Abstract 3993: Th1 cytokines regulate apoptotic cell death and HER family RTK expression in murine and human breast cancer lines

Abstract

Abstract A recent neoadjuvant vaccine trial to treat early breast cancer demonstrated powerful induction of Th1 immunity against the HER-2, complete pathologic responses in over 18% of subjects, and for many subjects, evidence of down-regulated HER-2 expression on residual disease. To explain these observations, we investigated the action of archetypical Th1 cytokines (TNF-α + IFN-γ) on both murine and human breast cancer cell lines that varied in the surface expression of HER-family receptor tyrosine kinases. We found that most tumor cell lines were sensitive to dual Th1 cytokines as evidenced by lower metabolic activity (alamar blue assay), lower proliferation, and enhanced apoptosis (AnnexinV/PI staining and TUNEL assay) as well as a reversible inhibition of surface expression of HER proteins. Apoptotic cell death was accompanied by demonstrated increases in activated caspase-3. Furthermore, the pharmacologic caspase-3 activator, procaspase-activating compound (PAC-1), mimicked both the killing effects and HER-2 suppressive activities of Th1 cytokines, while the caspase 3/7 inhibitor ((5-[(S)-(+)-2-(Methoxymethyl)pyrrolidino]sulfonylisatin), prevented cytokine-induced HER-2 downregulation. These studies therefore demonstrated that many of the in vivo effects of vaccination (apparent tumor cell death and loss of HER-2 expression) could be replicated in vitro using only the principle Th1 cytokines. These findings are consistent with the notion that IFN-γ and TNF-α work in concert to mediate some of the biological effects of therapeutic Th1-polarizing vaccination through the induction of a caspase 3-dependent cellular death mechanism. Citation Format: Prachi M. Namjoshi, Lori Showalter, Brian Czerniecki, Gary K. Koski. Th1 cytokines regulate apoptotic cell death and HER family RTK expression in murine and human breast cancer lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3993.