May 9, 2013
Chemistry Department, SUNY Binghamton
The pH-(Low) Insertion Peptide (pHLIP) as a Potential Drug Delivery System and Surgery Imaging Guide in Oncology - Interactions between pHLIP and Model Lipid Bilayers, Cells, and Whole Animals
Part I - The monomeric pH-(Low)-Insertion-Peptide (pHLIP) inserts its C-terminus across a membrane under slightly acidic conditions, forming a transmembrane helix at pH 6 but not at pH 7. Using liposome fluorescence quenching assays and live cell imaging, we showed that pHLIP could translocate membrane-impermeable model cargos (i.e. cyclic peptides of M.W. ~ 800 and LogP -3) across a lipid bilayer. Next, we wanted to deliver a toxin to kill the cancer cell. In due course, our work showed that pHLIP-facilitated translocation of phalloidin (an otherwise cell-impermeable polar toxin targeting F-actin) inhibited the proliferation of cancer cells in a pH-dependent fashion. After 3h of incubation at pH 6.1-6.2 with 2 to 4 µM concentrations of the pHLIP delivery construct, proliferation in cultures of HeLa, JC, and M4A4 cancer cells was severely disrupted (> 90% inhibition of cell growth), while the effect is absent at neutral pH. These results demonstrate pHLIP's potential as a drug delivery system that would selectively destroy cells in acidic tumors. Alternatively, since pHLIP can mark-out acidic solid tumors in mice, it is being investigated as an imaging aid during surgery in Oncology. Along this line of pursuit, to further reduce the background signal, we recently developed several self-quenched pHLIP imaging constructs (pHLIP 'molecular beacons') that would become >10x more fluorescent upon dequenching in vitro (chemical dequenching) and in vivo (in mammalian cells). We want to know how pHLIP interacts with biological membranes in cells in detail. Using the 'molecular beacon'-like behavior of these conjugates, we are learning, in a more quantitative fashion, where pHLIP molecules insert in cells - on the plasma-membrane and/or in the endosomes.
Part II. Synthesis of Inhibitors of Enol-Pyruvyl-Shikimate-3-Phosphate (EPSP) Synthase as Potential Antimicrobial Agents Abstract: The Shikimate – Chorismate pathway (SCP) is a biosynthetic route leading to a diverse array of primary and secondary aromatic metabolites. The SCP is present in bacteria, fungi, apicomplexa parasites and plants, but absent in mammals. As such, enzymes in this pathway are ideal targets for antimicrobial agents and herbicides. For example, the sixth enzyme along the pathway, EPSP synthase, is the target of glyphosate (the active ingredient of the herbicide Roundup®). With the rise of drug resistance in many human pathogens, seeking new classes of antimicrobial agents with novel mechanism of action have become an urgent task. Biological studies suggest that EPSP synthase may be an important target for controlling the growth of bacterial and apicomplaxa pathogens. Here we present our approach to the design and synthesis of EPSP synthase inhibitors based on the knowledge of the mechanism of catalysis.