STING agonism reprograms tumor-associated macrophages and overcomes resistance to PARP inhibition in BRCA1-deficient models of breast cancer.

PARP inhibitors (PARPi) have drastically changed the treatment landscape of advanced ovarian tumors with BRCA mutations. However, the impact of this class of inhibitors in patients with advanced BRCA-mutant breast cancer is relatively modest. Using a syngeneic genetically-engineered mouse model of breast tumor driven by Brca1 deficiency, we show that tumor-associated macrophages (TAMs) blunt PARPi efficacy both in vivo and in vitro. Mechanistically, BRCA1-deficient breast tumor cells induce pro-tumor polarization of TAMs, which in turn suppress PARPi-elicited DNA damage in tumor cells, leading to reduced production of dsDNA fragments and synthetic lethality, hence impairing STING-dependent anti-tumor immunity. STING agonists reprogram M2-like pro-tumor macrophages into an M1-like anti-tumor state in a macrophage STING-dependent manner. Systemic administration of a STING agonist breaches multiple layers of tumor cell-mediated suppression of immune cells, and synergizes with PARPi to suppress tumor growth. The therapeutic benefits of this combination require host STING and are mediated by a type I IFN response and CD8+ T cells, but do not rely on tumor cell-intrinsic STING. Our data illustrate the importance of targeting innate immune suppression to facilitate PARPi-mediated engagement of anti-tumor immunity in breast cancer.

Spatial proteomic characterization of HER2-positive breast tumors through neoadjuvant therapy predicts response.

The addition of HER2-targeted agents to neoadjuvant chemotherapy has dramatically improved pathological complete response (pCR) rates in early-stage, HER2-positive breast cancer. Nonetheless, up to 50% of patients have residual disease after treatment, while others are likely overtreated. Here, we performed multiplex spatial proteomic characterization of 122 samples from 57 HER2-positive breast tumors from the neoadjuvant TRIO-US B07 clinical trial sampled pre-treatment, after 14-21 d of HER2-targeted therapy and at surgery. We demonstrated that proteomic changes after a single cycle of HER2-targeted therapy aids the identification of tumors that ultimately undergo pCR, outperforming pre-treatment measures or transcriptomic changes. We further developed and validated a classifier that robustly predicted pCR using a single marker, CD45, measured on treatment, and showed that CD45-positive cell counts measured via conventional immunohistochemistry perform comparably. These results demonstrate robust biomarkers that can be used to enable the stratification of sensitive tumors early during neoadjuvant HER2-targeted therapy, with implications for tailoring subsequent therapy.

Metabolic perturbations sensitize triple-negative breast cancers to apoptosis induced by BH3 mimetics.

Cancer cells have differential metabolic dependencies compared to their nonmalignant counterparts. However, few metabolism-targeting compounds have been successful in clinical trials. Here, we investigated the metabolic vulnerabilities of triple-negative breast cancer (TNBC), particularly those metabolic perturbations that increased mitochondrial apoptotic priming and sensitivity to BH3 mimetics (drugs that antagonize antiapoptotic proteins). We used high-throughput dynamic BH3 profiling (HT-DBP) to screen a library of metabolism-perturbing small molecules, which revealed inhibitors of the enzyme nicotinamide phosphoribosyltransferase (NAMPT) as top candidates. In some TNBC cells but not in nonmalignant cells, NAMPT inhibitors increased overall apoptotic priming and induced dependencies on specific antiapoptotic BCL-2 family members. Treatment of TNBC cells with NAMPT inhibitors sensitized them to subsequent treatment with BH3 mimetics. The combination of a NAMPT inhibitor (FK866) and an MCL-1 antagonist (S63845) reduced tumor growth in a TNBC patient-derived xenograft model in vivo. We found that NAMPT inhibition reduced NAD+ concentrations below a critical threshold that resulted in depletion of adenine, which was the metabolic trigger that primed TNBC cells for apoptosis. These findings demonstrate a close interaction between metabolic and mitochondrial apoptotic signaling pathways and reveal that exploitation of a tumor-specific metabolic vulnerability can sensitize some TNBC to BH3 mimetics.

Clinical evaluation of BCL-2/XL levels pre- and post- HER2-targeted therapy.

Our previous pre-clinical work defined BCL-2 induction as a critical component of the adaptive response to lapatinib-mediated inhibition of HER2. To determine whether a similar BCL-2 upregulation occurs in lapatinib-treated patients, we evaluated gene expression within tumor biopsies, collected before and after lapatinib or trastuzumab treatment, from the TRIO-B-07 clinical trial (NCT#00769470). We detected BCL2 mRNA upregulation in both HER2+/ER- as well as HER2+/ER+ patient tumors treated with lapatinib or trastuzumab. To address whether mRNA expression correlated with protein expression, we evaluated pre- and post-treatment tumors for BCL-2 via immunohistochemistry. Despite BCL2 mRNA upregulation within HER2+/ER- tumors, BCL-2 protein levels were undetectable in most of the lapatinib- or trastuzumab-treated HER2+/ER- tumors. BCL-2 upregulation was evident within the majority of lapatinib-treated HER2+/ER+ tumors and was often coupled with increased ER expression and decreased proliferation. Comparable BCL-2 upregulation was not observed within the trastuzumab-treated HER2+/ER+ tumors. Together, these results provide clinical validation of the BCL-2 induction associated with the adaptive response to lapatinib and support evaluation of BCL-2 inhibitors within the context of lapatinib and other HER2-targeted receptor tyrosine kinase inhibitors.

Navitoclax enhances the effectiveness of EGFR-targeted antibody-drug conjugates in PDX models of EGFR-expressing triple-negative breast cancer.

BACKGROUND: Targeted therapies for triple-negative breast cancer (TNBC) are limited; however, the epidermal growth factor receptor (EGFR) represents a potential target, as the majority of TNBC express EGFR. The purpose of these studies was to evaluate the effectiveness of two EGFR-targeted antibody-drug conjugates (ADC: ABT-414; ABBV-321) in combination with navitoclax, an antagonist of the anti-apoptotic BCL-2 and BCL-XL proteins, in order to assess the translational relevance of these combinations for TNBC. METHODS: The pre-clinical efficacy of combined treatments was evaluated in multiple patient-derived xenograft (PDX) models of TNBC. Microscopy-based dynamic BH3 profiling (DBP) was used to assess mitochondrial apoptotic signaling induced by navitoclax and/or ADC treatments, and the expression of EGFR and BCL-2/XL was analyzed in 46 triple-negative patient tumors. RESULTS: Treatment with navitoclax plus ABT-414 caused a significant reduction in tumor growth in five of seven PDXs and significant tumor regression in the highest EGFR-expressing PDX. Navitoclax plus ABBV-321, an EGFR-targeted ADC that displays more effective wild-type EGFR-targeting, elicited more significant tumor growth inhibition and regressions in the two highest EGFR-expressing models evaluated. The level of mitochondrial apoptotic signaling induced by single or combined drug treatments, as measured by DBP, correlated with the treatment responses observed in vivo. Lastly, the majority of triple-negative patient tumors were found to express EGFR and co-express BCL-XL and/or BCL-2. CONCLUSIONS: The dramatic tumor regressions achieved using combined agents in pre-clinical TNBC models underscore the abilities of BCL-2/XL antagonists to enhance the effectiveness of EGFR-targeted ADCs and highlight the clinical potential for usage of such targeted ADCs to alleviate toxicities associated with combinations of BCL-2/XL inhibitors and systemic chemotherapies.

Pathologic and molecular responses to neoadjuvant trastuzumab and/or lapatinib from a phase II randomized trial in HER2-positive breast cancer (TRIO-US B07).

In this multicenter, open-label, randomized phase II investigator-sponsored neoadjuvant trial with funding provided by Sanofi and GlaxoSmithKline (TRIO-US B07, Clinical Trials NCT00769470), participants with early-stage HER2-positive breast cancer (N = 128) were recruited from 13 United States oncology centers throughout the Translational Research in Oncology network. Participants were randomized to receive trastuzumab (T; N = 34), lapatinib (L; N = 36), or both (TL; N = 58) as HER2-targeted therapy, with each participant given one cycle of this designated anti-HER2 therapy alone followed by six cycles of standard combination chemotherapy with the same anti-HER2 therapy. The primary objective was to estimate the rate of pathologic complete response (pCR) at the time of surgery in each of the three arms. In the intent-to-treat population, we observed similar pCR rates between T (47%, 95% confidence interval [CI] 30-65%) and TL (52%, 95% CI 38-65%), and a lower pCR rate with L (25%, 95% CI 13-43%). In the T arm, 100% of participants completed all protocol-specified treatment prior to surgery, as compared to 69% in the L arm and 74% in the TL arm. Tumor or tumor bed tissue was collected whenever possible pre-treatment (N = 110), after one cycle of HER2-targeted therapy alone (N = 89), and at time of surgery (N = 59). Higher-level amplification of HER2 and hormone receptor (HR)-negative status were associated with a higher pCR rate. Large shifts in the tumor, immune, and stromal gene expression occurred after one cycle of HER2-targeted therapy. In contrast to pCR rates, the L-containing arms exhibited greater proliferation reduction than T at this timepoint. Immune expression signatures increased in all arms after one cycle of HER2-targeted therapy, decreasing again by the time of surgery. Our results inform approaches to early assessment of sensitivity to anti-HER2 therapy and shed light on the role of the immune microenvironment in response to HER2-targeted agents.

Neutralization of BCL-2/XL Enhances the Cytotoxicity of T-DM1 In Vivo.

One of the most recent advances in the treatment of HER2+ breast cancer is the development of the antibody-drug conjugate, T-DM1. T-DM1 has proven clinical benefits for patients with advanced and/or metastatic breast cancer who have progressed on prior HER2-targeted therapies. However, T-DM1 resistance ultimately occurs and represents a major obstacle in the effective treatment of this disease. Because anti-apoptotic BCL-2 family proteins can affect the threshold for induction of apoptosis and thus limit the effectiveness of the chemotherapeutic payload, we examined whether inhibition of BCL-2/XL would enhance the efficacy of T-DM1 in five HER2-expressing patient-derived breast cancer xenograft models. Inhibition of BCL-2/XL via navitoclax/ABT-263 significantly enhanced the cytotoxicity of T-DM1 in two of three models derived from advanced and treatment-exposed metastatic breast tumors. No additive effects of combined treatment were observed in the third metastatic tumor model, which was highly sensitive to T-DM1, as well as a primary treatment-exposed tumor, which was refractory to T-DM1. A fifth model, derived from a treatment naïve primary breast tumor, was sensitive to T-DM1 but markedly benefited from combination treatment. Notably, both PDXs that were highly responsive to the combination therapy expressed low HER2 protein levels and lacked ERBB2 amplification, suggesting that BCL-2/XL inhibition can enhance sensitivity of tumors with low HER2 expression. Toxicities associated with combined treatments were significantly ameliorated with intermittent ABT-263 dosing. Taken together, these studies provide evidence that T-DM1 cytotoxicity could be significantly enhanced via BCL-2/XL blockade and support clinical investigation of this combination beyond ERBB2-amplified and/or HER2-overexpressed tumors.

Rapid Sequential in Situ Multiplexing with DNA Exchange Imaging in Neuronal Cells and Tissues.

To decipher the molecular mechanisms of biological function, it is critical to map the molecular composition of individual cells or even more importantly tissue samples in the context of their biological environment in situ. Immunofluorescence (IF) provides specific labeling for molecular profiling. However, conventional IF methods have finite multiplexing capabilities due to spectral overlap of the fluorophores. Various sequential imaging methods have been developed to circumvent this spectral limit but are not widely adopted due to the common limitation of requiring multirounds of slow (typically over 2 h at room temperature to overnight at 4 °C in practice) immunostaining. We present here a practical and robust method, which we call DNA Exchange Imaging (DEI), for rapid in situ spectrally unlimited multiplexing. This technique overcomes speed restrictions by allowing for single-round immunostaining with DNA-barcoded antibodies, followed by rapid (less than 10 min) buffer exchange of fluorophore-bearing DNA imager strands. The programmability of DEI allows us to apply it to diverse microscopy platforms (with Exchange Confocal, Exchange-SIM, Exchange-STED, and Exchange-PAINT demonstrated here) at multiple desired resolution scales (from ∼300 nm down to sub-20 nm). We optimized and validated the use of DEI in complex biological samples, including primary neuron cultures and tissue sections. These results collectively suggest DNA exchange as a versatile, practical platform for rapid, highly multiplexed in situ imaging, potentially enabling new applications ranging from basic science, to drug discovery, and to clinical pathology.

Erratum: Niche-localized tumor cells are protected from HER2-targeted therapy via upregulation of an anti-apoptotic program in vivo.

[This corrects the article DOI: 10.1038/s41523-017-0020-z.].

Niche-localized tumor cells are protected from HER2-targeted therapy via upregulation of an anti-apoptotic program in vivo.

Several lines of evidence suggest that components of the tumor microenvironment, specifically basement membrane and extracellular matrix proteins, influence drug sensitivities. We previously reported differential drug sensitivity of tumor cells localized adjacent to laminin-rich extracellular matrix in three-dimensional tumor spheroid cultures. To evaluate whether differential intra-tumor responses to targeted therapy occur in vivo, we examined the sensitivity of human epidermal growth factor receptor 2-positive tumors to lapatinib using a previously described ductal carcinoma in situ-like model characterized by tumor cell confinement within ductal structures surrounded by an organized basement membrane. Here we show that tumor cells localized to a 'niche' in the outer layer of the intraductal tumors adjacent to myoepithelial cells and basement membrane are resistant to lapatinib. We found that the pro-survival protein BCL2 is selectively induced in the niche-protected tumor cells following lapatinib treatment, and combined inhibition of HER2 and BCL-2/XL enhanced targeting of these residual tumor cells. Elimination of the niche-protected tumor cells was achieved with the HER2 antibody-drug conjugate T-DM1, which delivers a chemotherapeutic payload. Thus, these studies provide evidence that subpopulations of tumor cells within specific microenvironmental niches can adapt to inhibition of critical oncogenic pathways, and furthermore reveal effective strategies to eliminate these resistant subpopulations.

A key role for the integrin alpha2beta1 in experimental and developmental angiogenesis.

The alpha2beta1 integrin receptor plays a key role in angiogenesis. Here we investigated the effects of small molecule inhibitors (SMIs) designed to disrupt integrin alpha2 I or beta1 I-like domain function on angiogenesis. In unchallenged endothelial cells, fibrillar collagen induced robust capillary morphogenesis. In contrast, tube formation was significantly reduced by SMI496, a beta1 I-like domain inhibitor and by function-blocking anti-alpha2beta1 but not -alpha1beta1 antibodies. Endothelial cells bound fluorescein-labeled collagen I fibrils, an interaction specifically inhibited by SMI496. Moreover, SMI496 caused cell retraction and cytoskeletal collapse of endothelial cells as well as delayed endothelial cell wound healing. SMI activities were examined in vivo by supplementing the growth medium of zebrafish embryos expressing green fluorescent protein under the control of the vascular endothelial growth factor receptor-2 promoter. SMI496, but not a control compound, interfered with angiogenesis in vivo by reversibly inhibiting sprouting from the axial vessels. We further characterized zebrafish alpha2 integrin and discovered that this integrin is highly conserved, especially the I domain. Notably, a similar vascular phenotype was induced by morpholino-mediated knockdown of the integrin alpha2 subunit. By live videomicroscopy, we confirmed that the vessels were largely nonfunctional in the absence of alpha2beta1 integrin. Collectively, our results provide strong biochemical and genetic evidence of a central role for alpha2beta1 integrin in experimental and developmental angiogenesis.

Perlecan regulates developmental angiogenesis by modulating the VEGF-VEGFR2 axis.

Using the zebrafish, we previously identified a central function for perlecan during angiogenic blood vessel development. Here, we explored the nature of perlecan function during developmental angiogenesis. A close examination of individual endothelial cell behavior revealed that perlecan is required for proper endothelial cell migration and proliferation. Because these events are largely mediated by VEGF-VEGFR2 signaling, we investigated the relationship between perlecan and the VEGF pathway. We discovered that perlecan knockdown caused an abnormal increase and redistribution of total VEGF-A protein suggesting that perlecan is required for the appropriate localization of VEGF-A. Importantly, we linked perlecan function to the VEGF pathway by efficiently rescuing the perlecan morphant phenotype by microinjecting VEGF-A(165) protein or mRNA. Combining the strategic localization of perlecan throughout the vascular basement membrane along with its growth factor-binding ability, we hypothesized a major role for perlecan during the establishment of the VEGF gradient which provides the instructive cues to endothelial cells during angiogenesis. In support of this hypothesis we demonstrated that human perlecan bound in a heparan sulfate-dependent fashion to VEGF-A(165). Moreover, perlecan enhanced VEGF mediated VEGFR2 activation of human endothelial cells. Collectively, our results indicate that perlecan coordinates developmental angiogenesis through modulation of VEGF-VEGFR2 signaling events. The identification of angiogenic factors, such as perlecan, and their role in vertebrate development will not only enhance overall understanding of the molecular basis of angiogenesis, but may also provide new insight into angiogenesis-based therapeutic approaches.

Basement membrane proteoglycans: modulators Par Excellence of cancer growth and angiogenesis.

Proteoglycans located in basement membranes, the nanostructures underling epithelial and endothelial layers, are unique in several respects. They are usually large, elongated molecules with a collage of domains that share structural and functional homology with numerous extracellular matrix proteins, growth factors and surface receptors. They mainly carry heparan sulfate side chains and these contribute not only to storing and preserving the biological activity of various heparan sulfate-binding cytokines and growth factors, but also in presenting them in a more "active configuration" to their cognate receptors. Abnormal expression or deregulated function of these proteoglycans affect cancer and angiogenesis, and are critical for the evolution of the tumor microenvironment. This review will focus on the functional roles of the major heparan sulfate proteoglycans from basement membrane zones: perlecan, agrin and collagen XVIII, and on their roles in modulating cancer growth and angiogenesis.

A central role for decorin during vertebrate convergent extension.

Decorin, an archetypal member of the small leucine-rich proteoglycan gene family, regulates collagen fibrillogenesis and cell growth. To further explore its biological function, we examined the role of Decorin during zebrafish development. Zebrafish Decorin is a chondroitin sulfate proteoglycan that exhibits a high degree of conservation with its mammalian counterpart and displays a unique spatiotemporal expression pattern. Morpholino-mediated knockdown of zebrafish decorin identified a developmental role during medial-lateral convergence and anterior-posterior extension of the body plan, as well as in craniofacial cartilage formation. decorin morphants displayed a pronounced shortening of the head-to-tail axis as well as compression, flattening, and extension of the jaw cartilages. The morphant phenotype was efficiently rescued by zebrafish decorin mRNA. Unexpectedly, microinjection of excess zebrafish decorin mRNA or proteoglycan/protein core into one-cell stage embryos caused cyclopia. The morphant and overexpression phenotype represent a convergent extension defect. Our results indicate a central function for Decorin during early embryogenesis.

A central function for perlecan in skeletal muscle and cardiovascular development.

Perlecan's developmental functions are difficult to dissect in placental animals because perlecan disruption is embryonic lethal. In contrast to mammals, cardiovascular function is not essential for early zebrafish development because the embryos obtain adequate oxygen by diffusion. In this study, we use targeted protein depletion coupled with protein-based rescue experiments to investigate the involvement of perlecan and its C-terminal domain V/endorepellin in zebrafish development. The perlecan morphants show a severe myopathy characterized by abnormal actin filament orientation and disorganized sarcomeres, suggesting an involvement of perlecan in myopathies. In the perlecan morphants, primary intersegmental vessel sprouts, which develop through angiogenesis, fail to extend and show reduced protrusive activity. Live videomicroscopy confirms the abnormal swimming pattern caused by the myopathy and anomalous head and trunk vessel circulation. The phenotype is partially rescued by microinjection of human perlecan or endorepellin. These findings indicate that perlecan is essential for the integrity of somitic muscle and developmental angiogenesis and that endorepellin mediates most of these biological activities.

Proteomic profiling of endorepellin angiostatic activity on human endothelial cells.

BACKGROUND: Endorepellin, the C-terminal domain V of the heparan sulfate proteoglycan perlecan, exhibits powerful and targeted anti-angiogenic activity on endothelial cells. To identify proteins involved with endorepellin anti-angiogenic action, we performed an extensive comparative proteomic analysis between vehicle- and endorepellin-treated human endothelial cells. RESULTS: Proteomic analysis of endorepellin influence on human umbilical vein endothelial cells identified five differentially expressed proteins, three of which (beta-actin, calreticulin, and chaperonin/Hsp60) were down-regulated and two of which (vimentin and the beta subunit of prolyl 4-hydroxylase also known as protein disulfide isomerase) were up-regulated in response to endorepellin treatment-and associated with a fold change (endorepellin/control) /= 2.00, and a statistically significant p-value as determined by Student's t test. CONCLUSION: The proteins identified represent potential target areas involved with endorepellin anti-angiogenic mechanism of action. Further elucidation as such will ultimately provide useful in utilizing endorepellin as an anti-angiogenic therapy in humans.