Induction of apoptosis in human pancreatic carcinoma cells by a synthetic bleomycin-like ligand

Design, synthesis, and applications of ring-functionalized histidines in peptide-based medicinal chemistry and drug discovery

Modified and synthetic α-amino acids are known to show diverse applications. Histidine, which possesses numerous applications when subjected to synthetic modifications, is one such amino acid. The utility of modified histidines varies widely from remarkable biological activities to catalysis, and from nanotechnology to polymer chemistry. This renders histidine residue an important place in scientific research. Histidine is a well-studied scaffold and constitutes the active site of various enzymes catalyzing important reactions in the biological systems. A rational modification in histidine structure with a distinctly developed protocol extensively changes its physical and chemical properties. The utilization of modified histidines in search of potent, target selective and proteostable scaffolds is vital in the development of bioactive peptides with enhanced drug-likeliness. This review is a compilation and analysis of reported side-chain ring modifications at histidine followed by applications of ring-modified histidines in the synthesis of various categories of bioactive peptides and peptidomimetics.

Novel metal chelating molecules with anticancer activity. Striking effect of the imidazole substitution of the histidine-pyridine-histidine system

Previously we have reported a metal chelating histidine-pyridine-histidine system possessing a trityl group on the histidine imidazole, namely HPH-2Trt, which induces apoptosis in human pancreatic adenocarcinoma AsPC-1 cells. Herein the influence of the imidazole substitution of HPH-2Trt was examined. Five related compounds, HPH-1Trt, HPH-2Bzl, HPH-1Bzl, HPH-2Me, and HPH-1Me were newly synthesized and screened for their activity against AsPC-1 and brain tumor cells U87 and U251. HPH-1Trt and HPH-2Trt were highly active among the tested HPH compounds. In vitro DNA cleavage assay showed both HPH-1Trt and HPH-2Trt completely disintegrate pUC19 DNA. The introduction of trityl group decisively potentiated the activity.

Antiviral activities against herpes simplex virus type 1 by HPH derivatives and their structure-activity relationships

The compound named Histidine-pyridine-histidine (HPH) is an oxygen-activating ligand derived from the structure of bleomycin. We synthesized HPH derivatives, namely HPH-1 to -8, and investigated their antiviral activities against herpes simplex virus type 1. HPH-8 showed potent antiviral activity with an EC50 of 15 microM, and relatively high cytotoxicity with a CC50 of 37 microM. In contrast, HPH-4 indicated a weaker antiviral activity with an EC50 of 79 microM, but exhibited a far more less cytotoxicity (CC50 500 microM). Other HPH derivatives showed no effects against antiviral activities and cytotoxicities.

Radiotherapy and antiangiogenic TM in lung cancer

Tetrathiomolybdate (TM) is a potent nontoxic orally delivered copper complexing agent under development for the last several years for the treatment of Wilson's disease. It has been shown to block angiogenesis in primary and metastatic tumors. Therefore, the combination of cytotoxic radiotherapy (RT) and antiangiogenic TM could target both the existing tumor and the tumor microvasculature in a comprehensive strategy. Using a Lewis lung high metastatic (LLHM) carcinoma mouse tumor model, we demonstrate that the combination of TM and RT is more effective than either used as monotherapy. We also show that their therapeutic effects are additive, with no additional toxicity. We show that TM has no significant cytotoxicity in vitro against LLHM tumor cells, further supporting the antiangiogenic mechanism for its action.

Sensitization of hyperthermic treatment of leukemic cell lines by a synthetic peptide

A compound named HPH-Pep, a peptide constructed from pyridine and histidine units, showed sensitizing effect on the hyperthermic treatment of L-1210, Molt-4, and HL60 cells. The survival rate of these cells was greatly reduced by combined treatment with heating at 44 degrees C and HPH-pep. The treatment of L-1210 and Molt-4 cells with HPH-Pep resulted in a significant breakdown of the survival rate at 44 degrees C. The cell death induced by HPH-Pep under hyperthermic condition seemed to involve iron and peroxide.

Peplomycin-induced apoptosis in oral squamous carcinoma cells depends on bleomycin sensitivity

Oral squamous carcinoma cell line SSCKN cells were shown to be highly sensitive to bleomycin, whereas SCCTF cells were minimally sensitive to this reagent. To determine whether the anticancer drug resistance to oral squamous carcinoma cells could be related to the degree of the drug-induced apoptosis, we examined the effects of peplomycin on induction of apoptosis in these cells. After reaching subconfluence, SCCKN and SCCTF cells were exposed to various concentrations of peplomycin. Peplomycin caused cytotoxicity in both SCCKN and SCCTF cells in a dose-dependent fashion with the maximal effect at concentrations of 1 and 10 microM, respectively, as determined by phase-contrast microscopy and WST-1 cell viability assay. By using the Hoechst 33342 staining, we observed marked nuclear condensation and fragmentation of chromatin in SCCKN cells treated with 1 microM peplomycin. However, SCCTF cells treated with 1 microM peplomycin showed neither nuclear condensation nor fragmentation. DNA ladder formation was also detected in both cell lines by treatment with peplomycin. The induced DNA ladder formation in SCCKN and SCCTF cells was dose-dependent, with the maximal effect at concentrations of 5 and 50 microM, respectively. Bleomycin also induced DNA ladder formation in SCCKN and SCCTF cells with different sensitivities. Mitomycin C induced DNA laddering in both SCCKN and SCCTF cells; however, the intensity of DNA ladder formation was almost the same in both cell lines. The present results indicate that peplomycin-induced apoptosis in oral squamous carcinoma cell lines depends on the sensitivity of these cells to bleomycin.

Copper and genomic stability in mammals

As the free ion and in the form of some complexes, there is no doubt that copper can promote damage to cellular molecules and structures through radical formation. At the same time, and perhaps as a consequence, mammals have evolved means of minimizing levels of free copper ions and destructive copper complexes that enter the organism and its cells. These means include tight binding of copper ions to protein carriers and transporters; direct exchange of copper between protein carriers, transporters, and cuproenzymes; and mobilization of secretory mechanisms and excretory pathways, as needed. As a consequence, normally, and except under certain genetic conditions, copper is likely to be benign to most mammals and not responsible for genomic instability, including fragmentation of and/or alterations to DNA, induction of mutations or apoptosis, or other toxic events. Indeed, cuproenzymes are important members of the antioxidant system of the organism.

Screening for inducers of apoptosis in apoptosis-resistant human carcinoma cells

Many anticancer agents are known to induce apoptosis in cultured cells, but human solid tumor cells are often resistant to apoptosis induction. Human pancreatic adenocarcinoma AsPC-1 cells were found to be resistant to apoptosis. So, we screened microbial culture filtrates and synthetic chemicals for their ability to induce apoptosis in AsPC-1 cells. Polyoxypeptin A was isolated from a Streptomyces culture broth as a potent inducer of apoptosis. Its cyclic hexadepsipeptide structure contains a simple but hitherto unreported amino acid, (2S,3R)-3-hydroxy-3-methylproline. Polyoxypeptin A induced early cell death, apoptotic morphology, and internucleosomal DNA fragmentation in AsPC-1 cells at low concentrations. Polyoxypeptin A can induce caspase 3 activation in human T cell leukemia Jurkat cells but not in AsPC-1 cells. The mechanism of apoptosis in AsPC-1 cells has not been elucidated yet. Less toxic derivatives of polyoxypeptin A are being prepared. A macrocyclic lactam called BE-14106 was also isolated from Streptomyces as an inducer of apoptosis in AsPC-1 cells. Histidine-pyridine-histidine-3 (HPH-3) is an oxygen-activating ligand derived from the structure of bleomycin, and it also induced apoptosis in AsPC-1 cells. Induction of apoptosis by HPH-3 was inhibited by zinc and copper ions, indicating that chelation with ferrous ion is responsible for induction of apoptosis, as is chelation by bleomycin to cleave DNA. Bleomycin A2 and its portion having no DNA-binding region, glycopeptide-3(GP-3), did not induce apoptosis in AsPC-1 cells. Thus, among the actions of bleomycin-related compounds, the induction of apoptosis is a unique characteristic of HPH-3.