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Metastatic breast cancer is an intractable disease that responds poorly to immunotherapy. We show that p38MAPKα inhibition (p38i) limits tumor growth by reprogramming the metastatic tumor microenvironment in a CD4+ T cell-, IFNγ-, and macrophage-dependent manner. To identify targets that further increased p38i efficacy, we utilized a stromal labeling approach and single-cell RNA sequencing. Thus, we combined p38i and an OX40 agonist that synergistically reduced metastatic growth and increased overall survival. Intriguingly, patients with a p38i metastatic stromal signature had better overall survival that was further improved by the presence of an increased mutational load, leading us to ask if our approach would be effective in antigenic breast cancer. The combination of p38i, anti-OX40, and cytotoxic T-cell engagement cured mice of metastatic disease and produced long-term immunologic memory. Our findings demonstrate that a detailed understanding of the stromal compartment can be used to design effective antimetastatic therapies. Significance: Immunotherapy is rarely effective in breast cancer. We dissected the metastatic tumor stroma, which revealed a novel therapeutic approach that targets the stromal p38MAPK pathway and creates an opportunity to unleash an immunologic response. Our work underscores the importance of understanding the tumor stromal compartment in therapeutic design.

Metastatic breast cancer is an intractable disease that responds poorly to immunotherapy. We show that p38MAPKα inhibition (p38i) limits tumor growth by reprogramming the metastatic tumor microenvironment in a CD4+ T cell-, IFNγ-, and macrophage-dependent manner. To identify targets that further increased p38i efficacy, we utilized a stromal labeling approach and single-cell RNA sequencing. Thus, we combined p38i and an OX40 agonist that synergistically reduced metastatic growth and increased overall survival. Intriguingly, patients with a p38i metastatic stromal signature had better overall survival that was further improved by the presence of an increased mutational load, leading us to ask if our approach would be effective in antigenic breast cancer. The combination of p38i, anti-OX40, and cytotoxic T-cell engagement cured mice of metastatic disease and produced long-term immunologic memory. Our findings demonstrate that a detailed understanding of the stromal compartment can be used to design effective antimetastatic therapies.Significance:Immunotherapy is rarely effective in breast cancer. We dissected the metastatic tumor stroma, which revealed a novel therapeutic approach that targets the stromal p38MAPK pathway and creates an opportunity to unleash an immunologic response. Our work underscores the importance of understanding the tumor stromal compartment in therapeutic design.

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Table containing all of our reagents

Cyclin dependent kinase 4 and 6 inhibitors (CDK4/6i) such as abemaciclib are routinely used to treat metastatic estrogen receptor positive (ER+)/HER2-negative breast cancer. However, adaptive mechanisms inhibit their effectiveness and allow for disease progression. Using murine metastatic ER+ breast cancer cells, we show that acquired resistance to abemaciclib is accompanied by increase in metastatic potential. Mass spectrometry-based proteomics from abemaciclib sensitive and resistant cells showed that lysosomal proteins including CTSD (cathepsin D), CTSA (cathepsin A) and CD68 were significantly increased in resistant cells. Combination of abemaciclib and a lysosomal destabilizer, such as hydroxychloroquine (HCQ) or bafilomycin A1, re-sensitized resistant cells to abemaciclib. Also, combination of abemaciclib and HCQ decreased migration and invasive potential and increased lysosomal membrane permeability (LMP) in resistant cells. Pro-survival BCL2 protein levels were elevated in resistant cells, and a triple treatment with abemaciclib, HCQ, and BCL2 inhibitor, venetoclax, significantly inhibited cell growth compared to treatment with abemaciclib and HCQ. Furthermore, resistant cells showed increased levels of TFEB (Transcription Factor EB), a master regulator of lysosomal-autophagy genes, and siRNA mediated knockdown ofTFEBdecreased invasion in resistant cells.TFEBgene was found to be mutated in a subset of invasive human breast cancer samples, and overall survival analysis in ER+, lymph node-positive breast cancer showed that increasedTFEBexpression correlated with decreased survival. Collectively, we show that prolonged exposure to abemaciclib in ER+ breast cancer cells leads to resistance accompanied by an aggressive phenotype that is partly supported by deregulated lysosomal function.Implications: Our data implicate that resistance to abemaciclib is associated with deregulation of lysosomes and augmented metastatic potential, and therefore, the lysosomal pathway could be a therapeutic target in advanced ER+ breast cancer.GRAPHICAL ABSTRACT

Supplemental Figures 1-4. Supplemental figure 1: Representative schematic of lipid encapsulated nanoparticle design. Supplemental figure 2: The pharmacokinetics nanoparticles Supplemental figure 3:Biodistribution of the Nanoparticles Supplemental figure 4: Kalwrij mice survival data

Supplemental Figure 1-2. Supplemental Figure 1: Pharmacology of POL5551; Supplemental Figure 2: Correlation of CXCR4 expression in primary tumor with survival in patients

Flow cytometric analysis of integrin β3 staining on breast cancer cells.

PDF file - 248K,DNA fragmentation and BrdU incorporation assays on mouse and human osteoclast precursors, in response to BV6

Breast cancer bone metastases are common and incurable. Tumoral integrin β3 (β3) expression is induced through interaction with the bone microenvironment. Although β3 is known to promote bone colonization, its functional role during therapy of established bone metastases is not known. We found increased numbers of β3+ tumor cells in murine bone metastases after docetaxel chemotherapy. β3+ tumor cells were present in 97% of post-neoadjuvant chemotherapy triple-negative breast cancer patient samples (n = 38). High tumoral β3 expression was associated with worse outcomes in both pre- and postchemotherapy triple-negative breast cancer groups. Genetic deletion of tumoral β3 had minimal effect in vitro, but significantly enhanced in vivo docetaxel activity, particularly in the bone. Rescue experiments confirmed that this effect required intact β3 signaling. Ultrastructural, transcriptomic, and functional analyses revealed an alternative metabolic response to chemotherapy in β3-expressing cells characterized by enhanced oxygen consumption, reactive oxygen species generation, and protein production. We identified mTORC1 as a candidate for therapeutic targeting of this β3-mediated, chemotherapy-induced metabolic response. mTORC1 inhibition in combination with docetaxel synergistically attenuated murine bone metastases. Furthermore, micelle nanoparticle delivery of mTORC1 inhibitor to cells expressing activated αvβ3 integrins enhanced docetaxel efficacy in bone metastases. Taken together, we show that β3 integrin induction by the bone microenvironment promotes resistance to chemotherapy through an altered metabolic response that can be defused by combination with αvβ3-targeted mTORC1 inhibitor nanotherapy. Our work demonstrates the importance of the metastatic microenvironment when designing treatments and presents new, bone-specific strategies for enhancing chemotherapeutic efficacy.

Supplemental Figure 5. Eribulin dose ranging study.

PDF file - 593K, MicroCT analysis of bone in BV6-treated C57BL/6 mice

PDF file - 3716K,Osteoclastogenic response to constant BV6 and ML183, and effect of BV6 on osteoblastogenesis in culture

Supplemental Figure 3. Gaussia luciferase complementation imaging model and scratch migration assay with AMD3100.

Supplemental Figure 4. MDA-MB-231 primary tumor weight and liver metastases data.

PDF file - 175K, Chemical synthesis of 52S and ML183, methods for osteoblast culture, apoptosis and proliferation assays, and real time PCR

Supplemental Figure 6. Mobilization of leukocytes with POL5551.

PDF file - 382K,Western blot showing p100 to p52 processing in response to RANKL and BV6

PDF file - 3153K, Figure S1. WNT7B is regulated by the AR in CRPC 22RV1 cells. Figure S2. TUNEL assays after WNT7B knockdown. Figure S3. Knockdown efficiency of WNT7B shRNA determined by RT-qPCR. Figure S4. WNT7B is required for 22RV1 cell growth. Figure S5. WNT7B is overexpressed in CRPC tumors. Figure S6. β-Catenin distribution in C4-2B cells. Figure S7. PKCα and PKCδ are direct AR target genes in C4-2B cells. Figure S8. WNT7B promotes osteoblast differentiation of ST2 and C3H10T1/2 cells. Figure S9. Insoluble WNT7B is bound to the cell membrane. Figure S10. Mouse ALP, BSP and GAPDH primers are specific for mouse genes. Figure S11. PC-produced WNT7B promotes ST2 osteoblast differentiation. Figure S12. PC-produced WNT7B promotes C3H10T1/2 osteoblast differentiation.

PDF file - 50K, Primer sequences

Multiple myeloma pathogenesis is driven by the MYC oncoprotein, its dimerization with MAX, and the binding of this heterodimer to E-Boxes in the vicinity of target genes. The systemic utility of potent small molecule inhibitors of MYC-MAX dimerization was limited by poor bioavailability, rapid metabolism, and inadequate target site penetration. We hypothesized that new lipid-based MYC-MAX dimerization inhibitor prodrugs delivered via integrin-targeted nanoparticles (NP) would overcome prior shortcomings of MYC inhibitor approaches and prolong survival in a mouse model of cancer. An Sn 2 lipase-labile prodrug inhibitor of MYC-MAX dimerization (MI1-PD) was developed which decreased cell proliferation and induced apoptosis in cultured multiple myeloma cell lines alone (P < 0.05) and when incorporated into integrin-targeted lipid-encapsulated NPs (P < 0.05). Binding and efficacy of NPs closely correlated with integrin expression of the target multiple myeloma cells. Using a KaLwRij metastatic multiple myeloma mouse model, VLA-4–targeted NPs (20 nm and 200 nm) incorporating MI1-PD (D) NPs conferred significant survival benefits compared with respective NP controls, targeted (T) no-drug (ND), and untargeted (NT) control NPs (T/D 200: 46 days vs. NT/ND: 28 days, P < 0.05 and T/D 20: 52 days vs. NT/ND: 29 days, P = 0.001). The smaller particles performed better of the two sizes. Neither MI1 nor MI1-PD provided survival benefit when administered systemically as free compounds. These results demonstrate for the first time that a small molecule inhibitor of the MYC transcription factor can be an effective anticancer agent when delivered using a targeted nanotherapy approach. Mol Cancer Ther; 14(6); 1286–94. ©2015 AACR.

The SDF-1 receptor CXCR4 has been associated with early metastasis and poorer prognosis in breast cancers, especially the most aggressive triple-negative subtype. In line with previous reports, we found that tumoral CXCR4 expression in patients with locally advanced breast cancer was associated with increased metastases and rapid tumor progression. Moreover, high CXCR4 expression identified a group of bone marrow–disseminated tumor cells (DTC)-negative patients at high risk for metastasis and death. The protein epitope mimetic (PEM) POL5551, a novel CXCR4 antagonist, inhibited binding of SDF-1 to CXCR4, had no direct effects on tumor cell viability, but reduced migration of breast cancer cells in vitro. In two orthotopic models of triple-negative breast cancer, POL5551 had little inhibitory effect on primary tumor growth, but significantly reduced distant metastasis. When combined with eribulin, a chemotherapeutic microtubule inhibitor, POL5551 additively reduced metastasis and prolonged survival in mice after resection of the primary tumor compared with single-agent eribulin. Hypothesizing that POL5551 may mobilize tumor cells from their microenvironment and sensitize them to chemotherapy, we used a “chemotherapy framing” dosing strategy. When administered shortly before and after eribulin treatment, three doses of POL5551 with eribulin reduced bone and liver tumor burden more effectively than chemotherapy alone. These data suggest that sequenced administration of CXCR4 antagonists with cytotoxic chemotherapy synergize to reduce distant metastases. Mol Cancer Ther; 14(11); 2473–85. ©2015 AACR.

Additional details for methods and materials.

PDF file - 45K, Levels of WNT7B in LuCaP PC xenografts

Supplemental Table 1-3. Pharmacology of POL5551 and patient characteristics at baseline

Supplemental Figure 7. Effect of POL5551 combined with eribulin on hematopoietic cells

Supplemental Figure Legends

Integrin avb3-­targeting ligand and micelle nanoparticle localization within tumor-­free bone

Supplementary Data from Inhibition of the Stromal p38MAPK/MK2 Pathway Limits Breast Cancer Metastases and Chemotherapy-Induced Bone Loss

Bone metastases occur in approximately 70% of metastatic breast cancer patients, often leading to skeletal injuries. Current treatments are mainly palliative and underscore the unmet clinical need for improved therapies. In this study, we provide preclinical evidence for an antimetastatic therapy based on targeting integrin β3 (β3), which is selectively induced on breast cancer cells in bone by the local bone microenvironment. In a preclinical model of breast cancer, β3 was strongly expressed on bone metastatic cancer cells, but not primary mammary tumors or visceral metastases. In tumor tissue from breast cancer patients, β3 was significantly elevated on bone metastases relative to primary tumors from the same patient (n = 42). Mechanistic investigations revealed that TGFβ signaling through SMAD2/SMAD3 was necessary for breast cancer induction of β3 within the bone. Using a micelle-based nanoparticle therapy that recognizes integrin αvβ3 (αvβ3-MPs of ∼12.5 nm), we demonstrated specific localization to breast cancer bone metastases in mice. Using this system for targeted delivery of the chemotherapeutic docetaxel, we showed that bone tumor burden could be reduced significantly with less bone destruction and less hepatotoxicity compared with equimolar doses of free docetaxel. Furthermore, mice treated with αvβ3-MP-docetaxel exhibited a significant decrease in bone-residing tumor cell proliferation compared with free docetaxel. Taken together, our results offer preclinical proof of concept for a method to enhance delivery of chemotherapeutics to breast cancer cells within the bone by exploiting their selective expression of integrin αvβ3 at that metastatic site. Cancer Res; 77(22); 6299–312. ©2017 AACR.

Purpose: Micrometastatic cells detected in the bone marrow have prognostic significance in breast cancer. These cells are heterogeneous and likely do not exhibit uniform biological behavior. To understand the molecular diversity of disseminated cancer cells that reside in bone marrow, we enriched this cell population and did global gene expression profiling in the context of a prospective clinical trial involving women with clinical stage II/III breast cancer undergoing neoadjuvant chemotherapy.Experimental Design: Enrichment of TACSTD1 (EpCAM)–expressing cells from bone marrow of breast cancer patients was achieved using immunomagnetic beads. Gene expression profiles were compared between enriched cell populations and whole bone marrow from 5 normal volunteers and 23 breast cancer patients after neoadjuvant chemotherapy treatment. Enriched cells from bone marrow samples of breast cancer patients before treatment or at 1 year follow-up were also analyzed (total of 87 data sets). The expression of transcripts specifically detected in enriched cell populations from breast cancer patients was correlated with 1-year clinical outcome using quantitative reverse transcription-PCR in an independent cohort of bone marrow samples.Results: Analysis of EpCAM-enriched bone marrow cells revealed specific expression of a subgroup of transcripts, including the metastasis regulator, TWIST1. Most transcripts identified, including TWIST1, were not expressed in enriched populations of bone marrow from normal volunteers, suggesting that this expression profile reflects a signature of breast cancer bone marrow micrometastases that persist after chemotherapy. In an independent set of bone marrow samples obtained before any treatment, TWIST1 expression correlated with early disease relapse.Conclusions: Disseminated breast cancer cells present in bone marrow after chemotherapy possess unique transcriptional signatures. Genes whose expression is overrepresented in these cell populations, such as TWIST1, may prove to be excellent markers of early distant relapse in breast cancer patients.

NMR measurement: Sample preparation and analysis

Purpose: We hypothesized that in multiple myeloma cells (MMC), high membrane biosynthesis will induce acetate uptake in vitro and in vivo. Here, we studied acetate metabolism and targeting in MMC in vitro and tested the efficacy of 11C-acetate–positron emission tomography (PET) to detect and quantitatively image myeloma treatment response in vivo.Experimental design: Acetate fate tracking using 13C-edited-1H NMR (nuclear magnetic resonance) was performed to study in vitro acetate uptake and metabolism in MMC. Effects of pharmacological modulation of acetate transport or acetate incorporation into lipids on MMC cell survival and viability were assessed. Preclinical mouse MM models of subcutaneous and bone tumors were evaluated using 11C-acetate-PET/CT imaging and tissue biodistribution.Results: In vitro, NMR showed significant uptake of acetate by MMC and acetate incorporation into intracellular metabolites and membrane lipids. Inhibition of lipid synthesis and acetate transport was toxic to MMC, while sparing resident bone cells or normal B cells. In vivo, 11C-acetate uptake by PET imaging was significantly enhanced in subcutaneous and bone MMC tumors compared with unaffected bone or muscle tissue. Likewise, 11C-acetate uptake was significantly reduced in MM tumors after treatment.Conclusions: Uptake of acetate from the extracellular environment was enhanced in MMC and was critical to cellular viability. 11C-Acetate–PET detected the presence of myeloma cells in vivo, including uptake in intramedullary bone disease. 11C-Acetate–PET also detected response to therapy in vivo. Our data suggested that acetate metabolism and incorporation into lipids was crucial to MM cell biology and that 11C-acetate–PET is a promising imaging modality for MM. Clin Cancer Res; 23(2); 416–29. ©2016 AACR.

Supplementary Table S2 from Isolation and Molecular Profiling of Bone Marrow Micrometastases Identifies TWIST1 as a Marker of Early Tumor Relapse in Breast Cancer Patients

supplemental figure legend

Supplementary Figure 1 A) 1H NMR spectra (CPMG) of conditioned medium from human U266 MMC cells upon incubation for 0 (bottom), 4 (middle) or 18 (top) hours with 10 mM acetate. t-But= t-butanol standard, Lac= lactate (1.31-1.32 ppm), A= alanine (3-position at 1.5 ppm), Acetate=acetate (1.91 ppm), Glu=glutamate (2.34-2.38 ppm), Glc = glucose (5.24 ppm). Supplementary Figure 2 A) 1H NMR analysis in CPMG (top) and gHSQC (bottom) sequences of intracellular extracts from U266 upon 8h incubation with 13C-Acetate 10mM with CHC 2.5 mM (left) or vehicle (DMSO, right). Arrows: acetate peak (1.91 ppm) in HSQC sequences (13C-labeled). Supplementary Figure 3 A) Optical (GFP) and 11C-Acetate PET/CT in KaLwRij mice with bi-lateral flank subcutaneous 5TGM1 tumors (T1 and T2): imaging (i) and TAC (ii) of tumors vs. muscle, p

Supplementary Figure 1 from CD47 Regulates Bone Mass and Tumor Metastasis to Bone

Integrin beta3 antagonist treatment on tumor cells and BMMs in culture

Supplementary Figure Legends 1-2 from CD47 Regulates Bone Mass and Tumor Metastasis to Bone

Anti-CSF1 treatment on β3KOM mice

CD47, also called integrin-associated protein, plays a critical role in the innate immune response and is an atypical member of the immunoglobulin superfamily that interacts with and activates β3 integrins. β3 integrin−/− mice have defective platelet and osteoclast function and are protected from bone metastasis. The role of CD47 in skeletal homeostasis and bone metastasis has not been described. CD47−/− mice had increased bone mass and defective osteoclast function in vivo. Although the number of functional osteoclasts formed by differentiating CD47−/− bone marrow macrophages was decreased, high doses of RANKL rescued differentiation and function of CD47−/− osteoclasts ex vivo and rescued the osteoclast defect in CD47−/− mice. Inhibition of nitric oxide (NO) synthase, which is expressed at higher levels in CD47−/− osteoclasts, also rescued the osteoclast defect in CD47−/− cells. We then examined the consequences of this osteoclast defect in bone metastasis. In a model of tumor metastasis to bone, bone tumor burden was decreased in the CD47−/− mice compared with wild-type (WT) controls, with no decrease in s.c. tumor growth in CD47−/− mice. There was decreased tumor-associated bone destruction in the CD47−/− mice compared with WT controls, consistent with a defect in osteoclast function that was not rescued by the presence of tumor. Our data show that CD47 regulates osteoclastogenesis, in part, via regulation of NO production, and its disruption leads to a decrease in tumor bone metastasis. CD47 is a novel therapeutic target to strengthen bone mass and diminish metastatic tumor growth in bone. [Cancer Res 2009;69(7):3196–204]

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