Targeting ligand–receptor interactions for development of cancer therapeutics

A phase separation-fortified bi-specific adaptor for conditional tumor killing

A common approach in therapeutic protein development involves employing synthetic ligands with multivalency, enabling sophisticated control of signal transduction. Leveraging the emerging concept of liquid-liquid phase separation (LLPS) and its ability to organize cell surface receptors into functional compartments, we herein have designed modular ligands with phase-separation modalities to engineer programmable interreceptor communications and precise control of signal pathways, thus inducing the rapid, potent, and specific apoptosis of tumor cells. Despite their simplicity, these "triggers", named phase-separated Tumor Killers (hereafter referred to as psTK), are sufficient to yield interreceptor clustering of death receptors (represented by DR5) and tumor-associated receptors, with notable features: LLPS-mediated robust high-order organization, well-choreographed conditional activation, and broad-spectrum capacity to potently induce apoptosis in tumor cells. The development of novel therapeutic proteins with phase-separation modalities showcases the power of spatially reorganizing signal transduction. This approach facilitates the diversification of cell fate and holds promising potential for targeted therapies against challenging tumors.

Exploration of the molecular mechanism of intercellular communication in paediatric neuroblastoma by single-cell sequencing

Neuroblastoma (NB) is an embryonic tumour that originates in the sympathetic nervous system and occurs most often in infants and children under 2 years of age. Moreover, it is the most common extracranial solid tumour in children. Increasing studies suggest that intercellular communication within the tumour microenvironment is closely related to tumour development. This study aimed to construct a prognosis-related intercellular communication-associated genes model by single-cell sequencing and transcriptome sequencing to predict the prognosis of patients with NB for precise management. Single-cell data from patients with NB were downloaded from the gene expression omnibus database for comprehensive analysis. Furthermore, prognosis-related genes were screened in the TARGET database based on epithelial cell marker genes through a combination of Cox regression and Lasso regression analyses, using GSE62564 and GSE85047 for external validation. The patients' risk scores were calculated, followed by immune infiltration analysis, drug sensitivity analysis, and enrichment analysis of risk scores, which were conducted for the prognostic model. I used the Lasso regression feature selection algorithm to screen characteristic genes in NB and developed a 21-gene prognostic model. The risk scores were highly correlated with multiple immune cells and common anti-tumour drugs. Furthermore, the risk score was identified as an independent prognostic factor for NB. In this study, I constructed and validated a prognostic signature based on epithelial marker genes, which may provide useful information on the development and prognosis of NB.

Steric-Deficient Oligoglycine Surrogates Facilitate Multivalent and Bifunctional Nanobody Synthesis via Combined Sortase A Transpeptidation and Click Chemistry

Conferring multifunctional properties to proteins via enzymatic approaches has greatly facilitated recent progress in protein nanotechnology. In this regard, sortase (Srt) A transpeptidation has facilitated many of these developments due to its exceptional specificity, mild reaction conditions, and complementation with other bioorthogonal techniques, such as click chemistry. In most of these developments, Srt A is used to seamlessly tether oligoglycine-containing molecules to a protein of interest that is equipped with the enzyme's recognition sequence, LPXTG. However, the dependence on oligoglycine attacking nucleophiles and the associated cost of certain derivatives (e.g., cyclooctyne) limit the utility of this approach to lab-scale applications only. Thus, the quest to identify appropriate alternatives and understand their effectiveness remains an important area of research. This study identifies that steric and nucleophilicity-associated effects influence Srt A transpeptidation when two oligoglycine surrogates were examined. The approach was further used in complementation with click chemistry to synthesize bivalent and bifunctional nanobody conjugates for application in epithelial growth factor receptor targeting. The overall technique and tools developed here may facilitate the advancement of future nanotechnologies.

Melanoma molecular subtyping and scoring model construction based on ligand-receptor pairs

Melanoma is a malignancy of melanocytes, responsible for a high percentage of skin cancer mortality. Ligand-Receptor pairs, a type of cellular communication, are essential for tumor genesis, growth, metastasis, and prognosis. Yet, the role of Ligand-Receptor pairs in melanoma has not been fully elucidated. Our research focused on the function of Ligand-Receptor pairs in melanoma prognosis. We screened 131 melanoma prognosis corresponded ligand-receptor pairs by analyzing the TCGA data of melanoma and the 2293 LR pairs retrieved from the connectomeDB2020 database. And further developed subtypes of melanoma according to the expression of these ligand-receptor pairs by Consensus Clustering. Then we using lasso cox regression and stepwise multivariate regression analysis established a ligand-receptor pairs-based scoring model for the evaluation of melanoma prognosis. Our study demonstrated that the ligand-receptor pairs are vital to the molecular heterogeneity of melanoma, and characterized three different melanoma ligand-receptor pairs subtypes. Among them, the C3 subtype showed a better prognosis, while the C1 subtype exhibited a low prognosis state. And our analysis then found out that this could be related to the differed activation and inhabitation of the cell cycle and immune-related pathways. Using lasso cox regression and stepwise multivariate regression analysis, we further identified 9 key ligand-receptor pairs and established a scoring model that effectively correlated with the prognosis, immune pathways, and therapy of melanoma, showing that the LR.score model was a trustworthy and independent biomarker for melanoma prognosis evaluation. In sum, we found that ligand-receptor pairs are significantly associated with the prognosis and therapy of melanoma. And our ligand-receptor-based scoring model showed potential for the evaluation of melanoma prognosis and immune therapy outcome prediction, which is crucial to the survival for the patients.

The molecular subtypes of triple negative breast cancer were defined and a ligand-receptor pair score model was constructed by comprehensive analysis of ligand-receptor pairs

Background

Intercellular communication mediated by ligand-receptor interactions in tumor microenvironment (TME) has a profound impact on tumor progression. This study aimed to explore the molecular subtypes mediated by ligand-receptor (LR) pairs in triple negative breast cancer (TNBC), identify the most important LR pairs to construct a prognostic risk model, and study their effect on TNBC immunotherapy.

Methods

LR pairs subclasses of TNBC were categorized by consensus clustering based on LR Pairs in METABRIC dataset. Least absolute shrinkage and selection operator (LASSO) Cox regression and stepwise Akaike information criterion (stepAIC) were conducted to build a LR pairs score model. The relationship between LR pairs score and immune cell infiltration, stromal score and immune score associated with TME was analyzed, and the prediction of drug therapy and immunotherapy efficacy by LR pairs score was evaluated.

Results

According to the expression pattern of 145 TNBC prognostic LR pairs, the samples were divided into three subclasses with different survival outcomes, copy number variation (CNV), TME immune cell infiltration, stromal score and immune score. The LR pairs score model constructed in the METABRIC dataset was composed of four LR pairs, and its predictive significance for TNBC prognosis was verified in GSE58812 and GSE21653 cohorts. In addition, LR pairs score was negatively correlated with several immune pathways regulating immunity and immune score, and related to the sensitivity of anti-neoplastic drugs and the effect of anti-PD-L1 therapy.

Conclusion

Our study confirmed the impact of LR pairs on the molecular heterogeneity of TNBC, characterized three LR pairs subtypes with different survival outcomes and TME patterns, and proposed a LR pairs score system with predictive significance for TNBC prognosis and anti-PD-L1 therapeutic effect, which provides a potential evaluation scheme for TNBC management.

Enzyme-manipulated hydrogelation of small molecules for biomedical applications

Enzyme-manipulated hydrogelation based on self-assembly of small molecules is an attractive methodology for development of functional biomaterials. Upon the catalysis of enzymes, small-molecular precursors are converted into assemblable building blocks, which arrange into high-ordered nanofibers via non-covalent interactions at the molecular level, and further trap water to form hydrogels at the macroscopic level. Such approach has numerous advantages of region- and enantioselectivity, and mild reaction conditions for encapsulation of biomedications or cells that are fragile to environmental change. In addition to the common applications as drug reservoirs or cell scaffolds, the utilization of endogenous enzymes as stimuli to initiate self-assembly in the living cells and tissue is considered as an intelligent spatiotemporally controllable hydrogelation strategy for biomedical applications. The enzyme-instructed in situ self-assembly and hydrogelation can modulate the cell behavior, and even present therapeutic bioactivities, which provides a new perspective in the field of disease treatment. In this review, we categorize distinct enzymatic stimuli and elaborate substrate design, catalytic characteristics, and mechanisms of self-assembly and hydrogelation. The biomedical applications in drug delivery, tissue engineering, bioimaging, and in situ gelation-produced bioactivity are outlined. Advantages and limitations regarding the state-of-the-art enzyme-driven hydrogelation technologies and future perspectives are also discussed. STATEMENT OF SIGNIFICANCE: Hydrogel is a semi-solid soft material containing a large amount of water. Due to the features of adjustable flexibility, extremely porous architecture, and the high similarity of structure to natural extracellular matrices, the hydrogel has broad application prospects in biomedicine. In recent 20 years, enzyme-manipulated hydrogelation based on self-assembly of small molecules has developed rapidly as an attractive methodology for the construction of functional biomaterials. Upon the catalysis of enzymes, small-molecular precursors are converted into assemblable building blocks, which arrange into high-ordered nanofibers via non-covalent interactions at the molecular level, and further trap water to form hydrogels at the macroscopic level. This review summarized the characteristics of enzymatic hydrogel, as well as the traditional application and emerging prospect of enzyme-instructed self-assembly and hydrogelation.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Identification and Validation of an m7G-Related lncRNAs Signature for Prognostic Prediction and Immune Function Analysis in Endometrial Cancer

Background: N7-methylguanosine is a novel kind of internal modification that is widespread in human mRNA. The relationship between m7G-related lncRNAs (MRL) and endometrial cancer remains unknown. The aim of our study is to explore a predictive prognosis MRL signature in endometrial cancer and identify the underlying biological mechanism. Methods: We obtained RNA-seq profiles, clinical data, and information on somatic mutations from the TCGA database and obtained m7G-related genes from a previous study. MRLs were identified through a co-expression network. The prognostic model was constructed based on 10 m7G-related lncRNAs. Differentially expressed genes between low- and high-risk groups were identified for further analysis, consisting of functional enrichment analysis, immune function analysis, somatic mutation analysis, and potential drugs exploration. Results: We constructed a 10-MRLs signature. According to the risk score, the signature was classified into high- and low-risk groups. The signature had a reliable capacity for predicting the prognosis of endometrial cancer patients. The findings about differentially expressed genes were also of great significance for therapeutic treatments for endometrial cancer and gave novel insights into exploring the underlying molecular mechanism. Conclusion: The prognostic model based on 10 MRLs is a reliable and promising approach for predicting clinical outcomes and suggesting therapeutic methods for endometrial cancer patients.

Dependence receptors: new targets for cancer therapy

Dependence receptors are known to promote survival and positive signaling such as proliferation, migration, and differentiation when activated, but to actively trigger apoptosis when unbound to their ligand. Their abnormal regulation was shown to be an important feature of tumorigenesis, allowing cancer cells to escape apoptosis triggered by these receptors while promoting in parallel major aspects of tumorigenesis such as proliferation, angiogenesis, invasiveness, and chemoresistance. This involvement in multiple cancer hallmarks has raised interest in dependence receptors as targets for cancer therapy. Although additional studies remain necessary to fully understand the complexity of signaling pathways activated by these receptors and to target them efficiently, it is now clear that dependence receptors represent very exciting targets for future cancer treatment. This manuscript reviews current knowledge on the contribution of dependence receptors to cancer and highlights the potential for therapies that activate pro-apoptotic functions of these proteins.

Selective Integrin Ligands Promote Cell Internalization of the Antineoplastic Agent Fluorouracil

Drug conjugates consisting of an antineoplastic drug and a targeting receptor ligand could be effective to overcome the heavy side effects of unselective anticancer agents. To address this need, we report here the results of a project aimed to study agonist and antagonist integrin ligands as targeting head of molecular cargoes for the selective delivery of 5-fluorouracil (5-FU) to cancer or noncancer cells. Initially, two fluorescent β-lactam-based integrin ligands were synthesized and tested for an effective and selective internalization mediated by α4β1 or α5β1 integrins in Jurkat and K562 cells, respectively. No cellular uptake was observed for both fluorescent compounds in HEK293 noncancerous control cells. Afterward, three conjugates composed of the β-lactam-based integrin ligand, suitable linkers, and 5-FU were realized. The best compound E, acting as α5β1 integrin agonist, is able to selectively deliver 5-FU into tumor cells, successfully leading to cancer cell death.

Overexpression of IRF3 Predicts Poor Prognosis in Clear Cell Renal Cell Carcinoma

Background

Growing findings have demonstrated that interferon regulatory transcription factor (IRF) family members are linked to the progression of various cancers. However, the roles of IRFs in clear cell renal cell carcinoma (ccRCC) remain undefined. Herein, we conducted a comprehensive analysis using the bioinformatics method to evaluate the expression patterns, clinical significance, and regulation of IRFs-related mechanisms in patients with ccRCC.

Methods

Data from the Cancer Genome Atlas (TCGA), International Cancer Genome Consortium (ICGA), and Gene Expression Omnibus (GEO) databases were used for investigation comprehensively. Specifically, we carried out a series of analyses to identify the candidate IRF and to explore its potential action mechanisms using the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. What is more, we emphatically investigate the association of candidate IRF with tumor immunity in ccRCC through the CIBERSORT algorithm, TIMER and GEPIA databases.

Results

Herein, IRF3 was identified as candidate IRF, which was highly expressed in ccRCC, and its overexpression was significantly associated with worse clinical outcomes and adverse overall survival. Uni- and multi-variate Cox regression analysis demonstrated that IRF3 overexpression was an independent predictor of worse prognosis. Functional enrichment analysis showed that IRF3 might participate in several cancer-related biological processes and signaling pathways, thereby promoting the progression of ccRCC. Additionally, we found that IRF3 was remarkably associated with tumor-infiltrating immune cells (TIICs) and various immune-related genes.

Conclusion

Herein, we identified IRF3 from the IRF gene family members, which could serve as promising prognostic marker and therapeutic target in ccRCC.

Bispecific antibodies: A guide to model informed drug discovery and development

Affinity (KD) optimization of monoclonal antibodies is one of the factors that impacts the stoichiometric binding and the corresponding efficacy of a drug. This impacts the dose and the dosing regimen, making the optimum KD a critical component of drug discovery and development. Its importance is further enhanced for bispecific antibodies, where affinity of the drug needs to be optimized with respect to two targets. Mathematical modeling can have critical impact on lead compound optimization. Here we build on previous work of using mathematical models to facilitate lead compound selection, expanding analysis from two membrane bound targets to soluble targets as well. Our analysis reveals the importance of three factors for lead compound optimization: drug affinity to both targets, target turnover rates, and target distribution throughout the body. We describe a method that leverages this information to help make early stage decisions on whether to optimize affinity, and if so, which arm of the bispecific should be optimized. We apply the proposed approach to a variety of scenarios and illustrate the ability to make improved decisions in each case. We integrate results to develop a bispecific antibody KD optimization guide that can be used to improve resource allocation for lead compound selection, accelerating advancement of better compounds. We conclude with a discussion of possible ways to assess the necessary levels of target engagement for affecting disease as part of an integrative approach for model-informed drug discovery and development.

Development of technetium-99m labeled ultrafine gold nanobioconjugates for targeted imaging of folate receptor positive cancers

INTRODUCTION

Strategic design and synthesis of nanoparticle based preparations could improve diagnostic screening of several cancer types, thereby facilitating better clinical management of the disease. Towards this, the present work aims to develop and evaluate a radioactive technetium-99m (99mTc) labeled gold nanoparticle (NP) preparation modified with folic acid, so as to diagnose folate receptor positive cancers viz. ovarian, breast, etc. METHODS: 11-Bromoundecanoic acid (UA) was synthetically modified both with folic acid and Hydrazinonicotinic acid (HYNIC) chelate at the carboxylic acid end and subsequently converted to thiol functionality at the bromo terminal to yield folic acid-UA-SH and HYNIC-UA-SH ligands respectively. Gold NPs modified with folic acid and HYNIC chelator were obtained on direct addition of folic acid-UA-SH and HYNIC-UA-SH to chloroauric acid in polysorbate 80 solution under reducing conditions. These NPs were then radiolabeled with 99mTc following HYNIC labeling approach. Both the inactive and 99mTc-labeled gold NPs were then tested for their biological efficacy in folate receptor (FR) positive KB cancer cell lines. Also, biodistribution studies of 99mTc-labeled gold NPs were carried in KB tumor xenografts to ascertain the efficacy towards FR in in vivo system.

RESULTS

Polysorbate 80 could stabilize the gold NP preparation with average size <10 nm as determined by TEM. Inhibition of [3H]folic acid with functionalized gold nanoparticle revealed affinity towards FR positive KB cell lines with an IC50 ~ 9 μM. Biodistribution studies of 99mTc-labeled gold NP preparation in SCID mice bearing KB tumor showed an uptake of 1.39 ± 0.18%ID/g in tumor and 5.48 ± 0.72%ID/g in kidneys at 3 h post-injection. In vivo distribution in folic acid pre-treated animals could not establish the specificity towards folate receptors.

CONCLUSIONS

Biological evaluation of functionalized gold NP showed affinity towards FR positive cancer cell lines. 99mTc-labeled NP exhibited target uptake in both in vitro and in vivo models, but folic acid inhibition could not establish the target specificity. Nevertheless, in vivo pharmacokinetics envisaged in the present design was achieved using the present gold functionalized NP preparation.

A quantitative view on multivalent nanomedicine targeting

Although the concept of selective delivery has been postulated over 100 years ago, no targeted nanomedicine has been clinically approved so far. Nanoparticles modified with targeting ligands to promote the selective delivery of therapeutics towards a specific cell population have been extensively reported. However, the rational design of selective particles is still challenging. One of the main reasons for this is the lack of quantitative theoretical and experimental understanding of the interactions involved in cell targeting. In this review, we discuss new theoretical models and experimental methods that provide a quantitative view of targeting. We show the new advancements in multivalency theory enabling the rational design of super-selective nanoparticles. Furthermore, we present the innovative approaches to obtain key targeting parameters at the single-cell and single molecule level and their role in the design of targeting nanoparticles. We believe that the combination of new theoretical multivalent design and experimental methods to quantify receptors and ligands aids in the rational design and clinical translation of targeted nanomedicines.

Soluble ligands as drug targets

Historically, the main classes of drug targets have been receptors, enzymes, ion channels and transporters. However, owing largely to the rise of antibody-based therapies in the past two decades, soluble protein ligands such as inflammatory cytokines have become an increasingly important class of drug targets. In this Review, we analyse drugs targeting ligands that have reached clinical development at some point since 1992. We identify 291 drugs that target 99 unique ligands, and we discuss trends in the characteristics of the ligands, drugs and indications for which they have been tested. In the last 5 years, the number of ligand-targeting drugs approved by the FDA has doubled to 34, while the number of clinically validated ligand targets has doubled to 22. Cytokines and growth factors are the predominant types of targeted ligands (70%), and inflammation and autoimmune disorders, cancer and ophthalmological diseases are the top therapeutic areas for both approved agents and agents in clinical studies, reflecting the central role of cytokine and/or growth factor pathways in such diseases.

Engineering a potent receptor superagonist or antagonist from a novel IL-6 family cytokine ligand

Interleukin-6 (IL-6) family cytokines signal through multimeric receptor complexes, providing unique opportunities to create novel ligand-based therapeutics. The cardiotrophin-like cytokine factor 1 (CLCF1) ligand has been shown to play a role in cancer, osteoporosis, and atherosclerosis. Once bound to ciliary neurotrophic factor receptor (CNTFR), CLCF1 mediates interactions to coreceptors glycoprotein 130 (gp130) and leukemia inhibitory factor receptor (LIFR). By increasing CNTFR-mediated binding to these coreceptors we generated a receptor superagonist which surpassed the potency of natural CNTFR ligands in neuronal signaling. Through additional mutations, we generated a receptor antagonist with increased binding to CNTFR but lack of binding to the coreceptors that inhibited tumor progression in murine xenograft models of nonsmall cell lung cancer. These studies further validate the CLCF1-CNTFR signaling axis as a therapeutic target and highlight an approach of engineering cytokine activity through a small number of mutations.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Antitumor activity of an engineered decoy receptor targeting CLCF1-CNTFR signaling in lung adenocarcinoma

Proinflammatory cytokines in the tumor microenvironment can promote tumor growth, yet their value as therapeutic targets remains underexploited. We validated the functional significance of the cardiotrophin-like cytokine factor 1 (CLCF1)-ciliary neurotrophic factor receptor (CNTFR) signaling axis in lung adenocarcinoma (LUAD) and generated a high-affinity soluble receptor (eCNTFR-Fc) that sequesters CLCF1, thereby inhibiting its oncogenic effects. eCNTFR-Fc inhibits tumor growth in multiple xenograft models and in an autochthonous, highly aggressive genetically engineered mouse model of LUAD, driven by activation of oncogenic Kras and loss of Trp53. Abrogation of CLCF1 through eCNTFR-Fc appears most effective in tumors driven by oncogenic KRAS. We observed a correlation between the effectiveness of eCNTFR-Fc and the presence of KRAS mutations that retain the intrinsic capacity to hydrolyze guanosine triphosphate, suggesting that the mechanism of action may be related to altered guanosine triphosphate loading. Overall, we nominate blockade of CLCF1-CNTFR signaling as a novel therapeutic opportunity for LUAD and potentially for other tumor types in which CLCF1 is present in the tumor microenvironment.

Light-induced mechanisms for nanocarrier's cargo release

Nanomaterials have been the focus of attention in several fields, including biomedicine, electronics, or catalysis, mainly due to the novel properties of the materials at the nanoscale. In the field of diagnosis, nanomaterials have been contemplated as an opportunity to improve sensitivity and time of response, therefore, facilitating early treatment and monitoring of the disease. For therapeutic applications, new drug delivery nanosystems aiming to provide enhanced efficiency have been proposed often addressing selective or controlled delivery of therapeutic agents to particular cells to maximize treatment efficacy minimizing adverse effects. The therapeutic agents can be dissolved, adsorbed, entrapped, encapsulated or attached on the surface or inside the nanocarriers. Given the context of the different generations of nanocarriers and their wide range of applications, the present article aims to discuss the nature of external stimuli which will trigger the controlled release of different biomolecules. For each class, a brief description of the physical principle, basic concepts, as well as some examples, are reported. A final discussion focused on the real implications and needs for optimal drug delivery system is presented, altogether with some considerations and prospects in the trends that diagnostics applications could follow in the next years.

Reversibly Switchable, pH-Dependent Peptide Ligand Binding via 3,5-Diiodotyrosine Substitutions

Cell type-specific targeting ligands utilized in drug delivery applications typically recognize receptors that are overexpressed on the cells of interest. Nonetheless, these receptors may also be expressed, to varying extents, on off-target cells, contributing to unintended side effects. For the selectivity profile of targeting ligands in cancer therapy to be improved, stimuli-responsive masking of these ligands with acid-, redox-, or enzyme-cleavable molecules has been reported, whereby the targeting ligands are exposed in specific environments, e.g., acidic tumor hypoxia. One possible drawback of these systems lies in their one-time, permanent trigger, which enables the "demasked" ligands to bind off-target cells if released back into the systemic circulation. A promising strategy to address the aforementioned problem is to design ligands that show selective binding based on ionization state, which may be microenvironment-dependent. In this study, we report a systematic strategy to engineer low pH-selective targeting peptides using an M2 macrophage-targeting peptide (M2pep) as an example. 3,5-Diiodotyrosine mutagenesis into native tyrosine residues of M2pep confers pH-dependent binding behavior specific to acidic environment (pH 6) when the amino acid is protonated into the native tyrosine-like state. At physiological pH of 7.4, the hydroxyl group of 3,5-diiodotyrosine on the peptide is deprotonated leading to interruption of the peptide native binding property. Our engineered pH-responsive M2pep (Ac-Y-Î-Î) binds target M2 macrophages more selectively at pH 6 than at pH 7.4. In addition, 3,5-diiodotyrosine substitutions also improve serum stability of the peptide. Finally, we demonstrate pH-dependent reversibility in target binding via a postbinding peptide elution study. The strategy presented here should be applicable for engineering pH-dependent functionality of other targeting peptides with potential applications in physiology-dependent in vivo targeting applications (e.g., targeting hypoxic tumor/inflammation) or in in vitro receptor identification.

Towards clinical translation of ligand-functionalized liposomes in targeted cancer therapy: Challenges and opportunities

The development of therapeutic resistance to targeted anticancer therapies remains a significant clinical problem, with intratumoral heterogeneity playing a key role. In this context, improving the therapeutic outcome through simultaneous targeting of multiple tumor cell subtypes within a heterogeneous tumor is a promising approach. Liposomes have emerged as useful drug carriers that can reduce systemic toxicity and increase drug delivery to the tumor site. While clinically used liposomal drug formulations show marked therapeutic advantages over free drug formulations, ligand-functionalized liposomes that can target multiple tumor cell subtypes may further improve the therapeutic efficacy by facilitating drug delivery to a broader population of tumor cells making up the heterogeneous tumor tissue. Ligand-directed liposomes enable the so-called active targeting of cell receptors via surface-attached ligands that direct drug uptake into tumor cells or tumor-associated stromal cells, and so can increase the selectivity of drug delivery. Despite promising preclinical results demonstrating improved targeting and anti-tumor effects of ligand-directed liposomes, there has been limited translation of this approach to the clinic. Key challenges for translation include the lack of established methods to scale up production and comprehensively characterize ligand-functionalized liposome formulations, as well as the inadequate recapitulation of in vivo tumors in the preclinical models currently used to evaluate their performance. Herein, we discuss the utility of recent ligand-directed liposome approaches, with a focus on dual-ligand liposomes, for the treatment of solid tumors and examine the drawbacks limiting their progression to clinical adoption.

Adaptation of vectors and drug-inducible systems for controlled expression of transgenes in the tumor microenvironment

Biological therapies based on recombinant proteins such as antibodies or cytokines are continuously improving the repertoire of treatments against cancer. However, safety and efficacy of this approach is often limited by inappropriate biodistribution and pharmacokinetics of the proteins when they are administered systemically. Local administration of gene therapy vectors encoding these proteins would be a feasible alternative if they could mediate long-term and controlled expression of the transgene after a single intratumoral administration. We describe a new vector platform specially designed for this purpose. Different combinations of transactivators and promoters were evaluated to obtain a fully humanized inducible system responsive to the well-characterized drug mifepristone. The optimal transactivator conformation was based on DNA binding domains from the chimeric protein ZFHD1 fused to the progesterone receptor ligand binding domain and the NFkb p65 activation domain. The expression of this hybrid transactivator under the control of the elongation factor 1α (EF1α) or the chimeric CAG promoters ensured functionality of the system in a variety of cancer types. Expression cassettes with luciferase as a reporter gene were incorporated into High-Capacity adenoviral vectors (HC-Ad) for in vivo evaluation. Systemic administration of the vectors into C57BL/6 mice revealed that the vector based on the EF1α promoter (HCA-EF-ZP) allows tight control of transgene expression and remains stable for at least two months, whereas the CAG promoter suffers a progressive inactivation. Using an orthotopic pancreatic cancer model in syngeneic C57BL/6 mice we show that the local administration of HCA-EF-ZP achieves better tumor/liver ratio of luciferase production than the intravenous route. However, regional spread of the vector led to substantial transgene expression in peritoneal organs. We reduced this leakage through genetic modification of the vector capsid to display RGD and poly-lysine motifs in the fiber knob. Safety and antitumor effect of this gene therapy platform was demonstrated using interleukin-12 as a therapeutic gene. In conclusion, we have developed a new tool that allows local, sustained and controlled production of therapeutic proteins in tumors.