Peristromal niches protect lung cancers from targeted therapies through a combined effect of multiple molecular mediators.

Targeted therapies directed against oncogenic signaling addictions, such as inhibitors of ALK in ALK+ NSCLC often induce strong and durable clinical responses. However, they are not curative in metastatic cancers, as some tumor cells persist through therapy, eventually developing resistance. Therapy sensitivity can reflect not only cell-intrinsic mechanisms but also inputs from stromal microenvironment. Yet, the contribution of tumor stroma to therapeutic responses in vivo remains poorly defined. To address this gap of knowledge, we assessed the contribution of stroma-mediated resistance to therapeutic responses to the frontline ALK inhibitor alectinib in xenograft models of ALK+ NSCLC. We found that stroma-proximal tumor cells are partially protected against cytostatic effects of alectinib. This effect is observed not only in remission, but also during relapse, indicating the strong contribution of stroma-mediated resistance to both persistence and resistance. This therapy-protective effect of the stromal niche reflects a combined action of multiple mechanisms, including growth factors and extracellular matrix components. Consequently, despite improving alectinib responses, suppression of any individual resistance mechanism was insufficient to fully overcome the protective effect of stroma. Focusing on shared collateral sensitivity of persisters offered a superior therapeutic benefit, especially when using an antibody-drug conjugate with bystander effect to limit therapeutic escape. These findings indicate that stroma-mediated resistance might be the major contributor to both residual and progressing disease and highlight the limitation of focusing on suppressing a single resistance mechanism at a time.

Analysis of indoleamine 2-3 dioxygenase (IDO1) expression in breast cancer tissue by immunohistochemistry.

INTRODUCTION: The immunosuppressive enzyme, indoleamine 2,3 dioxygenase (IDO), is overexpressed in many different tumor types including breast cancer. IDO inhibitors synergize with chemotherapy in breast cancer murine models. Characterizing IDO expression in breast cancer could define which patients receive IDO inhibitors. This study analyzed IDO protein expression in 203 breast cancer cases. The relationship between IDO, overall survival (OS), disease-specific survival (DSS), clinicopathologic, molecular, and immune tumor infiltrate factors was evaluated. METHODS: Expression of IDO, estrogen receptor (ER), progesterone receptor (PR), human epithelial receptor 2, cytokeratin 5/6, epithelial growth factor receptor, phosphorylated AKT, neoangiogenesis, nitrogen oxide synthetase 2 (NOS2), cyclooxygenase 2 (COX2), FoxP3, CD8, and CD11b on archival breast cancer tissue sections was evaluated by immunohistochemistry. Associations between IDO and these markers were explored by a univariate and multivariate analysis. Survival was analyzed using Kaplan-Meier (OS) and Wilcoxon two-sample (DSS) tests. RESULTS: IDO expression was higher in ER+ tumors compared to ER- tumors. IDO was lower in those with higher neoangiogenesis. OS was better in ER+ patients with high IDO expression. DSS was better in node-positive patients with high IDO expression. IDO activity positively correlates with NOS2. COX2 as positively correlated with IDO on univariate but not multivariate analysis. There was a trend toward greater numbers of CD11b+ cells in IDO-low tumors. CONCLUSIONS: IDO protein expression is lower in ER- breast tumors with greater neoangiogenesis. Future clinical trials evaluating the synergy between IDO inhibitors and chemotherapy should take this finding into account and stratify for ER status in the trial design.

Inhibition of dendritic cell differentiation and accumulation of myeloid-derived suppressor cells in cancer is regulated by S100A9 protein.

Accumulation of myeloid-derived suppressor cells (MDSCs) associated with inhibition of dendritic cell (DC) differentiation is one of the major immunological abnormalities in cancer and leads to suppression of antitumor immune responses. The molecular mechanism of this phenomenon remains unclear. We report here that STAT3-inducible up-regulation of the myeloid-related protein S100A9 enhances MDSC production in cancer. Mice lacking this protein mounted potent antitumor immune responses and rejected implanted tumors. This effect was reversed by administration of wild-type MDSCs from tumor-bearing mice to S100A9-null mice. Overexpression of S100A9 in cultured embryonic stem cells or transgenic mice inhibited the differentiation of DCs and macrophages and induced accumulation of MDSCs. This study demonstrates that tumor-induced up-regulation of S100A9 protein is critically important for accumulation of MDSCs and reveals a novel molecular mechanism of immunological abnormalities in cancer.