Practical Theoretic Guidance for the Design of Tumor-Targeting Agents

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105

116

Cytokine therapy can activate potent, sustained antitumor responses, but collateral toxicity often limits dosages. Although antibody-cytokine fusions (immunocytokines) have been designed with the intent to localize cytokine activity, systemic dose-limiting side effects are not fully ameliorated by attempted tumor targeting. Using the s.c. B16F10 melanoma model, we found that a nontoxic dose of IL-2 immunocytokine synergized with tumor-specific antibody to significantly enhance therapeutic outcomes compared with immunocytokine monotherapy, concomitant with increased tumor saturation and intratumoral cytokine responses. Examination of cell subset biodistribution showed that the immunocytokine associated mainly with IL-2R-expressing innate immune cells, with more bound immunocytokine present in systemic organs than the tumor microenvironment. More surprisingly, immunocytokine antigen specificity and Fcγ receptor interactions did not seem necessary for therapeutic efficacy or biodistribution patterns because immunocytokines with irrelevant specificity and/or inactive mutant Fc domains behaved similarly to tumor-specific immunocytokine. IL-2-IL-2R interactions, rather than antibody-antigen targeting, dictated immunocytokine localization; however, the lack of tumor targeting did not preclude successful antibody combination therapy. Mathematical modeling revealed immunocytokine size as another driver of antigen targeting efficiency. This work presents a safe, straightforward strategy for augmenting immunocytokine efficacy by supplementary antibody dosing and explores underappreciated factors that can subvert efforts to purposefully alter cytokine biodistribution.immunocytokine | biodistribution | immunotherapy | antibody | IL-2

Section: Resultsmentioning

confidence: 99%

Antigen specificity can be irrelevant to immunocytokine efficacy and biodistribution

Tzeng

Kwan

Opel

et al. 2015

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116

“…The development of computational techniques in concert with preclinical testing may provide the abilities to rapidly assess system parameters, identify tunable nanomaterial properties, and predict allometric scaling to humans (11,(16)(17)(18)(19). Here, we established a computational framework to describe the pharmacokinetics of activity-based synthetic biomarkers and to quantitatively explore the parameters that are important for sensitive detection of disease.…”

Section: Discussionmentioning

confidence: 99%

“…S1). Benchmarked against the size of our previous nanoworm (NW) formulation (∼30 nm), PEG NPs were smaller by severalfold, which increases passive diffusion rates (18). To determine renal clearance efficiencies, we administered fluorescent PEG and NWs and detected urine levels up to ∼80% of injected dose (ID) for 10 kDa PEG and ∼40% ID for 20 kDa PEG within 60 min (Fig.…”

Section: Significancementioning

confidence: 99%

“…To date, pharmacokinetic models have been developed for abundance-based drugs and diagnostics-such as predicting nanoparticle (NP) targeting to tumor vasculature (11), identifying rate-limiting steps in the distribution of drugs within tumors (16)(17)(18), providing guidelines to increase NP penetration (19), and modeling NP disassembly at the glomerulus (20). Here, we establish a mathematical framework for synthetic biomarkers, a class of activity-based probes that amplify disease-derived signals into urine for easy analysis (3,(21)(22)(23)(24).…”

mentioning

confidence: 99%

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Mathematical framework for activity-based cancer biomarkers

Kwong

Dudani

Carrodeguas

et al. 2015

Advances in nanomedicine are providing sophisticated functions to precisely control the behavior of nanoscale drugs and diagnostics. Strategies that coopt protease activity as molecular triggers are increasingly important in nanoparticle design, yet the pharmacokinetics of these systems are challenging to understand without a quantitative framework to reveal nonintuitive associations. We describe a multicompartment mathematical model to predict strategies for ultrasensitive detection of cancer using synthetic biomarkers, a class of activity-based probes that amplify cancerderived signals into urine as a noninvasive diagnostic. Using a model formulation made of a PEG core conjugated with protease-cleavable peptides, we explore a vast design space and identify guidelines for increasing sensitivity that depend on critical parameters such as enzyme kinetics, dosage, and probe stability. According to this model, synthetic biomarkers that circulate in stealth but then activate at sites of disease have the theoretical capacity to discriminate tumors as small as 5 mm in diameter-a threshold sensitivity that is otherwise challenging for medical imaging and blood biomarkers to achieve. This model may be adapted to describe the behavior of additional activity-based approaches to allow cross-platform comparisons, and to predict allometric scaling across species.compartmental modeling | activity-based probes | cancer diagnostics | urine biomarkers | nanomedicine T he clinical management of cancer is increasingly dependent on the discovery of new biomarkers and the development of ultrasensitive technologies to detect them at a stage when therapeutic interventions may be effective (1, 2). However, despite their growing importance, biomarkers lack predictive power to impact patient outcomes during the earliest stages of disease. The challenges are multifaceted: Biomarkers are shed from tumors at rates that vary by four orders in magnitude (3), are significantly diluted in blood, and circulate for short periods. Recent mathematical studies showed that tumors may remain undetectable with blood biomarkers for an entire decade following tumorigenesis, reaching 1-2.5 cm in diameter (4, 5). To increase sensitivity, major research areas include the development of ultrasensitive in vitro diagnostic platforms (6-11), as well as methods to increase biomarker production by solid tumors (12, 13). These approaches are designed to measure the quantity, or abundance, of a disease biomarker.In contrast to abundance-based methods, activity-based probes are a class of agents that are administered in prodiagnostic form but produce strong diagnostic signals after enzymatic activation (14, 15). These approaches rely on disease-associated enzymes as catalysts to produce a detection signal, of which proteases are particularly potent because the cleavage of peptide bonds is irreversible, and a single protease can cleave many substrates to amplify signals. However, activity-based probes operate within a narrow time window and are activated by offtarget...

“…Recent theoretical and experimental studies have examined the relationship between molecular size and affinity needed for effective tumor targeting (35,36). In particular, small proteins have been shown to accumulate rapidly in tumors, provided that they bind their targets with high affinities (i.e., in the pM to nM range) (37,38).…”

Section: An Eeti 25f-fc Fusion Illuminates Intracranial Mb and Distrmentioning

confidence: 99%

Engineered knottin peptide enables noninvasive optical imaging of intracranial medulloblastoma

Moore

Gephart

Bergen

et al. 2013

Central nervous system tumors carry grave clinical prognoses due to limited effectiveness of surgical resection, radiation, and chemotherapy. Thus, improved strategies for brain tumor visualization and targeted treatment are critically needed. We demonstrate that mouse cerebellar medulloblastoma (MB) can be targeted and illuminated with a fluorescent, engineered cystine knot (knottin) peptide that binds with high affinity to α v β 3 , α v β 5 , and α 5 β 1 integrin receptors. This integrin-binding knottin peptide, denoted EETI 2.5F, was evaluated as a molecular imaging probe in both orthotopic and genetic models of MB. Following tail vein injection, fluorescence arising from dye-conjugated EETI 2.5F was localized to the tumor compared with the normal surrounding brain tissue, as measured by optical imaging. The imaging signal intensity correlated with tumor volume. Due to its unique ability to bind to α 5 β 1 integrin, EETI 2.5F showed superior in vivo and ex vivo brain tumor imaging contrast compared with other engineered integrin-binding knottin peptides and with c(RGDfK), a well-studied integrin-binding peptidomimetic. Next, EETI 2.5F was fused to an antibody fragment crystallizable (Fc) domain (EETI 2.5F–Fc) to determine if a larger integrin-binding protein could also target intracranial brain tumors. EETI 2.5F–Fc, conjugated to a fluorescent dye, illuminated MB following i.v. injection and was able to distribute throughout the tumor parenchyma. In contrast, brain tumor imaging signals were not detected in mice injected with EETI 2.5F proteins containing a scrambled integrin-binding sequence, demonstrating the importance of target specificity. These results highlight the potential of using EETI 2.5F and EETI 2.5–Fc as targeted molecular probes for brain tumor imaging.