The p53-independent tumoricidal activity of an adenoviral vector encoding a p27-p16 fusion tumor suppressor gene

P21Waf1/Cip1 and p27Kip1 are correlated with the development and invasion of prolactinoma

Cell cycle control can prevent excessive proliferative response in the pituitary homeostasis. Cyclin dependent kinases (Cdks) are modulated by cyclins or Cdk inhibitors, such as p21 and p27, which can regulate cell cycle progression from the G1 to S phases. This study was conducted to evaluate the levels and the promoter region methylation status of p21 and p27 in prolactinomas (PRL) and analyze their association with clinicopathologic features. We found high-p21 level cases were featured by 5/23 and H-scores 142.3 ± 23.7 in invasive-PRL specimens, and 19/25 and 221.3 ± 45.4 in non-invasive specimens (x² = 14.11, p = 0.000), while high-p27 level cases were featured by 6/23 and H-scores 129.8 ± 31.1 in invasive-PRL specimens, and 18/25 and 197.1 ± 46.6 in non-invasive specimens (x² = 10.11, p = 0.001). A similar trend was also observed for p21 and p27 protein levels in PRL specimens through western-blot (P < 0.01, respectively). The Ki-67 index was much higher in invasive specimens than in non-invasive specimens (x² = 10.10, p = 0.001). Average 33 CpG sites per sample were analyzed by using MALDI-TOF Mass array, and 7/33 CpG sites methylation levels of p27 were higher than 50%. There existed significant differences in 4 CpG sites between invasive specimens and non-invasive specimens (p < 0.01). We found that D2 receptor was closely correlated with p21 levels (P < 0.05, r = 0.567) and p27 levels (P < 0.05, r = 0.591). In PRL, the deficiency in p21 and p27 contributed to the tumor proliferation and migration and Cdk inhibitors may be used as a new therapeutic approach.

Cooperation between Cdk4 and p27kip1 in tumor development: a preclinical model to evaluate cell cycle inhibitors with therapeutic activity

Deregulation of the G1-S transition of the cell cycle is a common feature of human cancer. Tumor-associated alterations in this process frequently affect cyclin-dependent kinases (Cdk), their regulators (cyclins, INK4 inhibitors, or p27Kip1), and their substrates (retinoblastoma protein). Although these proteins are generally thought to act in a linear pathway, mutations in different components frequently cooperate in tumor development. Using gene-targeted mouse models, we report in this article that Cdk4 resistance to INK4 inhibitors, due to the Cdk4 R24C mutation, strongly cooperates with p27(Kip1) deficiency in tumor development. No such cooperation is observed between Cdk4 R24C and p18(INK4c) absence, suggesting that the only function of p18INK4c is inhibiting Cdk4 in this model. Cdk4(R/R) knock in mice, which express the Cdk4 R24C mutant protein, develop pituitary tumors with complete penetrance and short latency in a p27Kip1-/- or p27Kip1+/- background. We have investigated whether this tumor model could be useful to assess the therapeutic activity of cell cycle inhibitors. We show here that exposure to flavopiridol, a wide-spectrum Cdk inhibitor, significantly delays tumor progression and leads to tumor-free survival in a significant percentage of treated mice. These data suggest that genetically engineered tumor models involving key cell cycle regulators are a valuable tool to evaluate drugs with potential therapeutic benefit in human cancer.

Effects of STI571 and p27 gene clone on proliferation and apoptosis of K562 cells

AIM: To investigate the combined effect of STI571 and p27 gene clone on the regulation of proliferation, cell cycle and apoptosis of K562 cell line.

METHODS: p27 gene was obtained by RT-PCR, and its sequence was approved to be correct. Then p27-pcDNA3.1 vector was constructed and transfected into K562 cell line. p27-pcDNA3.1-K562 cell clone was screened by G418 after transfection, p27 protein was identified by Western blot. MTT was used to detect the survival rate of the cell. Flow cytometry was used to detect cell cycle and apoptosis index.

RESULTS: The expression of p27 protein could be detected by Western blot in p27-pcDNA3.1-K562 cells. A strong inhibition of cell proliferation was observed in p27-pcDNA3.1 -K562 cells as compared with that of the control (pcDNA3.1 -K562 cells). The cells at G0/G1 phase were significantly increased, and cells at S phase were greatly declined. The apoptosis index was increased greatly after p27-pcDNA3.1-K562 cells were treated with STI571, and survival rate of the cell was markedly declined (0.35-0.58, P<0.05-0.048 vs STI571-K562 cell, 0.35-0.72, P<0.01-0.001 vs p27-K562 cell).

CONCLUSION: p27 and STI571 have a synergistic action on inhibition of proliferation and induction of apoptosis on K562 cells.

p53-independent induction of p21(waf1/cip1) contributes to the activation of caspases in GTP-depletion-induced apoptosis of insulin-secreting cells

We investigated the role of some key regulators of cell cycle in the activation of caspases during apoptosis of insulin-secreting cells after sustained depletion of GTP by a specific inosine 5'-monophosphate dehydrogenase inhibitor, mycophenolic acid (MPA). p21(Waf1/Cip1) was significantly increased following MPA treatment, an event closely correlated with the time course of caspase activation under the same conditions. MPA-induced p21(Waf1/Cip1) was not mediated by p53, since p53 mass was gradually reduced over time of MPA treatment. The increment of p21(Waf1/Cip1) by MPA was further enhanced in the presence of a pan-caspase inhibitor, indicating that the increased p21(Waf1/Cip1) may occur prior to caspase activation. This notion of association of p21(Waf1/Cip1) accumulation with caspase activation and apoptosis was substantiated by using mimosine, a selective p21(Waf1/Cip1) inducer independent of p53. Mimosine, like MPA, also increased p21(Waf1/Cip1), promoted apoptosis and simultaneously increased the activity of caspases. Furthermore, knocking down of p21(Waf1/Cip1) transfection of siRNA duplex inhibited caspase activation and apoptosis due to GTP depletion. In contrast to p21(Waf1/Cip1), a reduction in p27(Kip1) occurred in MPA-treated cells. These results indicate that p21(Waf1/Cip1) may act as an upstream signal to block mitogenesis and activate caspases which in turn contribute to induction of apoptosis.

Inhibition of adenovirus-mediated p27kip1 gene on growth of esophageal carcinoma cell strain

AIM: To investigate the inhibition of p27kip1 gene on the growth of esophageal carcinoma cell strain (EC9706).

METHODS: Recombinant adenovirus Ad-p27kip1 was constructed and transfected into esophageal carcinoma cell EC-9706, and its effect on p27kip1 expression, the growth of esophageal carcinoma cell, DNA replication, protein synthesis, cell multiplication and apoptosis were explored by means of cell growth count, ³H-TdR, ³H-Leucine incorporation, flow cytometry, DNA fragment analysis and TUNEL.

RESULTS: Recombinant adenovirus Ad-p27kip1 was successfully constructed with a virus titer of 1.24 × 10¹² pfu/mL. p27kip protein expression increased markedly after EC-9706 transfection, while incorporation quantity of ³H-TdR and ³H-Leucine decreased significantly. The growth of esophageal carcinoma cell was inhibited obviously. Testing of flow cytometry displayed a typical apoptosis peak, and DNA gel electrophoresis showed a typical apoptosis ladder. TUNEL showed the apoptosis rate of Ad-p27kip1 group and control group to be 37.3% and 1.26% (P < 0.001) respectively.

CONCLUSION: Ad-p27kip1 can inhibit the growth and multiplication of esophageal carcinoma cells and induce apoptosis. Therefore, enhanced p27kip1 expression may be a new way to treat esophageal carcinoma.

Hybrid yeast-bacteria cloning system used to capture and modify adenoviral and nonviral genomes

Adenoviral vectors are widely used to express transgenes in vitro and in vivo. A major obstacle to the generation of adenoviral vectors is the manipulation of the large (35 kb) adenoviral genome. We developed a hybrid yeast-bacteria cloning system for the creation of novel adenoviral vectors. The adenovirus 5 (Ad5) genome was cloned into a shuttle vector that contains both yeast and bacterial elements for replication and therefore functions as both a yeast artificial plasmid (YAP) and as a plasmid artificial chromosome (PAC). Any sequence can be introduced into any region of the adenoviral genome via the highly efficient homologous recombination in yeast and then these recombinants are rapidly amplified in bacteria. Adenoviral vectors are generated by introduction of the PAC into the appropriate complementing mammalian cell without the need for plaque purification. Vectors were constructed with deletions in the E1, E3, and/or E4 regions. We have generated more than 100 vectors with a number of different transgenes and regulatory elements. In addition, the YAP/PAC vector was used to capture a DNA fragment encompassing the human factor IX gene, demonstrating the utility of this system to clone and analyze genomic DNA. This novel cloning strategy allows the rapid and versatile construction of adenoviral vectors for gene expression and gene therapy applications.

Adenoviral vector-mediated mRTVP-1 gene therapy for prostate cancer

We previously identified the mouse RTVP-1 (mRTVP-1; related to testes-specific, vespid, and pathogenesis proteins) gene as a direct target of p53 with proapoptotic activities in various cancer cell lines, including prostate cancer. To test the therapeutic potential of mRTVP-1 we constructed an adenoviral vector capable of efficient transduction and expression of mRTVP-1 (AdmRTVP-1) and used this vector in an orthotopic, metastatic mouse model of prostate cancer. A single intratumoral administration of AdmRTVP-1 gene therapy significantly reduced primary tumor wet weight compared with control Adbetagal-injected tumors at two time points after injection with two different vector doses (p < or = 0.01 at 7 and 14 days). Spontaneous metastasis to lung was also significantly reduced (p < or = 0.02). Evaluation of treated tumors revealed increased apoptosis and lower microvessel density counts. In a rat aortic ring sprouting assay, AdmRTVP-1 inhibited endothelial cell sprouting compared with Adbetagal, confirming its antiangiogenic activity. These therapeutic activities were associated with a significant increase in survival from 22.9 to 26.8 days (p = 0.003) in this aggressive model of prostate cancer. Interestingly, there were significant increases in the infiltration of tumor-associated macrophages, dendritic cells, and CD8+ T cells, which persisted at 14 days posttreatment in the AdmRTVP-1-treated tumors compared with Adbetagal control-treated tumors. In addition, significantly increased natural killer and cytotoxic T lymphocyte activities were demonstrated in the mice with AdmRTVP-1-treated tumors. The unique therapeutic properties of AdmRTVP-1 gene therapy demonstrated in this study provide new opportunities for gene and immunotherapy of prostate cancer and potentially other malignancies.

Adenovirus-mediated gene transfer of P16INK4/CDKN2 into bax-negative colon cancer cells induces apoptosis and tumor regression in vivo

The tumor-suppressor gene p16INK4/CDKN2 (p16) is a cyclin-dependent kinase (cdk) inhibitor and important cell cycle regulator. Here, we show that adenovirus-mediated gene transfer of p16 (AdCMV.p16) into colon cancer cells induces uncoupling of S phase and mitosis and subsequently apoptosis. Flow cytometric analysis revealed that cells infected with AdCMV.p16 showed an initial G2-like arrest followed by S phase without intervening mitosis (DNA >4N). Using microscopic analysis, deformed polyploid cells were detectable only in cells infected with AdCMV.p16 but not in control-infected cells. Subsequently, AdCMV.p16-infected polyploid cells underwent apoptosis, as assessed by AnnexinV staining and DNA fragmentation, suggesting that cell cycle dysregulation is upstream of the onset of apoptosis. Treatment of mice with subcutaneously transplanted tumors of colorectal cancer cells with AdCMV.p16 but not AdCMV.p53 resulted in significantly reduced tumor volume and prolonged survival. Using an orthotopic model of liver metastasis, we observed both reduced local tumor growth and secondary intrahepatic metastasis after AdCMV.p16 treatment. Importantly, induction of apoptosis in vitro and reduction of tumor growth in vivo by p16 was p53- as well as bax-independent because identical results were obtained using cancer cells, either wild type or mutant for p53 or bax. The studies suggest that an AdCMV.p16-based treatment may be especially effective in patients with bax-negative colon cancer where overexpression of p53 appears not to be of therapeutic value.

Cancer gene therapy: fringe or cutting edge?

Direct targeting of cancer cells with gene therapy has the potential to treat cancer on the basis of its molecular characteristics. But although laboratory results have been extremely encouraging, many practical obstacles need to be overcome before gene therapy can fulfil its goals in the clinic. These issues are not trivial, but seem less formidable than the challenge of killing cancers selectively and rationally--a challenge that has been successfully addressed.

Design of new anticancer therapies targeting cell cycle checkpoint pathways

The mammalian cell cycle is exquisitely controlled by the cyclin-dependent kinases, which regulate cell cycle progression. Cell cycle transitions are, in turn, controlled by checkpoints that monitor the integrity and replication status of the genetic material before cells commit to either replicate or segregate their DNA. On activation, checkpoints interface with cyclin-Cdk complexes to block the cell cycle. Pharmacologic compounds that exploit our current knowledge of cell cycle and checkpoint pathway regulation offer insights into the development of novel therapeutic strategies.

p27-p16 fusion gene inhibits angioplasty-induced neointimal hyperplasia and coronary artery occlusion

Inhibition of proliferative neointima formed by vascular smooth muscle cells is a potential target in preventing angioplasty-induced restenosis. We have created a potent antiproliferative by fusing the active regions of the p27 and p16 cell cycle inhibitors. Intravascular delivery of a replication-deficient adenoviral vector (AV) encoding this p27-p16 fusion protein, named W9, inhibited balloon injury-induced neointimal hyperplasia in rabbit carotid arteries. In a therapeutically more relevant model, AV-W9 was delivered to balloon-injured porcine coronary arteries in vivo using an infusion catheter. Of the three coronary arteries, two were injured with a 15-mm balloon catheter and either were left untreated or were treated with 10(12) viral particles of either AV-W9 or a control null virus. AV-W9 treatment significantly inhibited neointimal hyperplasia in this porcine arterial balloon injury model compared with untreated or control virus-treated vessels. The average intimal area of the AV-W9-treated group 10 days after balloon injury and treatment was 0.42+/-0.36 mm(2), whereas the AV-null group demonstrated an intimal area of 0.70+/-0.52 mm(2). At day 10 the average intimal thickness of the AV-W9-treated vessels was 9.1 microm (n=5, x 20 magnification) compared with 21.2 microm (n=5, x 20 magnification) in control virus-treated vessels. This trend was also observed at 28 days after balloon injury and gene transfer during which AV-W9-treated vessels demonstrated an average intimal thickness of 4.7 microm (n=8, x 20 magnification) compared with 13.3 microm (n=3, x 20 magnification) in control virus-treated vessels and 7.3 microm (n=5, x 20 magnification) in the sham-treated vessels. The AV-W9 treatment was safe and well tolerated. These data suggest that AV-W9 gene therapy may be useful in preventing angioplasty-induced intimal hyperplasia in the coronary artery.

p27(Kip1): regulation and function of a haploinsufficient tumor suppressor and its misregulation in cancer

A major function of p27, also known as Kip1, is to bind and inhibit cyclin/cyclin-dependent kinase complexes, thereby blocking cell cycle progression. As p27 operates at the heart of the cell cycle, it is perhaps not surprising that it is emerging as a key player in multiple cell fate decisions including proliferation, differentiation, and cell death. The central role of p27 makes it important in a variety of disease processes that involve aberrations in cellular proliferation and other cell fates. Most notable among these processes is neoplasia. A large number of studies have reported that p27 expression is frequently downregulated in human tumors. In most tumor types, reduced p27 expression correlates with poor prognosis, making p27 a novel and powerful prognostic marker. In addition to these practical implications, murine and tissue culture models have shown that p27 is a potent tumor suppressor gene for multiple epithelially derived neoplasias. Loss of p27 cooperates with mutations in several oncogenes and tumor suppressor genes to facilitate tumor growth, indicating that p27 may be a "nodal point" for tumor suppression. In contrast to most tumor suppressor genes studied to date, which are recessive at the cellular level, p27 is haploinsufficient for tumor suppression. The fact that tumor suppression by p27 is critically dependent on the absolute level of p27 expression indicates that p27 acts as a rheostat rather than as an on/off switch to control growth and neoplasia.