A boronate-linked linear-hyperbranched polymeric nanovehicle for pH-dependent tumor-targeted drug delivery

A boronate-based modular assembly nanosystem to block the undesirable crosstalk between hepatic stellate cells and Kupffer cells

Crosstalk between Kupffer cells (KCs) and hepatic stellate cells (HSCs) plays an important role in multiple liver disease conditions, including the formation of liver fibrosis in alcohol-associated liver disease (AALD). Therapeutic targeting of the KC-HSC crosstalk is a prime target for therapeutic interventions. Herein, a novel modular nanosystem was designed and prepared through the self-assembly utilizing boric acid and catechol interactions to prepare polymers modified with a CXCR4-inhibiting moieties. The polymers were used to encapsulate anti-miR-155 and to block the undesirable crosstalk between HSCs and KCs by downregulating miR-155 expression in KCs with the parallel inhibition of CXCR4 signaling in activated HSCs. The combined inhibition of miR-155 and CXCR4 at two different liver cell types achieved improved antifibrosis effects in a mouse model of AALD fibrosis. Our finding highlights the key role that blocking the undesirable crosstalk between HSCs and KCs plays in reversing AALD fibrosis as well as demonstrates a proof-of-concept approach for designing and constructing multifunctional delivery nanosystems using orthogonal functional modules based on the understanding of disease mechanisms.

Bioadhesive glycosylated nanoformulations for extended trans-corneal drug delivery to suppress corneal neovascularization

Eye-drop formulations as conventional regimens to tackle ocular diseases are far from efficient due to the rapid clearance by eye tears and the blockage of the corneal epithelium barrier. Here, we describe a bioadhesive glycosylated nanoplatform with boric acid pendants as a drug carrier for noninvasive trans-corneal delivery of drugs to treat corneal neovascularization (CNV), a serious corneal disease resulting in significant vision impairment. This biocompatible nanoplatform is formulated from a synthetic amphiphilic boric acid-based copolymer self-assembling to form highly stable micelles with a high loading capacity for dexamethasone (DEX). The nanoplatform is demonstrated to be in contact with the corneal epithelium for a long period under the bioadhesive function of boric acid modules and releases the drug over 96 h in a controlled manner. Our results also suggest that the nanoplatform can be efficiently internalized by corneal epithelial cells in vitro and realize transcytosis in vivo to greatly enhance the transcorneal penetration of the loaded drugs into the pathological corneal stroma. On topical application against rat corneal alkali burn, the nanoformulation presents more robust efficacy on neovascularization suppression and inflammation elimination than free DEX with a negligible effect on normal tissues. This bioadhesive strategy which focuses on extending ocular drug retention and improving trans-corneal drug delivery not only highlights an approach for alternative noninvasive therapy of CNV but also provides a versatile paradigm for other biomedical applications by overcoming protective barriers.

Innovations in Biomaterial Design toward Successful RNA Interference Therapy for Cancer Treatment

Gene regulation using RNA interference (RNAi) therapy has been developed as one of the frontiers in cancer treatment. The ability to tailor the expression of genes by delivering synthetic oligonucleotides to tumor cells has transformed the way scientists think about treating cancer. However, its clinical application has been limited due to the need to deliver synthetic RNAi oligonucleotides efficiently and effectively to target cells. Advances in nanotechnology and biomaterials have begun to address the limitations to RNAi therapeutic delivery, increasing the likelihood of RNAi therapeutics for cancer treatment in clinical settings. Herein, innovations in the design of nanocarriers for the delivery of oligonucleotides for successful RNAi therapy are discussed.

Apoptosis pathway in the combined treatment of x-ray and 5-FU-loaded triblock copolymer-coated magnetic nanoparticles

Aim: In this study, the effects of ionizing radiation and 5-fluorouracil (5-FU)-loaded triblock copolymer-coated magnetic nanoparticles (NPs) on the induction of apoptosis in HT-29 and HCT-116 were investigated. Materials & methods: The percentage of apoptotic cells and alteration of the expression of apoptotic-related proteins were evaluated in treated cells by flow cytometry and western blot analysis, respectively. Results: Combination treatment with 5-FU and radiation had a stronger effect on decreasing Bcl-2 expression and increasing expression of Bax, cleaved caspase-9, cleaved caspase-3, cleaved PARP compared with each treatment alone. Conclusion: The combination of radiation and triblock copolymer-coated magnetic NPs as 5-FU drug carriers works by triggering apoptosis to improve in vitro treatment efficacy. Additional study may present the NPs as an effective approach for the treatment of colon cancer.

A Macromolecule Reversing Antibiotic Resistance Phenotype and Repurposing Drugs as Potent Antibiotics

In order to mitigate antibiotic resistance, a new strategy to increase antibiotic potency and reverse drug resistance is needed. Herein, the translocation mechanism of an antimicrobial guanidinium-functionalized polycarbonate is leveraged in combination with traditional antibiotics to afford a potent treatment for drug-resistant bacteria. Particularly, this polymer-antibiotic combination approach reverses rifampicin resistance phenotype in Acinetobacter baumannii demonstrating a 2.5 × 105-fold reduction in minimum inhibitory concentration (MIC) and a 4096-fold reduction in minimum bactericidal concentration (MBC). This approach also enables the repurposing of auranofin as an antibiotic against multidrug-resistant (MDR) Gram-negative bacteria with a 512-fold MIC and 128-fold MBC reduction, respectively. Finally, the in vivo efficacy of polymer-rifampicin combination is demonstrated in a MDR bacteremia mouse model. This combination approach lays foundational ground rules for a new class of antibiotic adjuvants capable of reversing drug resistance phenotype and repurposing drugs against MDR Gram-negative bacteria.

Nanomaterials for Autophagy-Related miRNA-34a Delivery in Cancer Treatment

Autophagy is an evolutionary conserved physiological process with a fundamental role during development, differentiation, and survival of eukaryotic cells. On the other hand, autophagy dysregulation is observed in many pathological conditions, including cancer. In particular, tumor growth and progression are accompanied and promoted by increased autophagy that allows cancer cells to escape apoptosis and to proliferate also in harsh microenvironments. It is, therefore, clear that the impairment of the autophagic process may represent a valid strategy to inhibit or reduce cancer growth and progression. Among the plethora of molecular players controlling cancer growth, a group of small endogenous noncoding RNAs called microRNAs (miRNAs) has recently emerged. In fact, miRNAs can act as either oncogenes or oncosuppressors depending on their target genes. Moreover, among miRNAs, miRNA-34a has been connected with both tumor repression and autophagy regulation, and its expression is frequently lost in many cancers. Therefore, enforced expression of miRNA-34a in cancer cells may represent a valid strategy to reduce cancer growth. However, such strategy is limited by the fast biodegradation and short half-life of miRNA-34a and by the lack of an efficient intracellular delivery system. The following review describes the autophagic process and its role in cancer as well as the role of miRNAs in general and miRNA-34a in particular in regulating tumor growth by modulating autophagy. Finally, we describe the use of nanoparticles as a promising strategy to selectively deliver miRNA-34a to tumor cells for therapeutic and diagnostic purposes.

Amphiphilic tri- and tetra-block co-polymers combining versatile functionality with facile assembly into cytocompatible nanoparticles

In order for synthetic polymers to find widespread practical application as biomaterials, their syntheses must be easy to perform, utilising freely available building blocks, and should generate products which have no adverse effects on cells or tissue. In addition, it is highly desirable that the synthesis platform for the biomaterials can be adapted to generate polymers with a range of physical properties and macromolecular architectures, and with multiple functional handles to allow derivatisation with 'actives' for sensing or therapy. Here we describe the syntheses of amphiphilic tri- and tetra-block copolymers, using diazabicyclo[5.4.0]undec-5-ene (DBU) as a metal-free catalyst for ring-opening polymerisations of the widely-utilised monomer lactide combined with a functionalised protected cyclic carbonate. These syntheses employed PEGylated macroinitiators with varying chain lengths and architectures, as well as a labile-ester methacrylate initiator, and produced block copolymers with good control over monomer incorporation, molar masses, side-chain and terminal functionality and physico-chemical properties. Regardless of the nature of the initiators, the fidelity of the hydroxyl end group was maintained as confirmed by a second ROP chain extension step, and polymers with acryloyl/methacryloyl termini were able to undergo a second tandem reaction step, in particular thiol-ene click and RAFT polymerisations for the production of hyperbranched materials. Furthermore, the polymer side-chain functionalities could be easily deprotected to yield an active amine which could be subsequently coupled to a drug molecule in good yields. The resultant amphiphilic copolymers formed a range of unimolecular or kinetically-trapped micellar-like nanoparticles in aqueous environments, and the non-cationic polymers were all well-tolerated by MCF-7 breast cancer cells. The rapid and facile route to such highly adaptable polymers, as demonstrated here, offers promise for a range of bio materials applications.

O2 Economizer for Inhibiting Cell Respiration To Combat the Hypoxia Obstacle in Tumor Treatments

Hypoxia, a ubiquitously aberrant phenomenon implicated in tumor growth, causes severe tumor resistance to therapeutic interventions. Instead of the currently prevalent solution through intratumoral oxygen supply, we put forward an "O₂-economizer" concept by inhibiting the O₂ consumption of cell respiration to spare endogenous O₂ and overcome the hypoxia barrier. A nitric oxide (NO) donor responsible for respiration inhibition and a photosensitizer for photodynamic therapy (PDT) are co-loaded into poly(d,l-lactide- co-glycolide) nanovesicles to provide a PDT-specific O₂ economizer. Once accumulating in tumors and subsequently responding to the locally reductive environment, the carried NO donor undergoes breakdown to produce NO for inhibiting cellular respiration, allowing more O₂ in tumor cells to support the profound enhancement of PDT. Depending on the biochemical reallocation of cellular oxygen resource, this O₂-economizer concept offers a way to address the important issue of hypoxia-induced tumor resistance to therapeutic interventions, including but not limited to PDT.

Phenylboronic acid-functionalized polyamidoamine-mediated miR-34a delivery for the treatment of gastric cancer

In the present research, a tumor-targeted gene carrier, PPP, was constructed through the modification of phenylboronic acid onto the surface of a polyamidoamine dendrimer, and then miR-34a delivery was employed as a model to evaluate its anti-tumor efficacy.

Human Albumin Fragments Nanoparticles as PTX Carrier for Improved Anti-cancer Efficacy

For enhanced anti-cancer performance, human serum albumin fragments (HSAFs) nanoparticles (NPs) were developed as paclitaxel (PTX) carrier in this paper. Human albumins were broken into fragments via degradation and crosslinked by genipin to form HSAF NPs for better biocompatibility, improved PTX drug loading and sustained drug release. Compared with crosslinked human serum albumin NPs, the HSAF-NPs showed relative smaller particle size, higher drug loading, and improved sustained release. Cellular and animal results both indicated that the PTX encapsulated HSAF-NPs have shown good anti-cancer performance. And the anticancer results confirmed that NPs with fast cellular internalization showed better tumor inhibition. These findings will not only provide a safe and robust drug delivery NP platform for cancer therapy, but also offer fundamental information for the optimal design of albumin based NPs.

Shell-Sheddable Poly(N-2-hydroxypropyl methacrylamide) Polymeric Micelles for Dual-Sensitive Release of Doxorubicin

Poly(ethylene glycol) (PEG) shell-sheddable micelles are proved to be effective tools for rapid intracellular drug delivery. However, some adverse factors, such as the potential immunogenicity and the accelerated blood clearance, might be accompanied with the traditional PEG sheddable micelles. Here, a poly(N-2-hydroxypropyl methacrylamide) (PHPMA) sheddable block copolymer containing disulfide bonds on the main chain is prepared to form pH- and reduction-dual-responsive micelles. The most optimal synthetic route of the block copolymer is selected from three potential pathways. Doxorubicin is loaded via an acid-labile hydrazone bond to achieve high drug loading content and to prevent premature drug release. As expected, as-prepared shell-sheddable micelles exhibit faster intracellular drug release and more satisfactory in vitro anticancer efficacy than the nonsheddable counterpart did. This design provides a feasible guideline for the efficient synthesis of similar shell-sheddable micelles consisting of PHPMA coatings.

Fe₃O₄ Nanoparticles in Targeted Drug/Gene Delivery Systems

Fe₃O₄ nanoparticles (NPs), the most traditional magnetic nanoparticles, have received a great deal of attention in the biomedical field, especially for targeted drug/gene delivery systems, due to their outstanding magnetism, biocompatibility, lower toxicity, biodegradability, and other features. Naked Fe₃O₄ NPs are easy to aggregate and oxidize, and thus are often made with various coatings to realize superior properties for targeted drug/gene delivery. In this review, we first list the three commonly utilized synthesis methods of Fe₃O₄ NPs, and their advantages and disadvantages. In the second part, we describe coating materials that exhibit noticeable features that allow functionalization of Fe₃O₄ NPs and summarize their methods of drug targeting/gene delivery. Then our efforts will be devoted to the research status and progress of several different functionalized Fe₃O₄ NP delivery systems loaded with chemotherapeutic agents, and we present targeted gene transitive carriers in detail. In the following section, we illuminate the most effective treatment systems of the combined drug and gene therapy. Finally, we propose opportunities and challenges of the clinical transformation of Fe₃O₄ NPs targeting drug/gene delivery systems.

Recent progress on nanoparticle-based drug delivery systems for cancer therapy

The development of cancer nanotherapeutics has attracted great interest in the recent decade. Cancer nanotherapeutics have overcome several limitations of conventional therapies, such as nonspecific biodistribution, poor water solubility, and limited bioavailability. Nanoparticles with tuned size and surface characteristics are the key components of nanotherapeutics, and are designed to passively or actively deliver anti-cancer drugs to tumor cells. We provide an overview of nanoparticle-based drug delivery methods and cancer therapies based on tumor-targeting delivery strategies that have been developed in recent years.

Graphene oxide and adenosine triphosphate as a source for functionalized carbon dots with applications in pH-triggered drug delivery and cell imaging

A folate-functionalized carbon dot-based nanocarrier system has been successfully synthesized for cancer cell targeted drug delivery.

Redox-responsive star-shaped magnetic micelles with active-targeted and magnetic-guided functions for cancer therapy

Highly efficient delivery of therapeutic agents to target sites is of great importance for achieving excellent therapeutic efficacy in cancer treatment. Here, we report a redox-responsive star-shaped magnetic micelle with both active-targeted and magnetic-guided functions. The magnetic star-shaped micelles are formed by self-assembly of four-arm poly(ethylene glycol) (PEG)-poly(ε-caprolactone) (PCL) copolymers with disulfide bonds as intermediate linkers. Anticancer drug doxorubicin (DOX) and magnetic iron oxide nanoparticles (Fe3O4) are simultaneously encapsulated into the hydrophobic cores. PBA ligands are chemically conjugated to the end of the hydrophilic PEG segments, endowing the active targeting of nanocarriers. Both qualitative and quantitative analyses of the intracellular uptake of these micelles with active-targeting and dual-targeting are performed in vitro by cultured with salic acid (SA)-positive tumor cells (human liver carcinoma cell line HepG2, human cervical cancer cell line HeLa) and SA-negative tumor cells (human breast adenocarcinoma cell line MCF-7, human non-small cell lung cancer cell line A549) in the presence or absence of a permanent magnetic field. In vivo biodistribution studies with active-targeting and dual-targeting and in vivo anti-tumor effect are carried out in detail after being applied to the BALB/c mice bearing mouse H22 hepatocarcinoma cells tumor model. These in vivo results demonstrate that a great amount of dual-targeted magnetic micelles accumulate around the tumor tissues by the magnetic-guiding and in turn are taken up by the tumor cells through SA-mediated endocytosis, leading to a high therapeutic efficacy to the artificial solid tumor.

STATEMENT OF SIGNIFICANCE

A redox-responsive star-shaped magnetic micelle with both active-targeted and magnetic-guided functions was developed. Both qualitative and quantitative analysis of the intracellular uptake with dual-targeting of these micelles were performed in vitro by salic acid (SA)-positive tumor cells. The in vivo results demonstrate that a great amount of dual-targeted magnetic micelles accumulated around the tumor tissues, leading to a high therapeutic efficacy to artificial solid tumor.

Phenylboronic acid-functionalized polyamidoamine-mediated Bcl-2 siRNA delivery for inhibiting the cell proliferation

In this study, the conjugation of phenylboronic acid (PBA) to amine-terminated polyamidoamine (PAMAM) was successfully conducted to prepare a tumor-targeted gene carrier PBA-functionalized PAMAM (PPP) for Bcl-2 siRNA delivery, using a heterobifunctional crosslinker NHS-PEG5k-Mal. The carrier possessed favorable capacity for siRNA condensation and could protect siRNA from the degradation against RNase and serum. The introduction of PBA could facilitate the cellular uptake and further transfection of Bcl-2 siRNA demonstrated by confocal laser scanning microscopy and flow cytometry. Meanwhile, PPP-mediated transfection of Bcl-2 siRNA could significantly inhibit the expression of Bcl-2 gene at both mRNA and protein levels. Furthermore, owing to the knock-down of Bcl-2, PPP/siRNA could significantly inhibit the cell proliferation by inducing the cell apoptosis, and also enhance the antitumor efficiency of doxorubicin by suppressing the resistance of tumor cells to chemotherapeutics. In conclusion, the PPP-mediated Bcl-2 siRNA delivery could potentially be an effective platform for solving the drug resistance and further achieving the combined chemotherapy and gene therapy in tumor treatment.

Dendritic Polymers for Theranostics

Dendritic polymers are highly branched polymers with controllable structures, which possess a large population of terminal functional groups, low solution or melt viscosity, and good solubility. Their size, degree of branching and functionality can be adjusted and controlled through the synthetic procedures. These tunable structures correspond to application-related properties, such as biodegradability, biocompatibility, stimuli-responsiveness and self-assembly ability, which are the key points for theranostic applications, including chemotherapeutic theranostics, biotherapeutic theranostics, phototherapeutic theranostics, radiotherapeutic theranostics and combined therapeutic theranostics. Up to now, significant progress has been made for the dendritic polymers in solving some of the fundamental and technical questions toward their theranostic applications. In this review, we briefly summarize how to control the structures of dendritic polymers, the theranostics-related properties derived from their structures and their theranostics-related applications.

Multifunctional Nanotherapeutics with All-in-One Nanoentrapment of Drug/Gene/Inorganic Nanoparticle

It is challenging but imperative to merge together specific inorganic nanomaterials with macromolecular and small-molecule therapeutics into one nanoentity for all-in-one theranostic/remedy. We establish a versatile nanotechnology to nanoentrap magnetic nanoparticles, doxorubicin, and DNA, thus allowing the combination of magnetic targeting, magnetic resonance (MR) imaging, gene transport, and bioresponsive chemotherapy. We hope this nanotechnology can prompt the development of complex inorganic/organic nanosystems for various applications.

One-pot construction of boronate ester based pH-responsive micelle for combined cancer therapy

In this study, one-pot strategy for the construction of micelles loaded with two types of anticancer drugs (i.e., doxorubicin and methotrexate) together is reported. On the basis of the reaction between boronic acid and 1,2-diol to form boronate ester, the formation of amphiphiles, their self-assembly into micelles and drug encapsulation occurs simultaneously under simple dialysis at the appropriate pH condition. In the one-pot strategy, the micelle yield is high (78.2%) and the drug encapsulation efficiency of the two drugs is improved compared with that of the traditional method. The micelles can selectively increase the drug release ratio at acidic pH, showing the pH-responsive behavior inherited from the property of boronate ester. By combining doxorubicin and methotrexate, the half-maximum inhibition concentrations of the two drugs are obviously reduced, showing synergistic efficacy against cancer cells. This strategy is promising and may be expanded to various applications.

In Vitro Studies of Polyhedral Oligo Silsesquioxanes: Evidence for Their Low Cytotoxicity

As scientific literature considers polyhedral oligosilsesquioxanes (POSS) as potential drug delivery systems, it is necessary to check their impact on mammalian cells. Toxicity of octaammonium chloride salt of octaaminopropyl polyhedral oligomeric silsesquioxane (oap-POSS) towards two cell lines: mouse neuroblastoma (N2a) and embryonic mouse hippocampal cells (mHippoE-18) was studied. Experiments consisted of analysis of a cell cycle, cell viability, amount of apoptotic and necrotic cells, and generation of reactive oxygen species (ROS). POSS caused a shift in the cell population from the S and M/G₂ phases to the G₀/G₁ phase. However, the changes affected less than 10% of the cell population and were not accompanied by increased cytotoxicity. POSS did not induce either apoptosis or necrosis and did not generate reactive oxygen species. A cytotoxicity profile of POSS makes it a promising starting material as drug carrier.

Efficient nuclear drug translocation and improved drug efficacy mediated by acidity-responsive boronate-linked dextran/cholesterol nanoassembly

The present study reported a lysosome-acidity-targeting bio-responsive nanovehicle self-assembled from dextran (Dex) and phenylboronic acid modified cholesterol (Chol-PBA), aiming at the nucleus-tropic drug delivery. The prominent advantage of this assembled nanoconstruction arose from its susceptibility to acidity-labile dissociation concurrently accompanied with the fast liberation of encapsulated drugs, leading to efficient nuclear drug translocation and consequently favorable drug efficacy. By elaborately exploiting NH4Cl pretreatment to interfere with the cellular endosomal acidification progression, this study clearly evidenced at a cellular level the strong lysosomal-acidity dependency of nuclear drug uptake efficiency, which was shown to be the main factor influencing the drug efficacy. The boronate-linked nanoassembly displayed nearly no cytotoxicity and can remain structural stability under the simulated physiological conditions including 10% serum and the normal blood sugar concentration. The cellular exposure to cholesterol was found to bate the cellular uptake of nanoassembly in a dose-dependent manner, suggesting a cholesterol-associated mechanism of the intracellular internalization. The in vivo antitumor assessment in xenograft mouse models revealed the significant superiority of DOX-loaded Dex/Chol-PBA nanoassembly over the controls including free DOX and the DOX-loaded non-sensitive Dex-Chol, as reflected by the more effective tumor-growth inhibition and the better systematic safety. In terms of the convenient preparation, sensitive response to lysosomal acidity and efficient nuclear drug translocation, Dex/Chol-PBA nanoassembly derived from natural materials shows promising potentials as the nanovehicle for nucleus-tropic drug delivery especially for antitumor agents. More attractively, this study offers a deeper insight into the mechanism concerning the contribution of acidity-responsive delivery to the enhanced chemotherapy performance.

Target delivery of β-cyclodextrin/paclitaxel complexed fluorescent carbon nanoparticles: externally NIR light and internally pH sensitive-mediated release of paclitaxel with bio-imaging

The carbonized fluorescence hyaluronic acid (HA-FCN) for triggered target bioimaging ability have conjugated with β-cyclodextrin (CD) to release PTX by intracellular pH as well as remote photothermal NIR light control.

Polymeric assembly of hyperbranched building blocks to establish tunable nanoplatforms for lysosome acidity-responsive gene/drug co-delivery

This study plans to develop a nanoparticle technology that can assemble different polymeric "building blocks" with various desired functionalities into one nanosystem in a pH-dependent manner. For this purpose, polymeric building blocks were specifically designed with hyperbranched architectures, and orthogonal pH-reversible phenylboronic acid-diols were taken as "joints" to integrate them together. To verify the idea, a corona-core dual-polymer nanoassembly was prepared as the vehicle for lysosomotropic gene/drug co-delivery. Phenylboronic acid modified hyperbranched oligoethylenimine (OEI-PBA) was arranged to cluster around the hydrophobic core composed of hyperbranched polyglycerol, just by mixing two polymers in an appropriate ratio at neutral conditions. Compared with the parent OEI-PBA, this nanoassembly demonstrated better capture of plasmid DNA, highly enhanced activity for cellular transport and gene transfection (up to 100 fold), the ability to further load hydrophobic drugs, lysosome acidity-targeting pH-dependent release of both carried cargoes, and improved cell-biocompatibility. To evaluate its potential for combinational gene/drug therapy, in vitro experiments using the therapeutic p53 gene and antitumor doxorubicin as models were carried out. This intracellular co-delivery led to apparently synergetic anti-cancer effects in cultured cancer cells. This dynamic paradigm shows interesting features including easy manipulation, reversible conjugation, lysosome-targeting pH-responsiveness, high co-delivery efficiency, and functional expandability by further accommodating other building blocks.

GUCY2C lysosomotropic endocytosis delivers immunotoxin therapy to metastatic colorectal cancer

The emergence of targeted cancer therapy has been limited by the paucity of determinants which are tumor-specific and generally associated with disease, and have cell dynamics which effectively deploy cytotoxic payloads. Guanylyl cyclase C (GUCY2C) may be ideal for targeting because it is normally expressed only in insulated barrier compartments, including intestine and brain, but over-expressed by systemic metastatic colorectal tumors. Here, we reveal that GUCY2C rapidly internalizes from the cell surface to lysosomes in intestinal and colorectal cancer cells. Endocytosis is independent of ligand binding and receptor activation, and is mediated by clathrin. This mechanism suggests a design for immunotoxins comprising a GUCY2C-directed monoclonal antibody conjugated through a reducible disulfide linkage to ricin A chain, which is activated to a potent cytotoxin in lysosomes. Indeed, this immunotoxin specifically killed GUCY2C-expressing colorectal cancer cells in a lysosomal- and clathrin-dependent fashion. Moreover, this immunotoxin reduced pulmonary tumors>80% (p<0.001), and improved survival 25% (p<0.001), in mice with established colorectal cancer metastases. Further, therapeutic efficacy was achieved without histologic evidence of toxicity in normal tissues. These observations support GUCY2C-targeted immunotoxins as novel therapeutics for metastatic tumors originating in the GI tract, including colorectum, stomach, esophagus, and pancreas.