Viagra as an Adjunctive Cancer Therapy

Jacob Schor, ND

Published in the May 2007 issue of Naturopathy Doctor News and Review

 

The majority of the cancer patients in our practice choose to combine standard medical treatment with naturopathic care. Thus, most of these patients will undergo some form of chemotherapy and or radiation therapy. While they undergo these treatments, our primary goal is to make the cancer cells as sensitive to the chosen treatment as possible. On the standard list of supplements that do this are melatonin, vitamin D, green tea, quercetin, curcumin, ellagic acid, resveratrol and so on. As a general rule, we seek substances that either increase Reactive Oxygen Species (ROS) or lower glutathione levels (GSH) in the cancer cells to make them more susceptible to either drug or radiation damage. There is a new addition to our thinking, we now seek to change nitric oxide levels (NO) before and during treatment.

 

This is a potentially amusing suggestion as the easiest way to increase NO is with the drug sildenafil, more commonly known as Viagra. The basic Viagra joke about a shipment of medication that has been hijacked during transit comes to mind. The punch line of all the versions of this joke all suggest that the thieves will be easy to recognize because, “They're all hardened criminals.”

 

Treating cancer though is usually serious business and the drugs used to treat it are no laughing matter. It our responsibility when our patients undergo treatment to do everything we can to ensure that the treatment is as effective as possible. Take Adriamycin as an example.

 

A 2004 in vitro study showed you could increase the effect of Adriamycin by adding nitric oxide to the mix. Breast cancer cells exposed to nitric oxide (NO) 30 minutes before treatment were much more sensitive to Adriamycin. Adriamycin treatment alone killed 60% of the cancer cells, but pre-treating the cells with NO and then treating with Adriamycin killed 95% of the cancer cells in the experiment. [i]

 

Simultaneous treatment with both NO and Adriamycin produced only a slight increase in cancer kill over treatment with Adriamycin alone. Giving NO after Adriamycin produced no change at all.

 

In an a variation of this experiment, 24 hour pretreatment of the cancer cells with a chemical that depletes glutathione, further increased the effectiveness of the NO and Adriamycin treatment. This combination killed 100% of the cancer cells in the experiment.

 

The obvious concern with using NO along with Adriamycin is whether this regime will increase the drug's toxic effect on healthy tissue. In this same study, the researchers ran healthy rat heart cells through the same protocols of NO pretreatment followed by Adriamycin. NO exposure did not increase the damage caused by Adriamycin on the healthy cells. A more recent study suggests pretreatment with Viagra actually protects the heart cells from damage caused by chemotherapy. [ii]

 

These results suggest that patients undergoing treatment with Adriamycin should look at two approaches to increasing the benefit. First, increase NO production prior to treatment. Second, lower glutathione levels during treatment.

 

 

I've written elsewhere about glutathione depletion as a cancer treatment strategy, so in this article, let me just focus on nitric oxide. NO produces a number of different effects, the easy one to remember is dilation of blood vessels. This action leads to NO stimulation being useful for a variety of applications ranging from treating angina by increasing blood flow to the heart, to treating erectile dysfunction (ED) by increasing blood flow to you know where.

 

Again, the easiest way to increase NO is with a dose of Viagra and that is just what some researchers in Virginia tried. Two studies published in 2005 report that pre-dosing mice with Viagra prior to Adriamycin treatment decreased cardiotoxicity while at the same time increasing the damage caused by Adriamycin to the cancer cells. [iii] [iv]

 

This same NO strategy is useful during radiation treatment. A 2002 study by researchers in Belgium showed that insulin increased the effect of radiation on tumor cells. This radiosensitization of the tumor cells was inhibited by a nitric oxide (NO) synthase inhibitor so they realized that this sensitization was due to NO stimulation. [v] The same researchers went on to publish another study in May of 2005, which concluded, “…..that NO acts as an intrinsic radiosensitizer in vivo.” [vi]

 

Let us back up to the first of these studies and to the fact that insulin increases tumor cell sensitivity to radiation treatment even if it is off the topic. This fact is significant. It tells that we should strive to increase our patients' insulin levels during radiation treatment. The obvious implication is that they should eat before treatment and not be fasting. The other implications suggested may sound sacrilegious for a naturopath to say. When I query cancer patients regarding their diet, the many proudly inform me that, “I've cut out all sugar and simple carbohydrates from my diet.” When I ask them why, “Because sugar feeds cancer.” If we take this insulin data seriously, we should tell these patients to forget this notion and encourage high sugar consumption during radiation therapy to keep their insulin levels elevated.

 

 

Back to NO as a radiation enhancer. In September 2006, a group of Irish researchers report that they, “….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).” [vii] In October, a paper in Medical Hypotheses reports on using a combination of hyperbaric oxygen and NO donors to make malignant brain tumors more sensitive to radiation treatment. To generate NO in the brain they used l-arginine and vitamin E. [viii]

 

Not all the news about NO looks good. High levels of NOS, that is nitric oxide synthase the enzyme that makes NO, are associated with a worse prognosis for cervical cancer. [ix]

And high levels of iNOS, inducible NO synthase, increases the risk of breast cancer from radiation exposure 7 fold. [x] [xi] It seems we want more NO but do not want to get there by increasing the synthase enzyme that makes NO.

 

This brings us back to Viagra. Viagra belongs to a class of drugs known as phophodiesterase-5- inhibitors (PDE-5- inhibitors). These drugs slow down the action of an enzyme that breaks down nitric oxide thus increasing its apparent effect. They do not increase NOS.

 

There are other drugs that are PDE-inhibitors, cousins to Viagra, which last longer and may be more effective. Viagra has a half-life of just 4 hours; Tadalafil's half-life is 17.5 hours.

 

Viagra is not the only way to increase NO production in the body. Taking the amino acid l-arginine achieves, over time, nearly the same result as Viagra. The body converts arginine into nitric oxide; if there is more arginine around, the body makes more NO.

 

Thus, l-arginine has become the natural Viagra. Several studies have tested arginine as a treatment for erectile dysfunction with varied results. Doses of 1500 mg day were not adequate. [xii] However, doses of 5 grams a day apparently were. [xiii] Better effect resulted when pycnogenol was taken with arginine. [xiv]   Another amino acid, citrulline, may also be useful. [xv] Many of the “NO” products now sold combine arginine and citrulline in a four to one ratio.

 

This entire idea of using NO as a pretreatment to chemotherapy is new, and admittedly still weakly researched. The studies mentioned involve test tubes and mice, not people. In reviewing this article prepublication, several of my esteemed colleagues expressed reservation about using l-arginine long term in cancer patients who were not undergoing chemo or radiation therapy. Their logic makes sense; l-arginine increases NO, which increases blood flow, and we would prefer that tumors get less rather than more blood flow. At this point, it does seem prudent to not encourage NO production except during treatments. On the other hand, we have seen no warning label attached to Viagra bottles that suggest discontinuing use if you have cancer. Better safe than sorry or primo non nocere and all that. At this point, I agree with this thought and only suggest using l-arginine and other NO enhancers shortly before and at the start of each chemo cycle or with radiation therapy, starting before and continuing through the duration of treatment.

 

This Viagra and nitric oxide approach although real and serious is still entertaining to joke about; it is but one of numerous possible adjunctive treatments to be considered whenever a patient contemplates standard oncology treatment. The take home point of this discussion is not whether patients should be force-fed Viagra but rather that there are a growing number of ways to increase the benefit of both chemotherapy and radiation. The medical oncology community rarely considers these potential options, often to the detriment of patients. The more we talk about these adjunctive therapies, the more the public will ask for and expect them. Too often people wait until finished with standard therapy before embarking on ‘alternative therapy.' This is a mistake and we are obligated to popularize the notion of, ‘making chemo work better' and ‘making cancer cells more sensitive to radiation.'

 

Practicing in Colorado , we do not have the option of prescribing Viagra so I admit that I have not tried this with any of our patients. I certainly consider using one of the nutritional supplements sold to increase nitric oxide with any patient scheduled for Adriamycin or radiation therapy.

 

Perhaps in the future the joke will start like this: “Our hospital is running a placebo control trial of Viagra for cancer treatment. How do you know who is getting the active drug?” You can make up the punch line.

 

 

 

 

 

 

 References:

 

[i] Nitric Oxide. 2004 May;10(3):119-29.

Endogenous production and exogenous exposure to nitric oxide augment doxorubicin cytotoxicity for breast cancer cells but not cardiac myoblasts.

•  Evig CB ,

•  Kelley EE ,

•  Weydert CJ ,

•  Chu Y ,

•  Buettner GR ,

•  Burns CP .

Department of Medicine, The University of Iowa Carver College of Medicine and The University of Iowa Holden Comprehensive Cancer Center, Iowa City, IA 52242, USA.

We studied the effect of nitric oxide (*NO) on the anticancer activity of doxorubicin. When MCF-7 human breast cancer cells were exposed to an aqueous solution of *NO delivered as a bolus 30 min prior to doxorubicin, the cytotoxic effect as measured in a clonogenic assay was increased (doxorubicin alone, 40% survival, doxorubicin plus *NO, 5% survival). The *NO donor diethylamine nitric oxide, but not inactivated donor, also yielded an increase in doxorubicin cytotoxicity. The sequence was important since the simultaneous application of *NO with doxorubicin yielded only a small augmentation of effect, and the exposure of the cells to doxorubicin prior to the *NO obliterated the augmentation. Prior depletion of glutathione by incubation of the cells for 24h with D,L-buthionine-S,R-sulfoximine (BSO) further increased the cytotoxicity so that BSO plus *NO plus doxorubicin killed all of the clones. MCF-7 cells transduced with inducible nitric oxide synthase gene (iNOS) through an adenoviral vector overexpressed iNOS and produced increased amounts of nitrite, an indicator of increased *NO production. These iNOS transduced cells were more susceptible to doxorubicin than vector control or wild-type cells. Cell cycle progression of iNOS transduced cells was not different from controls. Likewise, iNOS transduction resulted in no change in cellular glutathione levels. For comparison, we examined the effect of iNOS transduction on the sensitivity of MCF-7 to edelfosine, a membrane-localizing anticancer drug without direct DNA interaction. Insertion of the iNOS had no effect on killing of the MCF-7 cells by this ether lipid class drug. We also tested the effect of iNOS transduction on doxorubicin sensitivity of H9c2 rat heart-derived myoblasts. We found no augmentation of cytotoxicity by *NO, and this observation offers potential therapeutic tumor selectivity by using *NO with doxorubicin. Therefore, we conclude that *NO produced intracellularly by iNOS overexpression or delivered as a bolus sensitizes human breast cancer cells in culture to doxorubicin, but not to a cardiac cell line or to edelfosine. This augmentation is not due to a modulation of cell cycle distribution or measurable cellular glutathione resulting from the transduction.

PMID: 15158691 [PubMed - indexed for MEDLINE]

 

 

[ii] J Biol Chem. 2005 Apr 1;280(13):12944-55. Epub 2005 Jan 24. Click here to read  Links

Phosphodiesterase-5 inhibitor sildenafil preconditions adult cardiac myocytes against necrosis and apoptosis. Essential role of nitric oxide signaling.

•  Das A ,

•  Xi L ,

•  Kukreja RC .

Division of Cardiology, Department of Internal Medicine, Virginia Commonwealth University Medical Center , Richmond , Virginia 23298-0281 , USA .

We investigated the effect of sildenafil in protection against necrosis or apoptosis in cardiomyocytes. Adult mouse ventricular myocytes were treated with sildenafil (1 or 10 microM) for 1 h before 40 min of simulated ischemia (SI). Necrosis was determined by trypan blue exclusion and lactate dehydrogenase release following SI alone or plus 1 or 18 h of reoxygenation (RO). Apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated nick end labeling assay and mitochondrial membrane potential measured using a fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1). Sildenafil reduced necrosis as indicated by decrease in trypan blue-positive myocytes and leakage of lactate dehydrogenase compared with untreated cells after either SI or SI-RO. The number of terminal deoxynucleotidyl transferase-mediated nick end labeling-positive myocytes or loss of JC-1 fluorescence following SI and 18 h of RO was attenuated in the sildenafil-treated group with concomitant inhibition of caspase 3 activity. An early increase in Bcl-2 to Bax ratio with sildenafil treatment was also observed in myocytes after SI-RO. The increase of Bcl-2 expression by sildenafil was inhibited by nitric-oxide synthase (NOS) inhibitor, L-nitro-amino-methyl-ester. The drug also enhanced mRNA and protein content of inducible NOS (iNOS) and endothelial NOS (eNOS) in the myocytes. Sildenafil-induced protection against necrosis and apoptosis was absent in the myocytes derived from iNOS knock-out mice and was attenuated in eNOS knock-out myocytes. The up-regulation of Bcl-2 expression by sildenafil was also absent in iNOS-deficient myocytes. Reverse transcription-PCR, Western blots, and immunohistochemical assay confirmed the expression of phosphodiesterase-5 in mouse cardiomyocytes. These data provide strong evidence for a direct protective effect of sildenafil against necrosis and apoptosis through NO signaling pathway. The results may have possible therapeutic potential in preventing myocyte cell death following ischemia/reperfusion.

PMID: 15668244 [PubMed - indexed for MEDLINE]

 

[iii] Circulation. 2005 Apr 5;111(13):1601-10. Phosphodiesterase-5 inhibition with sildenafil attenuates cardiomyocyte apoptosis and left ventricular dysfunction in a chronic model of doxorubicin cardiotoxicity.

 

* Fisher PW,

* Salloum F,

* Das A,

* Hyder H,

* Kukreja RC.

 

Department of Internal Medicine, Division of Cardiology, Virginia Commonwealth University Medical Center , Richmond 23298 , USA .

 

BACKGROUND: Sildenafil, a phosphodiesterase-5 inhibitor, induces cardioprotection against ischemia/reperfusion injury via opening of mitochondrial K(ATP) channels. It is unclear whether sildenafil would provide similar protection from doxorubicin-induced cardiotoxicity. METHODS AND RESULTS: Male ICR mice were randomized to 1 of 4 treatments: saline, sildenafil, doxorubicin (5 mg/kg IP), and sildenafil (0.7 mg/kg IP) plus doxorubicin (n=6 per group). Apoptosis was assessed with the use of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and in situ oligo ligation methods. Desmin distribution was determined via immunofluorescence. Bcl-2 expression was analyzed by Western blot. Left ventricular function was assessed by measuring developed pressure and rate pressure product in Langendorff mode. ECG changes indicative of doxorubicin cardiotoxicity were also measured. For in vitro studies, adult ventricular cardiomyocytes were exposed to doxorubicin (1 micromol/L), sildenafil (1 micromol/L) with or without N(G)-nitro-L-arginine methyl ester (L-NAME) (100 micromol/L), or 5-hydroxydecanoate (100 micromol/L) 1 hour before doxorubicin and incubated for 18 hours. Doxorubicin-treated mice demonstrated increased apoptosis and desmin disruption, which was attenuated in the sildenafil+doxorubicin group. Bcl-2 was decreased in the doxorubicin group but was maintained at basal levels in the sildenafil+doxorubicin group. Left ventricular developed pressure and rate pressure product were significantly depressed in the doxorubicin group but were attenuated in the sildenafil+doxorubicin group. ST interval was significantly increased in the doxorubicin group over 8 weeks. In the sildenafil+doxorubicin group, ST interval remained unchanged from baseline. Doxorubicin caused a significant increase in apoptosis, caspase-3 activation, and disruption of mitochondrial membrane potential in vitro. In contrast, sildenafil significantly protected against doxorubicin cardiotoxicity; however, this protection was abolished by both L-NAME and 5-hydroxydecanoate. CONCLUSIONS: Prophylactic treatment with sildenafil prevented apoptosis and left ventricular dysfunction in a chronic model of doxorubicin-induced cardiomyopathy.

 

PMID: 15811867

 

[iv] J Biol Chem. 2005 Apr 1;280(13):12944-55. Epub 2005 Jan 24.   Links

Phosphodiesterase-5 inhibitor sildenafil preconditions adult cardiac myocytes against necrosis and apoptosis. Essential role of nitric oxide signaling.

•  Das A ,

•  Xi L ,

•  Kukreja RC .

Division of Cardiology, Department of Internal Medicine, Virginia Commonwealth University Medical Center , Richmond , Virginia 23298-0281 , USA .

We investigated the effect of sildenafil in protection against necrosis or apoptosis in cardiomyocytes. Adult mouse ventricular myocytes were treated with sildenafil (1 or 10 microM) for 1 h before 40 min of simulated ischemia (SI). Necrosis was determined by trypan blue exclusion and lactate dehydrogenase release following SI alone or plus 1 or 18 h of reoxygenation (RO). Apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated nick end labeling assay and mitochondrial membrane potential measured using a fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1). Sildenafil reduced necrosis as indicated by decrease in trypan blue-positive myocytes and leakage of lactate dehydrogenase compared with untreated cells after either SI or SI-RO. The number of terminal deoxynucleotidyl transferase-mediated nick end labeling-positive myocytes or loss of JC-1 fluorescence following SI and 18 h of RO was attenuated in the sildenafil-treated group with concomitant inhibition of caspase 3 activity. An early increase in Bcl-2 to Bax ratio with sildenafil treatment was also observed in myocytes after SI-RO. The increase of Bcl-2 expression by sildenafil was inhibited by nitric-oxide synthase (NOS) inhibitor, L-nitro-amino-methyl-ester. The drug also enhanced mRNA and protein content of inducible NOS (iNOS) and endothelial NOS (eNOS) in the myocytes. Sildenafil-induced protection against necrosis and apoptosis was absent in the myocytes derived from iNOS knock-out mice and was attenuated in eNOS knock-out myocytes. The up-regulation of Bcl-2 expression by sildenafil was also absent in iNOS-deficient myocytes. Reverse transcription-PCR, Western blots, and immunohistochemical assay confirmed the expression of phosphodiesterase-5 in mouse cardiomyocytes. These data provide strong evidence for a direct protective effect of sildenafil against necrosis and apoptosis through NO signaling pathway. The results may have possible therapeutic potential in preventing myocyte cell death following ischemia/reperfusion.

PMID: 15668244 [PubMed - indexed for MEDLINE]

 

[v] Cancer Res. 2002 Jun 15;62(12):3555-61.   Links

Insulin increases the sensitivity of tumors to irradiation: involvement of an increase in tumor oxygenation mediated by a nitric oxide-dependent decrease of the tumor cells oxygen consumption.

•  Jordan BF ,

•  Gregoire V ,

•  Demeure RJ ,

•  Sonveaux P ,

•  Feron O ,

•  O'Hara J ,

•  Vanhulle VP ,

•  Delzenne N ,

•  Gallez B .

Laboratory of Medicinal Chemistry and Radiopharmacy, Laboratory of Biomedical Magnetic Resonance, Universite Catholique de Louvain, B-1200 Brussels, Belgium.

The effects of insulin on tumor oxygenation, perfusion, oxygen consumption,and radiation sensitivity were studied on two different mouse tumor models (TLT, a liver tumor, and FSAII, a fibrosarcoma). Anesthetized mice were infused with insulin i.v. at a rate of 16 milliUnits/kg/min for 25 min. Local tumor oxygenation measurements were carried out using two independent techniques: electron paramagnetic resonance oximetry and a fiber-optic device (OxyLite). Two complementary techniques were also used to assess the blood flow inside the tumor: a laser Doppler system (OxyFlo) and contrast-enhanced magnetic resonance imaging. The oxygen consumption rate of tumor cells after in vivo insulin infusion was measured using high frequency electron paramagnetic resonance oximetry. To know if insulin was able to enhance radiation-induced tumor regrowth delay, tumor-bearing mice were treated with 16 Gy of 250 kV radiation dose after insulin infusion. We provide evidence that insulin increases the local pressure of oxygen of tumors (from 0-3 mm Hg to 8-11 mm Hg) as well as the tumor response to irradiation (increasing regrowth delay by a factor of 2.11). We found that the insulin-induced increase of tumor pressure of oxygen: (a) is not caused by an increase in the tumor blood flow, which is even decreased after insulin infusion; (b) is because of a decrease in the tumor cell oxygen consumption (in vivo insulin consumed oxygen three times slower than control cells); and (c) is inhibited by a nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester, when injected i.p. at 15 micromol/kg(-1), 1 h before insulin infusion. We demonstrate by immunoblotting that the NO pathway involves a phosphorylation of endothelial NO synthase and showed a concomitant increase in the cyclic GMP tumor level. These findings provide unique insights into biological processes in tumors, new possible management for treating cancer patients, and raise major questions about the role of insulin secretion (fasting status and diabetes) in the clinical response of tumors to radiation therapy.

PMID: 12068004 [PubMed - indexed for ME

 

[vi] Int J Cancer. 2004 May 1;109(5):768-73.   Links

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

•  Jordan BF ,

•  Sonveaux P ,

•  Feron O ,

•  Gregoire V ,

•  Beghein N ,

•  Dessy C ,

•  Gallez B .

Laboratory of Medicinal Chemistry and Radiopharmacy, Universite Catholique de Louvain, Avenue Mounier 73.40, B-1200 Brussels, Belgium.

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. Copyright 2004 Wiley-Liss, Inc.

PMID: 14999787 [PubMed - indexed for MEDLINE]

 

[vii] Gene Ther. 2006 Sep 28; [Epub ahead of print]   Links

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

•  McCarthy HO ,

•  Worthington J ,

•  Barrett E ,

•  Cosimo E ,

•  Boyd M ,

•  Mairs RJ ,

•  Ward C ,

•  McKeown SR ,

•  Hirst DG ,

•  Robson T .

1School of Pharmacy, McClay Research Centre, Queen's University, Belfast , Northern Ireland , UK .

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.Gene Therapy advance online publication, 28 September 2006 ; doi:10.1038/sj.gt.3302871.

PMID: 17006546 [PubMed - as supplied by publisher]

 

[viii] Med Hypotheses. 2006 Oct 25; [Epub ahead of print]   Links

A combination of radiotherapy, nitric oxide and a hyperoxygenation sensitizing protocol for brain malignant tumor treatment.

•  Al-Waili NS ,

•  Butler GJ .

Life Support Technologies Group, NEWT Technologies, Inc., The Mount Vernon Hospital , Sound Shore Health System , New York , USA .

Brain malignant tumor such as glioblastoma is a challenging medical and surgical problem. In spite of surgery, radiotherapy and chemotherapy, the prognosis is still very poor. The limitations of currently available treatment modalities to cure or significantly prolong and improve the quality of life should stimulate rigorous research and studies to combat brain malignant tumors. While precision radiotherapy to reduce tumor size and ameliorate symptoms is still the standard of care, tumor sensitivity to radiation is compromised by low oxygen tensions and a necrotic tumor center. We propose to take advantage of the fact that elevated oxygen increases sensitivity of tumor cells to radiation. A specific application of hyperbaric oxygen (HBO(2)), using nitric oxide (NO) donors and inducers (such as l-arginine, dinitrite or tocopheryl succinate) and ascorbic acid to dilate blood vessels, should permit oxygen tensions in the range of 1000mmHg to diffuse into the cells and thus increase sensitivity to radiation. This should permit doses that are low enough to cause the death of tumors cells yet minimize injury to brain tissue near the tumor and induced neurological sequelae.

PMID: 17069987 [PubMed - as supplied by publisher]

 

[ix] Int J Radiat Oncol Biol Phys. 2005 Nov 15;63(4):1093-100. Epub 2005 Aug 15.   Links

Increased expression of nitric oxide synthase and cyclooxygenase-2 is associated with poor survival in cervical cancer treated with radiotherapy.

•  Chen HH ,

•  Su WC ,

•  Chou CY ,

•  Guo HR ,

•  Ho SY ,

•  Que J ,

•  Lee WY .

Department of Radiation Oncology, National Cheng Kung University Hospital, Tainan, Taiwan; Institute of Clinical Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan.

PURPOSE: To investigate the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in cervical cancer and their association with clinical outcome in patients treated with radical radiotherapy. METHODS AND MATERIALS: One hundred sixty-seven consecutive patients with FIGO Stages IB-IVA squamous cell cervical cancer underwent radical radiotherapy, including external-beam radiotherapy or high-dose-rate brachytherapy, or both, between 1989 and 2002. Immunohistochemical studies of their formalin-fixed, paraffin-embedded tissues were performed. Univariate and multivariate analyses were performed to identify and evaluate the effects of the factors affecting patient survival. RESULTS: Positive immunostainings of iNOS and COX-2 were observed in 58.7% and 64.1% of the participants, respectively. The expression of both iNOS and COX-2 was positively correlated (Spearman correlation coefficient = 0.49, p < 0.01), and their overexpression provided independent predictors of distant metastasis (odds ratio = 5.22 and 10.07, respectively; p < 0.01 for all). iNOS- and COX-2-expressing patients had significantly shorter disease-free survival (p < 0.01, both) and cause-specific overall survival (p = 0.01, p < 0.01, respectively). Patients with iNOS-positive/COX-2-positive tumors had the poorest survival rates. Coexpression of iNOS/COX-2, together with bulky tumor and advanced stage were independent prognostic factors for disease-free survival. CONCLUSION: Overexpression of iNOS or COX-2 or both was associated with decreased survival and a greater propensity to metastasize in cervical cancer patients treated with radiotherapy. Coexpression of iNOS and COX-2 may represent a useful biologic marker in patients receiving radical radiotherapy for cervical cancer.

PMID: 16099602 [PubMed - indexed for MEDLINE]

 

[x] Nitric Oxide. 2005 Feb;12(1):15-20. Epub 2004 Dec 22.   Links

Nitric oxide produced by inducible nitric oxide synthase is associated with mammary tumorigenesis in irradiated rats.

•  Inano H ,

•  Onoda M .

Redox Regulation Research Group, Research Center for Radiation Safety, National Institute of Radiological Sciences, 9-1 Anagawa-4-chome, Inage-ku, Chiba 263-8555, Japan . inano@nirs.go.jp

This study evaluated whether nitric oxide (NO) derived from nitric oxide synthase (NOS) induced by radiation is associated with tumorigenesis in the mammary glands. When rats were exposed to whole-body irradiation with gamma-rays (1.5 Gy) immediately after weaning and then treated with diethylstilbestrol, as an irradiated control, the tumor incidence (85%) was increased 7.6-fold in comparison with that (11.1%) of the non-irradiated control. The tumor incidence declined to 28.6% in the rats injected intraperitoneally with phenyl-N-tert-butylnitrone (PBN, 160 mg/kg), an inhibitor of inducible NOS (iNOS) expression and also a spin trapping agent, 30 min before irradiation. Also, the tumor incidence (25%) in rats orally administered with N-(3-(aminomethyl)-benzyl)-acetamide (1400W, 2.3+/-0.1 mg/day), a highly selective inhibitor of iNOS, dissolved in drinking water for 3 days after the irradiation was less than one-third of that in the irradiated control. On treatment with PBN or 1400W, no adenocarcinoma developed. Many of the mammary tumors that developed in the irradiated rats were positive for the estrogen receptor (ER). In contrast, ER was not detected in the tumors yielded from irradiated rats administered with PBN or 1400W. These results indicate that iNOS-derived NO may participate in the formation of estrogen-dependent mammary adenocarcinomas following radiation.

PMID: 15631943 [PubMed - indexed for MEDLINE]

 

[xi] Nitric Oxide. 2003 Mar;8(2):144-8.   Links

Role of nitric oxide in radiation-induced initiation of mammary tumorigenesis in rats.

•  Inano H ,

•  Onoda M .

Redox Regulation Research Group, Research Center for Radiation Safety, National Institute of Radiological Sciences, 9-1, Anagawa-4-chome, Inage-ku, Chiba-shi, Chiba-ken, 263-8555, Japan. inano@nirs.go.jp

Nitric oxide (NO) and its reaction products have been shown to cause DNA damage and to be mutagenic. To elucidate whether NO produced by irradiation participates in the initiation of mammary tumorigenesis, we performed experiments using the nitric oxide-specific scavenger Fe(2+)-diethyldithiocarbamate complex (Fe(DETC)(2)) or a selective inhibitor for inducible nitric oxide synthase (iNOS), S,S(')-(4-phenylene-bis(1,2-ethanedinyl))bis-isothiourea (1,4-PB-ITU). Mother rats at day 21 of lactation were injected simultaneously with diethyldithiocarbamate intraperitoneally and Fe(2+)-citrate subcutaneously to form Fe(DETC)(2), in vivo, and then irradiated with 1.5Gy gamma-rays immediately after the injection. An additional injection of chemicals followed twice at 8 and 24h after the irradiation in the same manner. Both control and treated rats were then implanted with diethylstilbestrol pellets as a tumor promoter. The mammary tumor incidence in the experimental group was significantly reduced to one-fourth of that in the irradiated-alone group as the control. On the other hand, when mother rats took drinking water containing 0.005% 1,4-PB-ITU for 6 days from 3 days prior to irradiation at day 21 of lactation, a low tumor incidence in the iNOS inhibitor-treated groups was observed in the 1-year period. This report is the first to show that the NO derived from iNOS is an important radical for radiation-induced initiation of tumorigenesis of mammary glands in rats.

PMID: 12620378 [PubMed - indexed for MEDLINE]

 

[xii] Urol Int. 1999;63(4):220-3.

Effectiveness of oral L-arginine in first-line treatment of erectile dysfunction in a controlled crossover study.

Klotz T, Mathers MJ, Braun M, Bloch W, Engelmann U.

 

Department of Urology, University of Cologne , Germany . tklotz@t-online.de

 

BACKGROUND AND AIMS: Relaxation of cavernous smooth muscle is a parasympathetic and non-adrenergic, non-cholinergic mediated process which requires nitric oxide (NO). NO is synthesized from L-arginine by NO synthase (NOS). Some studies report good clinical results under oral L-arginine medication in the treatment of erectile dysfunction. We examined the effectiveness and safety of L-arginine in the treatment of mixed-type impotence. METHODS: 32 patients (mean age 51.6 years) with mixed-type impotence diagnosed according to the results of sexual history and urological examination were enrolled in a randomized, placebo-controlled, crossover comparison of an oral placebo with 3 x 500 mg L-arginine/day. A validated questionnaire (KEED) was used to define the grade of impotence with a score. The treatment consisted of two 17-day courses (50 tablets). After a 7-day washout period the patients who initially received the placebo for 17 days were switched to L-arginine and vice versa. We assessed the efficacy with the validated questionnaire at the end of each drug period. RESULTS: 30 patients (94%) completed the whole treatment schedule. Five (17%) patients reported a significant improvement in erectile function at the end of the L-arginine phase and 6 (20%) patients after the placebo period. 17 (56%) patients showed little improvement with L-arginine and 13 (43%) with placebo. In 8 patients (27%) of the verum group there was either no change in the ED score or even a slight worsening. No statistical difference in the impotence scores were found. No drug-related adverse effects occurred with L-arginine treatment. CONCLUSION: Oral L-arginine 3 x 500 mg/day is not better than placebo as a first-line treatment for mixed-type impotence.

 

 

[xiii] BJU Int. 1999 Feb;83(3):269-73

Effect of oral administration of high-dose nitric oxide donor L-arginine in men with organic erectile dysfunction: results of a double-blind, randomized, placebo-controlled study.

  

Chen J, Wollman Y, Chernichovsky T, Iaina A, Sofer M, Matzkin H.

 

Department of Urology, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

 

OBJECTIVES: To determine, in a prospective randomized, double-blind placebo-controlled study, the effect of 6 weeks of high-dose (5 g/day) orally administered nitric oxide (NO) donor L-arginine on men with organic erectile dysfunction (ED). PATIENTS AND METHODS: The study included 50 men with confirmed organic ED who were randomized after a 2-week placebo run-in period to receive L-arginine or placebo. A detailed medical and sexual history, O'Leary's questionnaire, a specially designed sexual function questionnaire and a sexual activity diary were obtained for each patient. All participants underwent a complete physical examination including an assessment of bulbocavernosus reflex and penile haemodynamics. Plasma and urine nitrite and nitrate (designated NOx), both stable metabolites of nitric oxide, were determined at the end of the placebo run-in period, and after 3 and 6 weeks. RESULTS: Nine of 29 (31%) patients taking L-arginine and two of 17 controls reported a significant subjective improvement in sexual function. All objective variables assessed remained unchanged. All nine patients treated with L-arginine and who had subjectively improved sexual performance had had an initially low urinary NOx, and this level had doubled at the end of the study. CONCLUSIONS: Oral administration of L-arginine in high doses seems to cause significant subjective improvement in sexual function in men with organic ED only if they have decreased NOx excretion or production. The haemodynamics of the corpus cavernosum were not affected by oral L-arginine at the dosage used.

 

 

 

[xiv] J Sex Marital Ther. 2003 May-Jun;29(3):207-13.   

Treatment of erectile dysfunction with pycnogenol and L-arginine.

Stanislavov R, Nikolova V.

Seminological Laboratory SBALAG, Maichin Dom, Sofia , Bulgaria . rstanik@abv.bg

 

Penile erection requires the relaxation of the cavernous smooth muscle, which is triggered by nitric oxide (NO). We investigated the possibility of overcoming erectile dysfunction (ED) by increasing the amounts of endogenous NO. For this purpose, we orally administered Pycnogenol, because it is known to increase production of NO by nitric oxide syntase together with L-arginine as substrate for this enzyme. The study included 40 men, aged 25-45 years, without confirmed organic erectile dysfunction. Throughout the 3-month trial period, patients received 3 ampoules Sargenor a day, a drinkable solution of the dipeptide arginyl aspartate (equivalent to 1.7 g L-arginine per day). During the second month, patients were additionally supplemented with 40 mg Pycnogenol two times per day; during the third month, the daily dosage was increased to three 40-mg Pycnogenol tablets. We obtained a sexual function questionnaire and a sexual activity diary from each patient. After 1 month of treatment with L-arginine, a statistically nonsignificant number of 2 patients (5%) experienced a normal erection. Treatment with a combination of L-arginine and Pycnogenol for the following month increased the number of men with restored sexual ability to 80%. Finally, after the third month of treatment, 92.5% of the men experienced a normal erection. We conclude that oral administration of L-arginine in combination with Pycnogenol causes a significant improvement in sexual function in men with ED without any side effects.

 

 

 

[xv] Eur J Pharmacol. 2006 Sep 28;546(1-3):171-6. Epub 2006 Jul 27.  

Role of the l-citrulline/l-arginine cycle in iNANC nerve-mediated nitric oxide production and airway smooth muscle relaxation in allergic asthma.

•  Maarsingh H ,

•  Leusink J ,

•  Zaagsma J ,

•  Meurs H .

Department of Molecular Pharmacology, University Centre for Pharmacy, A. Deusinglaan 1, 9713 AV Groningen , The Netherlands .

Nitric oxide synthase (NOS) converts l-arginine into nitric oxide (NO) and l-citrulline. In NO-producing cells, l-citrulline can be recycled to l-arginine in a two-step reaction involving argininosuccinate synthase (ASS) and -lyase (ASL). In guinea pig trachea, l-arginine is a limiting factor in neuronal nNOS-mediated airway smooth muscle relaxation upon inhibitory nonadrenergic noncholinergic (iNANC) nerve stimulation. Moreover, in a guinea pig model of asthma iNANC nerve-induced NO production and airway smooth muscle relaxation are impaired after the allergen-induced early asthmatic reaction, due to limitation of l-arginine. Using guinea pig tracheal preparations, we now investigated whether (i) the l-citrulline/l-arginine cycle is active in airway iNANC nerves and (ii) the NO deficiency after the early asthmatic reaction involves impaired l-citrulline recycling. Electrical field stimulation-induced relaxation was measured in tracheal open-rings precontracted with histamine. l-citrulline as well as the ASL inhibitor succinate did not affect electrical field stimulation-induced relaxation under basal conditions. However, reduced relaxation induced by a submaximal concentration of the NOS inhibitor N(omega)-nitro-l-arginine was restored by l-citrulline, which was prevented by the additional presence of succinate or the ASS inhibitor alpha-methyl-d,l-aspartate. Remarkably, the impaired iNANC relaxation after the early asthmatic reaction was restored by l-citrulline. In conclusion, the l-citrulline/l-arginine cycle is operative in guinea pig iNANC nerves in the airways and may be effective under conditions of low l-arginine utilization by nNOS (caused by NOS inhibitors), and during reduced l-arginine availability after allergen challenge. Enzymatic dysfunction in the l-citrulline/l-arginine cycle appears not to be involved in the l-arginine limitation and reduced iNANC activity after the early asthmatic reaction.

PMID: 16919264 [PubMed - in process]