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RAS‐MAPK signaling promotes immune evasion and cancer cell survival, and MAPK inhibitors (MAPKis) are frequently used as cancer therapies. Despite progress elucidating the direct effects of MAPKi on immune cells, their indirect effect on the tumor microenvironment (TME) through changes in tumor cells remains incompletely understood. Here, we present evidence of a rapid compensatory response to MAPKi that is driven by sustained p38 MAPK signaling and by which cancer cells can upregulate the immunosuppressive protein CD73 to reduce the antitumor immune response. This compensatory response also results in decreased sensitivity toward MAPKi, and, accordingly, combining anti‐CD73 antibodies and MAPKi significantly enhances the antitumor effect compared to single‐agent treatment in vivo. Combining MAPKi and anti‐CD73 was accompanied by significant alterations in intratumor immune cell composition, supporting the effect of MAPKi‐induced CD73 expression on the TME. We show that high CD73 expression significantly correlates with worse outcome in MAPKi‐treated colorectal cancer patients, highlighting the potential clinical importance of increased CD73 expression following MAPKi treatment. Our findings may explain the diminished effect of MAPKi in cancer patients and provides further rationale for combined anti‐CD73 and MAPKi treatment., RAS‐MAPK signaling promotes immune evasion and cancer cell survival, and MAPK inhibitors (MAPKis) are frequently used in cancer therapy. Here, we present evidence that RAS‐MAPK inhibition increased the expression of the immunosuppressive protein CD73 by a rapid adaptive bypass mechanism involving MAPK‐p38 signaling. Compensatory MAPK‐p38 signaling increased tumor cell growth during MAPKi treatment. Additionally, targeting of CD73 in vivo augmented MAPKi. High CD73 expression was associated with a worse outcome in RAS‐MAPKi‐treated patients with colorectal cancer (CRC), indicating that combined anti‐CD73 and MAPKi treatment could be beneficial for patients with CRC resistant to MAPKi therapy.

BackgroundImmunosuppressive extracellular adenosine is generated by the enzymatic activity of CD73. In preclinical models, antibodies (Abs) targeting different epitopes on CD73 exert anticancer activity through distinct mechanisms such as inhibition of enzymatic activity, engagement of Fc receptors, and spatial redistribution of CD73.MethodsUsing controlled Fab arm exchange, we generated biparatopic bispecific antibodies (bsAbs) from parental anti-CD73 Abs with distinct anticancer activities. The resulting anticancer activity was evaluated using in vitro and in vivo models.ResultsWe demonstrate that different anticancer activities can be combined in a biparatopic bsAb. Remarkably, the bsAb significantly improved the enzyme inhibitory activity compared with the parental Abs, which led to neutralization of adenosine-mediated T-cell suppression as demonstrated by proliferation and interferon gamma (IFN-γ) production and prolonged survival of tumor-bearing mice. Additionally, the bsAb caused more efficient internalization of cell surface CD73 and stimulated potent Fc-mediated engagement of human immune effector cells in vitro and in vivo.ConclusionsOur data collectively demonstrate that complementary anticancer mechanisms of action of distinct anti-CD73 Abs can be combined and enhanced in a biparatopic bsAb. The multiple mechanisms of action and superior activity compared with the monospecific parental Abs make the bsAb a promising candidate for therapeutic targeting of CD73 in cancer. This concept may greatly improve future Ab design.

Resistance to endocrine therapy in estrogen receptor-positive (ER+) breast cancer is a major clinical problem with poorly understood mechanisms. There is an unmet need for prognostic and predictive biomarkers to allow appropriate therapeutic targeting. We evaluated the mechanism by which minichromosome maintenance protein 3 (MCM3) influences endocrine resistance and its predictive/prognostic potential in ER+ breast cancer. We discovered that ER+ breast cancer cells survive tamoxifen and letrozole treatments through upregulation of minichromosome maintenance proteins (MCMs), including MCM3, which are key molecules in the cell cycle and DNA replication. Lowering MCM3 expression in endocrine-resistant cells restored drug sensitivity and altered phosphorylation of cell cycle regulators, including p53(Ser(315,33)), CHK1(Ser(317)), and cdc25b(Ser(323)), suggesting that the interaction of MCM3 with cell cycle proteins is an important mechanism of overcoming replicative stress and anti-proliferative effects of endocrine treatments. Interestingly, the MCM3 levels did not affect the efficacy of growth inhibitory by CDK4/6 inhibitors. Evaluation of MCM3 levels in primary tumors from four independent cohorts of breast cancer patients receiving adjuvant tamoxifen mono-therapy or no adjuvant treatment, including the Stockholm tamoxifen (STO-3) trial, showed MCM3 to be an independent prognostic marker adding information beyond Ki67. In addition, MCM3 was shown to be a predictive marker of response to endocrine treatment. Our study reveals a coordinated signaling network centered around MCM3 that limits response to endocrine therapy in ER+ breast cancer and identifies MCM3 as a clinically useful prognostic and predictive biomarker that allows personalized treatment of ER+ breast cancer patients. Funding Agencies|Danish Cancer SocietyDanish Cancer Society; Danish Cancer Research Foundation; Danish Research CouncilDet Frie Forskningsrad (DFF); Danish Strategic Research CouncilDanske Strategiske Forskningsrad (DSF); A Race Against Breast Cancer; Region of Southern Denmark Research Foundation; Odense University Hospital Research Council

Aromatase inhibitors (AI), either alone or together with chemotherapy, have become the standard adjuvant treatment for postmenopausal, estrogen receptor-positive (ER+) breast cancer. Although AIs improve overall survival, resistance is still a major clinical problem, thus additional biomarkers predictive of outcome of ER+ breast cancer patients treated with AIs are needed. Global gene expression analysis was performed on ER+ primary breast cancers from patients treated with adjuvant AI monotherapy; half experienced recurrence (median follow-up 6.7 years). Gene expression alterations were validated by qRT-PCR, and functional studies evaluating the effect of siRNA-mediated gene knockdown on cell growth were performed. Twenty-six genes, including TFF3, DACH1, RGS5, and GHR, were shown to exhibit altered expression in tumors from patients with recurrence versus non-recurrent (fold change ≥1.5, p < 0.05), and the gene expression alterations were confirmed using qRT-PCR. Ten of these 26 genes could be linked in a network associated with cellular proliferation, growth, and development. TFF3, which encodes for trefoil factor 3 and is an estrogen-responsive oncogene shown to play a functional role in tamoxifen resistance and metastasis of ER+ breast cancer, was also shown to be upregulated in an AI-resistant cell line model, and reduction of TFF3 levels using TFF3-specific siRNAs decreased the growth of both the AI-resistant and -sensitive parental cell lines. Moreover, overexpression of TFF3 in parental AI-sensitive MCF-7/S0.5 cells resulted in reduced sensitivity to the AI exemestane, whereas TFF3 overexpression had no effect on growth in the absence of exemestane, indicating that TFF3 mediates growth and survival signals that abrogate the growth inhibitory effect of exemestane. We identified a panel of 26 genes exhibiting altered expression associated with disease recurrence in patients treated with adjuvant AI monotherapy, including TFF3, which was shown to exhibit a growth- and survival-promoting effect in the context of AI treatment.

Since the online publication of the above article, the authors have noted errors in subfigures 1c and 3b. Therefore, new images of the original immmunocytochemistry stainings have been obtained for Fig. 1c, and the Western blots for siRNA-mediated FYN knockdown in Fig. 3b were repeated. The amended versions of Figs. 1c and 3b are now provided.

To elucidate the molecular mechanisms of tamoxifen resistance in breast cancer, we performed gene array analyses and identified 366 genes with altered expression in four unique tamoxifen-resistant (TamR) cell lines vs the parental tamoxifen-sensitive MCF-7/S0.5 cell line. Most of these genes were functionally linked to cell proliferation, death and control of gene expression, and include FYN, PRKCA, ITPR1, DPYD, DACH1, LYN, GBP1 and PRLR. Treatment with FYN-specific small interfering RNA or a SRC family kinase inhibitor reduced cell growth of TamR cell lines while exerting no significant effect on MCF-7/S0.5 cells. Moreover, overexpression of FYN in parental tamoxifen-sensitive MCF-7/S0.5 cells resulted in reduced sensitivity to tamoxifen treatment, whereas knockdown of FYN in the FYN-overexpressing MCF-7/S0.5 cells restored sensitivity to tamoxifen, demonstrating growth- and survival-promoting function of FYN in MCF-7 cells. FYN knockdown in TamR cells led to reduced phosphorylation of 14-3-3 and Cdc25A, suggesting that FYN, by activation of important cell cycle-associated proteins, may overcome the anti-proliferative effects of tamoxifen. Evaluation of the subcellular localization of FYN in primary breast tumors from two cohorts of endocrine-treated ER+ breast cancer patients, one with advanced disease (N=47) and the other with early disease (N=76), showed that in the former, plasma membrane-associated FYN expression strongly correlated with longer progression-free survival (P

Objective: Altered gene expression associated with endocrine resistance in breast cancer cell lines may have potential prognostic/predictive values in patients with ER+ breast cancer receiving endocrine therapy. In this study, we investigated mRNA expression profiles associated with the tamoxifen-resistant phenotype using a panel of isogenic MCF-7-based breast cancer cell lines to elucidate the endocrine resistance mechanism and assess whether the pattern of gene expression predicted clinical outcome in breast cancer patients treated with endocrine therapy. Method: Gene array was performed on a panel of clinically-relevant tamoxifen-resistant breast cancer cell lines (TamR) and their tamoxifen-sensitive parental cell line. Genes that showed significant alteration in expression (FDR 0.01) in TamRs vs parental cell lines were evaluated for their potential to stratify tamoxifen-treated breast cancer patients based on outcome using published gene expression data sets. Results: Using a testing set consisting of microarray data from 163 ER+ primary breast cancer patients treated with tamoxifen we identified 20 genes among those that showed significant altered expression in TamR that could stratify patients according to clinical outcome. . The potential of this 20-gene signature to stratify patients was further confirmed in 2 independent data sets consisting of ER+ tamoxifen-treated breast cancer patients with a sensitivity and specificity 53% and 79% respectively in the first cohort (N=153), and sensitivity and specificity of 37% and 91% respectively in the second cohort (N=201). Evaluation of relapse-free survival of tamoxifen-treated patients classified by the signature as having bad or good outcomes showed significant differences in time-to-relapse, with median disease-free survival times of 5.1 vs 8.9 years in the first cohort (N=153, p=0.03) and 4.2 vs 7.7 years in the second (N=201, p=0.006). Conclusions: The expression pattern of the 20-gene signature identified in this study appears to have a strong potential as a biomarker of clinical outcome of endocrine-treated breast cancer patients. Citation Format: Daniel Elias Roro, Henriette Vever, Anne Lykkesfeldt, Henrik Ditzel. Global gene expression analysis of tamoxifen-resistant breast cancer cell lines identified a gene signature predictive of clinical outcome of breast cancer patients treated with endocrine therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1887. doi:10.1158/1538-7445.AM2014-1887

To elucidate the molecular mechanisms of tamoxifen resistance in breast cancer we performed microarray profiling and identified 366 genes with altered expression in 4 tamoxifen-resistant (TamRs) vs. the parental tamoxifen-sensitive MCF-7/S0.5 cell lines. Most of these genes were functionally linked to cell growth, proliferation, death and control of gene expression and included FYN, PRKCα, ITPR1, DPYD, DACH1, GBP1 and PRLR. Increased expression of FYN was observed in TamR cells and treatment with FYN-specific interfering RNA or a specific Src family kinase (SFK) inhibitor restored the anti-proliferative effect of tamoxifen in these cells. TamR cells also expressed increased levels of phosphorylated breast cancer antiestrogen resistance protein 1 (pBCAR1), an important downstream SFK substrate in the MAPK pathway. Evaluation of the association of subcellular localization of FYN in cancer tissue and clinical endpoints was made in 2 cohorts of ER+ breast cancer patients, one with advanced disease (N=47) and the other with early breast cancer (N=76). The result showed that plasma membrane-associated FYN expression in the cancer cells strongly correlated with longer progression-free survival compared to FYN expression not associated with the plasma membrane (p Citation Format: Daniel Elias Roro, Henriette Vever, Henrik Ditzel. Gene expression profiling identified FYN as an important gene in tamoxifen resistance and a predictor of early recurrence in patients treated with endocrine therapy . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1190. doi:10.1158/1538-7445.AM2013-1190