Senescence and immunotherapy in cancer mediated by Stat3 blockade

MERCOGLIANO MF; ELIZALDE PV; TKACH M; PROIETTI CJ; SCHILLACI R; DE MARTINO M; CHERVO, MF; PIAGGIO E

Paris

Congreso; International Cell Senescence Association Congress 2017; 2017

International Cell Senescence Association

Constitutive activation of Stat3 in diverse cancers is associated with tumor progression and immune evasion. We described in murine breast cancer (BC) models that Stat3 inhibition induces senescence and that immunization of mice with Stat3-blocked BC cells induces an antitumoral immune response that involves CD4+Th and NK cells. Here, we studied the mechanism of senescence induced by Stat3 inactivation and the use of the supernatant (SN) from Stat3-blocked cells to formulate an immunotherapy (IT). Knockdown of Stat3 with siRNA increased SA-β-gal staining in triple negative (4T1, MDA-MB-231 and MDA-MB-468 cells) and ErbB2 positive (C4HD, JIMT-1 and KPL-4 cells) BC models, in colon cancer and melanoma. However, in cells that have low levels of Stat3 activation (BT-474, T47D and MCA101), the inhibition of Stat3 did not produce changes in this marker. In senescent cells, we observed an increase in trimethylation of histone H3 at Lys9 and in cell cycle inhibitors expression (p16INK4a (p16) or p21CIP1). Interestingly, Stat3 inhibition in vivo increased SA-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 of Stat3 and p16siRNAs-non senescent cells- (SN-Stat3+p16) in a slow delivery pellet. The IT protocol was to implant s.c. these pellets together with an injection of irradiated wild-type tumor cells. Prophylactic IT with SN-Stat3 and SN-Stat3+p16 using C4HD tumor model, decreased tumor growth (72% and 51%, respectively vs. SN-Control). Therapeutic IT with SN-Stat3 and SN-Stat3+p16 in mice bearing 4T1 tumor decreased tumor growth (51% and 41%, respectively vs. SN-Control) and pulmonary metastasis (70% and 50%, respectively vs. SN-Control). In both IT protocols the antitumor effect was associated with greater activation and cytotoxic activity of NK cells and an increase in memory CD4+-T cells vs. SN-Control. We observed that SN-Stat3 and SN-Stat3+p16 inhibited proliferation of 4T1 cells but increased the proliferation of T lymphocytes and the number of IFNɣ producing CD4+-T cells in vitro. These results suggest that Stat3 blockade drives a senescence program in tumor cells with high activation of Stat3 and the SN-Stat3 is an effective adjuvant for IT.