Miles A. Miller

The Receptor AXL Diversifies EGFR Signaling and Limits the Response to EGFR-Targeted Inhibitors in Triple-Negative Breast Cancer Cells

Amplification of downstream signaling by AXL receptor tyrosine kinase alters the migratory response of breast cancer cells. Transactivating Resistance Resistance to receptor tyrosine kinase (RTK) inhibitors in cancer is often mediated by the activation of alternate receptors that provide compensatory signaling. Meyer et al. showed that the RTK AXL predicts resistance to EGFR (epidermal growth factor receptor) inhibitors in cancer cell lines. Through a ligand-independent mode of transactivation by EGFR, AXL mediated the downstream activation of proteins in a distinct combination, thereby augmenting EGFR signaling and contributing unique output. Diversified, AXL-mediated signaling was required for EGF (epidermal growth factor)–induced migration of TNBC (triple-negative breast cancer) cells. Expression profiles of AXL and EGFR in cancer cell lines predicted resistance to EGFR inhibitors, and treatment with an AXL inhibitor reduced EGFR-elicited proliferation and migration, suggesting that targeting AXL may improve EGFR-targeted drug therapy in TNBC. The relationship between drug resistance, changes in signaling, and emergence of an invasive phenotype is well appreciated, but the underlying mechanisms are not well understood. Using machine learning analysis applied to the Cancer Cell Line Encyclopedia database, we identified expression of AXL, the gene that encodes the epithelial-to-mesenchymal transition (EMT)–associated receptor tyrosine kinase (RTK) AXL, as exceptionally predictive of lack of response to ErbB family receptor–targeted inhibitors. Activation of EGFR (epidermal growth factor receptor) transactivated AXL, and this ligand-independent AXL activity diversified EGFR-induced signaling into additional downstream pathways beyond those triggered by EGFR alone. AXL-mediated signaling diversification was required for EGF (epidermal growth factor)–elicited motility responses in AXL-positive TNBC (triple-negative breast cancer) cells. Using cross-linking coimmunoprecipitation assays, we determined that AXL associated with EGFR, other ErbB receptor family members, MET (hepatocyte growth factor receptor), and PDGFR (platelet-derived growth factor receptor) but not IGF1R (insulin-like growth factor 1 receptor) or INSR (insulin receptor). From these AXL interaction data, we predicted AXL-mediated signaling synergy for additional RTKs and validated these predictions in cells. This alternative mechanism of receptor activation limits the use of ligand-blocking therapies and indicates against therapy withdrawal after acquired resistance. Further, subadditive interaction between EGFR- and AXL-targeted inhibitors across all AXL-positive TNBC cell lines may indicate that increased abundance of EGFR is principally a means to transactivation-mediated signaling.

Predicting therapeutic nanomedicine efficacy using a companion magnetic resonance imaging nanoparticle

Magnetic nanoparticles predict the efficacy of drug-loaded polymeric nanoparticles in vivo, helping select for tumors more responsive to nanomedicine. Particle prediction One particle, it seems, can predict the behavior of another. Thankfully, this is not the beginning of a lesson on quantum physics; instead, it is the basis for potentially designing targeted clinical trials in nanomedicine, by knowing if a tumor is likely to respond to a particular therapeutic nanoparticle. Miller et al. hypothesized that if a tumor readily takes up magnetic nanoparticles (MNP), it will also accumulate other nanoparticles carrying a deadly payload. The authors injected MNPs and a fluorescent version of the therapeutic nanoparticles into mice and followed their biodistribution using imaging. Both types of nanoparticles had similar pharmacokinetics and uptake in tumor-associated host cells owing to the enhanced permeability and retention effect. In mice with human tumors, Miller and colleagues found that the tumors with high MNP uptake were significantly more responsive than those with medium or low uptake to nanoparticles delivering chemotherapeutics. Thus, MNPs can be used as companion imaging agents during nanomedicine trials to predict the therapeutic effect of their nanosized counterparts. Therapeutic nanoparticles (TNPs) have shown heterogeneous responses in human clinical trials, raising questions of whether imaging should be used to identify patients with a higher likelihood of NP accumulation and thus therapeutic response. Despite extensive debate about the enhanced permeability and retention (EPR) effect in tumors, it is increasingly clear that EPR is extremely variable; yet, little experimental data exist to predict the clinical utility of EPR and its influence on TNP efficacy. We hypothesized that a 30-nm magnetic NP (MNP) in clinical use could predict colocalization of TNPs by magnetic resonance imaging (MRI). To this end, we performed single-cell resolution imaging of fluorescently labeled MNPs and TNPs and studied their intratumoral distribution in mice. MNPs circulated in the tumor microvasculature and demonstrated sustained uptake into cells of the tumor microenvironment within minutes. MNPs could predictably demonstrate areas of colocalization for a model TNP, poly(d,l-lactic-co-glycolic acid)-b-polyethylene glycol (PLGA-PEG), within the tumor microenvironment with >85% accuracy and circulating within the microvasculature with >95% accuracy, despite their markedly different sizes and compositions. Computational analysis of NP transport enabled predictive modeling of TNP distribution based on imaging data and identified key parameters governing intratumoral NP accumulation and macrophage uptake. Finally, MRI accurately predicted initial treatment response and drug accumulation in a preclinical efficacy study using a paclitaxel-encapsulated NP in tumor-bearing mice. These approaches yield valuable insight into the in vivo kinetics of NP distribution and suggest that clinically relevant imaging modalities and agents can be used to select patients with high EPR for treatment with TNPs.

Tumour-associated macrophages act as a slow-release reservoir of nano-therapeutic Pt(IV) pro-drug

Therapeutic nanoparticles (TNPs) aim to deliver drugs more safely and effectively to cancers, yet clinical results have been unpredictable owing to limited in vivo understanding. Here we use single-cell imaging of intratumoral TNP pharmacokinetics and pharmacodynamics to better comprehend their heterogeneous behaviour. Model TNPs comprising a fluorescent platinum(IV) pro-drug and a clinically tested polymer platform (PLGA-b-PEG) promote long drug circulation and alter accumulation by directing cellular uptake toward tumour-associated macrophages (TAMs). Simultaneous imaging of TNP vehicle, its drug payload and single-cell DNA damage response reveals that TAMs serve as a local drug depot that accumulates significant vehicle from which DNA-damaging Pt payload gradually releases to neighbouring tumour cells. Correspondingly, TAM depletion reduces intratumoral TNP accumulation and efficacy. Thus, nanotherapeutics co-opt TAMs for drug delivery, which has implications for TNP design and for selecting patients into trials.

In vivo imaging reveals a tumor-associated macrophage–mediated resistance pathway in anti–PD-1 therapy

Tumor-associated macrophages limit anti–PD-1 effects by removing the antibody from CD8+ T cells. Tug-of-war with anti–PD-1 Antibodies against immune checkpoints such as programmed death–1 (PD-1) are gaining increasing prominence in cancer treatment, but even these promising therapeutics do not always work. To be effective in preventing T cells from becoming exhausted, anti–PD-1 antibodies must be able to remain bound to the T cells. Unfortunately, this does not always happen, as Arlauckas et al. discovered. Although anti–PD-1 antibodies initially bound to T cells as intended, the authors found that tumor-associated macrophages quickly removed these antibodies from T cells, thus inactivating them. The researchers also identified a potential way to overcome this problem, showing that inhibition of Fcγ receptors prevented removal of anti–PD-1 and prolonged its effects in vivo. Monoclonal antibodies (mAbs) targeting the immune checkpoint anti–programmed cell death protein 1 (aPD-1) have demonstrated impressive benefits for the treatment of some cancers; however, these drugs are not always effective, and we still have a limited understanding of the mechanisms that contribute to their efficacy or lack thereof. We used in vivo imaging to uncover the fate and activity of aPD-1 mAbs in real time and at subcellular resolution in mice. We show that aPD-1 mAbs effectively bind PD-1+ tumor-infiltrating CD8+ T cells at early time points after administration. However, this engagement is transient, and aPD-1 mAbs are captured within minutes from the T cell surface by PD-1− tumor-associated macrophages. We further show that macrophage accrual of aPD-1 mAbs depends both on the drug’s Fc domain glycan and on Fcγ receptors (FcγRs) expressed by host myeloid cells and extend these findings to the human setting. Finally, we demonstrate that in vivo blockade of FcγRs before aPD-1 mAb administration substantially prolongs aPD-1 mAb binding to tumor-infiltrating CD8+ T cells and enhances immunotherapy-induced tumor regression in mice. These investigations yield insight into aPD-1 target engagement in vivo and identify specific Fc/FcγR interactions that can be modulated to improve checkpoint blockade therapy.

ADAM-10 and -17 regulate endometriotic cell migration via concerted ligand and receptor shedding feedback on kinase signaling

Significance Regulated cell-surface proteolysis underpins processes of cellular migration in both physiological and pathological contexts. However, comprehending how multiple proteolytic events cohesively integrate to yield context-dependent cellular behavior remains a challenge. Here we present an experimental/computational paradigm for analyzing networks of protease activities that interface with signaling pathways to influence cellular migration in the invasive disease of endometriosis. We find that induced cellular migration is a quantitative consequence of positive feedback through ligand release and negative feedback through receptor shedding, which furthermore drives rapid resistance to kinase inhibitor treatment. Targeted clinical proteomics confirms dysregulated proteolysis in endometriosis. A Disintegrin and Metalloproteinases (ADAMs) are the principal enzymes for shedding receptor tyrosine kinase (RTK) ectodomains and ligands from the cell surface. Multiple layers of activity regulation, feedback, and catalytic promiscuity impede our understanding of context-dependent ADAM “sheddase” function and our ability to predictably target that function in disease. This study uses combined measurement and computational modeling to examine how various growth factor environments influence sheddase activity and cell migration in the invasive disease of endometriosis. We find that ADAM-10 and -17 dynamically integrate numerous signaling pathways to direct cell motility. Data-driven modeling reveals that induced cell migration is a quantitative function of positive feedback through EGF ligand release and negative feedback through RTK shedding. Although sheddase inhibition prevents autocrine ligand shedding and resultant EGF receptor transactivation, it also leads to an accumulation of phosphorylated receptors (HER2, HER4, and MET) on the cell surface, which subsequently enhances Jnk/p38 signaling. Jnk/p38 inhibition reduces cell migration by blocking sheddase activity while additionally preventing the compensatory signaling from accumulated RTKs. In contrast, Mek inhibition reduces ADAM-10 and -17 activities but fails to inhibit compensatory signaling from accumulated RTKs, which actually enhances cell motility in some contexts. Thus, here we present a sheddase-based mechanism of rapidly acquired resistance to Mek inhibition through reduced RTK shedding that can be overcome with rationally directed combination inhibitor treatment. We investigate the clinical relevance of these findings using targeted proteomics of peritoneal fluid from endometriosis patients and find growth-factor–driven ADAM-10 activity and MET shedding are jointly dysregulated with disease.

Regulated ADAM17-dependent EGF family ligand release by substrate-selecting signaling pathways.

Ectodomain cleavage of cell-surface proteins by A disintegrin and metalloproteinases (ADAMs) is highly regulated, and its dysregulation has been linked to many diseases. ADAM10 and ADAM17 cleave most disease-relevant substrates. Broad-spectrum metalloprotease inhibitors have failed clinically, and targeting the cleavage of a specific substrate has remained impossible. It is therefore necessary to identify signaling intermediates that determine substrate specificity of cleavage. We show here that phorbol ester or angiotensin II-induced proteolytic release of EGF family members may not require a significant increase in ADAM17 protease activity. Rather, inducers activate a signaling pathway using PKC-α and the PKC-regulated protein phosphatase 1 inhibitor 14D that is required for ADAM17 cleavage of TGF-α, heparin-binding EGF, and amphiregulin. A second pathway involving PKC-δ is required for neuregulin (NRG) cleavage, and, indeed, PKC-δ phosphorylation of serine 286 in the NRG cytosolic domain is essential for induced NRG cleavage. Thus, signaling-mediated substrate selection is clearly distinct from regulation of enzyme activity, an important mechanism that offers itself for application in disease.

Single-cell pharmacokinetic imaging reveals a therapeutic strategy to overcome drug resistance to the microtubule inhibitor eribulin

Single-cell pharmacokinetic analysis of a fluorescent eribulin derivative in vivo revealed drug resistance mediated by MDR1-driven efflux, which was overcome by a nanoencapsulated MDR1 inhibitor. Single-Cell Imaging of Cancer Drug Resistance Resistance to drugs is common in cancer and is often caused by the multidrug resistance protein 1 (MDR1). To get to the bottom of this mechanism of drug resistance—and hopefully develop better therapeutics from this knowledge—Laughney et al. created a fluorescent cancer drug and probed tissue distribution and kinetics at both the single-cell and population levels. The authors developed a mouse model of drug-resistant human cancer, with tumors that were heterogeneously resistant (various levels of MDR1 expression). By tracking the fluorescent drug eribulin in vivo, they saw that MDR1-expressing cells accumulated less drug than their wild-type counterparts—and this was a function of distance from blood vessels. MDR1 inhibitors did not appear to increase drug uptake in MDR1-overexpressing cells in vivo, so the authors redesigned the MDR inhibitor as a nanoparticle. In mice, inhibitor loaded in nanoparticles demonstrated bioactivity in the tumor. The combination of single-cell pharmacokinetics, intravital imaging, and drug reengineering suggests a new platform for understanding and overcoming resistance in human cancer. Eribulin mesylate was developed as a potent microtubule-targeting cytotoxic agent to treat taxane-resistant cancers, but recent clinical trials have shown that it eventually fails in many patient subpopulations for unclear reasons. To investigate its resistance mechanisms, we developed a fluorescent analog of eribulin with pharmacokinetic (PK) properties and cytotoxic activity across a human cell line panel that are sufficiently similar to the parent drug to study its cellular PK and tissue distribution. Using intravital imaging and automated tracking of cellular dynamics, we found that resistance to eribulin and the fluorescent analog depended directly on the multidrug resistance protein 1 (MDR1). Intravital imaging allowed for real-time analysis of in vivo PK in tumors that were engineered to be spatially heterogeneous for taxane resistance, whereby an MDR1-mApple fusion protein distinguished resistant cells fluorescently. In vivo, MDR1-mediated drug efflux and the three-dimensional tumor vascular architecture were discovered to be critical determinants of drug accumulation in tumor cells. We furthermore show that standard intravenous administration of a third-generation MDR1 inhibitor, HM30181, failed to rescue drug accumulation; however, the same MDR1 inhibitor encapsulated within a nanoparticle delivery system reversed the multidrug-resistant phenotype and potentiated the eribulin effect in vitro and in vivo in mice. Our work demonstrates that in vivo assessment of cellular PK of an anticancer drug is a powerful strategy for elucidating mechanisms of drug resistance in heterogeneous tumors and evaluating strategies to overcome this resistance.

ADAM8 as a drug target in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) has a grim prognosis with less than 5% survivors after 5 years. High expression levels of ADAM8, a metalloprotease-disintegrin, are correlated with poor clinical outcome. We show that ADAM8 expression is associated with increased migration and invasiveness of PDAC cells caused by activation of ERK 1/2 and higher MMP activities. For biological function, ADAM8 requires multimerisation and associates with β1-integrin on the cell surface. A peptidomimetic ADAM8 inhibitor, BK-1361, designed by structural modelling of the disintegrin domain, prevents ADAM8 multimerisation. In PDAC cells, BK-1361 affects ADAM8 function leading to reduced invasiveness, and less ERK 1/2 and MMP activation. BK-1361 application in mice decreased tumour burden and metastasis of implanted pancreatic tumour cells and provides improved metrics of clinical symptoms and survival in a KrasG12D-driven mouse model of PDAC. Thus, our data integrate ADAM8 in pancreatic cancer signalling and validate ADAM8 as a target for PDAC therapy.

ADAM9 Inhibition Increases Membrane Activity of ADAM10 and Controls α-Secretase Processing of Amyloid Precursor Protein

Background: Raising ADAM10 α-secretase activity has been considered as an attractive therapeutic option in Alzheimer disease. Results: Administration of the prodomain of ADAM9 (proA9) prevents ADAM10 shedding and increases membrane α-secretase activity in a neuronal cell line. Conclusion: Use of proA9 is a means to modulate cellular ADAM10 activity. Significance: proA9 can be used in vivo to increase ADAM10 α-secretase activity. Prodomains of A disintegrin and metalloproteinase (ADAM) metallopeptidases can act as highly specific intra- and intermolecular inhibitors of ADAM catalytic activity. The mouse ADAM9 prodomain (proA9; amino acids 24–204), expressed and characterized from Escherichia coli, is a competitive inhibitor of human ADAM9 catalytic/disintegrin domain with an overall inhibition constant of 280 ± 34 nm and high specificity toward ADAM9. In SY5Y neuroblastoma cells overexpressing amyloid precursor protein, proA9 treatment reduces the amount of endogenous ADAM10 enzyme in the medium while increasing membrane-bound ADAM10, as shown both by Western and activity assays with selective fluorescent peptide substrates using proteolytic activity matrix analysis. An increase in membrane-bound ADAM10 generates higher levels of soluble amyloid precursor protein α in the medium, whereas soluble amyloid precursor protein β levels are decreased, demonstrating that inhibition of ADAM9 increases α-secretase activity on the cell membrane. Quantification of physiological ADAM10 substrates by a proteomic approach revealed that substrates, such as epidermal growth factor (EGF), HER2, osteoactivin, and CD40-ligand, are increased in the medium of BT474 breast tumor cells that were incubated with proA9, demonstrating that the regulation of ADAM10 by ADAM9 applies for many ADAM10 substrates. Taken together, our results demonstrate that ADAM10 activity is regulated by inhibition of ADAM9, and this regulation may be used to control shedding of amyloid precursor protein by enhancing α-secretase activity, a key regulatory step in the etiology of Alzheimer disease.

Platinum compounds for high-resolution in vivo cancer imaging

Platinum(II) compounds, principally cisplatin and carboplatin, are commonly used front‐line cancer therapeutics. Despite their widespread use and continued interest in the development of new derivatives, including nanoformulations with improved properties, it has been difficult to visualize platinum compounds in live subjects, in real time, and with subcellular resolution. Here, we present four novel cisplatin‐ and carboplatin‐derived fluorescent imaging compounds for quantitative intravital cancer imaging. We conjugated 4,4‐difluoro‐5,7‐dimethyl‐4‐bora‐3a,4a‐daiza‐s‐indacene (BODIPY) to PtII complexes to generate derivatives with robust in vivo fluorescence and retained DNA‐damaging and cytotoxic properties. We successfully applied these compounds to image pharmacokinetics and tumor uptake in a xenograft cancer mouse model. By using a genetic reporter of single‐cell DNA damage for in vivo imaging, Pt drug accumulation and resultant DNA damage could be monitored in individual tumor cells, at subcellular resolution, and in real time in a live animal model of cancer. These derivatives represent promising imaging tools that will be useful in understanding further the distribution and interactions of platinum within tumors.