Chemosensitivity profiles of human cancers assessed by the 6-day SRC assay on serially xenografted tumors

The human lung adenocarcinoma cell line EKVX produces an infectious xenotropic murine leukemia virus

The cell lines of the NCI-60 panel represent different cancer types and have been widely utilized for drug screening and molecular target identification. Screening these cell lines for envelope proteins or gene sequences related to xenotropic murine leukemia viruses (X-MLVs) revealed that one cell line, EKVX, was a candidate for production of an infectious gammaretrovirus. The presence of a retrovirus infectious to human cells was confirmed by the cell-free transmission of infection to the human prostate cancer cell line LNCaP. Amplification and sequencing of additional proviral sequences from EKVX confirmed a high degree of similarity to X-MLV. The cell line EKVX was established following passage of the original tumor cells through nude mice, providing a possible source of the X-MLV found in the EKVX cells.

A novel human recombinant single-chain antibody targeting CD166/ALCAM inhibits cancer cell invasion in vitro and in vivo tumour growth

Screening a phage-display single-chain antibody library for binding to the breast cancer cell line PM-1 an antibody, scFv173, recognising activated leukocyte cell adhesion molecule (ALCAM, CD166) was isolated and its binding profile was characterized. Positive ALCAM immunohistochemical staining of frozen human tumour sections was observed. No ALCAM staining was observed in the majority of tested normal human tissues (nine of ten). Flow cytometry analyses revealed binding to 22 of 26 cancer cell lines of various origins and no binding to normal blood and bone marrow cells. Antibody binding inhibited invasion of the breast cancer cell line MDA-MB-231 by 50% in an in vitro Matrigel-coated membrane invasion assay. Reduced growth of tumours in nude mice was observed in an in vivo model in which the mice were injected subcutaneously with colorectal carcinoma HCT 116 cells and treated with scFv173 when compared to control. In summary, we have characterized a novel fully human scFv antibody recognising ALCAM on cancer cells and in tumour tissues that reduces cancer cell invasion and tumour growth in accordance with the hypothesised role for ALCAM in cell growth and migration control.

Evaluation of different photosensitizers for use in photochemical gene transfection

Many potentially therapeutic macromolecules, e.g. transgenes used in gene therapy, are taken into the cells by endocytosis, and have to be liberated from endocytic vesicles in order to express a therapeutic function. To achieve this we have developed a new technology, named photochemical internalization (PCI), based on photochemical reactions inducing rupture of endocytic vesicles. The aim of this study was to clarify which properties of photosensitizers are important for obtaining the PCI effect improving gene transfection. The photochemical effect on transfection of human melanoma THX cells has been studied employing photosensitizers with different physicochemical properties and using two gene delivery vectors: the cationic polypeptide polylysine and the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Photochemical treatment by photosensitizers that do not localize in endocytic vesicles (tetra[3-hydroxyphenyl]porphyrin and 5-aminolevulinic acid-induced protoporphyrin IX) do not stimulate transfection, irrespective of the gene delivery vector. In contrast, photosensitizers localized in endocytic vesicles stimulate polylysine-mediated transfection, and amphiphilic photosensitizers (disulfonated aluminium phthalocyanine [AlPcS2a] and meso-tetraphenylporphynes) show the strongest positive effect, inducing approximately 10-fold increase in transfection efficiency. In contrast, DOTAP-mediated transfection is inhibited by all photochemical treatments irrespective of the photosensitizer used. Neither AlPcS2a nor Photofrin affects the uptake of the transfecting DNA over the plasma membrane, therefore photochemical permeabilization of endocytic vesicles seems to be the most likely mechanism responsible for the positive PCI effect on gene transfection.

Role of endosomes in gene transfection mediated by photochemical internalisation (PCI)

BACKGROUND

Most non-viral gene therapy vectors deliver transgenes into cells through the endocytic pathway. Lack of escape from endocytic vesicles in many cases constitutes a major barrier for delivery of the functional gene. We have developed a new technology named photochemical internalisation (PCI) to achieve light-inducible cytosolic delivery of the transgene. The technology is based on a photochemical treatment employing photosensitisers localised in endocytic vesicles. In this work mechanisms involved in PCI-mediated transfection (photochemical transfection) were studied.

METHODS

Human melanoma or colon carcinoma cells were pre-incubated with the photosensitiser aluminium phthalocyanine disulfonate (AlPcS2a) followed by treatment with plasmid encoding enhanced green fluorescent protein (EGFP) complexed with poly-L-lysine, N-(1-(2,3-dioleoxyloxy)propyl)-N,N,N,-trimethylammonium-methyl-sulfate (DOTAP) or polyethylenimine (PEI) and light exposure. The expression of the EGFP-gene was scored by fluorescence microscopy and flow cytometry.

RESULTS

The photochemical treatment using light doses corresponding to D50 substantially improves the efficiency of transfection mediated by poly-L-lysine and PEI, but not by DOTAP. The treatment does not enhance the delivery of the plasmid complex across the plasma membrane, since the amount of internalised plasmid is similar for irradiated and non-irradiated cells. Light-inducible transfection occurs only under temperature conditions allowing endocytic uptake and is not improved by chloroquine or ammonium chloride, but is inhibited by bafilomycin A1 (agents that increase vesicular pH and interfere with the endocytic transport).

CONCLUSIONS

Photochemical transfection occurs through endocytosis, followed by cytosolic release of the transfecting DNA from photochemically permeabilised endocytic vesicles. Release of plasmid from early endosomes seems to be of importance in photochemical transfection, although a role of later endocytic vesicles can, however, not be ruled out.

Photochemical internalisation increases the cytotoxic effect of the immunotoxin MOC31-gelonin

Photochemical internalisation (PCI) was recently demonstrated as a unique procedure for site-specific delivery of several types of membrane impermeable macromolecules from endocytotic vesicles to the cytosol (Berg et al., 1999). The technology is based on the cytosolic release of endocytosed macromolecules from endosomes and lysosomes upon exposure of cells to photosensitising compounds, which became localised to these vesicles, and light. In our study the possibility to increase the cytotoxic effect of the immunotoxin MOC31-gelonin by PCI was examined. The type I ribosome-inactivating protein gelonin was covalently linked to the monoclonal IgG1 antibody MOC31, directed against epithelial glycoprotein-2 (EGP-2), an antigen expressed on most carcinoma cells. Five different cell lines, of which 4 expressed EGP-2, were treated with MOC31-gelonin and endosomal and lysosomal localising photosensitisers, followed by exposure to light. Insignificant cytotoxicity of the MOC31-gelonin was observed when the cells were incubated with the immunotoxin alone. However, in combination with endosomal and lysosomal localising photosensitizers, we demonstrate synergistic toxic effect of the MOC31-gelonin conjugate in a light-dependent manner. Our results indicate that PCI is a promising tool for increasing the cytotoxicity of immunotoxins, which is important for further improvement of the PCI concept towards possible use in cancer therapy.

Photochemical transfection: a new technology for light-induced, site-directed gene delivery

The development of methods for specific delivery of therapeutic genes into target tissues is an important issue for the further progress of in vivo gene therapy. In this article we report on a novel technology, named photochemical transfection, to use light to direct a precise delivery of therapeutic genes to a desired location. The technology makes use of photosensitizing compounds that localize mainly in the membranes of endosomes and lysosomes. On illumination these membrane structures will be destroyed, releasing endocytosed DNA into the cell cytosol. Using a green fluorescent protein gene as a model we show that illumination of photosensitizer-treated cells induces a substantial increase in the efficiency of transfection by DNA-poly-L-lysine complexes. Thus, in a human melanoma cell line the light treatment can increase the transfection efficiency more than 20-fold, reaching transfection levels of about 50% of the surviving cells. In this article various parameters of importance for the use of this technology are examined, and the potential use of the technology in gene therapy is discussed.

Ectopic expression of target genes may represent an inherent limitation of RT-PCR assays used for micrometastasis detection: studies on the epithelial glycoprotein gene EGP-2

Our objective was to develop and study the feasibility of a quantitative, nested reverse-transcription polymerase chain reaction (RT-PCR) assay for detection of micrometastatic, epithelial tumor cells using the epithelial glycoprotein EGP-2 gene as a target. Several carcinoma cell lines and peripheral blood samples of 10 healthy volunteers were screened for levels of EGP-2 mRNA. The assay included EGP-2 competitor molecules, carrying an internal deletion, that had been titrated by limiting dilution. Seven carcinoma cell lines showed a wide spectrum of EGP-2 mRNA expression levels, with the highest values (20-100 molecules/cell) seen in 3 breast-cancer cell lines. Unexpectedly, a consistent low level of EGP-2 mRNA expression (0.0004 molecules/cell) was observed in peripheral blood mononuclear cells, probably representing ectopic non-functional expression. Because of this background level, spiking experiments with T47D breast-carcinoma cells added to blood mononuclear cells exhibited a detection limit that was not better than approximately one tumor cell in 2 x 10(4) normal cells. Together with the considerable variation of EGP-2 transcript levels that is observed in different carcinoma cell lines, the extent of expression in normal blood cells would prevent a reliable estimation of low numbers of carcinoma cells in clinical samples. A similar situation might well apply for other target genes. This emphasizes the need for a critical evaluation of the different steps involved in the methods used for RT-PCR detection of micrometastatic tumor cells.

Efficacy of ifosfamide, dacarbazine, doxorubicin and cisplatin in human sarcoma xenografts

The primary chemosensitivity of 16 highly malignant xenografted human soft-tissue sarcomas to ifosfamide, dacarbazine, adriamycin and cisplatin and the development of secondary drug resistance in two chemosensitive sarcoma cell lines was tested in the xenograft system. Single-dose, single-agent treatments with 350 mg kg-1 ifosfamide, 200 mg kg-1 dacarbazine, 10 mg kg-1 doxorubicin and 6.6 mg kg-1 cisplatin were administered and response measured as specific growth delay. Since ifosfamide induced unexpectedly higher toxicity, response was corrected based on the shape of the dose-response curve for ifosfamide. Taking a specific growth delay > 3 as the cut-off point for chemosensitivity, ifosfamide, dacarbazine, doxorubicin and cisplatin were effective in 10/16, 4/16, 2/16 and 1/16 sarcoma cell lines respectively. Five out of 16 sarcoma cell lines were resistant to all tested drugs. Ifosfamide-resistant sarcoma lines were also resistant to doxorubicin and cisplatin, indicating a high degree of cross-resistance. Dacarbazine was still effective in 1/6 ifosfamide-resistant sarcoma cell lines. Secondary drug resistance developed slowly after doxorubicin and ifosfamide pretreatments at moderate selection pressure and developed rapidly after dacarbazine pretreatment at high selection pressure.

Chemosensitivity of squamous cell carcinoma grown in implantable chambers

This study was motivated by the need to develop new methods to predict tumor response to chemotherapeutic agents. Using implantable cell-growth chambers, squamous carcinoma cells from head and neck tumors were xenografted into the peritoneal cavity of immunocompetent rats. Animals were divided into control and treatment groups. The treatment groups received intravenous cisplatin (CDDP) or 5-fluorouracil (5-FU) v normal saline solution for the control. Animals from each group were randomly selected and killed on days 3, 5, and 7 postimplantation. The chambers were retrieved, the media aspirated, and cells counted. Exponential growth curves were derived for the control and treatment groups. Statistically significant growth inhibition was observed for both treatment arms, compared with controls. This method of chemosensitivity testing proved to be inexpensive and reliable, and demonstrated tumor cell killing by 5-FU and CDDP.