Browsing by Author "Liu, Yang"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Selective Delivery of a Quinone Methide Precursor by Peptide Nucleic Acids(2007-12-10) Liu, Yang; Rokita, Steve; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quinone methides (QMs) are electrophilic intermediates that can be generated in vivo to alkylate DNA and function as anti-cancer drugs. Previously, DNA-QM conjugates have shown the ability to selectively deliver a QM to specific sequences of DNA. Peptide nucleic acids (PNAs) conjugates of QM are now being developed since PNA binds DNA with higher affinity than natural DNA. Synthesis of PNA oligomers and conjugation of the PNA to QM precursor are reported here. Synthesis of peptides was used to study the optimum conditions for preparation of the ultimate peptide-PNA conjugate. Both peptides and peptide-PNA have been synthesized after optimizing solid-phase techniques. Conditions for coupling a quinone methide precursor (QMP) and peptide-PNA conjugates were also evaluated. 8-Amino-3,6-dioxaoctanoic acid that links PNA and QMP is essential for coupling. MOPS buffer containing the peptide-PNA and an acetonitrile/dimethylformamide mixture containing QMP were combined for coupling. Finally, reactive QM derivative of peptide-PNA-QM was studied.Item Simultaneous analyses of N-linked and O-linked glycans of ovarian cancer cells using solid-phase chemoenzymatic method(Springer Nature, 2017-01-13) Yang, Shuang; Höti, Naseruddin; Yang, Weiming; Liu, Yang; Chen, Lijun; Li, Shuwei; Zhang, HuiGlycans play critical roles in a number of biological activities. Two common types of glycans, N-linked and O-linked, have been extensively analyzed in the last decades. N-glycans are typically released from glycoproteins by enzymes, while O-glycans are released from glycoproteins by chemical methods. It is important to identify and quantify both N- and O-linked glycans of glycoproteins to determine the changes of glycans. The effort has been dedicated to study glycans from ovarian cancer cells treated with O-linked glycosylation inhibitor qualitatively and quantitatively. We used a solid-phase chemoenzymatic approach to systematically identify and quantify N-glycans and O-glycans in the ovarian cancer cells. It consists of three steps: (1) immobilization of proteins from cells and derivatization of glycans to protect sialic acids; (2) release of N-glycans by PNGase F and quantification of N-glycans by isobaric tags; (3) release and quantification of O-glycans by β-elimination in the presence of 1-phenyl-3-methyl-5-pyrazolone (PMP). We used ovarian cancer cell lines to study effect of O-linked glycosylation inhibitor on protein glycosylation. Results suggested that the inhibition of O-linked glycosylation reduced the levels of O-glycans. Interestingly, it appeared to increase N-glycan level in a lower dose of the O-linked glycosylation inhibitor. The sequential release and analyses of N-linked and O-linked glycans using chemoenzymatic approach are a platform for studying N-glycans and O-glycans in complex biological samples. The solid-phase chemoenzymatic method was used to analyze both N-linked and O-linked glycans sequentially released from the ovarian cancer cells. The biological studies on O-linked glycosylation inhibition indicate the effects of O-glycosylation inhibition to glycan changes in both O-linked and N-linked glycan expression.Item Target Alkylation of Single and Double Strand DNA by Peptide Nucleic Acids(2011) Liu, Yang; Rokita, Steven E; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quinone methides (QMs) generated in vivo can alkylate DNA and function as anti-cancer drugs. Delivery of QMs to target DNA is necessary to reduce the side effects caused by indiscriminate reaction. Previous, DNA was conjugated with a QM and was successfully used to deliver this QM to complementary DNA sequences. Peptide nucleic acids (PNAs) conjugates of QM are now being developed for in vivo application since PNA binds to its complementary DNA or RNA and PNA resists degradation by nucleases and proteases. The PNA1-QMP1 conjugate is capable of alkylating more than 60% of a complementary ssDNA when added at nearly stoichiometric quantities. No alkylation was observed if non-complementary DNA was treated with the conjugate. PNA1-QMP1 can alkylate a non-complementary DNA only when both the PNA and DNA target bind to a template strand. When no target sequences were present in solution, QM can react with nucleophiles from PNA1 and generate PNA1-QM1 self adduct. ssDNA can be alkylated by PNA1-QM1 self adduct with a 40% yield. The self adduct can survive after an incubation for 7 days in aqueous solution and preserve half of its original ability to alkylate complementary DNA. The reversibility and stability of the self adduct suggest that it can be used in cells. ssRNA can also be recognized and modified by PNA conjugates with a similar yield as earlier demonstrated with ssDNA. A PNA1-QM1 self adduct may also function as a telomerase inhibitor by alkylating RNA within telomerase. Polypyrimidine PNAs were prepared to bind to the major groove of duplex DNA selectively and expand the potential targets from single to double strand DNA. A cytosine-rich PNA recognized dsDNA and delivered an electron-rich QMP2 to its target sequences. The polypurine strand within a target dsDNA was alkylated at 37°C with a yield of 26%. PAN-QMP2 also showed strong selectivity toward its fully matched dsDNA over one base mismatch in the triplex recognition site. Successful delivery of a QMP to target single and double strand DNA by PNAs confirms that the use of PNA in vivo to target pre-selected sequences is feasible.