Targeting Stat3 oncogene addiction together with anti PD-1 antibodies as an effective combination for cancer immunotherapy

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

Mainz, Germany

Congreso; 16th CIMT Annual Meeting.; 2018

Association for Cancer Immunotherapy

Stat3 isconstitutively activated in diverse cancers and acts as a critical mediator oftumor immune evasion. Previously, we described in murine breast cancer (BC)models, that blockade of Stat3 activation induces senescence and thatimmunization of mice with irradiated Stat3-blocked BC cells inhibits tumorgrowth. Although senescent cells are growth arrested, they remain metabolicallyactive and develop a senescence-associated secretory phenotype (SASP) that canhave pro as well as antitumorigenic effects. Our objectives were to study thesenescence mechanism induced by Stat3 blockade and to characterize and developan immunotherapy (IT) based on the secretome of Stat3-blocked cells. Here wereport that Stat3 knockdown induced senescence markers in diverse tumor typesincluding BC, colon cancer and melanoma. Stat3 inhibition only inducedsenescence in cells addicted to Stat3, meaning that they depend on Stat3activation to maintain its malignant phenotype. Moreover, we observed that theSASP from Stat3-blocked cells increased the proliferation of T lymphocytes andthe number of IFNɣ producing CD4+T cells in vitro. In addition,this secretome inhibited proliferation of endothelial cells (HUVEC) whencompared to control secretome. These data suggest that the SASP fromStat3-blocked cells can promote an anti-tumor activity. To test thishypothesis in vivo, we designed an immunization protocol based onthe administration of the SASP from Stat3-blocked cells. We used supernatant(SN) from 4T1 (BC) or B16-OVA (melanoma) cells transfected with Control siRNA(SN-Control) or Stat3 siRNA (SN-Stat3) as a slow depot adjuvant of a cellularvaccine based on irradiated wild-type tumor cells. Therapeutic IT with SN-Stat3in mice bearing 4T1 or B16-OVA tumors decreased tumor growth compared withSN-Control. In 4T1 tumors, we also observed a decrease in pulmonary metastasisand an increase in activated NK cells and CD4+T cells in spleen vs. SN-Control.Addition of an anti-PD-1 antibody, that itself has no impact on B16-OVA growth,enhanced the antitumor activity of the SN-Stat3 IT, delays B16-OVA tumor growthand increases tumor infiltration and IFNɣ-producing antigen specific CD8+Tlymphocytes. Next, we characterized the components of SN-Stat3. With amultiplex cytokine array we detected an increase in CD4+T and NKcells-attracting chemokines and IFNɣ-induced cytokines (IP-10, RANTES, TNFα and IL-15) compared to SN-Control. Then weperformed a SILAC-based quantitative proteomics to decode the secretedproteins. We found enrichment in proteins involved in cell adhesion, metabolicand immune system processes. Our work suggests that Stat3 inhibition in severaltumors can activate a senescence-associated antitumor immunity. These resultsdemonstrate that cytokines and proteins released by Stat3 blockade from tumorcells can be used to formulate an effective adjuvant to enhance the antitumoreffect of anti-PD-1 antibodies.