Arginine Is a Novel Drug Target for Arginine Decarboxylase in Human Colorectal Cancer Cells.

Colorectal cancer (CRC) has been proven to be highly reliant on arginine availability. Limiting arginine-rich foods or treating patients with arginine-depleting enzymes arginine deiminase (ADI) or arginase can suppress colon cancer. However, arginase and ADI are not the best drug candidates for CRC. Ornithine, the product of arginase, can enhance the supply of polyamine, which favors CRC cell growth, while citrulline, the product of ADI, faces the problem of arginine recycling due to the overexpression of argininosuccinate synthetase (ASS). Biosynthetic arginine decarboxylase (ADC), an enzyme that catalyzes the conversion of arginine to agmatine and carbon dioxide, may be a better choice as it combines both arginine depletion and suppression of intracellular polyamine synthesis via its product agmatine. ADC has anti-tumor potential yet has received much less attention than the other two arginine-depleting enzymes. In order to gain a better understanding of ADC, the preparation and the anti-cancer properties of this enzyme were explored in this study. When tested in vitro, ADC inhibited the proliferation of three colorectal cancer cell lines regardless of their ASS cellular expression. In contrast, ADC had a lesser cytotoxic effect on the human foreskin fibroblasts and rat primary hepatocytes. Further in vitro studies revealed that ADC induced S and G2/M phase cell-cycle arrest and apoptosis in HCT116 and LoVo cells. ADC-induced apoptosis in HCT116 cells followed the mitochondrial apoptotic pathway and was caspase-3-dependent. With all results obtained, we suggest that arginine is a potential target for treating colorectal cancer with ADC, and the anti-cancer properties of ADC should be more deeply investigated in the future.

Gossypol acetate: A natural polyphenol derivative with antimicrobial activities against the essential cell division protein FtsZ.

Antimicrobial resistance has attracted worldwide attention and remains an urgent issue to resolve. Discovery of novel compounds is regarded as one way to circumvent the development of resistance and increase the available treatment options. Gossypol is a natural polyphenolic aldehyde, and it has attracted increasing attention as a possible antibacterial drug. In this paper, we studied the antimicrobial properties (minimum inhibitory concentrations) of gossypol acetate against both Gram-positive and Gram-negative bacteria strains and dig up targets of gossypol acetate using in vitro assays, including studying its effects on functions (GTPase activity and polymerization) of Filamenting temperature sensitive mutant Z (FtsZ) and its interactions with FtsZ using isothermal titration calorimetry (ITC), and in vivo assays, including visualization of cell morphologies and proteins localizations using a microscope. Lastly, Bacterial membrane permeability changes were studied, and the cytotoxicity of gossypol acetate was determined. We also estimated the interactions of gossypol acetate with the promising target. We found that gossypol acetate can inhibit the growth of Gram-positive bacteria such as the model organism Bacillus subtilis and the pathogen Staphylococcus aureus [both methicillin-sensitive (MSSA) and methicillin-resistant (MRSA)]. In addition, gossypol acetate can also inhibit the growth of Gram-negative bacteria when the outer membrane is permeabilized by Polymyxin B nonapeptide (PMBN). Using a cell biological approach, we show that gossypol acetate affects cell division in bacteria by interfering with the assembly of the cell division FtsZ ring. Biochemical analysis shows that the GTPase activity of FtsZ was inhibited and polymerization of FtsZ was enhanced in vitro, consistent with the block to cell division in the bacteria tested. The binding mode of gossypol acetate in FtsZ was modeled using molecular docking and provides an understanding of the compound mode of action. The results point to gossypol (S2303) as a promising antimicrobial compound that inhibits cell division by affecting FtsZ polymerization and has potential to be developed into an effective antimicrobial drug by chemical modification to minimize its cytotoxic effects in eukaryotic cells that were identified in this work.

Recombinant Bacillus caldovelox Arginase Mutant (BCA-M) Induces Apoptosis, Autophagy, Cell Cycle Arrest and Growth Inhibition in Human Cervical Cancer Cells.

With our recent success in developing a recombinant human arginase drug against broad-spectrum cancer cell lines, we have explored the potential of a recombinant Bacillus caldovelox arginase mutant (BCA-M) for human cervical cancer treatment. Our studies demonstrated that BCA-M significantly inhibited the growth of human cervical cancer cells in vitro regardless of argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) expression. Drug susceptibilities correlate well with the expressions of major urea cycle genes and completeness of L-arginine regeneration pathways. With the expressions of ASS and ASL genes conferring resistance to L-arginine deiminase (ADI) which is undergoing Phase III clinical trial, BCA-M offers the advantage of a broader spectrum of susceptible cancer cells. Mechanistic studies showed that BCA-M inhibited the growth of human cervical cancer cells by inducing apoptosis and cell cycle arrest at S and/or G2/M phases. Our results also displayed that autophagy served as a protective mechanism, while the growth inhibitory effects of BCA-M could be enhanced synergistically by its combination to the autophagy inhibitor, chloroquine (CQ), on human cervical cancer cells.

Enhanced Activity against Multidrug-Resistant Bacteria through Coapplication of an Analogue of Tachyplesin I and an Inhibitor of the QseC/B Signaling Pathway.

Tachyplesin I (TPI) is a cationic ß-hairpin antimicrobial peptide with broad-spectrum, potent antimicrobial activity. In this study, the all d-amino acid analogue of TPI (TPAD) was synthesized, and its structure and activity were determined. TPAD has comparable antibacterial activity to TPI on 14 bacterial strains, including four drug-resistant bacteria. Importantly, TPAD has significantly improved stability against enzymatic degradation and decreased hemolytic activity compared to TPI, indicating that it has better therapeutic potential. The induction of bacterial resistance using low concentrations of TPAD resulted in the activation of the QseC/B two-component system. Deletion of this system resulted in at least five-fold improvement of TPAD activity, and the combined use of TPAD with LED209, a QseC/B inhibitor, significantly enhanced the bactericidal effect against three classes of multidrug-resistant bacteria.

Influences of disulfide connectivity on structure and antimicrobial activity of tachyplesin I.

Tachyplesin I is a potent antimicrobial peptide with broad spectrum of antimicrobial activity. It has 2 disulfide bonds and can form 3 disulfide bond isomers. In this study, the structure and antimicrobial activity of 3 tachyplesin I isomers (tachyplesin I, 3C12C, 3C7C) were investigated using molecular dynamic simulations, circular dichroism structural study, as well as antimicrobial activity and hemolysis assay. Our results suggest that in comparison to the native peptide, the 2 isomers (3C12C, 3C7C) have substantial structural and activity variations. The native peptide is in the ribbon conformation, while 3C12C and 3C7C possess remarkably different secondary structures, which are referred as "globular" and "beads" isomers, respectively. The substantially decreased hemolysis effects for these 2 isomers is accompanied by significantly decreased anti-gram-positive bacterial activity.

Identification of a new class of FtsZ inhibitors by structure-based design and in vitro screening.

The Filamenting temperature-sensitive mutant Z (FtsZ), an essential GTPase in bacterial cell division, is highly conserved among Gram-positive and Gram-negative bacteria and thus considered an attractive target to treat antibiotic-resistant bacterial infections. In this study, a new class of FtsZ inhibitors bearing the pyrimidine-quinuclidine scaffold was identified from structure-based virtual screening of natural product libraries. Iterative rounds of in silico studies and biological evaluation established the preliminary structure-activity relationships of the new compounds. Potent FtsZ inhibitors with low micromolar IC50 and antibacterial activity against S. aureus and E. coli were found. These findings support the use of virtual screening and structure-based design for the rational development of new antibacterial agents with innovative mechanisms of action.

Recombinant human arginase inhibits the in vitro and in vivo proliferation of human melanoma by inducing cell cycle arrest and apoptosis.

Melanoma has been shown to require arginine for growth, thus providing a potential Achilles' heel for therapeutic exploitation. Our investigations show that arginine depletion, using a recombinant form of human arginase I (rhArg), efficiently inhibits the growth of mammalian melanoma cell lines in vitro. These cell lines are consistently deficient in ornithine transcarbamylase (OTC) expression, correlating with their sensitivity to rhArg. Cell cycle distribution of A375 human melanoma cells treated with rhArg showed a remarkable dual-phase cell cycle arrest in S and G2/M phases, in contrast to the G2/M single-phase arrest observed with arginine deiminase (ADI), another arginine-degrading enzyme. rhArg and ADI both induced substantial apoptosis in A375 cells, accompanied by global modulation of cell cycle- and apoptosis-related transcription. Moreover, PEGylated rhArg dramatically inhibited the growth of A375 and B16 melanoma xenografts in vivo. Our results establish for the first time that (PEGylated) rhArg is a promising candidate for effective melanoma treatment, with fewer safety issues than ADI. Insight into the mechanism behind the antiproliferative activity of rhArg could inform us in designing combination therapies for future clinical trials.