Adenovirus-mediated p53 gene transfer in advanced non-small-cell lung cancer

Gene therapy for mesothelioma and lung cancer

Both malignant pleural mesothelioma and advanced stage lung cancer are associated with a poor prognosis. Unfortunately, current treatment regimens have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in a number of clinical trials over the last two decades. Using viral vectors or anti-sense RNA, strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review will consider the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

Experimental study of antiangiogenic gene therapy targeting VEGF in oral cancer

It is well known that tumor angiogenesis plays an important role in local growth and metastasis of oral cancer; therefore, inhibiting angiogenesis is considered to be effective for treating oral cancer. This study aimed to investigate the effectiveness of systemically available antiangiogenic gene therapy targeting vascular endothelial growth factor (VEGF), which is one of the most important angiogenesis accelerators. We administered a soluble form of VEGF receptor-expressing gene incorporated into adenovirus (AdVEGF-ExR) intraperitoneally to nude mice to which oral cancer cell lines (SAS, HSC-3, and Ca9-22) had been transplanted subcutaneously in vivo to inhibit angiogenesis and tumor proliferation. Then, we measured tumor volumes over time, and tumors were enucleated and examined histopathologically and immunohistologically at 28 days after AdVEGF-ExR administration. Compared to the controls to which we administered AdLacZ or saline, significant antiproliferative effects were observed (P < 0.05) in the AdVEGF-ExR administration group, and extensive tumor necrosis was found histopathologically. Immunohistochemical analysis with CD34 (NU-4A1) revealed tumor angiogenesis was suppressed significantly (P < 0.05), and that with ssDNA revealed apoptosis induction was significantly high (P < 0.05) in the AdVEGF-ExR group. However, analysis with Ki-67 (MIB-1) revealed tumor proliferative capacity was not significantly different between the groups. Consequently, we consider that AdVEGF-ExR administration achieved tumor growth suppression by inhibiting angiogenesis and inducing apoptosis, but not by inhibiting the proliferative capacity of tumor cells. Neither topical administration of a soluble form of VEGF receptor (sVEGFR) to the tumor nor a megadose was needed to achieve this inhibition effect. These results suggest gene therapy via sVEGFR would be an effective oral cancer therapy and benefit future clinical applications.

Viral shedding after p53 adenoviral gene therapy in 10 cases of esophageal cancer

We detected adenoviral DNA fragments in excretions of 10 esophageal cancer patients by DNA-PCR after tumor injection of Ad-CMV-vector. A total of 220 samples consisting of feces, gargling saliva, urine, and blood plasma were assessed. A total of 29.7% of feces samples and 13.2% of gargling saliva samples were positive for adenoviral DNA fragments, but 89.7% of the positive feces samples and all of the positive gargling saliva samples turned negative on day 12 after tumor injection. Although adenoviral DNA fragments may be pathogen-free, patients' feces and gargling saliva contain adenoviral DNA fragments for 12 days after injection.

Silk-elastinlike protein polymer hydrogels for localized adenoviral gene therapy of head and neck tumors

Vector dissemination, transient gene expression, and rapid clearance are major obstacles to successful human gene therapy. In this study, we investigated the effect of silk-elastinlike protein polymer (SELP) hydrogels on biodistribution and anticancer efficacy of adenoviral gene therapy in a head and neck cancer model. Transcriptional activities of adenovirus carrying beta-galactosidase (Ad-LacZ) and luciferase (Ad-Luc) reporter genes were evaluated in (nu/nu) mice with head and neck cancer as a function of polymer concentration. Antitumor efficacy of thymidine kinase encoding adenovirus (Ad-Tk) and ganciclovir (GSV) combination was also evaluated. SELP (4 wt %) matrices localized viral release, minimized dissemination to liver, and enhanced reporter gene expression levels by 4-8-fold compared to virus alone. SELP- Ad-Tk with GSV reduced tumor volume significantly compared to the virus alone. SELPs provide a means for temporal and spatial control of viral gene delivery to head and neck tumors.

Restoration of wild-type p53 function in human tumors: strategies for efficient cancer therapy

The p53 tumor suppressor gene is mutated in around 50% of all human tumors. Most mutations inactivate p53's specific DNA binding, resulting in failure to activate transcription of p53 target genes. As a consequence, mutant p53 is unable to trigger a p53-dependent biological response, that is cell cycle arrest and apoptosis. Many tumors express high levels of nonfunctional mutant p53. Several strategies for restoration of wild-type p53 function in tumors have been designed. Wild-type p53 reconstitution by adenovirus-mediated gene transfer has shown antitumor efficacy in clinical trials. Screening of chemical libraries has allowed identification of small molecules that reactivate mutant p53 and trigger mutant p53-dependent apoptosis. These novel strategies raise hopes for more efficient cancer therapy.

Sampling-rate-dependent probabilistic Boolean networks

External control of a genetic regulatory network is used for the purpose of avoiding undesirable states, such as those associated with a disease. To date, intervention has mainly focused on the external control of probabilistic Boolean networks via the associated discrete-time discrete-space Markov processes. Implementation of an intervention policy derived for probabilistic Boolean networks requires nearly continuous observation of the underlying biological system since precise application requires the observation of all transitions. In medical applications, as in many engineering problems, the process is sampled at discrete time intervals and a decision to intervene or not must be made at each sample point. In this work, sampling-rate-dependent probabilistic Boolean network is proposed as an extension of probabilistic Boolean network. The proposed framework is capable of capturing the sampling rate of the underlying system.

Adenovirus-mediated wild-type p53 gene transfer in combination with bronchial arterial infusion for treatment of advanced non-small-cell lung cancer, one year follow-up

OBJECTIVE

In the present study, we have examined the safety and efficacy of recombinant adenovirus encoding human p53 tumor suppressor gene (rAd-p53) injection in patients with advanced non-small-cell lung cancer (NSCLC) in the combination with the therapy of bronchial arterial infusion (BAI).

METHODS

A total of 58 patients with advanced NSCLC were enrolled in a non-randomized, two-armed clinical trial. Of which, 19 received a combination treatment of BAI and rAd-p53 (the combo group), while the remaining 39 were treated with only BAI (the control group). Patients were followed up for 12 months, with safety and local response evaluated by the National Cancer Institute's Common Toxicity Criteria and response evaluation criteria in solid tumor (RECIST), respectively. Time to progression (TTP) and survival rates were also analyzed by Kaplan-Meier method.

RESULTS

In the combo group, 19 patients received a total of 49 injections of rAd-p53 and 46 times of BAI, respectively, while 39 patients in the control group received a total of 113 times of BAI. The combination treatment was found to have less adverse events such as anorexia, nausea and emesis, pain, and leucopenia (P<0.05) but more arthralgia, fever, influenza-like symptom, and myalgia (P<0.05), compared with the control group. The overall response rates (complete response (CR)+partial response (PR)) were 47.3% and 38.4% for the combo group and the control group, respectively (P>0.05). Patients in the combo group had a longer TTP than those in the control group (a median 7.75 vs 5.5 months, P=0.018). However, the combination treatment did not lead to better survival, with survival rates at 3, 6, and 12 months in the combo group being 94.74%, 89.47%, and 52.63%, respectively, compared with 92.31%, 69.23%, and 38.83% in the control group (P=0.224).

CONCLUSION

Our results show that the combination of rAd-p53 and BAI was well tolerated in patients with NSCLC and may have improved the quality of life and delayed the disease progression. A further study to better determine the efficacy of this combination therapy is warranted.

Multiple hepatic arterial injections of recombinant adenovirus p53 and 5-fluorouracil after transcatheter arterial chemoembolization for unresectable hepatocellular carcinoma: a pilot phase II trial

This pilot phase II study was designed to determine the efficacy, toxicities, and biological activity of multiple hepatic arterial injections of recombinant adenovirus p53 (rAd-p53) and 5-fluorouracil (5-FU) after transcatheter arterial chemoembolization (TACE) when compared with TACE alone in patients with unresectable hepatocellular carcinoma (HCC). Forty-six patients with unresectable HCC were randomized in either group 1 [23 patients, multiple hepatic arterial injections of Ad-p53 (1x10 viral particles) and 5-FU (500-750 mg), after TACE] or group 2 (23 patients, TACE alone). In group 1, the number of Ad-p53/5-FU courses administered was 166 (median 7, range 3-12). In group 2, the number of TACE courses administered was 47 (median 2, range 1-3). Partial response and stable disease were 69.5% in group 1 and 65.2% in group 2. Times to progression were 9.6 months (range 2.1-21.7) in group 1 and 8.3 months (range 2.1-16.8) in group 2. Overall survivals were 12.8 months (range 2.7-26.2) in group 1 and 10.4 months (range 2.7-22.5) in group 2. Toxicities in both groups were generally mild and reversible. The most common Ad-p53-related toxicity was a transient fever. Specific p53 transgene expression was detected using reverse-transcriptase polymerase chain reaction in biopsied tumor tissues. Distribution studies revealed that the vector was detected in the plasma, but rarely in the gargle and urine. This study shows that multiple hepatic arterial injections of Ad-p53 and 5-FU after TACE can be active and safe as a treatment for patients with unresectable HCC.

Telomerase-specific virotherapy for human squamous cell carcinoma

BACKGROUND

Replication-selective tumor-specific viruses present a novel approach for treatment of neoplastic disease. They are designed to induce lysis after propagation within the tumor. Human telomerase is active in over 85% of primary cancers and its activity correlates closely with human telomerase reverse transcriptase (hTERT) expression.

OBJECTIVES

Oncolytic viruses, Telomelysin and TelomeScan, that combine the specificity of hTERT promoter-based expression systems with the lytic efficacy of replicative viruses were developed. The goal was to confirm the efficacy of the viruses for human squamous cell carcinoma.

RESULTS/CONCLUSION

Squamous cell carcinoma of the head and neck (SCCHN) is characterized by locoregional spread, and is clinically accessible, making it an attractive target for intratumoral virotherapy. The viruses replicated efficiently and induced killing in a panel of human cancer cell lines including SCCHN cells in vitro and in vivo. These results illustrate the potential of telomerase-specific oncolytic viruses for treatment of human SCCHN.

Intervention in context-sensitive probabilistic Boolean networks revisited

An approximate representation for the state space of a context-sensitive probabilistic Boolean network has previously been proposed and utilized to devise therapeutic intervention strategies. Whereas the full state of a context-sensitive probabilistic Boolean network is specified by an ordered pair composed of a network context and a gene-activity profile, this approximate representation collapses the state space onto the gene-activity profiles alone. This reduction yields an approximate transition probability matrix, absent of context, for the Markov chain associated with the context-sensitive probabilistic Boolean network. As with many approximation methods, a price must be paid for using a reduced model representation, namely, some loss of optimality relative to using the full state space. This paper examines the effects on intervention performance caused by the reduction with respect to various values of the model parameters. This task is performed using a new derivation for the transition probability matrix of the context-sensitive probabilistic Boolean network. This expression of transition probability distributions is in concert with the original definition of context-sensitive probabilistic Boolean network. The performance of optimal and approximate therapeutic strategies is compared for both synthetic networks and a real case study. It is observed that the approximate representation describes the dynamics of the context-sensitive probabilistic Boolean network through the instantaneously random probabilistic Boolean network with similar parameters.

Potential of Advexin: a p53 gene-replacement therapy in Li-Fraumeni syndrome

Li-Fraumeni syndrome is a rare autosomal dominant cancer predisposition syndrome. The majority of families fulfilling definition of Li-Fraumeni syndrome demonstrate inherited abnormalities involving the p53 gene. Cells with dysfunctional p53 are predisposed to the development of cancer phenotype. Advexin (Introgen Therapeutics Inc., TX, USA) is an adenoviral-based experimental therapeutic that provides delivery of wild-type p53 to cancer cells and demonstrates anticancer activity following adequate expression of p53. Theoretically, correction of p53 function in cancer developing in patients with Li-Fraumeni syndrome through treatment with Advexin will provide anti-tumor activity. One patient with Li-Fraumeni syndrome has been reported to have responded to Advexin. This review will summarize background knowledge of Li-Fraumeni syndrome, mechanisms of Advexin and clinical response of cancer to Advexin with a focus on Li-Fraumeni syndrome.

Gene medicine for cancer treatment: commercially available medicine and accumulated clinical data in China

Loss of p53 function compromises genetic homeostasis, which induces deregulated DNA replication, damages DNA, and subsequently results in increased resistance to anticancer agents. Pharmacological approaches using recombinant adenoviruses (Ad) have been developed to restore the p53 functions. Another approach for gene medicine is to modify Ad replication in a tumor-specific manner, which induces tumor cell death without damaging normal tissues in the vicinity. The Ad-derived gene medicines, Ad expressing the wild-type p53 gene and replication-competent Ad defective of the E1B-55kDa gene, have been tested for their clinical feasibility and became commercially available in China. These agents demonstrated their antitumor activities as a monotherapy and in combination with conventional chemotherapeutic agents. In this article, we summarize the outcomes of clinical trials in China, most of which have been published in domestic Chinese journals, and discuss potential directions of cancer gene therapy with these agents.

Quantitative molecular imaging of viral therapy for pancreatic cancer using an engineered measles virus expressing the sodium-iodide symporter reporter gene

OBJECTIVE

Our objectives were to, first, determine the oncolytic potential of an engineered measles virus expressing the sodium-iodide symporter gene (MV-NIS) for intratumoral (i.t.) therapy of pancreatic cancer and, second, evaluate NIS as a reporter gene for in vivo monitoring and quantitation of MV-NIS delivery, viral spread, and gene expression in this tumor model.

MATERIALS AND METHODS

Cultured human pancreatic cancer cells were infected with MV-NIS. Light microscopy, cell viability, and iodide uptake assays were used to confirm viral infection and NIS gene expression and function in vitro. Human pancreatic tumor xenografts were established in mice and infected via i.t. MV-NIS injections. NIS-mediated i.t. iodide uptake was quantitated by (123)I micro-SPECT/CT. i.t. MV-NIS infection was confirmed by immunohistochemistry of excised pancreatic xenografts. The oncolytic efficacy of MV-NIS was determined by measurement of tumor growth and mouse survival.

RESULTS

Infection of human pancreatic cancer cell lines with MV-NIS in vitro resulted in syncytia formation, marked iodide uptake, and ultimately cell death. Tumor xenografts infected with MV-NIS concentrated radioiodine, allowing serial quantitative imaging with (123)I micro-SPECT/CT. i.t. MV-NIS therapy of human pancreatic cancer xenografts resulted in a significant reduction in tumor volume and increased survival time of the treated mice compared with the control mice.

CONCLUSION

MV-NIS efficiently infects human pancreatic tumor cells and results in sufficient radioiodine uptake to enable noninvasive serial imaging and quantitation of the intensity, distribution, and time course of NIS gene expression. MV-NIS also shows oncolytic activity in human pancreatic cancer xenografts: Tumor growth is reduced and survival is increased in mice treated with the virus.

IAP-targeted therapies for cancer

DNA damage, chromosomal abnormalities, oncogene activation, viral infection, substrate detachment and hypoxia can all trigger apoptosis in normal cells. However, cancer cells acquire mutations that allow them to survive these threats that are part and parcel of the transformation process or that may affect the growth and dissemination of the tumor. Eventually, cancer cells accumulate further mutations that make them resistant to apoptosis mediated by standard cytotoxic chemotherapy or radiotherapy. The inhibitor of apoptosis (IAP) family members, defined by the presence of a baculovirus IAP repeat (BIR) protein domain, are key regulators of cytokinesis, apoptosis and signal transduction. Specific IAPs regulate either cell division, caspase activity or survival pathways mediated through binding to their BIR domains, and/or through their ubiquitin-ligase RING domain activity. These protein-protein interactions and post-translational modifications are the subject of intense investigations that shed light on how these proteins contribute to oncogenesis and resistance to therapy. In the past several years, we have seen multiple approaches of IAP antagonism enter the clinic, and the rewards of such strategies are about to reap benefit. Significantly, small molecule pan-IAP antagonists that mimic an endogenous inhibitor of the IAPs, called Smac, have demonstrated an unexpected ability to sensitize cancer cells to tumor necrosis factor-alpha and to promote autocrine or paracrine production of this cytokine by the tumor cell and possibly, other cells too. This review will focus on these and other developmental therapeutics that target the IAPs in cancer.

Phase I study of adenovirus p53 administered by bronchoalveolar lavage in patients with bronchioloalveolar cell lung carcinoma: ECOG 6597

PURPOSE

This pilot phase I trial evaluated the safety and maximum-tolerated dose of p53 gene transfer using an adenovirus vector (Ad-p53) delivered via bronchoalveolar lavage (BAL) to patients with bronchioloalveolar lung carcinoma (BAC).

PATIENTS AND METHODS

Patients were initially administered two treatments of Ad-p53 to a single involved lobe, beginning at 2 x 10(9) viral particles (vp) per dose and escalated to a maximum of 2 x 10(12) vp. If a clinical benefit was seen and the treatment was well tolerated, additional doses could be administered to additional lobes.

RESULTS

Twenty-five patients were treated at doses between 2 x 10(9) and 2 x 10(12) vp. At 2 x 10(12) vp, one patient experienced grade 4 pulmonary toxicity, and one patient died 25 days after his second cycle; therefore, a cohort of 10 patients was treated at the recommended phase II dose of 5 x 10(11) vp, with no grade 4 toxicity observed. The most frequent toxicities included low-grade fever, hypoxia, and dyspnea. Of the 23 assessable patients, 16 had stable disease as their best response. Subjective improvement in breathing was noted in eight patients. Limited distribution of vector was observed, with transient detection in patient sputum for 1 to 2 days after administration.

CONCLUSION

Ad-p53 can be administered safely by BAL at 5 x 10(11) vp with repeated dosing. Stabilization of disease and symptomatic improvement may warrant further studies of Ad-p53 or other adenoviruses administered by BAL in patients with BAC.

The inhibitors of apoptosis (IAPs) as cancer targets

Apoptosis has been accepted as a fundamental component in the pathogenesis of cancer, in addition to other human diseases including neurodegeneration, coronary disease and diabetes. The origin of cancer involves deregulated cellular proliferation and the suppression of apoptotic processes, ultimately leading to tumor establishment and growth. Several lines of evidence point toward the IAP family of proteins playing a role in oncogenesis, via their effective suppression of apoptosis. The central mechanisms of IAP apoptotic suppression appear to be through direct caspase and pro-caspase inhibition (primarily caspase 3 and 7) and modulation of, and by, the transcription factor NF-kappaB. Thus, when the IAPs are over-expressed or over-active, as is the case in many cancers, cells are no longer able to die in a physiologically programmed fashion and become increasingly resistant to standard chemo- and radiation therapies. To date several approaches have been taken to target and eliminate IAP function in an attempt to re-establish sensitivity, reduce toxicity, and improve efficacy of cancer treatment. In this review, we address IAP proteins as therapeutic targets for the treatment of cancer and emphasize the importance of novel therapeutic approaches for cancer therapy. Novel targets of IAP function are being identified and include gene therapy strategies and small molecule inhibitors that are based on endogenous IAP antagonists. As well, molecular mechanistic approaches, such as RNAi to deplete IAP expression, are in development.

Novel therapies targeting signaling pathways in lung cancer

Despite advances in chemotherapy, the prognosis for advanced non-small-cell lung cancer (NSCLC) remains dismal. Increasing understanding of the biological processes responsible for lung carcinogenesis has led to development of new therapeutic strategies targeting this disease at a molecular level. This article examines the molecular events believed to lead to cellular changes in lung cancer, and how knowledge of these is used to develop new agents used individually or in combination with available cytotoxic drugs to improve survival. Finally, it explores how a deeper understanding of the embryonic signaling pathways responsible for airway epithelial repair and tumorogenesis, such as Hedgehog (Hh), Notch, and Wingless (Wnt), can lead to the development of newer and more specific therapies for lung cancer.

Isolated limb perfusion: a novel delivery system for wild-type p53 and fiber-modified oncolytic adenoviruses to extremity sarcoma

Isolated limb perfusion (ILP) is a limb salvage surgical modality used to deliver chemotherapy and biologic agents to locally advanced and recurrent extremity soft tissue sarcoma (STS), and may be readily tailored for delivery of gene therapy. We set out to test the feasibility of delivering AdFLAGp53 (replication incompetent adenovirus bearing FLAG-tagged wild-type p53) and Ad.hTC.GFP/E1a.RGD (a fiber-modified, replication selective oncolytic adenovirus) into human leiomyosarcoma xenografts by ILP. Nude rats bearing SKLMS-1 tumors in their hind limbs underwent ILP with escalating doses of AdLacZ or AdFLAGp53 (study 1), or with Ad.CMV.GFP.RGD or Ad.hTC.GFP/E1a.RGD (study 2) following in vitro confirmation of therapeutic potential in STS cell lines and strains. Seventy-two hours after delivery, reverse transcription-polymerase chain reaction confirmed FLAGp53 expression, and immunohistochemistry confirmed diffuse upregulation of p21CIP1/WAF1 in ILP-treated tumors. Ad.hTC.GFP/E1a.RGD perfused tumors demonstrated robust macroscopic transgene expression throughout their substance, but not in perfused normal tissues, 21 days after delivery. Intra-tumoral viral replication was confirmed by immunohistochemical staining for early (E1a) and late (hexon) viral protein expression. Terminal deoxynucleotidyl transferase-mediated-digoxigenin nick end-labeling staining identified foci of cell death within regions of viral replication. In conclusion, therapeutic adenoviral gene therapy against limb borne human STS can be successfully delivered by ILP and warrants further investigation.

DT. Targeting lung cancer using an infectivity enhanced CXCR4-CRAd

Conventional treatments are not adequate for the majority of lung cancer patients. Conditionally replicating adenoviruses (CRAds) represent a promising new modality for the treatment of neoplastic diseases, including non-small cell lung cancer. Specifically, following cellular infection, the virus replicates selectively in the infected tumor cells and kills the cells by cytolysis. Next, the progeny virions infect a new population of surrounding target cells, replicate again and eradicate the infected tumor cells while leaving normal cells unaffected. However, to date, there have been two main limitations to successful clinical application of these CRAd agents; i.e. poor infectivity and poor tumor specificity. Here we report the construction of a CRAd agent, CRAd-CXCR4.RGD, in which the adenovirus E1 gene is driven by a tumor-specific CXCR4 promoter and the viral infectivity is enhanced by a capsid modification, RGD4C. This agent CRAd-CXCR4.RGD, as expected, improved both of the viral infectivity and tumor specificity as evaluated in an established lung tumor cell line and in primary tumor tissue from multiple patients. As an added benefit, the activity of the CXCR4 promoter was low in human liver as compared to three other promoters regularly used for targeting tumors. In addition, this agent has the potential of targeting multiple other tumor cell types. From these data, the CRAd-CXCR4.RGD appears to be a promising novel CRAd agent for lung cancer targeting with low host toxicity.

Clinical significance of the p53 pathway and associated gene therapy in non-small cell lung cancers

Many molecules, including several regulators and various target genes, are involved in the biological functions of p53, thus making the p53 pathway rather complicated. However, recent clinical studies have demonstrated that most human cancers have an abnormality in some of the molecules associated with the p53 pathway. Most non-small cell lung cancers (NSCLCs) have either mutations of p53, a reduced p14 alternate reading frame expression, a reduced herpesvirus-associated ubiquitin-specific protease expression or a reduced p33 inhibitor of growth gene1b expression. As a result, the balance of expression of p53 target genes, such as p21, Bax and PUMA, regulates the biological behavior and determines the fate of tumor cells. To date, many studies on cancer gene therapy using these molecules associated with the p53 pathway have been performed to develop new strategies for treating NSCLC patients. Thus, the establishment of a comprehensive and simple evaluation protocol for the p53 pathway is required for clinical use.

Gene therapy for lung cancer

Lung cancer patients suffer a 15% overall survival despite advances in chemotherapy, radiation therapy, and surgery due to the usual finding of advanced disease at diagnosis. Attempts to improve survival in advanced disease using various combinations of chemotherapy have demonstrated that no regimen is superior, suggesting a therapeutic plateau and the need for novel, more specific, and less toxic therapeutic strategies. Techniques have been developed that allow transfer of functional genes into mammalian cells, such as those that block activated tumor-promoting oncogenes and/or those that replace inactivated tumor-suppressing or apoptosis-promoting genes. This article will discuss the therapeutic implications of these molecular changes associated with bronchogenic carcinomas, and will then review the status of gene therapies for treatment of lung cancer.

The proteasome inhibitor bortezomib acts differently in combination with p53 gene transfer or cytotoxic chemotherapy on NSCLC cells

In this report, the effects of a combined treatment with the proteasome inhibitor bortezomib and either a recombinant adeno-associated virus type 2 (rAAV-2)-mediated p53 gene transfer or chemotherapeutic agents, docetaxel and pemetrexed, were tested on p53 positive and p53negative non-small cell lung cancer (NSCLC) cell lines. The combination of bortezomib and rAAV-p53 led to a significant synergistic inhibition of cell growth between 62-82% depending on the p53 status of the cell line and drug concentration. Surviving cells of the combined treatment showed a significant reduced ability to form colonies. Enhanced cell toxicity was associated with a 5.3-14.4-fold increase of the apoptotic rate and intracellular p53 level up to 50.4% following vector-mediated p53 restoration and bortezomib treatment. In contrast, an antagonistic effect on tumor cell growth and colony formation was observed for the combination of bortezomib and docetaxel or pemetrexed as a reduction of cell growth between 31 and 48% was found in comparison to 50% using the single agents. Lower cytotoxic effects were associated with significantly reduced apoptosis and an increase of clonogenic growth. The observed antagonistic effects between bortezomib and docetaxel or pemetrexed might influence clinical trials using these compounds. Conversely, p53 restoration and bortezomib treatment led to enhanced, synergistic tumor cell toxicity.

Suppression of gastric cancer cell growth by targeting the β-catenin/T-cell factor pathway

BACKGROUND

Functional activation of beta-catenin/T-cell factor (Tcf) signaling plays an important role in the early events of carcinogenesis. Recently, it was demonstrated that adenomatous polyposis coli or beta-catenin genes are mutated frequently in gastric cancer cells. The objective of the current study was to use a gene-targeting approach to kill human gastric cancer cells selectively with activated beta-catenin/Tcf signaling.

METHODS

A recombinant adenovirus that carries a lethal gene (p53 up-regulated modulator of apoptosis [PUMA]) under the control of a beta-catenin/Tcf-responsive promoter (AdTOP-PUMA) was used selectively to target gastric cancer cells (AGS) that posses an active beta-catenin/Tcf pathway. The combined effect of AdTOP-PUMA and several chemotherapeutic agents (5-florouracil, doxorubicin, paclitaxel) also was evaluated. Cell viability was measured by methylene blue assay, protein expression was measured by Western blot analysis, and cell cycle and apoptosis were evaluated by fluorescent-activated cell sorter analysis. RESULTS.: The TOP-PUMA adenovirus inhibited AGS cell growth in a dose- and time-dependent fashion. Growth inhibition was associated with the up-regulation of PUMA expression and the induction of apoptosis. Chemotherapy synergistically enhanced the killing effect of AdTOP-PUMA.

CONCLUSIONS

Selective targeting of gastric cancer cells with the activated beta-catenin pathway may be a novel and effective therapy in gastric cancer. Combination of this gene-therapy approach with standard therapy may improve efficacy and reduce toxicity.

Gene therapy for lung cancer

Lung cancer patients suffer a 15% overall survival despite advances in chemotherapy, radiation therapy, and surgery. This unacceptably low survival rate is due to the usual finding of advanced disease at diagnosis. However, multimodality strategies using conventional therapies only minimally improve survival rates even in early stages of lung cancer. Attempts to improve survival in advanced disease using various combinations of platinum-based chemotherapy have demonstrated that no regimen is superior, suggesting a therapeutic plateau and the need for novel, more specific, and less toxic therapeutic strategies. Over the past three decades, the genetic etiology of cancer has been gradually delineated, albeit not yet completely. Understanding the molecular events that occur during the multistep process of bronchogenic carcinogenesis may make these tasks more surmountable. During these same three decades, techniques have been developed which allow transfer of functional genes into mammalian cells. For example, blockade of activated tumor-promoting oncogenes or replacement of inactivated tumor-suppressing or apoptosis-promoting genes can be achieved by gene therapy. This article will discuss the therapeutic implications of these molecular changes associated with bronchogenic carcinomas and will then review the status of gene therapies for treatment of lung cancer.

A nonreplicating adenoviral vector that contains the wild-type p53 transgene combined with chemotherapy for primary breast cancer: safety, efficacy, and biologic activity of a novel gene-therapy approach

BACKGROUND

: Primary systemic therapy (PST) is the standard approach to the management of patients with locally advanced breast cancer (LABC). The authors hypothesized that the intratumoral administration of a nonreplicating adenoviral vector (Ad5) that contains the human wild-type p53, AdCMV-p53, combined with chemotherapy, could increase the efficacy of PST as measured by pathologic complete response.

METHODS

: In a prospective, open-label, Phase II trial, 13 patients with LABC were treated with 6 3-week cycles of PST, which consisted of intratumoral injections of Ad5CMV-p53 for 2 consecutive days plus docetaxel and doxorubicin followed by surgery. p53 status was determined at baseline and was assessed immediately after the first injection (up to 48 hours). Clinical response was assessed by clinical and radiologic methods.

RESULTS

: The trial was terminated early, because none of the patients achieved a pathologic complete response. The median age was 56 years (range, 39-71 years), and the median tumor size was 8 cm (range, 5-11 cm). Eight patients (73%) had a p53 mutation. Serial biopsies showed an increase in p53 messenger RNA (mRNA) and p21(WAF1/Cip1) mRNA. All 12 evaluable patients achieved an objective clinical response. The surgical specimens revealed scattered tumor cells with extensive tumor-infiltrate leukocytes (predominantly T-lymphocytes). At a median follow-up of 37 months (range, 30-41 months), 4 patients (30%) developed systemic recurrence, and 2 patients died. The estimate breast cancer-specific survival rate at 3 years was 84% (95% confidence interval, 65.7-100%). There was no increase in systemic toxicity.

CONCLUSIONS

: Ad5CMV-p53 combined with PST is safe, active, and associated with local immunomodulatory effects. The promising clinical activity of this combination deserves further investigation in randomized studies.

Evaluation of the Spatial Diffusion of Methylene Blue Injected in vivo by Bronchoscopy into Non-Small Cell Lung Carcinoma

BACKGROUND

Due to smoking prevalence and the poor efficiency of current therapy, lung cancer is the leading cause of cancer death in developed countries, and its worldwide incidence is steadily increasing. Gene therapy by direct intratumoral injection of different types of gene constructs through a fiberscope has been suggested and evaluated in a few patients.

OBJECTIVE

It was the aim of this study to observe the actual volume of diffusion within a lung tumor using a color marker.

METHODS

Using bronchoscopy, just after anesthesia, methylene blue was injected into patient tumors. These patients subsequently underwent surgery for treatment of a non-small cell lung cancer.

RESULTS

We observed a diffusion of methylene blue in resected lung tumors with a mean infiltrated versus noninfiltrated tumor volume ratio of 29 +/- 15%. Interestingly, some large tumor areas were not stained. At the cellular level, a preferential diffusion of the dye was observed in the tumor stroma compartment versus the tumor cellular compartment, where basal cells were more frequently and strongly labeled than the other tumor cells.

CONCLUSIONS

Since a cancer is cured when most, if not all, cancer cells are killed, the preliminary evaluation of the spatial diffusion of any injected gene construct should be carried out as a first step in any cancer type.

Current developments in adenovirus-based cancer gene therapy

Adenovirus (Ad)-based cancer gene therapy is a promising, novel approach for treating cancer resistant to established treatment modalities. Unfortunately, the efficacy of nonreplicative first generation Ads was low and data from clinical trials were disappointing. To address this problem, conditionally replicating Ads have been constructed. Infection of tumor cells with conditionally replicating Ads results in tumor-specific replication, subsequent oncolysis and release of the virus progeny. Recently, it has been suggested that the low expression of the coxsackie-Ad receptor is the rate-limiting factor for infectivity with serotype 5 (Ad5). Unfortunately, coxsackie-Ad receptor expression is highly variable and often low on many tumor types. Consequently, molecular strategies have been applied for the development of coxsackie-Ad receptor-independent oncolytic Ads. This review describes recent developments of Ad-based cancer gene therapy, including novel engineering techniques of the Ad capsid for efficient tumor targeting, as well as targeting techniques, to restrict transgene expression to cancer cells.

Coxsackievirus and adenovirus receptor expression in non-malignant lung tissues and clinical lung cancers

Adenoviral vector mediated gene delivery has been applied in clinical trials and mechanistic studies to explore new treatment approaches for lung cancers. The expression of coxsackievirus adenovirus receptor (CAR), the primary receptor for the most commonly used adenovirus serotype 5 (Ad5)-based vectors, predominantly determines the permissiveness of lung cancer cells. CAR expression is also suggested to modulate tumor cell proliferation capacity. Here, we studied CAR expression in archival lung cancer specimens by using well-characterized CAR 72 antibodies. High levels of CAR expression were observed in most of the 32 cases of squamous cell carcinoma lung cancers and in all the five cases of small cell lung cancers investigated. In contrast, high levels of CAR expression were detected only in 6 of 22 adenocarcinoma lung cancers. The relative levels of CAR expression did not correlate with the pathologic grade in lung cancers, and was thus inconsistent with a role of modulating cancer cell proliferation. Of note, CAR expression was not detected in non-malignant alveolar cells. Our data suggest a preferred utility of Ad5 vector mediated gene delivery to squamous cell carcinoma lung cancers, small cell lung cancers, but not to the majority of adenocarcinoma lung cancers.

Phase I/II adenoviral p53 gene therapy for chemoradiation resistant advanced esophageal squamous cell carcinoma

We investigated the feasibility, safety, biological activity and therapeutic efficacy of adenovirus-mediated p53 gene transfer in patients with chemoradiation resistant advanced esophageal carcinoma. Eligible patients were not surgical candidates and had measurable, advanced squamous cell carcinoma of the esophagus that was resistant to chemoradiation therapy. On a 28-day cycle, intratumoral injections of Ad5CMV-p53 (INGN 201; ADVEXIN) were administered on days 1 and 3 at four dose levels (10 x 10(11) particles to 25 x 10(11) particles) and treated for up to five cycles. Ten patients received a total of 26 cycles with no dose-limiting toxicity. Administration of multiple courses was feasible and well-tolerated. Local tumor responses revealed stable disease in nine cases and progressive disease in one case. The overall responses were stable in six and progressive in four cases. Using polymerase chain reaction (PCR) analyses, gene transfer and p53 specific transgene expression were detected in tumor biopsy tissue from all patients. mRNA levels of p53, p21 and MDM2 increased in all but one case. Three patients showed absence of disease upon repeat biopsies. Substantial improvement in swallowing was observed in one patient with stenotic lesions. Intratumoral injection of Ad5CMV-p53 is safe, feasible and biologically active when administered in multiple doses to patients with esophageal cancer. Observations from this study indicate that this treatment results in local antitumor effects in chemoradiation resistant esophageal squamous cell carcinoma.

The role of p53 mutations as a prognostic factor and therapeutic target in inflammatory breast cancer

Inflammatory breast cancer is a rare but lethal form of locally advanced breast cancer. Despite improvements in survival with the advent of multidisciplinary treatment regimens, 5-year survival rates remain disappointing, at approximately 30%. Numerous molecular markers have been investigated for their potential as useful prognostic and predictive markers of treatment response that would impact on the management of inflammatory breast cancer. This review discusses the current status of p53 mutations both as a prognostic marker and as a potential target for directed therapies.

p53 as a target for anti-cancer drug development

Loss of p53 function compromises genetic homeostasis in cells exhibiting deregulated DNA replication and/or DNA damage, and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Progress has recently been made in the clinical use of replication-deficient virus carrying wt-TP53 (Ad5CMV-p53) and/or cancer-selective oncolytic adenoviruses (ONYX-015). These strategies demonstrated clinical activity as monotherapy and were synergistic with traditional chemotherapy agents in the treatment of some types of cancer. In addition, pharmacological methods are under development to either stimulate wild-type p53 protein function, or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3) or single-chain Fv antibody fragments corresponding to defined p53 domains. Here, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

Adenovirus p53 gene therapy

To date, dysfunctional tumour suppressor genes are the most common genetic lesions identified in human cancers. Functional copies of tumour suppressor genes can be introduced into cancer cells by gene transfer using adenoviral vectors. This approach has been extensively studied in the clinic with intratumoural injection of a replication-defective adenovirus that expresses p53 (Ad-p53). Overexpression of p53 in cancer cells induces growth arrest and apoptosis. Ad-p53 injections have an excellent safety profile, and have mediated tumour regression and growth arrest as monotherapy, or have overcome resistance or increased the effectiveness of radiation therapy and chemotherapy. Expression of the p53 transgene has occurred at high levels and is associated with the activation of other genes in the p53 pathway. These studies indicate proof-of-principle for tumour suppressor gene therapy and represent a new paradigm in targeted therapy.

The HAUSP gene plays an important role in non-small cell lung carcinogenesis through p53-dependent pathways

Herpesvirus-associated ubiquitin-specific protease (HAUSP) directly stabilizes the tumour suppressor p53 by de-ubiquitination. Therefore, the HAUSP gene might play an important role in carcinogenesis. In this paper, HAUSP expression and p53 gene status have been studied in relation to the expression of p53 target genes in 131 patients with non-small cell lung cancer (NSCLC). p53 gene status was evaluated by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) followed by sequencing. Quantitative reverse-transcription polymerase chain reaction (RT-PCR) was performed to evaluate the gene expression of HAUSP, p21, and bax. Immunohistochemistry was performed to evaluate the protein expression of p53, HAUSP, mdm2, p21, and bax. Fifty-nine carcinomas (45.0%) showed reduced expression of HAUSP, and 58 carcinomas (44.3%) had mutations of p53. Concerning tumour histology, HAUSP mRNA expression was significantly lower in adenocarcinomas than in squamous cell carcinomas (p = 0.0038), while the frequency of p53 mutation was significantly higher in squamous cell carcinomas than in adenocarcinomas (p = 0.0461). There was no significant difference in HAUSP mRNA expression according to p53 gene status. In total, 93 carcinomas (71.0%) showed either mutant p53 or reduced HAUSP expression. The down-regulation of HAUSP was associated with reduced p53 protein expression (p = 0.0593 in tumours with wild-type p53 and p = 0.0004 in tumours with mutant p53). Furthermore, p21 and bax protein expression was significantly lower in tumours with either mutant p53 or reduced HAUSP expression than in tumours with both wild-type p53 and positive HAUSP expression (p = 0.0440 and p = 0.0046, respectively). In addition, the simultaneous evaluation of both HAUSP expression and p53 gene status was a significant indicator of poor prognosis in adenocarcinoma patients (hazard ratio 4.840, p = 0.0357). These results suggest that reduction of HAUSP gene expression may play an important role in NSCLC carcinogenesis, especially in adenocarcinomas, through p53-dependent pathways.

Phase I, Pharmacokinetic, and Pharmacodynamic Study of Intravenously Administered Ad5CMV-p53, an Adenoviral Vector Containing the Wild-Type p53 Gene, in Patients With Advanced Cancer

Purpose

The purpose of this study was to assess the feasibility of administering Ad5CMV-p53, an adenoviral vector containing the wild-type p53 gene to patients with advanced malignancies, characterize the pertinent pharmacokinetic parameters, identify evidence of viral uptake in both normal and tumor tissue, and seek evidence of antitumor activity.

Methods

Patients were treated with escalating doses of Ad5CMV-p53 intravenously over 30 minutes on days 1, 2, and 3, every 28 days. The clearance of circulating Ad5CMV-p53 (INGN 201) DNA was characterized in the plasma and paired tumor and skin biopsies were performed in patients treated at the two highest dose levels to assess vector uptake into tissues.

Results

Seventeen patients received 36 courses of Ad5CMV-p53 at doses ranging from 3 × 1010 to 3 × 1012 virus particles (vp). Fatigue, nausea, vomiting, and fever were common, but rarely severe. Abnormalities of coagulation parameters, including decreases in fibrinogen and increases in fibrin degradation products at 3 × 1012vp, precluded additional dose escalation. Ad5CMV-p53 DNA could be detected in the plasma by polymerase chain reaction assay in the majority of patients at 14 days and 28 days at doses of 3 × 1010 and higher. Six patients treated at 1 × 1012vp and 3 × 1012vp dose levels had Ad5CMV-p53 DNA detected within paired tumor tissue collected day 4.

Conclusion

Ad5CMV-p53 can be safely and repetitively administered up to 1 × 1012vp intravenously daily for 3 consecutive days. The absence of severe toxicities, the presence of circulating adenovirus 24 hours after administration, and detectable p53 transgene within tumor tissue distant from the site of administration demonstrates that systemic therapy with this adenoviral vector containing p53 is feasible.

Induction of apoptosis in human lung cancer cells following treatment with amifostine and an adenoviral vector containing wild-type p53

Adenoviral delivery of the p53 gene is a potential therapeutic approach for the treatment of lung cancer. Furthermore, amifostine is a cytoprotective agent and recent reports have described its potentiation of chemotherapy's antitumor activity in lung cancer. Therefore, we wished to investigate the ability of amifostine both alone and in combination with p53-based therapy to induce apoptosis, and to understand the mechanisms by which this apoptosis occurs. Using p53 null and wild-type p53 human lung cancer cells and normal human bronchial epithelial cells, we evaluated the effects of amifostine on proliferation and apoptosis. We then analyzed Adp53 in combination with amifostine and performed isobologram analysis. Expression of p53, p21(WAF1), Bax, Bak, bcl-2, as well as total and phosphorylated Cdc2 in the absence and presence of olomoucine, a phosphorylated Cdc2 kinase inhibitor, was then determined. Amifostine-induced apoptosis in human lung cancer cells in a dose-dependent fashion. The combination of amifostine and Adp53 significantly enhanced, with a supra-additive effect, the inhibition of proliferation of lung cancer cells. This enhancement of apoptosis by amifostine was associated with activation of p53 and dephosphorylation of Cdc2 proteins. Notably, olomoucine effectively prevented amifostine and/or Adp53-induced Cdc2 kinase activation and subsequent apoptosis. Our data shows that amifostine alone can induce apoptosis of human lung cancer cells, and that the combination of Adp53 with amifostine resulted in significantly higher levels of apoptosis. In addition, it appears that Cdc2 kinase plays an important role in the induction of apoptosis by amifostine and Adp53.

Multicenter Phase I Study of Repeated Intratumoral Delivery of Adenoviral p53 in Patients With Advanced Non–Small-Cell Lung Cancer

Purpose

To determine the feasibility, safety, humoral immune response, and biologic activity of multiple intratumoral injections of Ad5CMV-p53, and to characterize the pharmacokinetics of Ad5CMV-p53 in patients with advanced non–small-cell lung cancer (NSCLC).

Patients and Methods

Fifteen patients with histologically confirmed NSCLC and p53 mutations were enrolled onto this phase I trial. Nine patients received escalating dose levels of Ad5CMV-p53 (1 × 109 to 1 × 1011 plaque-forming units) as monotherapy once every 4 weeks. Six patients were treated on a 28-day schedule with Ad5CMV-p53 in combination with intravenous administration of cisplatin (80 mg/m2). Patients were monitored for toxicity, vector distribution, antibody formation, and tumor response.

Results

Fifteen patients received a total of 63 intratumoral injections of Ad5CMV-p53 without dose-limiting toxicity. The most common treatment-related toxicity was a transient fever. Specific p53 transgene expression was detected using reverse-transcriptase polymerase chain reaction in biopsied tumor tissues throughout the period of treatment despite of the presence of neutralizing antiadenovirus antibody. Distribution studies revealed that the vector was detected in the gargle and plasma, but rarely in the urine. Thirteen of 15 patients were assessable for efficacy; one patient had a partial response (squamous cell carcinoma at the carina), 10 patients had stable disease, with three lasting at least 9 months, and two patients had progressive disease.

Conclusion

Multiple courses of intratumoral Ad5CMV-p53 injection alone or in combination with intravenous administration of cisplatin were feasible and well tolerated in advanced NSCLC patients, and appeared to provide clinical benefit.

Future directions in the second-line treatment of non-small cell lung cancer

Single-agent chemotherapy has shown limited activity as second-line treatment in metastatic non-small cell lung cancer (NSCLC), with short-lived responses and modest survival benefit over best supportive care or placebo. There are multiple ways to improve the poor outcome of patients whose disease progresses after first-line chemotherapy. First, individualizing second-line chemotherapy could optimize its effect; the discovery of dramatic responses and significant improvement in survival in patients with epidermal growth factor receptor (EGFR) gene mutations who are treated with EGFR tyrosine kinase inhibitors may lead to the application of other novel therapeutic approaches. Cancer vaccines, using autologous tumor cells genetically modified with granulocyte-macrophage colony-stimulating factor, constitute a new therapeutic option for patients with chemoresistant advanced NSCLC. Vaccines based on lymphocyte-defined tumor antigens, such as melanoma-associated antigen-3, toll-like receptor 9, and mucin 1, are also in the first stages of testing and have shown promising preliminary results. New approaches in gene therapy, including a p53-based method, are currently being investigated. The ultimate goal of gene therapy is to target cancerous stem cells, the importance of which is beginning to be recognized in NSCLC through the study of abnormalities in the wingless (Wnt) pathway. At the preclinical level, small interfering RNA sequences have been used successfully to neutralize multiple abnormal components of the Wnt pathway.

Adenoviral vectors--how to use them in cancer gene therapy?

Gene therapy is most often described as a technique for introducing the foreign genetic material into cells with a correction of a dysfunctional gene as its final goal. Today, it is well known that cancer is one of the leading causes of mortality in the world. Besides classical methods for cancer treatment new strategies against cancer are needed. Although originally being designed as a treatment for monogenetic illness, soon after, gene therapy appeared as a potential new strategy in cancer therapy. One of the widely used vectors for cancer gene therapy is adenovirus. In this review we have described molecular biology of adenoviruses and basis for construction of adenoviral vectors. We have also described concepts for cancer gene therapy including their in vitro and in vivo application. Special attention is drawn toward retargeting of adenovirus as a new approach in vector design for cancer gene therapy, in order to restrict transgene expression in tumor tissue. This approach uses biophysical as well as genetic characteristics of tumor itself and its supporting tissue, allowing new "bypass" in cancer gene therapy.

Modulating apoptosis as a target for effective therapy

Alterations in cell proliferation and cell death are essential determinants in the pathogenesis and progression of several diseases such as cancer, neurodegenerative disorders or autoimmune diseases among others. Complex networks of regulatory factors determine whether cells proliferate or die. Recent progress in understanding the molecular changes offer the possibility of specifically targeting molecules and pathways to achieve more effective and rational therapies. Drugs that target molecules involved in apoptosis are used as treatment against several diseases. Candidates such as TNF death receptor family, caspase inhibitors, antagonists of the p53-MDM2 interaction, NF-kappaB and PI3K pathways and Bcl-2 family members have been targeted as cancer cell killing agents. Moreover, apoptosis of tumor cells can also be achieved by targeting the inhibitor of apoptosis proteins, IAPs, in addition to the classical antiproliferative approach. Disruption of STAT activation and interferon beta therapy have been used as a treatment to prevent the progression of some autoimmune diseases. In models of Parkinson's, Alzheimer's and amyotrophic lateral sclerosis, blocking of Par-4 expression or function, as well as caspase activation, prevents neuronal cell death. Finally, it has been shown that gene therapy may be an encouraging approach for treatment of neurodegenerative disorders.

Gene therapy for lung cancer

Over the past three decades, the molecular biology of lung cancer has been progressively delineated. Concurrently, gene therapy techniques have been developed that allow targeting or replacement of dysfunctional genes in cancer cells, such as activated tumor-promoting oncogenes, inactivated tumor-suppressing, or apoptosis-promoting genes. This article will review the therapeutic implications of molecular changes associated with non-small cell lung cancer and the status of gene therapy.

Modification of the p53 transgene of a replication-competent adenovirus prevents mdm2- and E1b-55kD-mediated degradation of p53

Clinical efficacy of adenovirus-mediated cancer gene therapy has been limited thus far. To improve its oncolytic effect, a replication-competent adenoviral vector was previously constructed to express high levels of p53 at a late time point in the viral life cycle. p53 expression from this vector improved tumor cell killing and viral spread in vitro. However, p53 function is antagonized by cellular mdm2 and adenoviral E1b-55kD, both of which are known to bind to and inactivate p53. Therefore, a new vector (Adp53W23S) that expresses a modified p53 transgene, which does not bind to E1b-55kd and mdm2, was constructed. The modified p53 protein was demonstrated to have a substantially prolonged half-life, and its localization was predominantly nuclear. Viral replication was unaffected by expression of the modified p53 and cancer cell killing was improved in vitro. However, in a xenograft model, efficacy was not significantly different from control virus. In conclusion, expression of a degradation-resistant p53 transgene late in the life cycle of a replication-competent adenovirus improves p53 stability and cancer cell killing in vitro. However, other factors, such as the adenoviral E1b-19kD and E1a proteins, which oppose p53 function, and limitations to viral spread need to be addressed to further improve in vivo efficacy.