Tumour cell radiosensitization using constitutive (CMV) and radiation inducible (WAF1) promoters to drive the iNOS gene: a novel suicide gene therapy

Cross Talk between COVID-19 and Breast Cancer

Cancer patients are more susceptible to COVID-19; however, the prevalence of COVID-19 in different types of cancer is still inconsistent and inconclusive. Here, we delineate the intricate relationship between breast cancer and COVID-19. Breast cancer and COVID-19 share the involvement of common comorbidities, hormonal signalling pathways, gender differences, rennin- angiotensin system (RAS), angiotensin-converting enzyme-2 (ACE-2), transmembrane protease serine 2 (TMPRSS2) and dipeptidyl peptidase-IV (DPP-IV). We also shed light on the possible effects of therapeutic modalities of COVID-19 on breast cancer outcomes. Briefly, we conclude that breast cancer patients are more susceptible to COVID-19 in comparison with their normal counterparts. Women are more resistant to the occurrence and severity of COVID-19. Increased expressions of ACE2 and TMPRSS2 are correlated with occurrence and severity of COVID-19, but higher expression of ACE2 and lower expression of TMPRSS2 are prognostic markers for overall disease free survival in breast cancer. The ACE2 inhibitors and ibuprofen therapies for COVID-19 treatment may aggravate the clinical condition of breast cancer patients through chemo-resistance and metastasis. Most of the available therapeutic modalities for COVID-19 were also found to exert positive effects on breast cancer outcomes. Besides drugs in clinical trend, TMPRSS2 inhibitors, estrogen supplementation, androgen deprivation and DPP-IV inhibitors may also be used to treat breast cancer patients infected with SARS-CoV-2. However, drug-drug interactions suggest that some of the drugs used for the treatment of COVID-19 may modulate the drug metabolism of anticancer therapies which may lead to adverse drug reaction events.

Regulation of Cell Survival, Apoptosis, and Epithelial-to-Mesenchymal Transition by Nitric Oxide-Dependent Post-Translational Modifications

SIGNIFICANCE

Nitric oxide (NO) is a physiopathological messenger generating different reactive nitrogen species (RNS) according to hypoxic, acidic and redox conditions. Recent Advances: RNS and reactive oxygen species (ROS) promote relevant post-translational modifications, such as nitrosation, nitration, and oxidation, in critical components of cell proliferation and death, epithelial-to-mesenchymal transition, and metastasis.

CRITICAL ISSUES

The pro- or antitumoral properties of NO are dependent on local concentration, redox state, cellular status, duration of exposure, and compartmentalization of NO generation. The increased expression of NO synthase has been associated with cancer progression. However, the experimental strategies leading to high intratumoral NO generation have been shown to exert antitumoral properties. The effect of NO and ROS on cell signaling is critically altered by factors modulating tumor progression such as oxygen content, metabolism, and inflammatory response. The review describes the alteration of key components involved in cell survival and death, metabolism, and metastasis induced by RNS- and ROS-related post-translational modifications.

FUTURE DIRECTIONS

The identification of the molecular targets affected by nitrosation, nitration, and oxidation, as well as their interactions with other post-translational modifications, will improve the understanding on the complex signaling and cell fate decision in cancer. The therapeutic NO-based strategies have to address the complex crosstalk among NO and ROS with regard to critical components affecting tumor cell survival, metabolism, and metastasis in the progression of cancer, as well as close interaction with ionizing radiation and chemotherapy.

Radiation and Endostatin Gene Therapy in a Lung Carcinoma Model: Pilot Data on Cells and Cytokines that Affect Angiogenesis and Immune Status

The dose of radiation that can be safely delivered to cancers residing in sensitive areas such as the lungs is limited by concern for normal tissue damage. Therapies that target tumor vasculature have potential to enhance the efficacy of radiotherapy, with minimal risk for toxicity. We constructed a unique plasmid, pXLG-mEndo, containing the mouse endostatin gene. A significantly greater anti-tumor effect was obtained against Lewis lung carcinoma (LLC) in mice when pXLG-mEndo was combined with radiation compared to radiation alone. Here we report results of cellular and cytokine assessments performed one day after treatment. These analyses were done to obtain baseline data on leukocytes that affect angiogenesis, as well as anti-tumor immunity, and to detect possible treatment-related toxicities. White blood cell counts were dramatically elevated in blood and spleens of untreated tumor-bearing mice, primarily due to granulocytosis. Overall, the effect of radiation was more evident than that of the plasmids (pXLG-mEndo and parental pWS4); radiosensitivity of specific lymphocyte subsets was variable (B > T > NK; CD8+ Tc > CD4+ Th). Tumor presence resulted in dramatically elevated interleukin-2 (IL-2) and decreased tumor necrosis factor-α (TNF-α) in supernatants of activated splenocytes, but had no significant effect on interferon-γ (IFN-γ). Administration of pXLG-mEndo, radiation, or both modified the tumor-induced aberrations in IL-2 and TNF-α; IFN-γ production was decreased by radiation. Red blood cell counts, hemoglobin, and hematocrit were low in tumor-bearing mice, but there were no treatment-related differences among groups. Platelet counts were reduced, whereas their volumes were increased in tumor-bearing mice; both parameters were only slightly affected by either pXLG-mEndo or control plasmid injection, however. The data demonstrate in the Lewis lung carcinoma model that tumor-localized endostatin gene therapy and radiation had significant effects on cells and cytokines that can influence angiogenesis, tumor growth, and immune status.

Radiogenic Therapy: Novel Approaches for Enhancing Tumor Radiosensitivity

Radiotherapy (RT) is a well established modality for treating many forms of cancer. However, despite many improvements in treatment planning and delivery, the total radiation dose is often too low for tumor cure, because of the risk of normal tissue damage. Gene therapy provides a new adjunctive strategy to enhance the effectiveness of RT, offering the potential for preferential killing of cancer cells and sparing of normal tissues. This specificity can be achieved at several levels including restricted vector delivery, transcriptional targeting and specificity of the transgene product. This review will focus on those gene therapy strategies that are currently being evaluated in combination with RT, including the use of radiation sensitive promoters to control the timing and location of gene expression specifically within tumors. Therapeutic transgenes chosen for their radiosensitizing properties will also be reviewed, these include:

gene correction therapy, in which normal copies of genes responsible for radiation-induced apoptosis are transfected to compensate for the deletions or mutated variants in tumor cells (p53 is the most widely studied example). enzymes that synergize the radiation effect, by generation of a toxic species from endogenous precursors ( e.g., inducible nitric oxide synthase) or by activation of non toxic prodrugs to toxic species ( e.g., herpes simplex virus thymidine kinase/ganciclovir) within the target tissue. conditionally replicating oncolytic adenoviruses that synergize the radiation effect. membrane transport proteins ( e.g., sodium iodide symporter) to facilitate uptake of cytotoxic radionuclides.

The evidence indicates that many of these approaches are successful for augmenting radiation induced tumor cell killing with clinical trials currently underway.

NO to cancer: The complex and multifaceted role of nitric oxide and the epigenetic nitric oxide donor, RRx-001

The endogenous mediator of vasodilation, nitric oxide (NO), has been shown to be a potent radiosensitizer. However, the underlying mode of action for its role as a radiosensitizer – while not entirely understood – is believed to arise from increased tumor blood flow, effects on cellular respiration, on cell signaling, and on the production of reactive oxygen and nitrogen species (RONS), that can act as radiosensitizers in their own right. NO activity is surprisingly long-lived and more potent in comparison to oxygen. Reports of the effects of NO with radiation have often been contradictory leading to confusion about the true radiosensitizing nature of NO. Whether increasing or decreasing tumor blood flow, acting as radiosensitizer or radioprotector, the effects of NO have been controversial. Key to understanding the role of NO as a radiosensitizer is to recognize the importance of biological context. With a very short half-life and potent activity, the local effects of NO need to be carefully considered and understood when using NO as a radiosensitizer. The systemic effects of NO donors can cause extensive side effects, and also affect the local tumor microenvironment, both directly and indirectly. To minimize systemic effects and maximize effects on tumors, agents that deliver NO on demand selectively to tumors using hypoxia as a trigger may be of greater interest as radiosensitizers. Herein we discuss the multiple effects of NO and focus on the clinical molecule RRx-001, a hypoxia-activated NO donor currently being investigated as a radiosensitizer in the clinic.

•NO radiosensitizer activity is complex with variable results in clinical and non-clinical studies

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NO radiosensitizes by reaction with DNA radicals, by its metabolites and by impact on the vasculature.

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Understanding the local and context-specific activity of NO is key for radiosensitizer development

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RRx-001 induces NO production under hypoxia with promising radiosensitizing activity.

Delivery of nitric oxide to the interior of mammalian cell by carbon nanotube: MD simulation

Computer simulations have been performed to study the nanoindentation of phospholipid bilayer by the single-walled armchair carbon nanotube, filled with the nitric oxide molecules. The process has been simulated by means of molecular dynamics (MD) technique at physiological temperature T = 310 K with a constant pulling velocity of the nanotube. The force acting on the nanotube during membrane penetration has been calculated. We show that the indentation by carbon nanotube does not permanently destroy the membrane structure (self-sealing of the membrane occurs). The mobility of nitric oxide molecules during the membrane nanoindentation is discussed.

Evaluation of p21 promoter for interleukin 12 radiation induced transcriptional targeting in a mouse tumor model

BACKGROUND

Radiation induced transcriptional targeting is a gene therapy approach that takes advantage of the targeting abilities of radiotherapy by using radio inducible promoters to spatially and temporally limit the transgene expression. Cyclin dependent kinase inhibitor 1 (CDKN1A), also known as p21, is a crucial regulator of the cell cycle, mediating G1 phase arrest in response to a variety of stress stimuli, including DNA damaging agents like irradiation. The aim of the study was to evaluate the suitability of the p21 promoter for radiation induced transcriptional targeting with the objective to test the therapeutic effectiveness of the combined radio-gene therapy with p21 promoter driven therapeutic gene interleukin 12.

METHODS

To test the inducibility of the p21 promoter, three reporter gene experimental models with green fluorescent protein (GFP) under the control of p21 promoter were established by gene electrotransfer of plasmid DNA: stably transfected cells, stably transfected tumors, and transiently transfected muscles. Induction of reporter gene expression after irradiation was determined using a fluorescence microplate reader in vitro and by non-invasive fluorescence imaging using fluorescence stereomicroscope in vivo. The antitumor effect of the plasmid encoding the p21 promoter driven interleukin 12 after radio-gene therapy was determined by tumor growth delay assay and by quantification of intratumoral and serum levels of interleukin 12 protein and intratumoral concentrations of interleukin 12 mRNA.

RESULTS

Using the reporter gene experimental models, p21 promoter was proven to be inducible with radiation, the induction was not dose dependent, and it could be re-induced. Furthermore radio-gene therapy with interleukin 12 under control of the p21 promoter had a good antitumor therapeutic effect with the statistically relevant tumor growth delay, which was comparable to that of the same therapy using a constitutive promoter.

CONCLUSIONS

In this study p21 promoter was proven to be a suitable candidate for radiation induced transcriptional targeting. As a proof of principle the therapeutic value was demonstrated with the radio-inducible interleukin 12 plasmid providing a synergistic antitumor effect to radiotherapy alone, which makes this approach feasible for the combined treatment with radiotherapy.

Modification of DNA damage mechanisms by nitric oxide during ionizing radiation

Nitric oxide ((•)NO) is a very effective radiosensitizer of hypoxic mammalian cells. In vivo (•)NO may have effects on tumor vasculature and hence on tumor oxygenation and it may also interact with radiation-produced radicals to modify DNA lesions. Few studies have addressed this last aspect, and we report here specific base modifications that result from reaction of (•)NO with radicals in DNA bases and in plasmid DNA after irradiation. 2'-Deoxyxanthosine monophosphate and 2'-deoxy-8-azaguanosine monophosphate (8azadGMP) are formed upon γ-irradiation of 2'-deoxyguanosine monophosphate (dGMP) in the presence of micromolar levels of (•)NO in anoxia. In addition, the presence of (•)NO at physiological pH inhibits the formation of the well-described (•)OH-induced oxidation product of dGMP, 8-oxo-2'-deoxyguanosine monophosphate. Single-strand breaks are induced in plasmid DNA when γ-irradiated in anoxia, whereas in the presence of (•)NO the number of breaks is reduced by approximately threefold, and evidence is shown for the formation of 8azadGMP in these plasmids. The consequence of the base modifications by (•)NO are as yet unknown although additional breaks are revealed in irradiated plasmid DNA after treatment with glycosylases involved in base excision repair. V79-4 cells irradiated in anoxia show an enhancement in the number of γH2AX foci when (•)NO is present, particularly evident a few hours postirradiation, indicative of the formation of replication-induced DNA damage. We propose that the consequence of (•)NO-induced base modifications in anoxia contributes to its radiosensitization of cells.

Gamma irradiation and targeted radionuclides enhance the expression of the noradrenaline transporter transgene controlled by the radio-inducible p21(WAF1/CIP1) promoter

The use of radiation-inducible promoters to drive transgene expression offers the possibility of temporal and spatial regulation of gene activation. This study assessed the potential of one such promoter element, p21(WAF1/CIP1) (WAF1), to drive expression of the noradrenaline transporter (NAT) gene, which conveys sensitivity to radioiodinated meta-iodobenzylguanidine (MIBG). An expression vector containing NAT under the control of the radiation-inducible WAF1 promoter (pWAF/NAT) was produced. The non-NAT expressing cell lines UVW (glioma) and HCT116 (colorectal cancer) were transfected with this construct to assess radiation-controlled WAF1 activation of the NAT gene. Transfection of UVW and HCT cells with pWAF/NAT conferred upon them the ability to accumulate [(131)I]MIBG, which led to increased sensitivity to the radiopharmaceutical. Pretreatment of transfected cells with γ radiation or the radiopharmaceuticals [(123)I]MIBG or [(131)I]MIBG induced dose- and time-dependent increases in subsequent [(131)I]MIBG uptake and led to enhanced efficacy of [(131)I]MIBG-mediated cell kill. Gene therapy using WAF1-driven expression of NAT has the potential to expand the use of this therapeutic modality to tumors that lack a radio-targetable feature.

Is Nitric Oxide (NO) the Last Word in Radiosensitization? A Review

As a short-lived radical that diffuses across membranes, rather than interacting with membrane-bound receptors, nitric oxide (NO) represents a significant departure from synthetically derived radiosensitizers. An endogenous compound, NO may equal or surpass its molecular cousin, oxygen, as a hypoxic radiosensitizer, through pleiotropic phenotypic effects on tumor perfusion, cell signaling, mitochondrial respiration, the fixation of radiation-induced damage, and the radioprotection of normal tissue. However, unlike oxygen, in the context of radiosensitization, the clinical role and utility of NO are poorly understood, with often contradictory and controversial reported effects: whether NO functions as a radiosensitizer may ultimately be contextual to the tumor microenvironment. This may make NO manipulation an ideal candidate for a personalized radiosensitization approach tailored to specific patient and tumor types/microenvironmental characteristics. Effective delivery of NO both systemically and directly to the tumor may be critical to the success of this approach. Compounds that release NO or NO precursors have the potential to drive innovation and result in a new fertile branch of the radiosensitizer tree.

Targeting nitric oxide for cancer therapy

A blueprint for the ideal anticancer molecule would include most of the properties of nitric oxide (NO•), but the ability to exploit these characteristics in a therapeutic setting requires a detailed understanding of the biology and biochemistry of the molecule. These properties include the ability of NO• to affect tumour angiogenesis, metastasis, blood flow and immuno surveillance. Furthermore NO• also has the potential to enhance both radio- and chemotherapy. However, all of these strategies are dependent on achieving appropriate levels of NO•, since endogenous levels of NO• appear to have a clear role in tumour progression. This review aims to summarize the role of NO• in cancer with particular emphasis on how the properties of NO• can be exploited for therapy.

Improvement and induction property of radiation-responsive promoter through DNA shuffling of 5'-flanking regions of the human p21 gene

A promoter that augments gene expression in response to stimulation of ionizing radiation would be a desired tool for radiogenetic therapy, a combination of radiotherapy and gene therapy. Although various promoters occurring naturally or artificially have been used for researches, one showing higher reactivity to ionizing radiation is desirable. In the present study, we attempted to improve a radiation-responsive promoter of the p21 through a technique called DNA shuffling. A library of DNA fragments was constructed by re-ligation of randomly digested promoter fragments and improved promoters were chosen out of the library. We repeated this process twice to obtain a promoter showing 2.6-fold better reactivity to ionizing radiation compared with its parent, p21 promoter after 10 Gy gamma-ray irradiation. Nucleotide sequence analyses revealed that the obtained promoter was densely packed with some of the cis-acting elements including binding sites for p53, NF-kappaB, NRF-2, AP-1 and NF-Y more than p21 promoter. In addition, it was shown that its induction by ionizing radiation was dependent upon p53 status of a cell line, suggesting that the promoter retained properties of the p21 promoter. This technique is simple and efficient to improve a promoter responsive to other stimulus of interest besides IR.

Mesenchymal stem cells as a gene therapy carrier for treatment of fibrosarcoma

BACKGROUND AIMS

Cell-based gene therapy is an alternative to viral and non-viral gene therapy. Emerging evidence suggests that mesenchymal stem cells (MSC) are able to migrate to sites of tissue injury and have immunosuppressive properties that may be useful in targeted gene therapy for sustained specific tissue engraftment.

METHODS

In this study, we injected intravenously (i.v.) 1x10(6) MSC, isolated from green fluorescent protein (GFP) transgenic rats, into Rif-1 fibrosarcoma-bearing C3H/HeN mice. The MSC had been infected using a lentiviral vector to express stably the luciferase reporter gene (MSC-GFP-luci). An in vivo imaging system (IVIS 200) and Western blotting techniques were used to detect the distribution of MSC-GFP-luci in tumor-bearing animals.

RESULTS

We observed that xenogenic MSC selectively migrated to the tumor site, proliferated and expressed the exogenous gene in subcutaneous fibrosarcoma transplants. No MSC distribution was detected in other organs, such as the liver, spleen, colon and kidney. We further showed that the FGF2/FGFR pathways may play a role in the directional movement of MSC to the Rif-1 fibrosarcoma. We performed in vitro co-culture and in vivo tumor growth analysis, showing that MSC did not affect the proliferation of Rif-1 cells and fibrosarcoma growth compared with an untreated control group. Finally, we demonstrated that the xenogenic MSC stably expressing inducible nitric oxide synthase (iNOS) protein transferred by a lentivirus-based system had a significant inhibitory effect on the growth of Rif-1 tumors compared with MSC alone and the non-treatment control group.

CONCLUSIONS

iNOS delivered by genetically modified iNOS-MSC showed a significant anti-tumor effect both in vitro and in vivo. MSC may be used as a target gene delivery vehicle for the treatment of fibrosarcoma and other tumors.

Activator protein 2alpha suppresses intestinal tumorigenesis in the Apc(min) mouse

Activator protein 2alpha (AP-2alpha) is a putative tumor suppressor, and various reports have described the loss or reduction of AP-2alpha expression in cutaneous malignant melanomas, as well as in cancers of the prostate, breast and colon. Previously, AP-2alpha was shown to attenuate beta-catenin/T-cell factor-4 (TCF-4) nuclear interactions and beta-catenin/TCF-4-dependent transcriptional activity in human colorectal cancer cells [Q. Li, R.H. Dashwood, Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells, J. Biol. Chem. 279 (2004) 45669-45675]. Here, we show that in vivo gene delivery of AP-2alpha suppressed intestinal polyp formation in the Apc(min) mouse, and protected against the development of anemia and splenomegaly. Immunoblot analyses and immunohistochemistry following gene delivery revealed an increase in AP-2alpha expression in the mouse intestinal mucosa and liver. Co-immunoprecipitation experiments provided evidence for interactions between AP-2alpha, beta-catenin, and adenomatous polyposis coli (APC) proteins in mouse intestinal mucosa, as well as in a primary human colorectal cancer. Collectively, these studies support a tumor suppressor role for AP-2alpha in the gastrointestinal tract, and suggest that AP-2alpha represents a novel target for therapeutic intervention in human cancers characterized by dysregulated Wnt signaling.

Nitric oxide synthase gene therapy enhances the toxicity of cisplatin in cancer cells

BACKGROUND

Nitric oxide (NO.) derived from donor drugs has been shown to be an effective chemosensitizer in vitro. We investigated the combination of inducible nitric oxide synthase (iNOS) gene transfer, driven by a strong constitutive promoter (cytomegalovirus; CMV) with the DNA cross-linking agent cisplatin in mouse and human tumour cell lines.

METHODS

Proof of principal experiments were performed in the radiation-induced fibrosarcoma-1 (RIF-1) murine cell line. Cells were transfected with constitutively expressed CMV/iNOS plasmid DNA using a cationic lipid vector, before exposure to cisplatin. In vivo efficacy was determined in an intradermal RIF-1 tumour model, with intraperitoneal administration of cisplatin. Additionally, treatment potential was investigated in various human tumour cell lines including human prostate (DU145 and PC3) and human colon (HT29 and HCT116) cancer cell lines. Experimental endpoints were established using western blot, Greiss test, clonogenic assay and tumour growth delay.

RESULTS

Transfection of RIF-1 tumour cells in vitro with the CMV/iNOS significantly enhanced the cytotoxicity of cisplatin (0.2-1.0 microM). In vivo transfer of CMV/iNOS by direct injection into established RIF-1 tumours caused a significant (p = 0.0027) delay in tumour growth. CMV/iNOS gene transfer in vitro resulted in the strong expression of iNOS DNA in all cell lines, and significantly increased levels of NO. in all cell lines except HCT116.

CONCLUSIONS

Significant chemosensitization of cisplatin cytotoxicity was observed in the presence of NO. derived from the overexpression iNOS. We conclude that p53 status of the various cell lines was unlikely to be responsible for cisplatin-induced apoptosis.

Gene therapy via inducible nitric oxide synthase: a tool for the treatment of a diverse range of pathological conditions

Nitric oxide (NO(.)) is a reactive nitrogen radical produced by the NO synthase (NOS) enzymes; it affects a plethora of downstream physiological and pathological processes. The past two decades have seen an explosion in the understanding of the role of NO(.) biology, highlighting various protective and damaging modes of action. Much of the controversy surrounding the role of NO(.) relates to the differing concentrations generated by the three isoforms of NOS. Both calcium-dependent isoforms of the enzyme (endothelial and neuronal NOS) generate low-nanomolar/picomolar concentrations of NO(.). By contrast, the calcium-independent isoform (inducible NOS (iNOS)) generates high concentrations of NO(.), 2-3 orders of magnitude greater. This review summarizes the current literature in relation to iNOS gene therapy for the therapeutic benefit of various pathological conditions, including various states of vascular disease, wound healing, erectile dysfunction, renal dysfunction and oncology. The available data provide convincing evidence that manipulation of endogenous NO(.) using iNOS gene therapy can provide the basis for future clinical trials.

iNOS as a therapeutic target for treatment of human tumors

Nitric oxide synthase (NOS) has been shown to be overexpressed in a number of human tumors compared to normal tissues and therefore potentially represents an exploitable target in future anticancer therapies. To achieve this, there will be a need to profile tumors to identify those expressing high levels of NOS; alternatively, endogenous (low) levels of NOS could be modulated by induction or through gene therapy approaches. NOS consists of a reductase domain which shares a high degree of sequence homology with P450 reductase and this domain supplies reducing equivalents to a haem containing oxygenase domain that is responsible for the production of nitric oxide. Thus, there are a number of routes of exploitation. Firstly, to take advantage of the reductase domain to activate bioreductive drugs as has been exemplified with tirapazamine and now extended to AQ4N (1,4-bis{2-(dimethylamino-N-oxide)ethylamino}5,8-dihydroxy-anthracene-9,10-dione). Secondly, to take advantage of nitric oxide production for its ability to increase the sensitivity of resistant hypoxic cells to radiation. Lastly, to utilize inhibition of HIF-1 to amplify NO based therapies. In this review we provide examples/evidence of how these objectives can be achieved.

Nitric oxide-induced resistance or sensitization to death in tumor cells

This report summarizes the present state of our knowledge pertaining to the NO-induced resistance or sensitization of tumor cell death. The effects of NO and its synergy with members of the TNF family, with cytotoxic drugs, and with ionizing radiations have been investigated. The dual effect of NO-induced resistance or sensitization and the underlying molecular mechanisms are discussed.

Bioreductive drugs: from concept to clinic

One of the key issues for radiobiologists is the importance of hypoxia to the radiotherapy response. This review addresses the reasons for this and primarily focuses on one aspect, the development of bioreductive drugs that are specifically designed to target hypoxic tumour cells. Four classes of compound have been developed since this concept was first proposed: quinones, nitroaromatics, aliphatic and heteroaromatic N-oxides. All share two characteristics: (1) they require hypoxia for activation and (2) this activation is dependent on the presence of specific reductases. The most effective compounds have shown the ability to enhance the anti-tumour efficacy of agents that kill better-oxygenated cells, i.e. radiation and standard cytotoxic chemotherapy agents such as cisplatin and cyclophosphamide. Tirapazamine (TPZ) is the most widely studied of the lead compounds. After successful pre-clinical in vivo combination studies it entered clinical trial; over 20 trials have now been reported. Although TPZ has enhanced some standard regimens, the results are variable and in some combinations toxicity was enhanced. Banoxantrone (AQ4N) is another agent that is showing promise in early phase I/II clinical trials; the drug is well tolerated, is known to locate in the tumour and can be given in high doses without major toxicities. Mitomycin C (MMC), which shows some bioreductive activation in vitro, has been tested in combination trials. However, it is difficult to assign the enhancement of its effects to targeting of the hypoxic cells because of the significant level of its hypoxia-independent toxicity. More specific analogues of MMC, e.g. porfiromycin and apaziquone (EO9), have had variable success in the clinic. Other new drugs that have good pre-clinical profiles are PR 104 and NLCQ-1; data on their clinical safety/efficacy are not yet available. This paper reviews the pre-clinical data and discusses the clinical studies that have been reported.

Selective radiosensitization by nitric oxide in tumor cell lines

The radiosensitizing effect of nitric oxide (NO) on mouse and human tumor cells with different degrees of malignancy was evaluated. Cells pre-treated with the NO donor diethylenetriamine-NO (DETA-NO), were irradiated with gamma rays. Survival curves were obtained by clonogenicity and fitted to the linear-quadratic model. Results demonstrated an association between radiosensitization and degree of malignancy. The more malignant the cell line, the higher the degree of radiosensitization by DETA-NO. In conclusion, the differential radiosensitizing effect of DETA-NO shown here is of great interest for the potential use of NO in radiotherapy, due to an enhanced radiation effect on tumor vs. normal tissue.

Human osteocalcin: a strong promoter for nitric oxide synthase gene therapy, with specificity for hormone refractory prostate cancer

BACKGROUND

Gene therapy has been identified as a promising treatment strategy for hormone refractory prostate cancer (HRPC). We report, for the first time, the use of the human osteocalcin (hOC) promoter to control inducible nitric oxide synthase (iNOS) transgene expression in HRPC.

METHODS

Human prostate carcinoma cells (PC3, DU145, LNCaP), colon cancer cells (HT29) and human microvascular endothelial cells (HMEC-1) were transfected in vitro with constitutively driven CMV/iNOS or hOC/iNOS plasmid DNA by cationic lipid vector. End points of these experiments were Western blotting, NO(.) generation using the Greiss test to measure accumulated nitrite, and clonogenic assay.

RESULTS

Transfection of the hOC/iNOS plasmid increased iNOS protein and total nitrite levels in PC3 and DU145 cells, but not LNCaP or HT29. Transfection with CMV/iNOS or hOC/iNOS resulted in no additional cytotoxicity in androgen-dependent LNCaP cells or in the non-prostate cell lines. However, transfection with either construct resulted in a greatly reduced cell survival (to 10-20%) in the androgen-independent PC3 and DU145 cell lines.

CONCLUSIONS

Utilising the tumour-type specific properties of the hOC promoter in tandem with the iNOS gene, we have demonstrated target cell specificity, and transgene activation, in the androgen-independent prostate cancer cell lines (PC3 and DU145), an effect absent in normal and androgen-dependent cells. Furthermore, the levels of NO(.) generated are comparable with those seen generated with constitutively (CMV)-driven iNOS. The data obtained from this study provide a basis for future development of hOC/iNOS gene therapy.

p21(WAF1)-mediated transcriptional targeting of inducible nitric oxide synthase gene therapy sensitizes tumours to fractionated radiotherapy

Cancer gene therapy that utilizes toxic transgene products requires strict transcriptional targeting to prevent adverse normal tissue effects. We report on the use of a promoter derived from the cyclin dependent kinase inhibitor, p21((WAF1)), to control transgene expression. We demonstrate that this promoter is relatively silent in normal cells (L132, FSK, HMEC-1) compared to the almost constitutive expression obtained in tumour cells (DU145, LNCaP, HT29 and MCF-7) of varying p53 status, a characteristic that will be important in gene therapy protocols. In addition, we found that the p21((WAF1)) promoter could be further induced by both external beam radiation (up to eight-fold in DU145 cells), intracellular-concentrated radionuclides ([(211)At]MABG) (up to 3.5-fold in SK-N-BE(2c) cells) and hypoxia (up to four-fold in DU145 cells). We have previously achieved significant radiosensitization of tumour cells both in vitro and in vivo by using inducible nitric oxide synthase (iNOS) gene therapy to generate the potent radiosensitizer, nitric oxide (NO(.-)). Here, we report that a clinically relevant schedule of p21((WAF1))-driven iNOS gene therapy significantly sensitized both p53 wild-type RIF-1 tumours and p53 mutant HT29 tumours to fractionated radiotherapy. Our data highlight the utility of this p21((WAF1))/iNOS-targeted approach.

Cancer gene therapy: Combination with radiation therapy and the role of bystander cell killing in the anti-tumor effect

Current anti-cancer modalities such as surgery, chemo- and radiation therapies have only limited success in cancer treatment. Gene therapy is a promising new tool to improve outcomes. In this review, first we summarize the various strategies to kill tumor cells, and then focus on the bystander effect of gene therapy. A variety of strategies, such as gene-directed enzyme pro-drug therapy, activation of an anti-tumor immune attack, application of replication-competent and oncolytic viral vectors, tumor-specific as well as radiation- and hypoxiainduced gene expression, might be applied to target tumor cells. We put special emphasis on the combination of these approaches with local tumor irradiation. Using the available vector systems, only a small portion of cancer cells contains the therapeutic genes under clinical situations. However, cells directly targeted by gene therapy will transfer death signals to neighboring cancer cells. This bystander cell killing improves the efficiency of cancer gene therapy. Death signals are delivered by cell-to-cell communication through gap junction intercellular contacts, release of toxic metabolites into the neighborhood or to larger distances, phagocytosis of apoptotic bodies, and the activation of the immune system. Bystander cell killing can be enhanced by the introduction of gap junction proteins into cells, by further activating the immune system with immune-stimulatory molecules, or by introducing genes that help the transfer of cytotoxic genes and/or metabolites into bystander cells. In conclusion, although bystander cell killing can improve therapeutic effects, there should be additional developments in cancer gene therapy for a more efficient clinical application.

Gene manipulation to enhance MIBG-targeted radionuclide therapy

The goal of targeted radionuclide therapy is the deposition in malignant cells of sterilizing doses of radiation without damaging normal tissue. The radiopharmaceutical [(131)I]meta-iodobenzylguanidine ([(131)I]MIBG) is an effective single agent for the treatment of neuroblastoma. However, uptake of the drug in malignant sites is insufficient to cure disease. A growing body of experimental evidence indicates exciting possibilities for the integration of gene transfer with [(131)I]MIBG-targeted radiotherapy.

Enhancement of radiation effects by pXLG-mEndo in a lung carcinoma model

PURPOSE

Endostatin is a potent antiangiogenesis protein with little or no toxicity that has potential to enhance radiotherapy. The major goal of this study was to evaluate the combination of radiation and endostatin gene therapy in a preclinical lung cancer model.

METHODS

Plasmid pXLG-mEndo, constructed in our laboratory, includes the mouse endostatin gene cloned into the pWS4 vector. The kinetics of endostatin expression and efficacy of the pXLG-mEndo and radiation ((60)Co gamma-rays) combination was evaluated in the C57BL/6 mouse-Lewis lung carcinoma (LLC) model. The LLC cells were implanted s.c. and pXLG-mEndo was injected intratumorally 12-14 days later without any transfection agent; a dose of 10 Gy radiation was applied approximately 16 h thereafter. Some groups received each modality twice. Endostatin, vascular endothelial growth factor (VEGF), and transforming growth factor-beta1 (TGF-beta1) were quantified in plasma and tumors, and tumor vasculature was examined.

RESULTS

Endostatin expression within LLC tumors peaked on Day 7 after pXLG-mEndo injection. Addition of radiation to pXLG-mEndo significantly enhanced the level of tumor endostatin compared with plasmid alone (p < 0.05). Tumor growth was significantly delayed in mice receiving pXLG-mEndo plus radiation compared with no treatment (p < 0.005), radiation (p < 0.05), and control plasmid (p < 0.05). The number of LLC tumor vessels was reduced after combined treatment (p < 0.05), and significant treatment-related changes were observed in both VEGF and TGF-beta1.

CONCLUSIONS

The data demonstrate that delivery of endostatin by pXLG-mEndo as an adjuvant to radiation can significantly enhance the antitumor efficacy of radiotherapy in the LLC mouse tumor model and support further investigation of this unique combination therapy.

Evaluation of a synthetic CArG promoter for nitric oxide synthase gene therapy of cancer

Nitric oxide synthase gene therapy has been shown to be effective at inducing apoptosis in experimental tumours and sensitizing them to radiotherapy. We have also shown that expression of inducible nitric oxide synthase (iNOS) can be effectively restricted to the tumour volume by the use of the radiation inducible promoter (WAF1) to drive the transgene in clinically relevant protocols. A synthetic construct (pE9), incorporating nine radiosensitive CArG elements from the Egr1 promoter, has recently been developed for cancer gene therapy. We have now investigated basal gene expression of transgenes driven by this promoter to assess its suitability for use in iNOS gene therapy protocols in vivo. Transfection of human microvascular endothelial cells (HMEC-1) with pE9iNOS, using a cationic lipid vector, resulted in progressively increasing (<5-fold) levels of iNOS protein expression up to 8 h after transfection. Transfection of an ex vivo rat artery preparation with pE9iNOS caused 83% inhibition of response to the vasoconstrictor phenylephrine (PE). CMViNOS transfection also reduced response to PE, but by only 52%. A single injection of 25 microg of pE9iNOS DNA in a lipid vector into the centre of a murine sarcoma (RIF1) induced iNOS protein expression by four-fold and increased nitrite concentration eight-fold. This caused a 7-day delay in tumour growth and was more effective than the constitutive CMV-driven construct. Our data suggest that generation of NO*, as a result of iNOS overexpression, is capable of further activating the E9 promoter, through a positive feedback loop, yielding stronger and sustained levels of NO*. This pE9iNOS combination may, therefore, be particularly useful in an anticancer gene therapy strategy as its antitumour effect in vivo was clearly superior to that of the strong constitutive promoter, CMV.

Nitric oxide and ionizing radiation synergistically promote apoptosis and growth inhibition of cancer by activating p53

Nitric oxide (NO) is a potent tumor radiosensitizer; however, its clinical use is limited by systemic side effects. We have demonstrated previously that gene transfer of the human inducible NO synthase (iNOS) gene into tumor cells and tumors induces high-output NO production that significantly enhances tumor radioresponsiveness, with no observed side effects. Notably, iNOS gene transfer enhances tumor radioresponsiveness via apoptotic cell death. Because NO and ionizing radiation are both known to promote p53-dependent apoptosis, we hypothesized that p53 activation might be a primary mechanism for the synergy of these two genotoxic stresses. We report that NO and ionizing radiation synergistically activate p53 in colorectal cancers grown in athymic mice by augmenting phosphorylation of p53 at serine 15. The effect of NO and ionizing radiation on tumor cell apoptosis and tumor radioresponsiveness is significantly reduced in p53 knockout isogenic cancer cell lines. Furthermore, the transfer of both p53 and iNOS genes into tumor cells lacking functional p53 enhanced their radioresponsiveness more than transfer of either gene alone.

Oxidative stress, redox, and the tumor microenvironment

Cellular metabolism is critical for the generation of energy in biological systems; however, as a result of electron transfer reactions, reactive oxygen species (ROS) are generated in aerobic cells. Although low amounts of ROS are easily tolerated by the cell, abnormally high levels of ROS induce oxidative stress. ROS are also produced after exposure to ionizing radiation, selected chemotherapeutic agents, hyperthermia, inhibition of antioxidant enzymes, or depletion of cellular reductants such as NADPH and glutathione. Oxidative stress such as ionizing radiation produces a variety of highly reactive free radicals that damage cells, initiate signal transduction pathways, and alter gene expression. Cells are capable of countering the effects of oxidative stress by virtue of a complex redox buffering system. With respect to the radiation treatment of cancer, components of the cellular redox armamentarium may be targeted to enhance cell killing in the case of tumors and/or protection in the case of normal tissues.

Nitric oxide as a radiosensitizer: evidence for an intrinsic role in addition to its effect on oxygen delivery and consumption

Different nitric oxide (NO)-mediated treatments (e.g., isosorbide dinitrate, insulin and electrical stimulation of the host tissue) have been investigated for their effects on tumor oxygenation and radiation sensitivity. We further address the issue of the role played by modulation of the NO-pathway in tumor radiosensitivity. For this purpose, the local concentration of NO was monitored after treatment in FSaII tumors and a comparison between the sensitivity of LLC tumors implanted both on eNOS(-/-) and wild-type (WT) mice was carried out. First, we demonstrate the central role played by eNOS in the radiosensitizing effect after application of insulin treatment and electrical stimulation: a significant increase in tumor NO content is induced by these treatments and the increase in tumor oxygenation, as well as the radiosensitizing effect are abolished in eNOS knock-out mice, in contrast to WT mice. Second, by comparing the level of oxygen and NO achieved in tumors after NO-mediated treatments and carbogen, we provide evidence that these NO-mediated treatments are not simply acting by a single oxygen effect. These treatments induced significant regrowth delays compared to carbogen, despite a smaller increase in tumor oxygenation. For the NO-mediated treatments, there was a direct correlation between the NO content and the radiosensitizing effect. These data strongly suggest that NO is a complementary factor additive to oxygen in determining the sensitivity to irradiation and we therefore propose that NO acts as an intrinsic radiosensitizer in vivo.

Adenoviral Gene Transfer of the Human Inducible Nitric Oxide Synthase Gene Enhances the Radiation Response of Human Colorectal Cancer Associated with Alterations in Tumor Vascularity

Nitric oxide is a potent radiosensitizer of tumors, but its use clinically is limited by serious side effects when administered systemically. We have demonstrated previously that gene transfer of the inducible nitric oxide synthase gene (iNOS) into colorectal cancer cells enhances radiation-induced apoptosis in vitro. The objectives of this study were to further characterize the effects of iNOS gene transfer on the radiosensitivity of human colorectal cancer cells in vitro and tumors grown in athymic nude mice. Adenoviral gene transfer of iNOS (AdiNOS) into human colorectal cancer cell lines (HCT-116 and SNU-1040 cells) significantly enhanced the effects of radiation with sensitizing enhancement ratios (0.1) of 1.65 and 1.6, respectively. The radiation enhancement induced by iNOS was associated with increased iNOS expression and nitric oxide production and prevented by L-NIO, an enzymatic inhibitor of iNOS. AdiNOS treatment of HCT-116 tumors combined with radiation (2 Gy x three fractions) led to a 3.4-fold greater (P < 0.005) tumor growth delay compared with radiation (RT) alone. AdiNOS plus RT also caused significant (P < 0.01) tumor regression with 63% of tumors regressing compared with only 6% of tumors treated with RT. AdiNOS plus RT significantly (P < or = 0.001) increased the percentage of apoptotic cells (22 +/- 4%) compared with either tumors treated with control vector plus RT (9 +/- 1%), AdiNOS alone (9 +/- 3%), or no treatment (2 +/- 1%). These radiosensitizing effects of AdiNOS occurred at low infection efficiency (4% of tumor infected), indicating a significant bystander effect.

Target validation of cytochrome P450 CYP1B1 in prostate carcinoma with protein expression in associated hyperplastic and premalignant tissue

PURPOSE

To investigate the localization and distribution of cytochrome P450 CYP1B1 protein expression in patients diagnosed with prostate carcinoma compared to those with bladder carcinoma. To validate CYP1B1 as a molecular target for the development of selective cancer therapeutics for use in combination with radiation.

METHODS AND MATERIALS

Prostatectomy specimens (n = 33) of moderate Gleason grade (3 + 3 and 3 + 4) were analyzed immunohistochemically for CYP1B1 protein expression using a specific monoclonal antibody for the enzyme. The intensity of CYP1B1 staining was assessed both semiquantitatively using visual scoring and quantitatively by spectral imaging microscopy using reference spectra and compared with bladder carcinoma (n = 22).

RESULTS

CYP1B1 protein expression was present in 75% of prostate carcinomas (n = 27) compared to 100% of bladder carcinomas (n = 22). In both cases, CYP1B1 protein expression was heterogeneous and localized in the cytoplasm of the tumor cells but absent from the surrounding stromal tissue. CYP1B1 was also detected in premalignant prostatic intraepithelial neoplasia (n = 2, 100%), as well as noncancerous tissues, including benign prostatic hyperplasia (n = 27, 82%), metaplastic prostatic urothelium (n = 8, 100%), and hyperplastic prostatic urothelium (n = 14, 100%). Higher CYP1B1 protein expression in bladder vs. prostate carcinoma was confirmed by their corresponding average normalized absorbances (+/- standard deviation), measured as 1.40 +/- 0.44 and 0.55 +/- 0.09, respectively. Overall CYP1B1 staining intensity in prostate carcinoma was similar to that in prostatic intraepithelial neoplasia, benign prostatic hyperplasia, and hyper-/metaplastic urothelial tissue. No CYP1B1 was detected in normal prostate tissue.

CONCLUSIONS

CYP1B1 is overexpressed in prostate carcinoma at a high frequency and is also detectable in the associated premalignant and hyperplastic tissue, implicating a possible link with malignant progression and CYP1B1 as a suitable target for therapy. Spectral imaging microscopy has highlighted differences in CYP1B1 protein expression between different cancers.

Recent developments in ocular gene therapy

The past two to three years have witnessed a remarkable increase in the number of gene therapy studies to treat almost every disease of the eye. All types of delivery systems, viral and non-viral, have been used. Experiments have begun to move from the use of reporters, to genes with potential therapeutic value. In this paper, rather than giving an overview from the beginning of ocular gene therapy, I have chosen to review its most recent advances. Although numerous issues remain to be solved, the emerging picture is encouraging. Within the experimental setting, conditions in the anterior and posterior segments have been improved by the administration of genes encoding beneficial proteins. In one case, vision has been restored in a congenitally blind animal. Limitations do exit, however a greater understanding of the molecular biology of eye tissues coupled with the development of low immunogenicity vectors will continue edging the way for a future use of gene therapy in the clinical setting.

Transcriptional Targeting in Cancer Gene Therapy

Cancer gene therapy has been one of the most exciting areas of therapeutic research in the past decade. In this review, we discuss strategies to restrict transcription of transgenes to tumour cells. A range of promoters which are tissue-specific, tumour-specific, or inducible by exogenous agents are presented. Transcriptional targeting should prevent normal tissue toxicities associated with other cancer treatments, such as radiation and chemotherapy. In addition, the specificity of these strategies should provide improved targeting of metastatic tumours following systemic gene delivery. Rapid progress in the ability to specifically control transgenes will allow systemic gene delivery for cancer therapy to become a real possibility in the near future.

Overexpression of the human inducible nitric oxide synthase gene enhances radiation-induced apoptosis in colorectal cancer cells via a caspase-dependent mechanism

Nitric oxide (NO) has been reported to sensitize cancer cells to radiation. Since delivery of NO to tumors is limited in vivo by systemic toxicity of NO, we examined the potential of gene delivery of the human inducible nitric oxide synthase (iNOS) gene as a means of achieving high output NO production. We successfully transduced two colorectal cancer cell lines as evidenced by increased iNOS protein accumulation and nitrite production. We found that overexpression of iNOS enhanced the effects of radiation on apoptosis in both cell lines in a caspase-dependent fashion. Gene transfer of iNOS holds much promise as a potential radiosensitizer of cancer cells since it increases apoptosis in an additive manner with radiation.