Signal peptide-CUB-EGF-like repeat-containing protein 1-promoted FLT3 signaling is critical for the initiation and maintenance of MLL-rearranged acute leukemia.

A hallmark of mixed lineage leukemia gene-rearranged (MLL-r) acute myeloid leukemia that offers an opportunity for targeted therapy is addiction to protein tyrosine kinase signaling. One such signal is the receptor tyrosine kinase Fms-like receptor tyrosine kinase 3 (FLT3) upregulated by cooperation of the transcription factors homeobox A9 (HOXA9) and Meis homeobox 1 (MEIS1). Signal peptide-CUB-EGF-like repeat-containing protein (SCUBE) family proteins have previously been shown to act as a co-receptor for augmenting signaling activity of a receptor tyrosine kinase (e.g., vascular endothelial growth factor receptor). However, whether SCUBE1 is involved in the pathological activation of FLT3 during MLL-r leukemogenesis remains unknown. Here we first show that SCUBE1 is a direct target of HOXA9/MEIS1 that is highly expressed on the MLL-r cell surface and predicts poor prognosis in de novo acute myeloid leukemia. We further demonstrate, by using a conditional knockout mouse model, that Scube1 is required for both the initiation and maintenance of MLL-AF9-induced leukemogenesis in vivo. Further proteomic, molecular and biochemical analyses revealed that the membrane-tethered SCUBE1 binds to the FLT3 ligand and the extracellular ligand-binding domains of FLT3, thus facilitating activation of the signal axis FLT3-LYN (a non-receptor tyrosine kinase) to initiate leukemic growth and survival signals. Importantly, targeting surface SCUBE1 by an anti-SCUBE1 monomethyl auristatin E antibody-drug conjugate led to significantly decreased cell viability specifically in MLL-r leukemia. Our study indicates a novel function of SCUBE1 in leukemia and unravels the molecular mechanism of SCUBE1 in MLL-r acute myeloid leukemia. Thus, SCUBE1 is a potential therapeutic target for treating leukemia caused by MLL rearrangements.

Inhibition of gut microbial ß-glucuronidase effectively prevents carcinogen-induced microbial dysbiosis and intestinal tumorigenesis.

The bidirectional interaction between carcinogens and gut microbiota that contributes to colorectal cancer is complicated. Reactivation of carcinogen metabolites by microbial ß-glucuronidase (ßG) in the gut potentially plays an important role in colorectal carcinogenesis. We assessed the chemoprotective effects and associated changes in gut microbiota induced by pre-administration of bacterial-specific ßG inhibitor TCH-3511 in carcinogen azoxymethane (AOM)-treated APCMin/+ mice. AOM induced intestinal ßG activity, which was reflected in increases in the incidence, formation, and number of tumors in the intestine. Notably, inhibition of gut microbial ßG by TCH-3511 significantly reduced AOM-induced intestinal ßG activity, decreased the number of polyps in both the small and large intestine to a frequency that was similar in mice without AOM exposure. AOM also led to lower diversity and altered composition in the gut microbiota with a significant increase in mucin-degrading Akkermansia genus. Conversely, mice treated with TCH-3511 and AOM exhibited a more similar gut microbiota structure as mice without AOM administration. Importantly, TCH-3511 treatment significant decreased Akkermansia genus and produced a concomitant increase in short-chain fatty acid butyrate-producing gut commensal microbes Lachnoospiraceae NK4A136 group genus in AOM-treated mice. Taken together, our results reveal a key role of gut microbial ßG in promoting AOM-induced gut microbial dysbiosis and intestinal tumorigenesis, indicating the chemoprotective benefit of gut microbial ßG inhibition against carcinogens via maintaining the gut microbiota balance and preventing cancer-associated gut microbial dysbiosis. Thus, the bacterial-specific ßG inhibitor TCH-3511 is a potential chemoprevention agent for colorectal cancer.

Double attack strategy for leukemia using a pre-targeting bispecific antibody (CD20 Ab-mPEG scFv) and actively attracting PEGylated liposomal doxorubicin to enhance anti-tumor activity.

BACKGROUND: Tumor-targeted nanoparticles hold great promise as new tools for therapy of liquid cancers. Furthermore, the therapeutic efficacy of nanoparticles can be improved by enhancing the cancer cellular internalization. METHODS: In this study, we developed a humanized bispecific antibody (BsAbs: CD20 Ab-mPEG scFv) which retains the clinical anti-CD20 whole antibody (Ofatumumab) and is fused with an anti-mPEG single chain antibody (scFv) that can target the systemic liquid tumor cells. This combination achieves the therapeutic function and simultaneously "grabs" Lipo-Dox® (PEGylated liposomal doxorubicin, PLD) to enhance the cellular internalization and anticancer activity of PLD. RESULTS: We successfully constructed the CD20 Ab-mPEG scFv and proved that CD20 Ab-mPEG scFv can target CD20-expressing Raji cells and simultaneously grab PEGylated liposomal DiD increasing the internalization ability up to 60% in 24 h. We further showed that the combination of CD20 Ab-mPEG scFv and PLD successfully led to a ninefold increase in tumor cytotoxicity (LC50: 0.38 nM) compared to the CD20 Ab-DNS scFv and PLD (lC50: 3.45 nM) in vitro. Importantly, a combination of CD20 Ab-mPEG scFv and PLD had greater anti-liquid tumor efficacy (P = 0.0005) in Raji-bearing mice than CD20 Ab-DNS scFv and PLD. CONCLUSION: Our results indicate that this "double-attack" strategy using CD20 Ab-mPEG scFv and PLD can retain the tumor targeting (first attack) and confer PLD tumor-selectivity (second attack) to enhance PLD internalization and improve therapeutic efficacy in liquid tumors.

Structural basis of polyethylene glycol recognition by antibody.

BACKGROUND: Polyethylene glycol (PEG) is widely used in industry and medicine. Anti-PEG antibodies have been developed for characterizing PEGylated drugs and other applications. However, the underlying mechanism for specific PEG binding has not been elucidated. METHODS: The Fab of two cognate anti-PEG antibodies 3.3 and 2B5 were each crystallized in complex with PEG, and their structures were determined by X-ray diffraction. The PEG-Fab interactions in these two crystals were analyzed and compared with those in a PEG-containing crystal of an unrelated anti-hemagglutinin 32D6-Fab. The PEG-binding stoichiometry was examined by using analytical ultracentrifuge (AUC). RESULTS: A common PEG-binding mode to 3.3 and 2B5 is seen with an S-shaped core PEG fragment bound to two dyad-related Fab molecules. A nearby satellite binding site may accommodate parts of a longer PEG molecule. The core PEG fragment mainly interacts with the heavy-chain residues D31, W33, L102, Y103 and Y104, making extensive contacts with the aromatic side chains. At the center of each half-circle of the S-shaped PEG, a water molecule makes alternating hydrogen bonds to the ether oxygen atoms, in a similar configuration to that of a crown ether-bound lysine. Each satellite fragment is clamped between two arginine residues, R52 from the heavy chain and R29 from the light chain, and also interacts with several aromatic side chains. In contrast, the non-specifically bound PEG fragments in the 32D6-Fab crystal are located in the elbow region or at lattice contacts. The AUC data suggest that 3.3-Fab exists as a monomer in PEG-free solution but forms a dimer in the presence of PEG-550-MME, which is about the size of the S-shaped core PEG fragment. CONCLUSIONS: The differing amino acids in 3.3 and 2B5 are not involved in PEG binding but engaged in dimer formation. In particular, the light-chain residue K53 of 2B5-Fab makes significant contacts with the other Fab in a dimer, whereas the corresponding N53 of 3.3-Fab does not. This difference in the protein-protein interaction between two Fab molecules in a dimer may explain the temperature dependence of 2B5 in PEG binding, as well as its inhibition by crown ether.

PEGylated Liposomal Methyl Prednisolone Succinate does not Induce Infusion Reactions in Patients: A Correlation Between in Vitro Immunological and in Vivo Clinical Studies.

PEGylated nanomedicines are known to induce infusion reactions (IRs) that in some cases can be life-threatening. Herein, we report a case study in which a patient with rare mediastinal and intracardiac IgG4-related sclerosing disease received 8 treatments of intravenously administered PEGylated liposomal methylprednisolone-succinate (NSSL-MPS). Due to the ethical requirements to reduce IRs, the patient received a cocktail of premedication including low dose of steroids, acetaminophen and H2 blockers before each infusion. The treatment was well-tolerated in that IRs, complement activation, anti-PEG antibodies and accelerated blood clearance of the PEGylated drug were not detected. Prior to the clinical study, an in vitro panel of assays utilizing blood of healthy donors was used to determine the potential of a PEGylated drug to activate complement system, elicit pro-inflammatory cytokines, damage erythrocytes and affect various components of the blood coagulation system. The overall findings of the in vitro panel were negative and correlated with the results observed in the clinical phase.

Simply Mixing Poly Protein G with Detection Antibodies Enhances the Detection Limit and Sensitivity of Immunoassays.

An insufficient amount of detection antibodies bound to their antigens usually limits the sensitivity of immunoassays. Here, we describe a simple method to improve the detection limit and sensitivity of various immunoassays by mixing detection antibodies with a soluble poly protein G (named 8pG). 8pG was developed by fusing eight repeated fragment crystallizable (Fc) binding domains of streptococcal protein G to a linear polymer. Simply mixing detection antibodies with 8pG to form an antibody/8pG complex largely increased the accumulation of detection antibody to target molecules, which dramatically enhanced the sensitivity in direct ELISA, sandwich ELISA, Western blot, and flow cytometry systems, separately. The detection limit of Western blot for low-abundance PEGylated interferon (Pegasys) and recombinant human CTLA4 (rhCTLA4) improved by at least 13-fold and 31-fold, respectively, upon mixing detection antibodies with 8pG. Moreover, the nanoscale size of the antibody/8pG complex did not influence the granularity and dimension of target cells in the flow cytometry system. Collectively, we provide a quick and easy-to-operate method to make various immunoassays to sensitively detect low-abundance target molecules by just mixing their detection antibodies with 8pG.

Endothelial SCUBE2 Interacts With VEGFR2 and Regulates VEGF-Induced Angiogenesis.

OBJECTIVE: Vascular endothelial growth factor (VEGF), a major mediator of angiogenesis, exerts its proangiogenic action by binding to VEGFR2 (VEGF receptor 2), the activity of which is further modulated by VEGFR2 coreceptors such as neuropilins. However, whether VEGFR2 is regulated by additional coreceptors is not clear. To investigate whether SCUBE2 (signal peptide-CUB-EGF domain-containing protein 2), a peripheral membrane protein expressed in vascular endothelial cells (ECs) known to bind other signaling receptors, functions as a VEGFR2 coreceptor and to verify the role of SCUBE2 in the VEGF-induced angiogenesis. APPROACH AND RESULTS: SCUBE2 lentiviral overexpression in human ECs increased and short hairpin RNA knockdown inhibited VEGF-induced EC growth and capillary-like network formation on Matrigel. Like VEGF, endothelial SCUBE2 was upregulated by hypoxia-inducible factor-1α at both mRNA and protein levels. EC-specific Scube2 knockout mice were not defective in vascular development but showed impaired VEGF-induced neovascularization in implanted Matrigel plugs and recovery of blood flow after hind-limb ischemia. Coimmunoprecipitation and ligand-binding assays showed that SCUBE2 forms a complex with VEGF and VEGFR2, thus acting as a coreceptor to facilitate VEGF binding and augment VEGFR2 signal activity. SCUBE2 knockdown or genetic knockout suppressed and its overexpression promoted the VEGF-induced activation of downstream proangiogenic and proliferating signals, including VEGFR2 phosphorylation and mitogen-activated protein kinase or AKT activation. CONCLUSIONS: Endothelial SCUBE2 may be a novel coreceptor for VEGFR2 and potentiate VEGF-induced signaling in adult angiogenesis.

Enhancement Effect of a Variable Topology of a Membrane-Tethered Anti-Poly(ethylene glycol) Antibody on the Sensitivity for Quantifying PEG and PEGylated Molecules.

Sensitive quantification of the pharmacokinetics of poly(ethylene glycol) (PEG) and PEGylated molecules is critical for PEGylated drug development. Here, we developed a sensitive sandwich enzyme-linked immunosorbent assay (ELISA) for PEG by tethering an anti-PEG antibody (AGP3) via tethers with different dimensions on the surface of 293T cells (293T/S-αPEG, short-type cells; 293T/L-αPEG, long-type cells; 293T/SL-αPEG, hybrid-type cells) to improve the binding capacity and detection limit for free PEG and PEGylated molecules. The binding capacity of hybrid-type cells for PEG-like molecules (CH3-PEG5K-FITC (FITC = fluorescein isothiocyanate) and eight-arm PEG20K-FITC) was at least 10-80-fold greater than that of 293T cells expressing anti-PEG antibodies with uniform tether lengths. The detection limit of free PEG (OH-PEG3K-NH2 and CH3-PEG5K-NH2) and PEG-like molecule (CH3-PEG5K-FITC, CH3-PEG5K-SHPP, and CH3-PEG5K-NIR797) was14-137 ng mL-1 in the hybrid-type cell-based sandwich ELISA. 293T/SL-αPEG cells also had significantly higher sensitivity for quantification of a PEGylated protein (PegIntron) and multiarm PEG macromolecules (eight-arm PEG20K-NH2 and eight-arm PEG40K-NH2) at 3.2, 16, and 16 ng mL-1, respectively. Additionally, the overall binding capacity of 293T/SL-αPEG cells for PEGylated macromolecules was higher than that of 293T/S-αPEG or 293T/L-αPEG cells. Anchoring anti-PEG antibodies on cells via variable-length tethers for cell-based sandwich ELISA, therefore, provides a sensitive, high-capacity method for quantifying free PEG and PEGylated molecules.

Measurement of Pre-Existing IgG and IgM Antibodies against Polyethylene Glycol in Healthy Individuals.

Polyethylene glycol (PEG) is a biocompatible polymer that is often attached to therapeutic molecules to improve bioavailability and therapeutic efficacy. Although antibodies with specificity for PEG may compromise the safety and effectiveness of PEGylated medicines, the prevalence of pre-existing anti-PEG antibodies in healthy individuals is unclear. Chimeric human anti-PEG antibody standards were created to accurately measure anti-PEG IgM and IgG antibodies by direct ELISA with confirmation by a competition assay in the plasma of 1504 healthy Han Chinese donors residing in Taiwan. Anti-PEG antibodies were detected in 44.3% of healthy donors with a high prevalence of both anti-PEG IgM (27.1%) and anti-PEG IgG (25.7%). Anti-PEG IgM and IgG antibodies were significantly more common in females as compared to males (32.0% vs 22.2% for IgM, p < 0.0001 and 28.3% vs 23.0% for IgG, p = 0.018). The prevalence of anti-PEG IgG antibodies was higher in younger (up to 60% for 20 year olds) as opposed to older (20% for >50 years) male and female donors. Anti-PEG IgG concentrations were negatively associated with donor age in both females (p = 0.0073) and males (p = 0.026). Both anti-PEG IgM and IgG strongly bound PEGylated medicines. The described assay can assist in the elucidation of the impact of anti-PEG antibodies on the safety and therapeutic efficacy of PEGylated medicines.

Optimization of an Anti-poly(ethylene glycol) (anti-PEG) Cell-Based Capture System To Quantify PEG and PEGylated Molecules.

Sensitive determination of the pharmacokinetics of PEGylated molecules can accelerate the process of drug development. Here, we combined different anti-PEG Fab expressing 293T cells as capture cells (293T/3.3, 293T/6.3, and 293T/15-2b cells) with four detective anti-PEG antibodies (3.3, 6.3, 7A4, or 15-2b) to optimize an anti-PEG cell-based sandwich ELISA. Then, we quantified free PEG (mPEG2K-NH2 and mPEG5K-NH2) or PEG-conjugated small molecules (mPEG5K-biotin and mPEG5K-NIR797), proteins (PegIntron and Pegasys), and nanoparticles (Liposomal-Doxorubicin and quantum-dots). The combination of 293T/15-2b cells and the 7A4 detection antibody was best sensitivity for free PEG, PEG-like molecules, and PEGylated proteins with detection at ng mL-1 levels. On the other hand, 293T/3.3 cells combined with the 15-2b antibody had the highest sensitivity for quantifying Lipo-Dox at 2 ng mL-1. All three types of anti-PEG cells combined with the 15-2b antibody had high sensitivity for quantum dot quantification down to 7 pM. These results suggest that the combination of 293T/15-2b cells and 7A4 detection antibody is the optimal pair for sensitive quantification of free PEG, PEG-like molecules, and PEGylated proteins, whereas the 293T/3.3 cells combined with 15-2b are more suitable for quantifying PEGylated nanoparticles. The optimized anti-PEG cell-based sandwich ELISA can provide a sensitive, precise, and convenient tool for the quantification of a range of PEGylated molecules.

Synthesis and Antitumor Properties of BQC-Glucuronide, a Camptothecin Prodrug for Selective Tumor Activation.

Major limitations of camptothecin anticancer drugs (toxicity, nonselectivity, water insolubility, inactivation by human serum albumin) may be improved by creating glucuronide prodrugs that rely on beta-glucuronidase for their activation. We found that the camptothecin derivative 5,6-dihydro-4H-benzo[de]quinoline-camptothecin (BQC) displays greater cytotoxicity against cancer cells than the clinically used camptothecin derivatives SN-38 and topotecan even in the presence of human serum albumin. We synthesized the prodrug BQC-glucuronide (BQC-G), which was 4000 times more water soluble and 20-40 times less cytotoxic than BQC. Importantly, even in the presence of human serum albumin, BQC-G was efficiently hydrolyzed by beta-glucuronidase and produced greater cytotoxicity (IC50 = 13 nM) than camptothecin, 9-aminocamptothecin, SN-38, or topotecan (IC50 > 3000, 1370, 48, and 28 nM, respectively). BQC-G treatment of mice bearing human colon cancer xenografts with naturally or artificially elevated beta-glucuronidase activity produced significant antitumor activity, showing that BQC-G is a potent prodrug suitable for selective intratumoral drug activation.

Inhibition of the plasma SCUBE1, a novel platelet adhesive protein, protects mice against thrombosis.

OBJECTIVE: Signal peptide-CUB-EGF domain-containing protein 1 (SCUBE1), a secreted and surface-exposed glycoprotein on activated platelets, promotes platelet-platelet interaction and supports platelet-matrix adhesion. Its plasma level is a biomarker of platelet activation in acute thrombotic diseases. However, the exact roles of plasma SCUBE1 in vivo remain undefined. APPROACH AND RESULTS: We generated new mutant (Δ) mice lacking the soluble but retaining the membrane-bound form of SCUBE1. Plasma SCUBE1-depleted Δ/Δ mice showed normal hematologic and coagulant features and expression of major platelet receptors, but Δ/Δ platelet-rich plasma showed impaired platelet aggregation in response to ADP and collagen treatment. The addition of purified recombinant SCUBE1 protein restored the aggregation of platelets in Δ/Δ platelet-rich plasma and further enhanced platelet aggregation in +/+ platelet-rich plasma. Plasma deficiency of SCUBE1 diminished arterial thrombosis in mice and protected against lethal thromboembolism induced by collagen-epinephrine treatment. Last, antibodies directed against the epidermal growth factor-like repeats of SCUBE1, which are involved in trans-homophilic protein-protein interactions, protected mice against fatal thromboembolism without causing bleeding in vivo. CONCLUSIONS: We conclude that plasma SCUBE1 participates in platelet aggregation by bridging adjacent activated platelets in thrombosis. Blockade of soluble SCUBE1 might represent a novel antithrombotic strategy.

Discovery of specific inhibitors for intestinal E. coli ß-glucuronidase through in silico virtual screening.

Glucuronidation is a major metabolism process of detoxification for carcinogens, 4-(methylnitrosamino)-1-(3-pyridy)-1-butanone (NNK) and 1,2-dimethylhydrazine (DMH), of reactive oxygen species (ROS). However, intestinal E. coli ß-glucuronidase (eßG) has been considered pivotal to colorectal carcinogenesis. Specific inhibition of eßG may prevent reactivating the glucuronide-carcinogen and protect the intestine from ROS-mediated carcinogenesis. In order to develop specific eßG inhibitors, we found that 59 candidate compounds obtained from the initial virtual screening had high inhibition specificity against eßG but not human ßG. In particular, we found that compounds 7145 and 4041 with naphthalenylidene-benzenesulfonamide (NYBS) are highly effective and selective to inhibit eßG activity. Compound 4041 (IC50 = 2.8 µM) shows a higher inhibiting ability than compound 7145 (IC50 = 31.6 µM) against eßG. Furthermore, the molecular docking analysis indicates that compound 4041 has two hydrophobic contacts to residues L361 and I363 in the bacterial loop, but 7145 has one contact to L361. Only compound 4041 can bind to key residue (E413) at active site of eßG via hydrogen-bonding interactions. These novel NYBS-based eßG specific inhibitors may provide as novel candidate compounds, which specifically inhibit eßG to reduce eßG-based carcinogenesis and intestinal injury.

Clearance kinetics of biomaterials affects stem cell retention and therapeutic efficacy.

The use of biomaterial carriers to improve the therapeutic efficacy of stem cells is known to augment cell delivery, retention, and viability. However, the way that carrier clearance kinetics boosts stem cell delivery and impacts stem cell function remains poorly characterized. In this study, we designed a platform to simultaneously quantify carrier clearance and stem cell retention to evaluate the impact of carrier clearance kinetics on stem cell retention. Additionally, a murine model of hindlimb ischemia was employed to investigate the effects of various cell retention profiles on mitigating peripheral arterial disease. To image the in vivo behaviors of material and cells, we used biotinylated hyaluronan with fluorescently labeled streptavidin and Discosoma sp. Red (Ds-Red)-expressing human mesenchymal stem cells. We found that the retention of transplanted stem cells was closely related to the remaining biomaterial. Furthermore, therapeutic effectiveness was also affected by stem cell retention. These results demonstrate that low-molecular-weight hyaluronan had a slow clearance and high cell retention profile, improving the therapeutic efficacy of human stem cells.

Versatile online SPE-HPLC method for the analysis of Irinotecan and its clinically relevant metabolites in biomaterials.

Monitoring levels of Irinotecan and its metabolites during cancer therapy could help link broad interpatient variations in antitumor activity and toxicity to the patient's metabolic status. We have developed and validated a versatile and highly sensitive method for the simultaneous determination of Irinotecan and its clinically relevant metabolites 7-ethyl-10-hydroxy-camptothecin (SN-38) and SN-38 glucuronide. Sample clean-up involves precipitation by acetone/methanol/0.5 M trichloroacetic acid at 4:4:2 v/v followed by extraction of the metabolites on an SPE column by 20% methanol in 25 mM KH2 PO4 pH 2.9. Online transfer to an analytical µBondapak C18 column, elution with 24% acetonitrile (ACN) in 0.1 M KH2 PO4 pH 2.9 and fluorescence detection with excitation at 375 nm and emission at 430 nm for SN-38 glucuronide and Irinotecan or 540 nm for SN-38 results in high sensitivity (1-2 pg) and short (∼10 min) run times. The method was used to determine the degree of SN-38 glucuronidation in mice after Irinotecan administration and in cultured cancer cells exposed to SN-38. The method may be used to better understand Irinotecan metabolism, personalize therapy, and develop Irinotecan-based tumor targeting therapies.

Liposomes with Low Levels of Grafted Poly(ethylene glycol) Remain Susceptible to Destabilization by Anti-Poly(ethylene glycol) Antibodies.

Binding of anti-PEG antibodies to poly(ethylene glycol) (PEG) on the surface of PEGylated liposomal doxorubicin (PLD) in vitro and in rats can activate complement and cause the rapid release of doxorubicin from the liposome interior. Here, we find that irinotecan liposomes (IL) and L-PLD, which have 16-fold lower levels of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE)-PEG2000 in their liposome membrane as compared to PLD, generate less complement activation but remain sensitive to destabilization and drug release by anti-PEG antibodies. Complement activation and liposome destabilization correlated with the theoretically estimated number of antibody molecules bound per liposome. Drug release from liposomes proceeded through the alternative complement pathway but was accelerated by the classical complement pathway. In contrast to PLD destabilization by anti-PEG immunoglobulin G (IgG), which proceeded by the insertion of membrane attack complexes in the lipid bilayer of otherwise intact PLD, anti-PEG IgG promoted the fusion of L-PLD, and IL to form unilamellar and oligo-vesicular liposomes. Anti-PEG immunoglobulin M (IgM) induced drug release from all liposomes (PLD, L-PLD, and IL) via the formation of unilamellar and oligo-vesicular liposomes. Anti-PEG IgG destabilized both PLD and L-PLD in rats, indicating that the reduction of PEG levels on liposomes is not an effective approach to prevent liposome destabilization by anti-PEG antibodies.

Engineering stable and non-immunogenic immunoenzymes for cancer therapy via in situ generated prodrugs.

Engineering human enzymes for therapeutic applications is attractive but introducing new amino acids may adversely affect enzyme stability and immunogenicity. Here we used a mammalian membrane-tethered screening system (ECSTASY) to evolve human lysosomal beta-glucuronidase (hBG) to hydrolyze a glucuronide metabolite (SN-38G) of the anticancer drug irinotecan (CPT-11). Three human beta-glucuronidase variants (hBG3, hBG10 and hBG19) with 3, 10 and 19 amino acid substitutions were identified that display up to 40-fold enhanced enzymatic activity, higher stability than E. coli beta-glucuronidase in human serum, and similar pharmacokinetics in mice as wild-type hBG. The hBG variants were two to three orders of magnitude less immunogenic than E. coli beta-glucuronidase in hBG transgenic mice. Intravenous administration of an immunoenzyme (hcc49-hBG10) targeting a sialyl-Tn tumor-associated antigen to mice bearing human colon xenografts significantly enhanced the anticancer activity of CPT-11 as measured by tumor suppression and mouse survival. Our results suggest that genetically-modified human enzymes represent a good alternative to microbially-derived enzymes for therapeutic applications.

Sensitivity of PEGylated interferon detection by anti-polyethylene glycol (PEG) antibodies depends on PEG length.

Attachment of poly(ethylene glycol) to proteins can mask immune epitopes to increase serum half-life, reduce immunogenicity, and enhance in vivo biological efficacy. However, PEGylation mediated epitope-masking may also limit sensitivity and accuracy of traditional ELISA. We previously described an anti-PEG-based sandwich ELISA for universal assay of PEGylated molecules. Here, we compared the quantitative assessment of PEGylated interferons by anti-PEG and traditional anti-interferon sandwich ELISA. The detection limits for PEG-Intron (12k-PEG) and Pegasys (40k-PEG) were 1.9 and 0.03 ng/mL for anti-PEG ELISA compared to 0.18 and 0.42 ng/mL for traditional anti-interferon sandwich ELISA. These results indicate that the anti-PEG sandwich ELISA was insensitive to PEGylation mediated epitope-masking and the sensitivity increased in proportion to the length of PEG. By contrast, PEG-masking interfered with detection by traditional anti-interferon sandwich ELISA. Human and mouse serum did not affect the sensitivity of anti-PEG ELISA but impeded traditional anti-interferon sandwich ELISA. The anti-PEG sandwich ELISA was comparable to anti-interferon sandwich ELISA and radioassay of 131I-Pegasys in pharmacokinetic studies in mice. The anti-PEG sandwich ELISA provides a sensitive, accurate, and convenient quantitative measurement of PEGylated protein drugs.

A recombinant scFv-FasLext as a targeting cytotoxic agent against human Jurkat-Ras cancer.

BACKGROUND: Targeted therapy of human cancers is an attractive approach and has been investigated with limited success. We have developed novel cytotoxic agents for targeted therapy of human cancers based on the extracellular cytotoxicity domain of CD178 (FasL) and the specificity offered by single chain antibodies (scFv) against dominant human tumor Ag TAG-72 (cc49scFv) and TAL6 (L6scFv). RESULTS: The cc49scFv-FasLext is highly effective in in vitro killing of human TAG-72+ Jurkat-Ras tumor cells with a 30,000 fold greater cytotoxicity as compared to soluble FasL (sFasL). On the other hand, L6scFv-FasLext only increased cytotoxicity 500-fold as compared with sFasL against TAL6+ HeLa cells in in vitro assays. The high specificity and strong cytotoxicity of cc49scFv-FasLext made it feasible to cure IP-implanted Jurkat-Ras tumors in SCID mice. CONCLUSION: Our study demonstrated that scFv-FasLext with a strong cytotoxicity against sensitive human tumor targets may be useful as effective chemotherapeutic agents.

Selective cancer therapy by extracellular activation of a highly potent glycosidic duocarmycin analogue.

Conventional cancer chemotherapy is limited by systemic toxicity and poor selectivity. Tumor-selective activation of glucuronide prodrugs by beta-glucuronidase in the tumor microenvironment in a monotherapeutic approach is one promising way to increase cancer selectivity. Here we examined the cellular requirement for enzymatic activation as well as the in vivo toxicity and antitumor activity of a glucuronide prodrug of a potent duocarmycin analogue that is active at low picomolar concentrations. Prodrug activation by intracellular and extracellular beta-glucuronidase was investigated by measuring prodrug 2 cytotoxicity against human cancer cell lines that displayed different endogenous levels of beta-glucuronidase, as well as against beta-glucuronidase-deficient fibroblasts and newly established beta-glucuronidase knockdown cancer lines. In all cases, glucuronide prodrug 2 was 1000-5000 times less cytotoxic than the parent duocarmycin analogue regardless of intracellular levels of beta-glucuronidase. By contrast, cancer cells that displayed tethered beta-glucuronidase on their plasma membrane were 80-fold more sensitive to glucuronide prodrug 2, demonstrating that prodrug activation depended primarily on extracellular rather than intracellular beta-glucuronidase activity. Glucuronide prodrug 2 (2.5 mg/kg) displayed greater antitumor activity and less systemic toxicity in vivo than the clinically used drug carboplatin (50 mg/kg) to mice bearing human lung cancer xenografts. Intratumoral injection of an adenoviral vector expressing membrane-tethered beta-glucuronidase dramatically enhanced the in vivo antitumor activity of prodrug 2. Our data provide evidence that increasing extracellular beta-glucuronidase activity in the tumor microenvironment can boost the therapeutic index of a highly potent glucuronide prodrug.