Raymond D. Meng

Tumor suppressor gene therapy for cancer: from the bench to the clinic

There is a growing list of possible tumor suppressors that can potentially be used to control cancer cell growth in the clinic. These include p53, Rb, p21, p16, p27, BRCAI and APC, some of which are already in clinical trials, p53 induces apoptosis and suppresses cancer cells containing multiple genetic alterations as well as multidrug-resistant cells, making it a promising and popular target. Other agents such as CDK-inhibitors are generally cytostatic with little evidence for apoptosis. The genetic make-up may help guide a rational therapy of particular tumors. Preclinical studies are exploring combinations of gene therapy and chemotherapy. Some early results are beginning to emerge from clinical trials including those using the E1b-deleted adenovirus that is unique in being a tumor-specific cytotoxic agent for the most common types of cancer.

Growth inhibitory effect of p21 and p53 containing adenoviruses on transitional cell carcinoma cell lines in vitro and in vivo.

Altered p53 expression has been demonstrated in the majority of advanced transitional cell carcinoma (TCC) of the bladder tumors. The objective of this investigation was to examine the effect of the introduction of a p53 or p21((WAF1/CIP1)) adenovirus on the proliferation and apoptosis of various human TCC cell lines in vitro and in vivo. Proliferation was measured by 3H-thymidine incorporation. Apoptosis was measured by DNA fragmentation and bax expression. We also examined the effect of ex vivo introduction of the p21((WAF1/CIP1)) or the p53 gene on growth of the T24 TCC cells and UMUC-3 TCC cells introduced subcutaneously into athymic nude mice. We found that although the effect of the p21-adenovirus on the proliferation of various TCC lines varied with each individual cell line, there was a substantial growth inhibition observed (greater than 80% growth inhibition) in seven of the eight TCC cell lines at the highest viral dosage. In contrast, after 24 h, the highest dosage of the p53-adenovirus produced only a heterogeneous decrease in proliferation compared to the highest dose of the p21((WAF1/CIP1))-adenovirus (40-90%). In ex vivo experiments, no tumors were found in nude mice injected subcutaneously with either TCC cell line exposed in vitro to the AdSCMV-p21((WAF1/CIP1)) or AdSCMV-p53 viruses before three weeks. There was a threefold decrease in tumor square area at week 5 in the Ad5CMV-p21((WAF1/CIP1)) or Ad5CMV-p53 TCC cells injected mice (p<0.001, p<0.009) compared to either mock or Ad5CMVLacZ TCC bladder tumor cells. These data suggest that significant portion of the effect of altered p53 on TCC phenotype may be mediated through the p21((WAF1/CIP1)) pathway. Thus, the restoration of p21((WAF1/CIP1)) function in this tumor system may be a beneficial therapeutic strategy.

“p53: Twenty Years On” in Trieste, Italy, May 20–22, 1999

Study of the p53 tumor suppressor has blossomed into a field of its own. From analysis of its mutations in several different cancers to deciphering the function of the protein in human cells, publications describing research on p53 annually number in the thousands. In the interest of presenting the most up‐to‐date information on the progress of cancer research involving p53, the workshop “p53: Twenty Years On” was organized in Trieste, Italy over May 20–22, 1999. The meeting highlighted some of the most exciting basic and clinical scientific findings on p53 within the last year. J. Cell. Physiol. 181:371–374, 1999.

CHAPTER 17 – Cancer Gene Therapy with Tumor Suppressor Genes Involved in Cell-Cycle Control

This chapter reviews tumor suppressors involved in cell-cycle regulation that have been studied as potential targets for gene replacement in the treatment of cancer. Loss of these tumor suppressors, most notably p53, results in tumor development and progression. p53 mediates the cellular response to DNA damage, resulting in growth arrest or in apoptosis. p21 is a main effector of p53 that mediates growth arrest and is a CDKI, along with p16 and p27, which help to regulate G1 transition. Rb helps to mediate cell-cycle progression from G1 to S phase. In addition, the tumor suppressors BRCA1, VHL, FHIT, and PTEN also suppress growth through novel mechanisms. The apoptosis induced by p53 is based on the activation of select targets. The recently cloned novel TRAIL target KILLER/DR5 and the Fas family of death receptors can be activated by p53 and can induce apoptosis through initiation of a proteolytic caspase cascade. Two other p53-mediated targets involved in apoptosis, bax and the p53-induced genes or (PIGs), initiate cell death through reactive oxygen species.