Metastasis of breast cancer to bones alters the tumor immune microenvironment.

BACKGROUND: Bone is one of the most frequent sites for breast cancer metastasis. Breast cancer bone metastasis (BCBM) leads to skeletal morbidities including pain, fractures, and spinal compression, all of which severely impact quality of life. Immunotherapy is a promising therapy for patients with advanced cancer, but whether it may provide benefit to metastatic bone cancer is currently unknown. Thus, a better understanding of the immune landscape of bone-disseminated breast cancers may reveal new therapeutic strategies. In this study, we use histopathological analysis to investigate changes within the immune microenvironment of primary breast cancer and paired BCBM. METHODS: Sixty-three patients with BCBM, including 31 with paired primary and bone metastatic lesions, were included in our study. The percentage of stroma and stromal tumor-infiltrating lymphocytes (TILs) was evaluated by histopathological analysis. The quantification of stromal TILs (CD4 + and CD8 +), macrophages (CD68 + and HLA-DR +), programmed cell death protein 1 (PD-1), and programmed cell death protein ligand 1 (PD-L1) was evaluated through immunohistochemical (IHC) staining. Statistical analysis was performed with paired t test, Wilcoxon test, spearman correlation test, and univariate and multivariate cox regression. RESULTS: Median survival after BCBM pathological diagnosis was 20.5 months (range: 3-95 months). Of the immune parameters measured, none correlated with survival after bone metastasis was diagnosed. Compared to the primary site, bone metastases exhibited more tumor stroma (mean: 58.5% vs 28.87%, p < 0.001) and less TILs (mean: 8.45% vs 14.03%, p = 0.042), as determined by H&E analysis. The quantification of primary vs metastatic tissue area with CD4 + (23.95/mm2 vs 51.69/mm2, p = 0.027 and with CD8 + (18.15/mm2 vs 58.95/mm2, p = 0.004) TILs similarly followed this trend and was reduced in number for bone metastases. The number of CD68 + and HLA-DR + macrophages showed no significant difference between primary sites and bone metastases. PD-1 expression was present in 68.25% of the bone metastasis, while PD-L1 expression was only present in 7.94% of the bone metastasis. CONCLUSIONS: Our findings suggest that compared to the primary breast cancer site, bone metastases harbor a less active immune microenvironment. Despite this relatively dampened immune landscape, expression of PD-1 and PD-L1 in the bone metastasis indicates a potential benefit from immune checkpoint inhibitors for some BCBM cases.

CD26-negative and CD26-positive tissue-resident fibroblasts contribute to functionally distinct CAF subpopulations in breast cancer.

Cancer-associated fibroblasts (CAFs) are abundantly present in the microenvironment of virtually all tumors and strongly impact tumor progression. Despite increasing insight into their function and heterogeneity, little is known regarding the origin of CAFs. Understanding the origin of CAF heterogeneity is needed to develop successful CAF-based targeted therapies. Through various transplantation studies in mice, we show that CAFs in both invasive lobular breast cancer and triple-negative breast cancer originate from mammary tissue-resident normal fibroblasts (NFs). Single-cell transcriptomics, in vivo and in vitro studies reveal the transition of CD26+ and CD26- NF populations into inflammatory CAFs (iCAFs) and myofibroblastic CAFs (myCAFs), respectively. Functional co-culture experiments show that CD26+ NFs transition into pro-tumorigenic iCAFs which recruit myeloid cells in a CXCL12-dependent manner and enhance tumor cell invasion via matrix-metalloproteinase (MMP) activity. Together, our data suggest that CD26+ and CD26- NFs transform into distinct CAF subpopulations in mouse models of breast cancer.

Combined inhibition of EZH2 and ATM is synthetic lethal in BRCA1-deficient breast cancer.

BACKGROUND: The majority of BRCA1-mutant breast cancers are characterized by a triple-negative phenotype and a basal-like molecular subtype, associated with aggressive clinical behavior. Current treatment options are limited, highlighting the need for the development of novel targeted therapies for this tumor subtype. METHODS: Our group previously showed that EZH2 is functionally relevant in BRCA1-deficient breast tumors and blocking EZH2 enzymatic activity could be a potent treatment strategy. To validate the role of EZH2 as a therapeutic target and to identify new synergistic drug combinations, we performed a high-throughput drug combination screen in various cell lines derived from BRCA1-deficient and -proficient mouse mammary tumors. RESULTS: We identified the combined inhibition of EZH2 and the proximal DNA damage response kinase ATM as a novel synthetic lethality-based therapy for the treatment of BRCA1-deficient breast tumors. We show that the combined treatment with the EZH2 inhibitor GSK126 and the ATM inhibitor AZD1390 led to reduced colony formation, increased genotoxic stress, and apoptosis-mediated cell death in BRCA1-deficient mammary tumor cells in vitro. These findings were corroborated by in vivo experiments showing that simultaneous inhibition of EZH2 and ATM significantly increased anti-tumor activity in mice bearing BRCA1-deficient mammary tumors. CONCLUSION: Taken together, we identified a synthetic lethal interaction between EZH2 and ATM and propose this synergistic interaction as a novel molecular combination for the treatment of BRCA1-mutant breast cancer.

A BRCA1 Coiled-Coil Domain Variant Disrupting PALB2 Interaction Promotes the Development of Mammary Tumors and Confers a Targetable Defect in Homologous Recombination Repair.

The BRCA1 tumor suppressor gene encodes a multidomain protein for which several functions have been described. These include a key role in homologous recombination repair (HRR) of DNA double-strand breaks, which is shared with two other high-risk hereditary breast cancer suppressors, BRCA2 and PALB2. Although both BRCA1 and BRCA2 interact with PALB2, BRCA1 missense variants affecting its PALB2-interacting coiled-coil domain are considered variants of uncertain clinical significance (VUS). Using genetically engineered mice, we show here that a BRCA1 coiled-coil domain VUS, Brca1 p.L1363P, disrupts the interaction with PALB2 and leads to embryonic lethality. Brca1 p.L1363P led to a similar acceleration in the development of Trp53-deficient mammary tumors as Brca1 loss, but the tumors showed distinct histopathologic features, with more stable DNA copy number profiles in Brca1 p.L1363P tumors. Nevertheless, Brca1 p.L1363P mammary tumors were HRR incompetent and responsive to cisplatin and PARP inhibition. Overall, these results provide the first direct evidence that a BRCA1 missense variant outside of the RING and BRCT domains increases the risk of breast cancer. SIGNIFICANCE: These findings reveal the importance of a patient-derived BRCA1 coiled-coil domain sequence variant in embryonic development, mammary tumor suppression, and therapy response.See related commentary by Mishra et al., p. 6080.

Microenvironment-triggered multimodal precision diagnostics.

Therapeutic outcomes in oncology may be aided by precision diagnostics that offer early detection, localization and the opportunity to monitor response to therapy. Here, we report a multimodal nanosensor engineered to target tumours through acidosis, respond to proteases in the microenvironment to release urinary reporters and (optionally) carry positron emission tomography probes to enable localization of primary and metastatic cancers in mouse models of colorectal cancer. We present a paradigm wherein this multimodal sensor can be employed longitudinally to assess burden of disease non-invasively, including tumour progression and response to chemotherapy. Specifically, we showed that acidosis-mediated tumour insertion enhanced on-target release of matrix metalloproteinase-responsive reporters in urine. Subsequent on-demand loading of the radiotracer 64Cu allowed pH-dependent tumour visualization, enabling enriched microenvironmental characterization when compared with the conventional metabolic tracer 18F-fluorodeoxyglucose. Through tailored target specificities, this modular platform has the capacity to be engineered as a pan-cancer test that may guide treatment decisions for numerous tumour types.

iRGD-guided Tumor-penetrating Nanocomplexes for Therapeutic siRNA Delivery to Pancreatic Cancer.

Pancreatic cancer is one of the leading causes of cancer-related death, with 5-year survival of 8.5%. The lack of significant progress in improving therapy reflects our inability to overcome the desmoplastic stromal barrier in pancreatic ductal adenocarcinoma (PDAC) as well as a paucity of new approaches targeting its genetic underpinnings. RNA interference holds promise in targeting key mutations driving PDAC; however, a nucleic acid delivery vehicle that homes to PDAC and breaches the stroma does not yet exist. Noting that the cyclic peptide iRGD mediates tumor targeting and penetration through interactions with αvß3/5 integrins and neuropilin-1, we hypothesized that "tandem" peptides combining a cell-penetrating peptide and iRGD can encapsulate siRNA to form tumor-penetrating nanocomplexes (TPN) capable of delivering siRNA to PDAC. The use of directly conjugated iRGD is justified by receptor expression patterns in human PDAC biopsies. In this work, we optimize iRGD TPNs with polyethylene glycol (PEG)-peptide conjugates for systemic delivery to sites of disease. We show that TPNs effectively knockdown siRNA targets in PDAC cell lines and in an immunocompetent genetically engineered mouse model of PDAC. Furthermore, we validate their tumor-penetrating ability in three-dimensional organoids and autochthonous tumors. In murine therapeutic trials, TPNs delivering anti-Kras siRNA significantly delay tumor growth. Thus, iRGD TPNs hold promise in treating PDAC by not only overcoming physical barriers to therapy, but by leveraging the stroma to achieve knockdown of the gold-standard genetic target. Moreover, the modular construction of this delivery platform allows for facile adaptation to future genetic target candidates in pancreatic cancer. Mol Cancer Ther; 17(11); 2377-88. ©2018 AACR.