and 41%, respectively vs.SN-Control) and pulmonary metastasis (70% and 50%, respectively vs. SNControl).In both IT protocols the antitumor effect was associated with greateractivation and cytotoxic activity of NK cells and an increase in memory CD4+ -Tcells vs. SN-Control. We observed that SN-Stat3 and SN-Stat3+p16 inhibitedproliferation of 4T1 cells but increased the proliferation of T lymphocytes andthe number of IFNɣ producing CD4+ -T cells in vitro. These results suggest thatStat3 blockade induces senescence in tumor cells with high activation of Stat3and the SN-Stat3 is an effective adjuvant for IT.