In this study, regional therapy of malignant liver tumors with ACN53 will be evaluated 
because of the likelihood that this agent will have both high total body clearance and high 
hepatic extraction. 
1 .3 Role of p53 in Liver Tumors 
The molecular pathogenesis of colorectal cancer is perhaps the best understood of all solid 
tumors. In particular, alteration of the tumor suppressor gene p53, via mutation and/or 
allelic loss, has been demonstrated to be a critical event in colorectal tumorigenesis. 
Because of the important role that p53 normally plays in cell cycle regulation, it is believed 
that loss of wild-type p53 function directly promotes tumorigenesis. At least 75% of 
colorectal cancers involve p53 alteration. 
p53 alterations also occur frequently in hepatocellular cancer. Recent studies indicate that 
30-50% of hepatocellular cancers involve p53 loss or mutation, and these include cancers 
arising in both high- and low-incidence populations. 
Restoration of wild-type p53 function by gene transfer in both colorectal and hepatocellular 
cancer cells in culture and in animal models has resulted in suppression of tumor growth, 
and in some models has resulted in tumor regression via apoptosis(8). 
1 .4 Recombinant Adenoviral Vectors for In Vivo Gene Therapy 
Live, wild-type (non-recombinant) adenoviruses have been used clinically as vaccines for 
the prophylaxis of adenoviral upper respiratory infection, a disease of low morbidity but 
high incidence. These vaccines, which were at one time given routinely to military recruits, 
are well-tolerated and are considered non-oncogenic. Recombinant versions of adenovirus 
have entered clinical trials, also as oral vaccines. Thus far, they too appear to be without 
significant toxicity. Recently, clinical trials using recombinant, replication-defective 
adenoviral vectors for gene therapy have been initiated. In these trials, recombinant 
adenoviral vectors carrying the gene for the cystic fibrosis transmembrane conductance 
regulator (CFTR) are given via intra-airway administration to patients with cystic fibrosis. 
There has been no prior research in human subjects involving the in vivo administration of 
the wild-type p53 gene for gene therapy. 
1.5 Preclinical Studies of ACN53 
ACN53 is a novel antineoplastic agent consisting of a recombinant adenoviral vector 
containing the cloned human wild-type p53 tumor suppressor gene. Several versions of 
recombinant adenoviral vectors containing p53, collectively designated rAd/p53, have been 
constructed. In each of these, the adenoviral vector is derived from adenovirus type 5, a 
common serotype belonging to subgroup C. For ACN53, the vector has been rendered 
replication-defective through deletion of region El, which contains the viral genes El a, 
Elb, and protein IX. It is propagated in the human embryonal kidney cell line 293, which 
contains adenoviral sequences to support replication of the otherwise replication-defective 
ACN53. A cDNA sequence encoding the entire open reading frame of human wild-type 
p53 gene has been inserted into the vector. Expression of p53 is directed by the highly 
efficient human cytomegalovirus immediate early promoter/enhancer element, while 
translation of p53 mRNA is enhanced by the addition of the adenovirus type 2 tripartite 
leader sequence. 
The antineoplastic activity of ACN53 has been studied both in vitro (tumor cells in culture) 
and in vivo (tumor models in animals). In vitro studies using a number of different tumor 
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