Scrape-loading: a simple method to induce chromosomal aberrations with restriction enzymes in CHO cells

PTD-mediated loading of tumor-seeking lymphocytes with prodrug-activating enzymes

Using the approach of peptide transduction domain (PTD)-mediated loading of interleukin-2(IL-2)-activated natural killer (A-NK) cells, tumor-seeking lymphocytes, with prodrug-activating enzymes, we primarily aim to generate a cytotoxic drug selectively within tumors and minimize damage to normal tissues. A-NK cells are able to accumulate selectively at tumor sites. While these cells by themselves possess significant antitumor effect in vivo, we suggest that they can also serve as Trojan horses, by bringing anticancer agents, such as prodrug-activating enzymes, selectively to tumors. We have successfully demonstrated in a mouse model that A-NK cells can be rapidly loaded with prodrug-activating enzymes, such as alkaline phosphatase (AP) and beta-galactosidase (beta-gal), in vitro using enzyme-conjugated peptide PTD5. Upon adoptive transfer into lung-tumor-bearing animals, the loaded A-NK cells are able to bring their cargo of the prodrug-activating enzymes selectively to pulmonary metastases. The targeting of the AP to the tumor tissues is highly specific, since more than a fivefold higher concentration of AP was found in the tumor tissues compared to the surrounding normal lung tissue at 24 h after injection. The approach of transporting prodrug-activating enzymes selectively into tumors clearly shows potential for future targeted chemotherapy. Ongoing studies in our laboratory are evaluating the antitumor efficacy of cellular-dependent enzyme prodrug therapy.

Electroporation of antibodies, DNA, and other macromolecules into cells: a highly efficient method

While antibodies are a major extracellular tool of the highest specificity to answer important biomedical questions, the improvements in electroporation discussed below may make it feasible to also use antibodies as an intracellular deletion tool to study (a) viruses inside the cell, (b) cancer cells, (c) signal transduction, (d) genetics, (e) metabolism, and (f) other structures and mechanisms. Already, others have succeeded in depositing macromolecules, including antibodies (Abs), and nucleic acids inside cells, using many techniques, including electroporation (EP). However, EP has limitations that have precluded its widespread use, particularly its high kill rate for cells and the low percentage of cells that are able to incorporate macromolecules. If these limitations could be overcome for Abs and nucleic acids, then it would be practical to use them as highly specific probes for intracellular molecules. In our experiments using EP, we were able to largely prevent lethality for cells during EP by employing a commercially available cold-storage solution for organ transplants containing high K(+) and Mg(++) (ViaSpan, Belzer UW cold-storage solution, DuPont Pharmaceuticals). This solution decreased cell death after standard EP by an average of 50% for a number of cell lines. Viability of WISH cells after EP approached 100%. In transfection studies, ViaSpan medium strongly increased both P3HR1 cell survival as well as the total number of cells transfected with DNA for green fluorescent protein (GFP). In additional experiments with Abs, we were able to strongly increase the percent of cells that incorporated Ab by using two serial EPs. This enhanced the intracellular protection by Abs against viruses in Vero cells from 64% to a maximum of 98%. We were able to further simplify the EP technique by using unpurified antiserum in place of purified IgG. Thus, this EP technique offers multiple advantages: simplicity, high cell viability, high effectiveness, high specificity, rapid action, usefulness with adherent or non-adherent cells, and no requirement for purification of antibodies from antiserum.

Cells in cryptophycin-induced cell-cycle arrest are susceptible to apoptosis

Exposure of murine leukemia L1210 cells to the antitumor antibiotic cryptophycin 52 (C52) led to cell-cycle arrest at the prometaphase/metaphase interface within 18 h, but apoptotic nuclei did not appear until 36 h later. To determine whether accumulation of cells in early metaphase might have delayed the apoptotic process, cells were treated with C52 for 18 h and a photodynamic process was used to initiate the release of mitochondrial cytochrome c. Apoptosis was observed within 60 min, indicating that the slow apoptotic response was not caused by an impaired ability of genomic DNA to undergo endonucleosomal cleavage during cell-cycle arrest induced by cryptophycin 52.

Inhibition of CD28/CD3-Mediated Costimulation of Naive and Memory Human T Lymphocytes by Intracellular Incorporation of Polyclonal Antibodies Specific for the Activator Protein-1 Transcriptional Complex

A number of indirect methods have been utilized in demonstrating activator protein-1 transcription factor function in IL-2 promoter activity. However, there has been no direct demonstration that activator protein-1 is involved in CD28-dependent costimulation of IL-2 gene transcription in freshly isolated naive and memory human T lymphocytes. To address this issue, the method of scrape loading was applied to purified peripheral blood T lymphocytes. Since scrape loading relies on adherent cells, peripheral blood human T (PB-T) cells were immobilized on the nonspecific cell attachment factor poly-l-lysine. Cells scraped off poly-l-lysine in the presence of Ig FITC efficiently incorporated Ig, with relatively uniform fluorescence. T cells retained their physical parameters as measured by forward and side light scatter, and functional activity as measured by costimulation of proliferation and IL-2 production after being scraped off this substrate. CD28/CD3-costimulated T cells produced intracellular IL-2 from all subsets measured (CD4+, CD4−, CD45RO+, and CD45RO−). IL-2 production and intracellular accumulation in nonscraped PB-T cells activated with CD28/CD3 coligation were skewed favoring CD45RO+ and CD4+ subsets, as was IL-2 production in scraped PB-T cells. The intracellular incorporation of Abs specific for c-Fos and c-Jun family members by scrape loading inhibited the production and intracellular accumulation of IL-2 within 6 h of costimulation with PMA/ionomycin, or costimulation by CD28 and CD3 ligation. Scrape loading thus provides an efficient mechanism for intracellular incorporation of macromolecules, and the first direct evidence that c-Fos and c-Jun are involved in transcription of the IL-2 gene within its correct chromosomal context, in resting human T lymphocyte subpopulations.

Ultrasound permeabilizes CHO cells for the endonucleases AluI and benzon nuclease

Ultrasound permeabilizes Chinese hamster ovary (CHO) cells for the endonucleases AluI and benzon nuclease which leads to the induction of chromosomal aberrations by these enzymes. A few aberrant cells were observed when trypsinized cells or adherent cells were exposed to the enzymes in the absence of ultrasound. Our data show that sonication can be used to introduce endonucleases into CHO cells. We further demonstrate that few cells can internalize endonucleases without previous permeabilization.

Frequencies of polycentric chromosomes following combinational treatments of Chinese hamster ovary cells with restriction endonucleases and X-rays, bleomycin or DNase I

Chinese hamster ovary cells were treated with combinations of the restriction endonucleases AluI, EcoRI or PstI and bleomycin, DNase I or X-rays. With few exceptions the frequencies of polycentric chromosomes calculated as dicentric chromosomes (DIC) were additive or less than additive after combinational treatments when compared with the effects of treatments with the single compounds. Less than additivity was found when the frequencies of DIC were higher than 150 DIC per 100 cells indicating a saturation effect. The data suggest that DNA double-strand breaks (DSB) with different end-structures produce polycentric chromosomes to the same extent as DSB with the same end-structures.

Chromosomal aberrations induced in human whole blood cultures by pipetting cell pellets in the presence of AluI

A physical method is described to permeabilize human peripheral lymphocytes in culture for the restriction endonuclease AluI. Blood cultures are incubated for 20 h, pelleted, strongly pipetted with different types of Pasteur pipettes in the presence of AluI and recovered for up to 54 h in the presence of 5-bromodeoxyuridine. Up to 20% of aberrant first posttreatment (M1) metaphases with chromosome-type aberrations are found. The method works with whole blood cultures and is therefore easy to perform.

Relationships between the cytotoxic effects of restriction endonucleases and radiation on mammalian cells

Wild-type Chinese hamster ovary (CHO) cells, a radiosensitive mutant CHO line (xrs6), and two human cervical carcinoma cell lines, MS751 and ME180, differ in sensitivity to ionizing radiation with surviving fractions at 2 Gy (SF2) of 0.84, 0.06, 0.90 and 0.24 respectively. Restriction endonucleases (REs) were introduced into the cells by treatment with streptolysin O (SLO) and the effects of this on clonogenic cell survival were compared. A comparison was made of REs inducing either blunt- (AluI) or cohesive-ended (Sau3AI) double-strand breaks. Whilst MS751 cells were resistant to the effects of both REs, AluI caused significantly greater cell killing than Sau3AI in the other three lines (p < 0.05 for all). Both ME180 and xrs6 were significantly more sensitive to REs than their radioresistant counterparts, MS751 and CHO (p < 0.05 for both). In order to investigate the effect of DNA methylation on dsb induction, the isoschizomers MspI and HpaII (cohesive-ended dsb inducers) were introduced into the cell lines. Both REs recognize the same sequence but HpaII cannot cleave if the internal cytosine is methylated. MS751 was also resistant to the effects of both of these enzymes and MspI was more cytotoxic than HpaII in the other three lines (p < 0.03 for all). The differential sensitivity to the two REs was more marked in the radiosensitive cell lines, suggesting that there may be a greater degree of DNA methylation in radiosensitive cells. The variation in sensitivities to REs between the cell lines could not be explained in terms of differences in cell poration following SLO treatment because, although MS751 was resistant to SLO (25% of cells porated), the other three lines showed the same level of cell poration (98% of cells). With these four cell lines, there was a significant correlation between sensitivity to RE and radiosensitivity for AluI, Sau3AI and MspI but not for HpaII.

Are rogue cells an indicator of cancer risk due to the action of bacterial restriction endonucleases?

Cytogenetic surveys in normal individuals have occasionally shown the occurrence of cells with multiple chromosome-type aberrations in some of the subjects. These cells, which are rare, have been termed as rogue cells. Rogue cells, which have been observed worldwide, have a mysterious nature. It has been suggested that they may give rise to cancer. Various mechanisms have been considered for the causation of the rouge-cell phenomenon in the past but none of them appears to be fully justified. In this paper we propose their occurrence due to the action of bacterial restriction endonucleases.

Combination treatments of Chinese hamster ovary cells with various restriction endonucleases result in chromosomal aberrations whose frequencies are additive or less than additive

Chinese hamster ovary cells were treated with combinations of different restriction endonucleases (RE). The frequencies of chromosomal aberrations after combination treatments were additive or less than additive when compared with the effects of the single RE. These data indicate that DNA double-strand breaks (DSB) induced by different types of RE in combination treatments lead to chromosomal aberrations in the same way as DSB induced by single RE.