The p53 tumor suppressor gene in breast cancer

Summary Alterations of the p53 tumor suppressor gene are the most common genetic changes found so far in breast cancer, suggesting that the gene plays a central role in the development of the disease. p53 functions as a negative regulator of cell growth, and alterations in the gene lead to loss of this negative growth regulation and more rapid cell proliferation. A number of independent groups using different methods of detection have shown that p53 alterations are associated with more aggressive tumor biologic factors and a poorer prognosis in breast cancer patients. Because of its possible role in the regulation of apoptosis and response to DNA damage, p53 status could also be a predictive marker for response to hormonal or chemotherapy.     

A case of advanced non-small lung cancer responding to tumor suppressor p53 gene therapy

The phase I study of the tumor suppressor p53 gene therapy for advanced lung cancer was performed. A 57-year-old man with locally advanced squamous cell carcinoma at the tracheal bifurcation, clinical stage IIIB, had previously been treated by radiotherapy and chemotherapy. Because of the local recurrence, he was enrolled to the study. He was treated by a local injection of ADVEXIN once every 4 weeks for 14 times without marked adverse events, which resulted in tumor regression and relief of his symptom for a year. In conclusion, gene therapy with ADVEXIN may be an effective treatment for locally advanced non-small lung cancer.     

Intracerebral adenovirus-mediated p53 tumor suppressor gene therapy for experimental human glioma.

Malignant gliomas of astrocytic origin are good candidates for gene therapy because they have proven incurable with conventional treatments. Although mutation or inactivation of the p53 tumor suppressor gene occurs at early stages in gliomas and is associated with tumor progression, many tumors including high-grade glioblastoma multiforme carry a functionally intact p53 gene. To evaluate the effectiveness of p53-based therapy in glioma cells that contain endogenous wild-type p53, a clinically relevant model of malignant human glioma was established in athymic nu/nu mice. Intracerebral, rapidly growing tumors were produced by stereotactic injection of the human U87 MG glioma cell line that had been genetically modified for tracking purposes to express the Escherichia coli lacZ gene encoding beta-galactosidase. Overexpression of the p53 gene by adenovirus-mediated delivery into the tumor mass resulted in rapid cell death with the eradication of beta-galactosidase-expressing glioma cells through apoptosis. In long-term experiments, the survival of mice treated with the p53 adenoviral recombinant was significantly longer than that of mice that had received control adenoviral recombinant. During the observation period of 1 year, a complete cure was achieved in 27% of animals after a single injection of p53 adenoviral recombinant, and 38% of the animals were tumor free in the group receiving multiple injections of p53 adenoviral recombinant into a larger tumor mass. These experiments demonstrate that overexpression of p53 in gliomas, even in the presence of endogenous functional wildtype p53, leads to efficient elimination of tumor cells. These results point to the potential therapeutic usefulness of this approach for all astrocytic brain tumors.     

Intraperitoneal gene therapy with adenoviral-mediated p53 tumor suppressor gene for ovarian cancer model in nude mouse

In an effort to develop a method for better local control of advanced ovarian cancers, we have established a peritoneal tumor model of ovarian cancer in the nude mouse and applied intraperitoneal gene therapy with the recombinant adenoviral-mediated wild-type p53 tumor suppressor gene (Avp53). The results indicate that: (a) the recombinant adenoviral vector system effectively infected the tumor and normal cells in the peritoneal cavity; and (b) Avp53 treatment effectively suppressed the growth of peritoneal tumors and prolonged the survival of the treated group, especially when the tumor burden was less. These results suggest that intraperitoneal gene therapy using Avp53 is potentially useful as an adjuvant therapeutic modality in human ovarian cancer.     

In vitro and in vivo adenovirus-mediated p53 and p16 tumor suppressor therapy in ovarian cancer.

PURPOSE: The objectives of this study were to determine the effects of adenovirus-mediated p16 and p53 on growth and apoptosis in ovarian cancer cells and on survival in nude mice implanted with human ovarian cancer cells. EXPERIMENTAL DESIGN: SKOV-3 ip1 (p53 and p16 null), 2774 (p53 and p16 mutant), and OVCA 420 (p53 and p16 wild-type) cells were used for in vitro studies. SKOV-3 ip1, 2774, and Hey A8 (p53 and p16 wild-type) cells were used in the nude mouse studies. The E1-deleted adenoviruses containing p53, p16, or beta-galactosidase cDNA were transfected into the different cell types or inoculated into the nude mice after injection with ovarian cancer cells. RESULTS: Cell counting, microtetrazolium, and anchorage-independent growth assays on transfected cells demonstrated that p16 and the p16/p53 combination suppressed growth, whereas p53 did not (except in the anchorage-independent growth assay). Although cells infected with the p16/p53 combination had decreased growth compared with cells infected with either tumor suppressor alone, the difference was only statistically significant compared with p53. p16, p53, and the p16/p53 combination all increased apoptosis in the cells. In the nude mice, p16 treatment resulted in the longest survival for all three models, although it only reached statistical significance for the 2774 and SKOV-3 ip1 groups. CONCLUSIONS: Overall, p16 demonstrated greater growth inhibition than p53 both in vivo and in vitro. The p16/p53 combination demonstrated a consistent trend toward increased growth suppression and apoptosis over p16 or p53 alone. Adenovirus-mediated p16 may be a viable future treatment for ovarian cancer.     

Dysfunction of the p53 tumor suppressor pathway in head and neck cancer

It is important to examine the abnormality of the entire p53 tumor suppressor pathway in head and neck cancer. We examined the mRNA expressions of p53 regulatory factors, p33ING1 and p14ARF, and a p53-target gene, p21WAF1 in head and neck cancer. Nine of 14 benign pleomorphic adenomas (PAs) and 7 of 8 malignant salivary gland tumors (MSGTs) expressed p33ING1 mRNA. Thirteen of 14 PAs expressed p14ARF mRNA, however, only 1 of 8 MSGTs expressed p14ARF mRNA. Eight of 14 PAs and 7 of 8 MSGTs expressed p21WAF1 mRNA. In salivary gland tumors, there was clear correlation between the expression of p33ING1 and p21WAF1 (p<0.0001, r2=0.53). However, there was no correlation between the expression of p14ARF and p21WAF1 (p=0.6543, r2=0.009). Twenty-six of 28 oral squamous cell carcinomas (SCCs) expressed p33ING1 mRNA. Nineteen of 28 oral SCCs expressed p14ARF mRNA. All of the oral SCCs expressed p21WAF1 mRNA. In oral SCCs, the expressions of both p33ING1 (p=0.009, r2=0.181) and p14ARF (p=0.0009, r2=0.271) correlated with the expression of p21WAF1. Interestingly, 24 of 26 oral SCCs (92%) showed either abnormality of p53 itself or loss of expression of p53 regulatory factors, p33ING or p14ARF. These results suggest that head and neck cancer often involve the dysfunction of p53 tumor suppressor pathway.     

Germ line polymorphisms of the tumor suppressor gene p53 and lung cancer

Two p53 variable sites (BstUI and MspI SNPs in exon 4 and intron 6, respectively) and their haplotype combinations were studied in 109 patients (84 males and 25 females) with lung cancer and 113 healthy controls from the region of Eastern Slovakia. There were no differences found between lung cancer patients and controls carrying the distribution of p53 BstUI and MspI alleles. However, the genotype distribution showed a significantly higher proportion of MspI heterozygotes in lung cancer patients (P=0.048, OR 1.83, 95% CI 1.00-3.34) than in controls. The analysis based on haplotype frequencies showed the presence of BstUI-MspI 2-1 haplotype in cancer patients (5.4%) in contrast to the absence of this haplotype in healthy controls. The results of this study suggest that the p53 MspI polymorphism may modify the susceptibility to lung cancer as a single factor rather than in combination with BstUI polymorphism.     

Mutations in the p53 tumor suppressor gene and early onset breast cancer

Among breast cancer patients p53 gene mutation is associated with a poor prognosis. Young women with breast cancer are more likely than older women to have a poor prognosis, but whether p53 gene mutation plays a role in breast cancer in young women is not clear. This study identified 199 breast cancer patients and tested the hypothesis that p53 gene mutation was associated with early onset breast cancer. Patients with p53 gene mutations were 3-times more likely to have an early onset breast cancer (age < or = 40 years at diagnosis) than those without p53 mutations (OR = 3.05, 95% CI = 1.10-8.45). Patients with both missense and silent mutations were 7-times more likely to have a diagnosis of early onset breast cancer (OR = 7.56, 95% CI = 2.22-25.8). Patients with mutations in exon 8 of the p53 gene were 6-times more likely to be diagnosed with early onset breast cancer (OR = 6.48, 95% CI = 1.37-30.6). These findings suggest that p53 gene mutation may hasten the onset of female breast cancer.     

Multiple roles of the tumor suppressor p53.

The tumor suppressor p53 controls numerous downstream targets that can result in variable outcomes, including apoptosis, transient growth arrest, and sustained growth arrest or senescence. The activation of p53, followed by its ability to play multiple roles in the control of genomic integrity or the elimination of damaged or tumorigenic cells, is performed by a complex process of cross-talk orchestrated to occur in the different compartments of the cell. Controlling performance of the many roles of p53 is a goal of many research groups and the focus of this review.     

Dissecting p53 tumor suppressor functions in vivo

Although the p53 tumor suppressor acts in a plethora of processes that influence cellular proliferation and survival, it remains unclear which p53 functions are essential for tumor suppression and, as a consequence, are selected against during tumor development. Using a mouse model harboring primary, genetically modified myc-driven lymphomas, we show that disruption of apoptosis downstream of p53 by Bcl2 or a dominant-negative caspase 9 confers-like p53 loss-a selective advantage, and completely alleviates pressure to inactivate p53 during lymphomagenesis. Despite their p53-null-like aggressive phenotype, apoptosis-defective lymphomas that retain intact p53 genes do not display the checkpoint defects and gross aneuploidy that are characteristic of p53 mutant tumors. Therefore, apoptosis is the only p53 function selected against during lymphoma development, whereas defective cell-cycle checkpoints and aneuploidy are mere byproducts of p53 loss.     

乳腺癌组织突变型p53和抑癌基因PTEN表达及其临床意义的研究

目的：探讨乳腺癌中是否存在突变型p53的过度表达和抑癌基因PTEN的失活,及其对预后的影响。方法：SP免疫组化法检测260例乳腺癌患者中突变型p53和PTEN的表达情况。结果：乳腺癌中突变型p53阳性率44．62％（116／260）,阳性患者5年生存率（52．59％）低于阴性患者（65．97％）,差异有统计学意义,χ^2=4．26,P=0．039。抑癌基因PTEN的阳性率为69．23％,阳性患者5年生存率（65．00％）高于PTEN阴性患者（48．75％）,差异有统计学意义,χ^2=5．44,P=0．0197。抑癌基因PTEN与突变型p53共同阳性69例,共同阴性33例,两者之间呈负相关,χ^2=25．924,P=0．0000。结论：p53基因的突变和PTEN基因的失活可能与乳腺癌发生密切相关,且均与预后相关,可作为预后评估指标之一。     

Altered expression of p53 and Rb tumor suppressor genes in lung cancer

The aim of this study was to evaluate the frequency of altered expression of pRb and p53, two well known tumor suppressor genes, in lung cancer and to relate it to the prognosis of the patients affected by this type of neoplasm. We evaluated 68 specimens from patients with surgically resected lung cancer. Of the 68 neoplasms investigated, 29 (42.6%) displayed a positive nuclear staining for p53. Ten (15.7%) of the investigated tumors showed absence of pRb nuclear immunoreactivity. p53 overexpression correlated statistically with short-term survival. On the other hand no statistically significant difference (p=ns) in survival was detected between pRb producers and nonproducer patients. In addition, we divided our specimens into two groups according to the p53 and pRb status. The first group consisted of all the p53(+) pRb specimens. The second group contained all the remaining specimens. Comparison between these two groups did not reveal any significant difference in overall survival time. These findings confirm that only p53 overexpression can be considered an independent prognostic factor in lung cancer.     

Evidence for nonautonomous effect of p53 tumor suppressor in carcinogenesis

Prostate, breast, and probably other epithelial tumors harbor inactivating mutations in the p53 tumor suppressor gene in the stromal cells, implying the nonautonomous action of p53 in carcinogenesis. We have tested this hypothesis by evaluating the tumorigenicity of MCF7 human breast cancer cells in severe combined immunodeficient mice that differ in their p53 status. Our results showed that, indeed, p53 ablation in the hosts reduced the latency for the development of MCF7 tumors. Furthermore, we show that heterozygous hosts frequently undergo loss of heterozygosity at the p53 locus in the tumor stroma tissue by mechanism that resembles the inactivation of p53 in primary tumors. To evaluate the impact of p53 ablation in the stromal fibroblasts, in tumorigenesis, tumors were reconstituted in mice bearing wild-type p53 alleles, by mixing MCF7 cells with fibroblasts isolated from mutant or wild-type p53 mice. Our results suggest that tumors containing p53-deficient fibroblasts developed faster and were more aggressive than their counterparts with wild-type fibroblasts, although their neoplastic component, namely MCF7 mammary carcinoma cells, was identical in both cases. These data strongly support the notion for the operation of a nonautonomous mechanism for p53 action in primary tumors and provide a mechanistic association between p53 mutations in the stromal component of epithelial tumors and carcinogenesis.