Efficiency of communication between tumour cells in collagen gel cultures

Clonal diversity in carcinomas: its implications for tumour progression and the contribution made to it by epithelial-mesenchymal transitions

The progression of tumours to malignancy is commonly considered to arise through lineal evolution, a process in which mutations conferring pro-oncogenic cellular phenotypes are acquired by a succession of ever-more dominant clones. However, this model is at odds with the persistent polyclonality observed in many cancers. We propose that an alternative mechanism for tumour progression, called interclonal cooperativity, is likely to play a role at stages of tumour progression when mutations cause microenvironmental changes, such as occur with epithelial-mesenchymal transitions (EMTs). Interclonal cooperativity occurs when cancer cell-cancer cell interactions produce an emergent malignant phenotype from individually non-malignant clones. In interclonal cooperativity, the oncogenic mutations occur in different clones within the tumour that complement each other and cooperate in order to drive progression. This reconciles the accepted genetic and evolutionary basis of cancers with the observed polyclonality in tumours. Here, we provide a conceptual basis for examining the importance of cancer cell-cancer cell interactions to the behaviour of tumours and propose specific mechanisms by which clonal diversity in tumours, including that provided by EMTs, can drive the progression of tumours to malignancy.

Retroviral vector-mediated gene transfer into keratocytes in vitro and in vivo

PURPOSE

To determine the potential of somatic gene transfer as a technique for modulating corneal wound healing after superficial keratectomy.

METHODS

The transduction of human and rabbit keratocytes with beta-galactosidase and herpes simplex virus thymidine kinase genes was performed. In vitro, human and rabbit keratocytes were transduced with retroviral vectors bearing beta-galactosidase or HStk (herpes simplex virus thymidine kinase) genes. In vivo, rabbit keratocytes were transduced by topical application of vector supernatant after a superficial keratectomy. In vitro and in vivo, expression of the beta-galactosidase gene was examined with histochemical staining. In vitro, ganciclovir cytotoxicity in HStk gene-transduced keratocytes and bystander effect in co-cultures of HStk(+) and HStk(-) keratocytes were measured by determining the degree of confluency of cells in 6-well plates after 10 days of incubation. Corneal haze in rabbits was measured after transduction with Hstk and subsequent treatment with topical ganciclovir.

RESULTS

In vitro, both human and rabbit keratocytes were transduced successfully with both beta-galactosidase and HStk genes. Transduction efficiency was greater with human (22%) than with rabbit (16%) cells, and both HStk-transduced cell lines showed dose-dependent ganciclovir cytotoxicity and a significant bystander effect. In vivo, expression of beta-galactosidase within vimentin-positive corneal stromal cells confirmed transduction of keratocytes in the rabbit after superficial stromal keratectomy with an efficiency of 25% to 40%. Postoperative application of topical ganciclovir reduced corneal stromal haze in rabbits.

CONCLUSIONS

The ability to genetically transduce stromal keratocytes provides a new strategy for understanding the important cellular and molecular events that influence corneal wound healing, thus offering a potential approach to decrease or prevent corneal haze and scarring after superficial keratectomy.

Use of retroviral vectors encoding murine inducible nitric oxide synthase gene to suppress tumorigenicity and cancer metastasis of murine melanoma

The purpose of this study was to determine whether retrovirus-mediated transfer of murine macrophage inducible nitric oxide synthase (iNOS) can produce inhibition of tumorigenicity and metastasis. Retroviral vectors encoding macrophage iNOS constructed in pLXSN, a retroviral vector with the iNOS gene under the control of a long terminal repeat promoter, were stably transfected into PA317 cells. Medium harvested from confluent monolayers of the virus-producing cell lines was used for infection of the murine K-1735 melanoma cells. Expression of iNOS was confirmed by northern and Western blot analyses. Functional iNOS protein expression was confirmed by bioassay of nitrite accumulation in the culture supernatant. Cells infected by a control iNOS-negative retrovirus produced fast-growing subcutaneous tumors and many lung metastases in nude mice, whereas iNOS-transduced cells produced slow-growing tumors and few lung metastases, showing that the infection of murine tumor cells by retroviruses harboring the iNOS gene can suppress tumorigenicity and metastasis.

Retrovirus-mediated suicide gene transduction in the vitreous cavity of the eye: feasibility in prevention of proliferative vitreoretinopathy

In proliferative vitreoretinopathy (PVR), retinal pigment epithelial cells, fibroblasts, or other proliferating cells form contractile membranes in the vitreous cavity of the eye, resulting in traction retinal detachment. Retroviral vector-mediated transfer is a suitable method to transduce the herpes simplex virus thymidine kinase (HSV-tk) gene into proliferating cells in PVR, allowing for the selective killing of these cells. To determine the potential of gene transduction in the environment of the vitreous cavity, we evaluated the effect of vitreous humor on retroviral vector-mediated gene transduction of rabbit dermal fibroblasts in vitro and studied in vivo transduction in rabbit experimental PVR with retroviral vector G1BgSvNa. In addition, we studied the bystander effect in vitro and in vivo in a rabbit model of PVR, with low percentages of HSV-tk-positive cells. Finally, we evaluated the efficacy of intravitreal administration of HSV-tk retroviral vector G1TkSvNa followed by ganciclovir (GCV) in the prevention of experimental PVR. Vitreous humor reduced gene transfer efficiency in vitro in a dose-dependent manner. LacZ expression was found in cells of preretinal or intravitreal membranes of animals of both in vivo and in vitro transduction groups; however, in vivo transduction resulted in a decreased number of transduced cells, with a relative transduction efficiency of approximately 2%. Transduction of HSV-tk was associated with a powerful bystander effect both in vitro and in vivo with significant effects even when HSV-tk-positive cells represented only 1% of the population. In vivo transduction with G1TkSvNa followed by GCV significantly inhibited the development of PVR (p < 0.05). These results suggest that retroviral vector-mediated transfer of HSV-tk into the proliferating cells in PVR may be feasible and may provide a novel therapeutic strategy for this disease.

Inhibition of experimental proliferative vitreoretinopathy by retroviral vector-mediated transfer of suicide gene. Can proliferative vitreoretinopathy be a target of gene therapy?

PURPOSE

To determine the potential of somatic gene transfer as a treatment for proliferative vitreoretinopathy (PVR), experimental PVR was induced in rabbits by intraocular injection of fibroblasts bearing the herpes simplex virus thymidine kinase (HStk) gene. These transduced cells should be susceptible to cytotoxicity by exposure to ganciclovir (GCV).

MATERIALS AND METHODS

Rabbit fibroblasts were transduced with retroviral vectors bearing an HStk gene. Proliferative vitreoretinopathy was induced by injection of 5 x 10(4) normal or HStk gene-transduced fibroblasts (HStk fibroblasts) into rabbit eyes. Ganciclovir (100 micrograms per eye) or saline was injected into the vitreous on days 0 and 4. Experimental animals were divided into three groups: group A received HStk fibroblasts with GCV; group B, normal fibroblasts with GCV; group C, HStk fibroblasts with saline. Proliferative vitreoretinopathy also was induced in several other groups of eyes, some receiving GCV and different proportions of HStk fibroblasts to normal fibroblasts, others receiving only normal fibroblasts and GCV. The eyes were examined by indirect ophthalmoscopy on days 4, 7, 14, and 28, and PVR was classified into six stages (0-5).

RESULTS

Proliferative vitreoretinopathy was induced and progressed over time in each group. On day 28, PVR was most severe in animals in group B (average stage, 4.6) and group C (average stage, 4.4). Proliferative vitreoretinopathy was inhibited in group A (average stage, 1.0). The groups that received mixed injection of HStk fibroblasts and normal fibroblasts had intermediate PVR. Results of histologic study showed no apparent toxic or pathologic reaction in the retinochoroidal tissue of group A animals.

CONCLUSIONS

Severity of experimental PVR clearly was reduced by transfer of the HStk gene and administration of GCV. This inhibitory effect also was produced by a combination of 10% HStk fibroblasts and 90% normal fibroblasts, indicating a significant bystander effect. These data suggest the potential of somatic gene therapy for the treatment of PVR.

The use of genetic marking to assess the interaction of sensitive and multidrug-resistant cells in mixed culture

The interaction of normal (CHO-K1) and multidrug-resistant (Adrr) Chinese hamster ovary cells was examined in mixed monolayer and spheroid culture. In order to assess the individual response of the two cell types in mixed culture, CHO-K1 was genetically marked by transfection with a bacterial beta-galactosidase gene. The enzyme product can be detected histochemically and allows identification of the marked cell line, designated CHO-K1-BG. Following administration of doxorubicin or mitozantrone, there was a large difference in the clonogenic survival of CHO-K1-BG and Adrr, whereas the overall survival of a 50:50 mixture of the two cell lines had intermediate values. When the survival of marked and unmarked colonies from mixed culture was assessed separately, there was no detectable alteration in chemosensitivity. We have found no evidence for interaction of sensitive and multidrug-resistant cells in this system.