Human papillomavirus 16 E6 expression disrupts the p53-mediated cellular response to DNA damage

Infection with certain types of human papillomaviruses (HPV) is highly associated with carcinomas of the human uterine cervix. However, HPV infection alone does not appear to be sufficient for the process of malignant transformation, suggesting the requirement of additional cellular events. After DNA damage, normal mammalian cells exhibit G1 cell-cycle arrest and inhibition of replicative DNA synthesis. This mechanism, which requires wild-type p53, presumably allows cells to undertake DNA repair and avoid the fixation of mutations. We directly tested whether the normal response of cervical epithelial cells to DNA damage may be undermined by interactions between the E6 protein expressed by oncogenic HPV types and wild-type p53. We treated primary keratinocytes with the DNA-damaging agent actinomycin D and demonstrated inhibition of replicative DNA synthesis and a significant increase in p53 protein levels. In contrast, inhibition of DNA synthesis and increases in p53 protein did not occur after actinomycin D treatment of keratinocytes immortalized with HPV16 E6/E7 or in cervical carcinoma cell lines containing HPV16, HPV18, or mutant p53 alone. To test the effects of E6 alone on the cellular response to DNA damage, HPV16 E6 was expressed in the carcinoma cell line RKO, resulting in undetectable baseline levels of p53 protein and loss of the G1 arrest that normally occurs in these cells after DNA damage. These findings demonstrate that oncogenic E6 can disrupt an important cellular response to DNA damage mediated by p53 and may contribute to the subsequent accumulation of genetic changes associated with cervical tumorigenesis.

Use of hydroxypropyl- and hydroxyethyl-derivatized beta-cyclodextrins for the thin-layer chromatographic separation of enantiomers and diastereomers

Partially substituted hydroxypropyl-beta-cyclodextrin and hydroxyethyl-beta-cyclodextrin proved to be effective chiral mobile phase additives (CMAs) for the thin-layer chromatographic (TLC) resolution of racemic benzyl-2-oxazolidinone, 5-(4-methyl-phenyl)-5-phenylhydantoin, mephenytoin and several dansyl and beta-naphthylamide amino acids. Several diastereomeric compounds including steroid epimers and alkaloids were separated as well. The derivatized beta-cyclodextrins tended to be much more soluble in water and hydro-organic solvents than native beta-cyclodextrin. Their chromatographic selectivity also was somewhat different. The use of CMAs in TLC is a potentially useful and powerful method that has not been considered adequately. The relative lack of chiral stationary phases available in planar format makes the use of CMAs particularly attractive.

Planar chromatographic separation of enantiomers and diastereomers with cyclodextrin mobile phase additives

A variety of racemic compounds were resolved using reversed-phase thin-layer chromatography (TLC) with mobile phases containing highly concentration solutions of beta-cyclodextrin (beta-CD). These include the drugs labetalol and mephenytoin, metallocenes, crown ethers, methyl-p-toluenesulfinate, nornicotine derivaties and several dansyl and beta-naphthylamide substituted amino acids. It was possible to resolve some racemates that could not be separated on beta-CD bonded phase liquid chromatography (LC) columns with this technique. Likewise there were some compounds that could be resolved with the LC approach that failed to separate with the present TLC method. In cases of racemates that could be resolved by either approach, it was found that the retention order was exactly opposite for the two methods. Enantiomeric resolution is highly dependent on mobile phase composition. In particular, the type and amount of organic modifier as well as the concentration of beta-CD affect the observed resolution. Possible reasons for the chromatographic behavior are discussed. Several diastereoisomeric compounds were separated as well, including steroid epimers and pharmaceutical compounds.

Separation of optical isomers of scopolamine, cocaine, homatropine, and atropine

Different drug stereoisomers can have different physiological and therapeutic effects. Difficulties in separating optical isomers often make it impractical to market stereochemically pure products or to monitor isomeric contamination. This is not thought to be a problem with drugs isolated from biological sources (the alkaloids, for example). However, small amounts of isomeric impurities also exist in many biological systems. More importantly the isolation and purification process can cause partial or complete racimization in some cases. Great care must be taken in the handling of some drugs and an efficient, sensitive means to monitor racimization is important. Liquid chromatographic separation on a chiral beta-cyclodextrin bonded phase can be an effective technique in many cases. Its use in separating optical isomers of dl-scopolamine, dl-hyoscyamine, dl-homatropine, and dl-cocaine is discussed.

Quantitative analytical aspects of reversed-phase liquid chromatography with slurry-packed capillary columns

Conditions for reproducible packing of fused-silica liquid chromatography capillary columns were demonstrated. The plate height vs. velocity curves were determined for successively prepared columns. In addition, the values of separation impedance were calculated. Several liquid chromatography systems were evaluated in conjunction with the slurry-packed capillaries for the retention and peak area reproducibility.