The Genesis of Gendicine: The Story Behind the First Gene Therapy

In this BioPharm International exclusive interview, SiBiono's founder relates the science and manufacture of his company's innovative cancer therapy.
May 01, 2004
By BioPharm International Editors
Volume 17, Issue 5

In October 2003, Shenzhen SiBiono GeneTech made history by becoming the first company approved to market a gene therapy medication. China's State Food and Drug Administration (SFDA) approved Gendicine for treatment of head and neck squamous cell carcinoma (HNSCC). SiBiono believes that continued clinical trials will prove Gendicine to be effective as a wide-spectrum anticancer agent.

In March, BioPharm International interviewed Dr. Zhaohui Peng, SiBiono's founder, chairman, and CEO, to learn more about the science behind gene therapy, the clinical experience with Gendicine, and the processes involved in manufacturing this ground-breaking new therapy. An English translation of "Points to Consider for Human Gene Therapy and Product Quality Control," a technical guide for gene therapy research, development, and commercialization written by SiBiono and adopted by the SFDA, can be found

Table 1. Production Apparatus Comparison
In addition to a distinguished academic career, Dr. Peng served as director of a research institute at The First Medical University in Guangzhou and as a visiting professor at both the University of Chiba in Japan and the University of California. He also conducted research at two US biotech companies. Dr. Peng has devoted more than ten years to gene therapy research, development, and commercialization.

GENE THERAPY BASICS BPI: You have used the term adenoviral vector +p53 tumor suppressor-gene delivery system. Will you briefly describe the science behind this?

Peng: Gendicine is a gene therapy product. To be more specific, it is a replication-incompetent, recombinant, human adenovirus of serotype 5 engineered to contain the human wild-type p53 tumor-suppressor gene. The Ad5-p53 virus particles are approximately 90 nm in diameter.

Gendicine is produced using SBN-Cel, which is a cell line that was subcloned from the human embryonic kidney (HEK) cell line 293. Gendicine is a sterile, slightly-white-to-clear liquid. A Gendicine vial contains 1 x 1012 viral particles in 1 mL of WFI (water for injection) buffered with Tris (made by Amresc) and glycerol. We store it frozen in a single-use vial at -20°C.

BPI: What is the role of the p53 gene?

Peng: The p53 gene is one of the most important tumor-suppressor genes existing in normal cells. In normal cells, the expression level of p53 protein is very low. p53 expression is activated upon oncogene activation, growth-factor deprivation, hypoxia, and DNA damage. The upregulation of p53 gene expression occurs at the posttranslational level and is achieved through stabilization of the expressed protein. The activation of p53 gene expression results in either cell cycle arrest or apoptotic cell death.

Table 2. The Initial Clinical Stage of Patients with HNSCC
The p53 gene is mutated or deleted (null) in approximately 50% to 70% of human tumors. Mutant forms of the p53 gene are not necessarily inactive and can gain oncogenic functions that contribute to tumorigenicity. Most importantly, mutant p53 proteins have been associated with the upregulation of the multidrug resistance (MDR) gene, which results in tumor resistance to a variety of chemotherapeutics. Introduction of exogenous wild-type p53 gene and subsequent over-expression of the p53 protein has been shown to control and eliminate tumor cell growth by growth cycle arrest or apoptosis. In addition, over-expresion of wild-type p53 protein has been demonstrated to have a synergistic effect with radiotherapy and chemotherapy.

BPI: What role does the adenoviral vector play?

Peng: Upon intratumor injection, Gendicine binds to the coxsakie adenovirus receptor (CAR) on tumor cells. Subsequently, Gendicine enters tumor cells via receptor-mediated endocytosis and begins to over-express the encoded exogenous p53 gene. The over-expressed p53 protein triggers multiple tumor fighting functions.

First, it induces tumor cell cycle arrest or apoptosis by functioning as a sequence-specific transcriptional-regulator that up-regulates the expression of some anticancer genes and downregulates the expression of some oncogenes.

Second, it can directly induce tumor cell apoptosis.

Table 3. Comparison of Tumor Shrink Rates
Third, it can function as a tumor-antigen by stimulating human immune cells (cytotoxic T cells) to selectively kill cancer cells that over-express the p53 gene. It can also activate natural killer cells to kill uninfected cancer cells via bystander effects.

Fourth, the expressed p53 protein can downregulate the expression of vascular endothelial growth factor (VEGF) genes and MDR genes, which are involved in tumor progress, metastasis, and chemo-drug resistance. The expression of p53 gene is not activated in normal cells because its DNA is undamaged, thus minimizing the side effects of Gendicine treatment.

SiBiono and New Brunswick Scientific
MATTERS OF SAFETY BPI: What are the results of toxicity tests with Gendicine?

Peng: Two groups of rhesus monkeys received intramuscular injections of Gendicine, based on weight, at doses 7.5-fold and 75-fold the proposed clinical dose for 16 successive days. On the 14th day, a neutralizing antibody to Gendicine appeared in all animal sera. A mild pathological effect was observed in kidney tissues in 2 out of the 12 animals at the end of the study. Gendicine can be detected in lung, liver, and kidney tissues by polymerase chain reaction (PCR) analysis. The expressed exogenous p53 protein can be detected by immunohistochemistry analysis in the intestines, lungs, bladders, and kidneys. At three weeks postinjection, the p53 gene and the expressed p53 protein were still detectable in the above-mentioned organs and tissues.

BPI: Did you conduct any genetic toxicology tests?

Peng: In our tests, no genetic toxicity was observed. Results from both a Chinese hamster lung (CHL) cell-chromosome-aberration test and mouse bone-marrow micronucleus assay were negative. Gendicine will not replicate in the infected cells and is incapable of multi-cycle infection and of spreading to the neighboring cells. Therefore, Gendicine will not cause horizontal adenovirus infection or environmental contamination. More importantly, infected adenoviral DNA will not integrate into the human host cell genome. Consequently, Gendicine poses no genetic toxicity.

BPI: What are the distribution and pharmacokinetic parameters?

Peng: In vivo animal studies demonstrated that Gendicine entered tumor cells within one hour after injection, whether administrated locally or systemically. A detectable amount of p53 protein is expressed from the transduced p53 gene at three hours postinjection. The level of p53 protein expression increased to 47% at the 12th hour, reached the highest level (100%) at the 72nd hour, and subsequently descended to 30% at the 120th hour postinjection. However, a detectable amount of p53 protein expression was still observed at the 14th day. At three weeks postinjection, recombinant Gendicine DNA began to diminish and eventually became undetectable. When injected locally, Gendicine is distributed mainly in the local tissues with minimal distribution in other organs and tissues. No Gendicine DNA was detected in excrements of urine, stool, or bile.

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