Amy D. Liu

A β-lactamase with reduced immunogenicity for the targeted delivery of chemotherapeutics using antibody-directed enzyme prodrug therapy

Antibody-directed enzyme prodrug therapy (ADEPT) delivers chemotherapeutic agents in high concentration to tumor tissue while minimizing systemic drug exposure. β-Lactamases are particularly useful enzymes for ADEPT systems due to their unique substrate specificity that allows the activation of a variety of lactam-based prodrugs with minimal interference from mammalian enzymes. We evaluated the amino acid sequence of β-lactamase from Enterobacter cloacae for the presence of human T-cell epitopes using a cell-based proliferation assay using samples from 65 community donors. We observed a low background response that is consistent with a lack of preexposure to this enzyme. β-Lactamase was found to contain four CD4+ T-cell epitopes. For two of these epitopes, we identified single amino acid changes that result in significantly reduced proliferative responses while retaining stability and activity of the enzyme. The β-lactamase variant containing both changes induces significantly less proliferation in human and mouse cell assays, and 5-fold lower levels of IgG1 in mice were observed after repeat administration of β-lactamase variant with adjuvant. The β-lactamase variant should be very suitable for the construction of ADEPT fusion proteins, as it combines high activity toward lactam prodrugs, high plasma stability, a monomeric architecture, and a relatively low risk of eliciting an immune response in patients.

Determination of product inhibition of CBH1, CBH2, and EG1 using a novel cellulase activity assay.

The hydrolysis of lignocellulosic biomass by degrading enzymes (cellulases) has emerged as a promising process within the bio-ethanol industry. Yet, understanding all the intricacies of how these enzymes work has been a challenging task. Substrate–enzyme interaction in complex feed mixtures, the recalcitrance of the crystalline structure of cellulose and enzyme inactivation by product inhibition, nonproductive binding to lignin, and process stress are only some of the problems standing in the way of creating an effective and efficient process to bio-ethanol production. This study focuses on the product inhibition of cellobiohydrolases and endoglucanases. Here, we present a method of studying product inhibition by measuring the decrease in substrate, utilizing the fluorescent properties of a calcofluor dye.

Rapid in vivo evolution of a β‐lactamase using phagemids

RNA viruses are capable of undergoing extremely rapid evolution due to their high rates of reproduction, small genome size, and a high frequency of spontaneous mutagenesis. Here we demonstrate that a virus-like, evolutionary state can be created by propagating a phagemid population in a hypermutator strain of Escherichia coli in the presence of a helper phage. This enables one to subject individual phagemid-encoded genes to rapid in vivo evolution. We applied this approach to TEM-1 β-lactamase which confers resistance to 0.05 mg/L of the antibiotic cefotaxime. After 3 weeks of in vivo evolution we were able to isolate a double mutant, E104K/G238S, of the enzyme which confers a 500-fold increased level of resistance to cefotaxime compared to the starting enzyme. In two independent experiments we obtained a triple mutant, E104K/G238S/T263M, which confers a 1000-fold increase in resistance compared to the wild type enzyme. The same three mutations have been previously observed in TEM-4 β-lactamase which was discovered in a highly cefotaxime-resistant clinical isolate. The probability of randomly obtaining a β-lactamase carrying three identical point mutations is less than 10−10. This indicates that phagemid evolution can rapidly reproduce evolution occurring in nature.