The p53 tumor suppressor gene and members of the transforming growth factor-␤ (TGF-␤) superfamily play central roles in signaling cell cycle arrest and apoptosis (programmed cell death) in normal development and differentiation, as well as in carcinogenesis. Here we describe a distantly related member of the TGF-␤ superfamily, designated placental TGF-␤ (PTGF-␤), that is upregulated in response to both p53-dependent and -independent apoptotic signaling events arising from DNA damage in human breast cancer cells. PTGF-␤ is normally expressed in placenta and at lower levels in kidney, lung, pancreas, and muscle but could not be detected in any tumor cell line studied. The PTGF-␤ promoter is activated by p53 and contains two p53 binding site motifs. Functional studies demonstrated that one of these p53 binding sites is essential for p53-mediated PTGF-␤ promoter induction and specifically binds recombinant p53 in gel mobility shift assays. PTGF-␤ overexpression from a recombinant adenoviral vector (AdPTGF-␤) led to an 80% reduction in MDA-MB-468 breast cancer cell viability and a 50 -60% reduction in other human breast cancer cell lines studied, including MCF-7 cells, which are resistant to growth inhibition by recombinant wild-type p53. Like p53, PTGF-␤ overexpression was seen to induce both G 1 cell cycle arrest and apoptosis in breast tumor cells. These results provide the first evidence for a direct functional link between p53 and the TGF-␤ superfamily and implicate PTGF-␤ as an important intercellular mediator of p53 function and the cytostatic effects of radiation and chemotherapeutic cancer agents.

Targeting therapeutic gene expression to tumor cells represents a major challenge for cancer gene therapy. The strong transcriptional response exhibited by heat shock genes, along with the beneficial therapeutic effects of hyperthermia have led us to develop a heatdirected gene -targeting strategy for cancer treatment. Heat shock gene expression is mediated in large part by the interaction of heat shock factor 1 with specific binding sites ( heat shock elements; HSE ) found in the promoters of heat -inducible genes. Here we present a quantitative analysis of heat -inducible gene expression mediated by the wild -type hsp70b gene promoter, as well as a modified hsp70b promoter containing additional HSE sequences. -Galactosidase ( -gal ) expression was induced between 50 -and 800 -fold in a panel of human breast cancer cell lines infected with an adenoviral vector containing the wild -type hsp70b promoter ( Ad.70b. g ) following treatment at 438C for 30 minutes. Infection with an adenoviral vector containing the modified hsp70b promoter ( Ad.HSE.70b. g ) resulted in a 200 -to 950 -fold increase in -gal expression under the same conditions, and also provided a 1 ± 28C decrease in the threshold of activation. Significant increases in the heat responsiveness of the Ad.HSE.70b. g construct were observed in five of six tumor cell lines tested, as well as under thermotolerant conditions. Finally, we demonstrate that localized heating of a HeLa cell xenograft can effectively target -gal gene expression following intratumoral injection of Ad.70b. g. Adenoviral vectors incorporating heat -inducible therapeutic genes may provide useful adjuncts for clinical hyperthermia. Cancer Gene Therapy ( 2000 ) 7, 1566 ± 1574

The development of resistance to radiation and chemotherapeutic agents that cause DNA damage is a major problem for the treatment of breast and other cancers. The p53 tumor suppressor gene plays a direct role in the signaling of cell cycle arrest and apoptosis in response to DNA damage, and p53 gene mutations have been correlated with increased resistance to DNA-damaging agents. Herpes simplex virus thymidine kinase (HSV-tk) gene transfer followed by ganciclovir (GCV) treatment is a novel tumor ablation strategy that has shown good success in a variety of experimental tumor models. However, GCV cytotoxicity is believed to be mediated by DNA damage-induced apoptosis, and the relationship between p53 gene status, p53-mediated apoptosis, and the sensitivity of human tumors to HSV-tk/GCV treatment has not been firmly established. To address this issue, we compared the therapeutic efficacy of adenovirusmediated HSV-tk gene transfer and GCV treatment in two human breast cancer cell lines: MCF-7 cells, which express wild-type p53, and MDA-MB-468 cells, which express high levels of a mutant p53 (273 Arg-His). Treating MCF-7 cells with AdHSV-tk/GCV led to the predicted increase in endogenous p53 and p21 WAF1/CIP1 protein levels, and apoptosis was observed in a significant proportion of the target cell population. However, treating MDA-MB-468 cells under the same conditions resulted in a much stronger apoptotic response in the absence of induction in p21 WAF1/CIP1 protein levels. This latter result suggested that HSV-tk/GCV treatment can activate a strong p53-independent apoptotic response in tumor cells that lack functional p53. To confirm this observation, four additional human breast cancer cell lines expressing mutant p53 were examined. Although a significant degree of variability in GCV chemosensitivity was observed in these cell lines, all displayed a greater reduction in cell viability than MCF-7 or normal mammary cells treated under the same conditions. These results suggest that endogenous p53 status does not correlate with chemosensitivity to HSV-tk/GCV treatment. Furthermore, evidence for a p53-independent apoptotic response serves to extend the potential of this therapeutic strategy to tumors that express mutant p53 and that may have developed resistance to conventional genotoxic agents.