Abstract 3892: EZH2 mediated kinome reprogramming drives AR phosphorylation and activation in receptor tyrosine kinase inhibitors resistant renal carcinoma models

Systemic treatment of recurrent/metastatic renal cell carcinoma (RCC) largely uses receptor tyrosine kinase inhibitors (RTKI), as single agents or in combination with immune checkpoint inhibitors. Unfortunately, patients commonly develop resistance to RTKI’s, leaving few options for further treatment. Therefore, understanding the mechanisms responsible for drug resistance is critical to improve the clinical outcome in this disease. Our previous studies of acquired resistance to the RTKI sunitinib identified two major regulators, EZH2 and androgen receptor (AR). Inhibition of EZH2 or AR in combination with sunitinib re-sensitizes cells to sunitinib both in vitro and in vivo. To further explore the link between EZH2 and AR in drug resistance, 786-0 RCC cells with acquired resistance to sunitinib (786-0RS) was compared to drug naive 786-0 cells with exogenous AR (786-0AR). Chromatin immunoprecipitation sequencing (ChIP-seq) showed that AR and EZH2 bind the same genomic locations, but only in the resistant strain. Interestingly, treatment of 786-0AR cells with sunitinib caused AR to translocate to the nucleus observed by the presence of AR at EZH2 bound sites. Additionally, mass spec of AR purified from 786-0RS cells and 786-0AR cells found high phosphorylation of S81 and S213, two markers associated with ligand independent activation, in 786-0RS cells, but not in 786-0AR cells. Previously, our lab has reported that 786-0RS cells display a reprogramming of the tyrosine kinome which is dependent on EZH2 likely via a non-canonical mechanism. Consistent with this, EZH2 with a phosphomimetic mutation in Serine 21 (S21D) could promote sunitinib resistance when over-expressed with AR, whereas wild-type and phosphonull (S21A) EZH2 could not. We have also expanded the serine/threonine phosphoproteomic analysis and found extensive rewiring of these signaling networks in 786-0RS cells with an enrichment of EGFR mediated MAPK and AKT signaling when compared to 786-0 cells. Finally, our lab has generated 786-0 strains resistant to other RTKI including pazopanib and lenvatinib, and found that AR is expressed in these resistant models, solidifying AR activation as a conserved feature of RTKI resistance. Overall, our results suggest that AR activation is driven by phosphorylation induced by EZH2 dependent kinome reprogramming. Untangling the cross talk between AR and EZH2 in RTKI resistant RCC will provide the rationale for novel therapeutic strategies to improve the clinical outcome in patients with this disease.

Citation Format: Christopher Rupert, Stephanie Metcalf, Saranya Rajendran, Sean Colligan, Peter Hollenhorst, Roberto Pili. EZH2 mediated kinome reprogramming drives AR phosphorylation and activation in receptor tyrosine kinase inhibitors resistant renal carcinoma models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3892.

Abstract 73: Blockade of p38 MAPK reduces the tumor-induced immune suppressive microenvironment in metastatic breast cancer

The ability of CD8+ T cells to mount an anti-tumor immune response is compromised by immune suppression in the tumor microenvironment (TME). Tumor Associated Macrophages (TAMs) and Myeloid Derived Suppressor Cells (MDSCs) are a major part of this immune suppressive network. Targeting these populations remains challenging. Previously, we have reported that pharmacological and genetic blockade of p38 MAPK impeded the expansion and mobilization of monocytic and granulocytic MDSCs in mouse mammary carcinoma models. We also found that blockade of p38 or depletion of MDSCs reduced tumor growth and metastasis while enhancing the levels of CD8+ T cells in the primary tumors. In the present study, we asked whether CD8+ T cells contribute to the anti-metastatic activity of p38 inhibitor (p38i) and how p38 blockade affects the functional status of T cells and MDSCs. By using the mouse mammary carcinoma 4T1 model, we found that depletion of CD8+ T cells negated the effects of p38i on tumor growth and metastasis, indicating that CD8+ T cells contribute to the anti-tumor and anti-metastatic effects of p38 blockade. Next, we examined whether p38i exhibits a direct effect on T cells. The results of the T cell proliferation in vitro assays revealed that p38 blockade did not have a direct impact on T cell proliferation in response to αCD3/αCD28 stimulation. To determine the effect of p38 blockade on T cells in vivo, we performed single cell RNA-seq on the 4T1 tumor models treated with p38i and the 4T1 model with p38α (Mapk14) knockout (p38ko). This study revealed that p38 blockade by p38i or by inactivation of p38 in tumor cells decreased the amount of exhausted T cells and increased Th1 cells in the TME, indicating a positive effect on T cell functions. Furthermore, we observed a significant decrease in inflammatory signaling in granulocytes and monocytes upon p38 blockade. Our previous study showed that p38i did not affect generation of MDSCs in vitro in response to G-CSF & GM-CSF. To determine whether p38i alters MDSCs in vivo, we assessed MDSC gene signature in monocytic and granulocytic MDSCs isolated from spleens of tumor-bearing mice subjected to p38 blockade. This work revealed that the MDSC gene signature was reduced in both p38i and p38ko groups compared to tumor bearing mice treated with vehicle-control. These results indicated a reduction in the MDSC generation in the in vivo model. Our study revealed that blockade of p38 reduces tumor induced immune suppression and may enhance anti-tumor immune response in metastatic breast cancer.

Citation Format: Priyanka Rajan, Justin Zonneville, Robert Zollo, Mackenzie Honikel, Sofija Raudins, Sean Colligan, Brian Morreale, Mohammed Alruwaili, Mohammed Alqarni, Scott Olejniczak, Joseph Barbi, Scott Abrams, Andrei Bakin. Blockade of p38 MAPK reduces the tumor-induced immune suppressive microenvironment in metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 73.

Abstract 4240: Tumor PD-L1 induction associated with dietary protein restriction is modulated by PERK activation

Tumor cells rely on the Integrated Stress Response (ISR) to adapt to different environmental and physiological stresses. The ISR is comprised of four eIF2 kinases that sense different stresses and catalyze phosphorylation of the alpha subunit of eIF2. This results in inhibition of global translation initiation, but at the same time results in preferential translation of select mRNA transcripts in order to relieve stress. Recent work has suggested that programmed death-ligand 1 (PD-L1), a cell surface protein commonly upregulated by tumors to evade the immune system, may be translationally regulated by the ISR in cancer. PD-L1 interaction with immune-checkpoint receptor programmed death-1 (PD-1) leads to the negative regulation of T cell activation and inhibitors that block the PD-L1/PD-1 interaction are widely used to treat different cancers. The ISR may serve as a novel therapeutic target to modulate PD-L1 protein levels and treat immune-evasive cancers. Our group has previously reported that dietary protein restriction increases the anti-tumor effect of PD-1 inhibition in the RENCA kidney cancer mouse model. Here, we show that in the RENCA model, phospho-PERK and phospho-eIF2α protein levels correlate with PD-L1 induction associated with dietary protein restriction. This is supported by TCGA data that shows a correlation between PERK and PD-L1 mRNA levels in different genitourinary cancers. In vitro, activation of the eIF2 kinases PERK and GCN2 by ER stress and amino acid starvation, respectively, in both RENCA cells and prostate cancer cells, leads to induction of PD-L1 protein without changing mRNA levels, suggesting preferential translation under stress conditions. Inhibiting PERK using selective inhibitors blocked ER stress-induced induction of PD-L1. These data support the notion that PD-L1 is induced by dietary protein restriction and is translationally regulated by the ISR. Modulating PD-L1 protein levels in immune-evasive tumors by targeting the ISR in the context of dietary protein restriction may enhance the anti-tumor response to immune checkpoint inhibitors.

Citation Format: Ricardo Cordova, Sean Colligan, Chris Rupert, Ronald Wek, Kirk Staschke, Roberto Pili. Tumor PD-L1 induction associated with dietary protein restriction is modulated by PERK activation. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4240.

Abstract P5-17-06: P38 kinase as a therapeutic target to reverse an immune suppressive tumor microenvironment in metastatic breast cancer

The immune suppressive tumor microenvironment (TME) in metastatic breast cancer (MBC) limits the benefits of immunotherapy with immune checkpoint inhibitors (ICIs). In particular, the primary TME drives the expansion and recruitment of immune suppressive myeloid cell populations, such as tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). Treatments targeting these populations can potentially improve the efficacy of ICI therapy. To that end, our published and new findings have revealed that the p38 Mitogen-Activated Protein Kinase (MAPK) contributes to the expansion and mobilization of TAMs and MDSCs. Further, we found that pharmacological blockade of p38 decreased metastasis and increased the levels of CD8+ T cells while decreasing TAMs in the primary TME. Depletion of PMN-MDSCs, a major MDSC subset, was accompanied by reduced TAM infiltration and phenocopied the anti-metastatic effects of p38 blockade. Next, we explored the impact of p38 blockade on the composition and functionality of the immune populations in the primary TME by using single-cell RNA-sequencing. We found that p38 blockade increased levels of Irf8+ monocytic populations, indicating a decrease in immune-suppressive properties of the TME. Notably, p38 blockade increased the expression of factors related to the activation of CD8+ cytotoxic T lymphocytes, i.e., Jchain, Icos, and Cd137. Thus, our data indicate that p38 blockade alters the immune landscape within the primary TME and favors an antitumor immune response. Our data also suggest that the p38 kinase controls the production of tumor-derived factors (TDFs) which facilitate the recruitment of those pro-tumor myeloid populations. Thus, we explored this p38-TDF-myeloid axis by using trans-well migration assays. We tested the migration of the monocyte-like cell line RAW 264.7 in response to tumor-conditioned media prepared from tumor cells treated with or without the p38 inhibitor, Ralimetinib. Our data showed that the migration of RAW 264.7 cells was significantly diminished towards the conditioned media from tumor cells treated with the p38 inhibitor or from tumor cells with a genetic inactivation of p38α by CRISPR/Cas9 compared to the corresponding controls. Altogether, our studies demonstrate that p38 kinase is a potential therapeutic target, which reshapes the immune suppressive contexture of TME in MBC to improve antitumor immunity.

Citation Format: Priyanka Rajan, Justin Zonneville, Sean Colligan, Scott Abrams, Andrei Bakin. P38 kinase as a therapeutic target to reverse an immune suppressive tumor microenvironment in metastatic breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-17-06.

Blockade of p38 kinase impedes the mobilization of protumorigenic myeloid populations to impact breast cancer metastasis

Patients with metastatic breast cancer (MBC) have limited therapeutic options and novel treatments are critically needed. Prior research implicates tumor-induced mobilization of myeloid cell populations in metastatic progression, as well as being an unfavorable outcome in MBC; however, the underlying mechanisms for these relationships remain unknown. Here, we provide evidence for a novel mechanism by which p38 promotes metastasis. Using triple-negative breast cancer models, we showed that a selective inhibitor of p38 (p38i) significantly reduced tumor growth, angiogenesis, and lung metastasis. Importantly, p38i decreased the accumulation of myeloid populations, namely, myeloid-derived suppressor cells (MDSCs) and CD163+ tumor-associated macrophages (TAMs). p38 controlled the expression of tumor-derived chemokines/cytokines that facilitated the recruitment of protumor myeloid populations. Depletion of MDSCs was accompanied by reduced TAM infiltration and phenocopied the antimetastatic effects of p38i. Reciprocally, p38i increased tumor infiltration by cytotoxic CD8+ T cells. Furthermore, the CD163+ /CD8+ expression ratio inversely correlated with metastasis-free survival in breast cancer, suggesting that targeting p38 may improve clinical outcomes. Overall, our study highlights a previously unknown p38-driven pathway as a therapeutic target in MBC.

Abstract 4968: Blockade of p38 kinase impedes the mobilization of myeloid populations that promote breast cancer metastasis

Patients with metastatic breast cancer (MBC) have limited therapeutic options and novel treatments are critically needed. Prior studies demonstrated that the p38 kinase (p38) promotes MBC, while the mechanisms remained unknown. Here, we provide evidence for a novel mechanism by which p38 promotes metastasis. Using triple-negative breast cancer models, we showed that a selective inhibitor of p38 (p38i) significantly reduced tumor growth, angiogenesis, and lung metastasis. Importantly, p38i decreased the accumulation of myeloid populations, namely myeloid-derived suppressor cells (MDSCs) and CD163+ tumor-associated macrophages (TAMs). p38 controlled the expression of tumor-derived chemokines/cytokines that facilitated the recruitment of pro-tumor myeloid populations. Depletion of MDSCs was accompanied by reduced TAM infiltration and phenocopied the anti-metastatic effects of p38i. Reciprocally, p38i increased tumor infiltration by cytotoxic CD8+ T cells. Metadata showed that a reduced CD163+/CD8+ expression ratio correlates with metastasis-free survival in breast cancer, suggesting that targeting p38 may improve clinical outcomes. This study highlights a novel p38-driven mechanism as a therapeutic target in MBC.

Citation Format: Justin Zonneville, Sean Colligan, Paul Wallace, Scott I. Abrams, Andrei V. Bakin. Blockade of p38 kinase impedes the mobilization of myeloid populations that promote breast cancer metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4968.

Abstract LB-316: Suppression of tumor angiogenesis and metastasis by targeting a novel p38-driven tumor-stromal crosstalk

Triple-negative breast cancers (TNBCs, ER/PR/HER2-negative) pose significant clinical challenges largely due to a lack of targeted therapy. Our prior work revealed a novel tumor-stromal crosstalk that increases p38 kinase signaling in the breast tumor microenvironment (TME). Here, we examined the effects of systemic blockade of p38 signaling in the relevant TNBC models. Blockade of p38 with a selective p38 inhibitor Ralimetinib reduced tumor growth and metastasis to the lungs and liver. Histology revealed that p38 blockade greatly reduced tumor angiogenesis. Within the TME, we found a massive infiltration of myeloid cells i.e. polymorphonuclear (PMN) myeloid-derived suppressor-like cells (MDSC-like) to the lungs and liver of tumor-bearing (TB) mice. Further, TB-mice showed a significant rise in the numbers of granulocytes and monocytes in the circulation, and the accumulation of CD163+ macrophages in the TME. Blockade of p38 greatly reduced these responses. In contrast, p38 blockade increased abundance of cytotoxic CD8+ T-cells in the TME. Addressing the mechanism, we found that inactivation of p38 in tumor cells was sufficient to reduce the influx of macrophages to the tumor, suggesting a tumor-driven mechanism of mobilization or expansion of myeloid cell populations. Further, depletion of PMN-MDSC-like cells and neutrophils using anti-Ly6G antibody reduced metastases to the lungs and liver. Assessing the prognostic value of our results, we found an inverse correlation of CD163 levels with metastasis-free survival in patients with breast cancer. Together, these results demonstrate that p38 kinase promotes breast cancer growth and colonization to distant organs by regulating mobilization of pro-tumor myeloid cells. This p38-driven mechanism highlights a novel target for treatment of patients with TNBC or advanced disease.

Citation Format: Andrei V. Bakin, Justin Zonneville, Rebecca Walden, Sydney Grant, Sean Colligan, Alexandra Miller, Alexander M. Truskinovsky, Scott Abrams. Suppression of tumor angiogenesis and metastasis by targeting a novel p38-driven tumor-stromal crosstalk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-316.

Tumor-derived thymic stromal lymphopoietin enhances lung metastasis through an alveolar macrophage-dependent mechanism

It is well-recognized that macrophages, which arise from circulating precursors, enhance tumor progression in patients and animal models. However, less is known regarding the role of tissue-resident macrophages in metastasis. Moreover, the identification of tumor factors which influence macrophage function in the metastatic niche remains incomplete. Here, we investigated one such cytokine known as thymic stromal lymphopoietin (TSLP). Our rationale to focus on TSLP was based on two non-overlapping findings; first, TSLP exacerbates asthma in part by altering the lung macrophage response and, secondly, TSLP is produced by certain mouse and human tumor systems, although its role in neoplasia remains understudied. Thus, we tested the hypothesis that tumor-derived TSLP augments lung metastasis by rendering alveolar macrophages pro-tumorigenic. To test this hypothesis, we principally employed the 4T1 tumor model, which produces high levels of TSLP and metastasizes to the lung. TSLP loss-of-function significantly reduced spontaneous lung metastasis, as well as lung colonization. Moreover, similar outcomes were observed in both wild-type and immune-deficient hosts, suggesting that TSLP acted on innate immune cells such as macrophages. To test this notion, pharmacologic depletion of alveolar macrophages significantly reduced lung tumor growth of the TSLP-expressing, but not TSLP-deficient tumor population. In contrast, depleting macrophages originating from the circulation did not impact lung tumor growth. Lastly, TSLP increased the invasive and angiogenic gene expression profile of the alveolar macrophage population. Altogether, our study identified a novel TSLP-alveolar macrophage axis in lung metastasis, which offers new insights into mechanisms of metastasis and potential therapeutic targets.

The Granulocyte Progenitor Stage Is a Key Target of IRF8-Mediated Regulation of Myeloid-Derived Suppressor Cell Production

Alterations in myelopoiesis are common across various tumor types, resulting in immature populations termed myeloid-derived suppressor cells (MDSCs). MDSC burden correlates with poorer clinical outcomes, credited to their ability to suppress antitumor immunity. MDSCs consist of two major subsets, monocytic and polymorphonuclear (PMN). Intriguingly, the latter subset predominates in many patients and tumor models, although the mechanisms favoring PMN-MDSC responses remain poorly understood. Ordinarily, lineage-restricted transcription factors regulate myelopoiesis that collectively dictate cell fate. One integral player is IFN regulatory factor (IRF)-8, which promotes monocyte/dendritic cell differentiation while limiting granulocyte development. We recently showed that IRF8 inversely controls MDSC burden in tumor models, particularly the PMN-MDSC subset. However, where IRF8 acts in the pathway of myeloid differentiation to influence PMN-MDSC production has remained unknown. In this study, we showed that: 1) tumor growth was associated with a selective expansion of newly defined IRF8^lo granulocyte progenitors (GPs); 2) tumor-derived GPs had an increased ability to form PMN-MDSCs; 3) tumor-derived GPs shared gene expression patterns with IRF8^-/- GPs, suggesting that IRF8 loss underlies GP expansion; and 4) enforced IRF8 overexpression in vivo selectively constrained tumor-induced GP expansion. These findings support the hypothesis that PMN-MDSCs result from selective expansion of IRF8^lo GPs, and that strategies targeting IRF8 expression may limit their load to improve immunotherapy efficacy.

Simultaneous, Single-Cell Measurement of Messenger RNA, Cell Surface Proteins, and Intracellular Proteins

Nucleic acid content can be quantified by flow cytometry through the use of intercalating compounds; however, measuring the presence of specific sequences has hitherto been difficult to achieve by this methodology. The primary obstacle to detecting discrete nucleic acid sequences by flow cytometry is their low quantity and the presence of high background signals, rendering the detection of hybridized fluorescent probes challenging. Amplification of nucleic acid sequences by molecular techniques such as in situ PCR have been applied to single-cell suspensions, but these approaches have not been easily adapted to conventional flow cytometry. An alternative strategy implements a Branched DNA technique, comprising target-specific probes and sequentially hybridized amplification reagents, resulting in a theoretical 8,000- to 16,000-fold increase in fluorescence signal amplification. The Branched DNA technique allows for the quantification of native and unmanipulated mRNA content with increased signal detection and reduced background. This procedure utilizes gentle fixation steps with low hybridization temperatures, leaving the assayed cells intact to permit their concomitant immunophenotyping. This technology has the potential to advance scientific discovery by correlating potentially small quantities of mRNA with many biological measurements at the single-cell level.