SENESCENCE AND IMMUNOTHERAPY IN BREAST CANCER MEDIATED BY STAT3 BLOCKADE

MARA DE MARTINO, MARÍA F. MERCOGLIANO, MERCEDES TKACH, LEANDRO VENTURUTTI, CECILIA J. PROIETTI, PATRICIA V. ELIZALDE, ROXANA SCHILLACI

Congreso; LXIV Reunión Anual de la Sociedad de Inmunología (SAI); 2016

Stat3 is constitutively active in 60% of breast cancer(BC) where it promotes tumor progression and immuneevasion. We described in murine BC models that Stat3inhibition leads to a senescence program and that immunizationof mice with Stat3-blocked BC cells inducesan antitumoral immune response that involves CD4+ Thcells and NK cells. Here, we studied the mechanism ofsenescence induced by Stat3 inactivation and the useof the supernatant (SN) from Stat3-blocked cells to formulatean effective immunotherapy (IT). Knockdown ofStat3 with siRNA induced senescence in triple negative(4T1, MDA-MB-231 and MDA-MB-468 cells) and ErbB2positive (C4HD, JIMT-1 and KPL-4 cells) BC models,determined by SA-â-gal staining. Also, we observedan increase in trimethylation of histone H3 at lysine 9and in cell cycle inhibitors expression (p16INK4a (p16) orp21CIP1). Simultaneous transfection with siRNAs targetingStat3 and p16 or p21CIP1 reverted the senescentphenotype. Interestingly, Stat3 inhibition in vivo inducedsenescence and an increased p16 expression in 4T1tumor. Then, we embedded the SN of C4HD or 4T1cells transfected with Control siRNA (SN-Control), Stat3siRNA (SN-Stat3) or the combination of Stat3 and p16siRNAs (SN-Stat3+p16) in a slow delivery depot as anadjuvant of a cellular IT. Prophylactic IT before C4HDtumor challenge with SN-Stat3 and SN-Stat3+p16 decreasedtumor growth (72%, p<0.05 and 51%, p<0.05respectively vs. SN-Control). Therapeutic IT after 4T1tumor implantation with SN-Stat3 and SN-Stat3+p16decreased tumor growth (51%, p<0.001 and 41%,p<0.01 respectively vs. SN-Control) and pulmonarymetastasis (70%, p<0.05 and 50%, ns. respectivelyvs. SN-Control). In both IT protocols the result was associatedwith greater cytotoxic activity of NK cells andan increase in the number of memory CD4+ T cells vs.SN-Control. These results suggest that Stat3 blockadedrives a senescence program in BC cells and the SNStat3is an effectiveadjuvant for IT.