Tumor-selective gene transduction and cell killing with an oncotropic autonomous parvovirus-based vector.

A recombinant MVMp of the fibrotropic strain of minute virus of mice (MVMp) expressing the chloramphenicol acetyltransferase reporter gene was used to infect a series of biologically relevant cultured cells, normal or tumor-derived, including normal melanocytes versus melanoma cells, normal mammary epithelial cells versus breast adenocarcinoma cells, and normal neurons or astrocytes versus glioma cells. As a reference cell system we used normal human fibroblasts versus the SV40-transformed fibroblast cell line NB324K. After infection, we observed good expression of the reporter gene in the different tumor cell types, but only poor expression if any in the corresponding normal cells. We also constructed a recombinant MVMp expressing the green fluorescent protein reporter gene and assessed by flow cytometry the efficiency of gene transduction into the different target cells. At a multiplicity of infection of 30, we observed substantial transduction of the gene into most of the tumor cell types tested, but only marginal transduction into normal cells under the same experimental conditions. Finally, we demonstrated that a recombinant MVMp expressing the herpes simplex virus thymidine kinase gene can, in vitro, cause efficient killing of most tumor cell types in the presence of ganciclovir, whilst affecting normal proliferating cells only marginally if at all. However, in the same experimental condition, breast tumor cells appeared to be resistant to GCV-mediated cytotoxicity, possibly because these cells are not susceptible to the bystander effect. Our data suggest that MVMp-based vectors could prove useful as selective vehicles for anticancer gene therapy, particularly for in vivo delivery of cytotoxic effector genes into tumor cells.

Nanomolar range docetaxel treatment sensitizes MCF-7 cells to chemotherapy induced apoptosis, induces G2M arrest and phosphorylates bcl-2.

Docetaxel (Taxotere), a member of the taxoid family of chemotherapy drugs is currently being tested in clinical trials simultaneously with other apoptosis inducing drugs like doxorubicin. We show, in vitro, in MCF-7 breast cancer cells that when it is used at doses as low as 5nM, 24 hours before either doxorubicin or etoposide, docetaxel is capable of inducing a significant increase in cell death compared to the reverse sequence or simultaneous treatment. We further show that this increase in cell death is due to an increase in apoptosis, and that this sensitization coincides with a docetaxel induced G2-M arrest and phosphorylation of the bcl-2 oncoprotein. We speculate that this phosphorylation of the apoptosis blocker bcl-2 might be responsible for the sensitization, and we suggest a clinical study comparing a 24 hour docetaxel pretreatment to the current simultaneous schedules.

Androgens induce resistance to bcl-2-mediated apoptosis in LNCaP prostate cancer cells.

We describe an in vitro model for prostate cancer treatment that suggests a potential benefit for combined androgen ablation and cytotoxic chemotherapy. Androgen treatment of the LNCaP hormone-dependent human prostate cancer cell line induces increased expression of the BCL-2 protein. Increased levels of this protein are known to mediate inhibition of apoptosis. LNCaP cells, however, did not undergo apoptosis in response to androgen withdrawal. Etoposide exerts its cytotoxicity on LNCaP and other cells by inducing apoptosis. In vitro etoposide cytotoxicity was diminished 83% in the presence of either 10(-8) M dihydrotestosterone or 10(-9) M R1881 in LNCaP cells. The interaction between androgen and etoposide was mediated through the BCL-2 protein, since bcl-2 antisense oligonucleotides blocked the protective effect of androgens on etoposide cytotoxicity.

Regulation of vimentin gene transcription in human breast cancer cell lines.

We have investigated the control of vimentin expression in human breast cancer cell lines because of its transcriptional activation during malignant progression in breast cancer. Comparison of vimentin-positive (V+) and vimentin-negative (V-) breast cancer cell lines revealed several potential areas of vimentin gene regulation. Analysis of the chromatin structure of the vimentin gene in V+ and V- breast cancer cells showed DNase I hypersensitive sites in the 5' promoter region in V+ cell lines and 3' to the start of transcription in V- cell lines. Promoter deletion and reporter gene analysis revealed the importance of two adjacent AP-1 sites separated by seven GC-rich nucleotides for vimentin expression in V+ breast cancer cells. Mutational analysis of these sequences showed that although both AP-1 sites could bind nuclear proteins from V+ cells in vitro, one AP-1 site was sufficient to drive transcription in CAT reporter gene assays. The GC-rich spacer region had a modulating function on the activity of the AP-1 sites. In addition, levels of c-jun mRNA were elevated in V+ versus V- cells. In summary, distinct sites within the vimentin gene appear to be important for the control of vimentin expression in V+ and V- breast cancer cells with multiple elements acting coordinately to regulate vimentin expression.