Radiosensitization of HT-29 cells and xenografts by the nitric oxide donor DETANONOate
Department of Surgery, Dallas VA Medical Center, University of Texas Southwestern, Dallas, Texas, USA. Journal of Surgical Oncology
(Impact Factor: 3.24).
08/2009; 100(2):149-58. DOI: 10.1002/jso.21318
Mechanisms of radioresistance in rectal cancer remain unclear.
To determine mechanisms of radioresistance in rectal cancer cells and to assess the role of the nitric oxide donor DETANONOate as a radiosensitizing agent.
Survival was determined by clonogenic assays, apoptosis by PARP-1 cleavage, and phenotypic differences by Western blot analysis. SCID mice bearing HT-29 xenografts were treated with ionizing radiation (IR) [2.0 Gy x 5], DETANONOate [0.4 mg/kg i.p.], or combination treatment.
Colorectal cancer HT-29-p53-null cells were resistant and HCT-116-p53 wild-type cells sensitive to IR, which correlated with cleaved PARP-1. Increased levels of p21 occurred in HCT-116 cells, while Bcl-2 and survivin were elevated in HT-29 cells. Radiosensitization was achieved with a substantial elevation of cleaved PARP-1 in DETANONOate-HT-29-treated versus control cells, which was accompanied by elevation of p21, p27, and BAX, and a concomitant decrease in Bcl-2. SCID mice bearing HT-29 xenografts demonstrated a 37.6%, 51.1%, and 70.1% inhibition in tumor growth in mice receiving IR, DETANONOate, and combination treatment versus control, respectively.
Radioresistant HT-29 cells are p53-null and have substantially decreased levels of p21. DETANONOate radiosensitized HT-29 cells in vitro and in vivo by an additive effect in apoptosis.
Available from: Michelle M. Kim
- "As discussed above, systemic NO-donors have been shown to be radiosensitizers: while radiosensitization with NO gas itself has been demonstrated [50,51], the use of NO donors such as DEA/NO , the nitroxyl donor Angeli salt , DETANONOate , spermine nonoate  or isosorbide dinitrate  is more common . In addition to radiosensitization, in the studies of these NO donors, increases in tumor blood flow were also observed when the administration of NO synthase inhibitors led to radioresistance  . "
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ABSTRACT: 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.
Copyright © 2015. Published by Elsevier B.V.
Available from: Valentina Rapozzi
- "According to our previous pharmacodistribution data, when the mice were irradiated, mPEG-Pba was present in the tumor mass . We assumed that DETA/NO, being a small molecule, was also present in the tumor  . The treatment was carried out three times at days 1, 7 and 14. "
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ABSTRACT: Cell recurrence in cancer photodynamic therapy (PDT) is an important issue that is poorly understood. It is becoming clear that nitric oxide (NO) is a modulator of PDT. By acting on the NF-κB/Snail/RKIP survival/anti-apoptotic loop, NO can either stimulate or inhibit apoptosis. We found that pheophorbide a/PDT (Pba/PDT) induces the release of NO in B78-H1 murine amelanotic melanoma cells in a concentration-dependent manner. Low-dose PDT induces low NO levels by stimulating the anti-apoptotic nature of the above loop, whereas high-dose PDT stimulates high NO levels inhibiting the loop and activating apoptosis. When B78-H1 cells are treated with low-dose Pba/PDT and DETA/NO, an NO-donor, intracellular NO increases and cell growth is inhibited according to scratch-wound and clonogenic assays. Western blot analyses showed that the combined treatment reduces the expression of the anti-apoptotic NF-κB and Snail gene products and increases the expression of the pro-apoptotic RKIP gene product. The combined effect of Pba and DETA/NO was also tested in C57BL/6 mice bearing a syngeneic B78-H1 melanoma. We used pegylated Pba (mPEG-Pba) due to its better pharmacokinetics compared to free Pba. mPEG-Pba (30 mg/kg) and DETA/NO (0.4 mg/Kg) were i.p. injected either as a single molecule or in combination. After photoactivation at 660 nm (fluence of 193 J/cm(2)), the combined treatment delays tumor growth more efficiently than each individual treatment (p<0.05). Taken together, our results showed that the efficacy of PDT is strengthened when the photosensitizer is used in combination with an NO donor.
Available from: ncbi.nlm.nih.gov
- "Accordingly, some studies have demonstrated improved tumor oxygenation and blood flow linked with radiosensitization resulting in tumor shrinkage, whereas other studies have reported the opposite, that is, decreased blood flow with increased rate of tumor growth, presumably linked to the expression of hypoxiamediated transcription factors . Nevertheless, more recent reports have demonstrated a radiation and chemosensitizing effect of low concentrations of nitric oxide, delivered as an NO patch or by a donor molecule   . These apparently contradictory results could also be attributed to the heterogeneous vasoresponsive capacity of tumor vessels depending on the presence or absence of smooth muscle cells and the structural relationship between vascular beds of the tumor relative to surrounding normal tissues, resulting in blood flow redistribution through steal or antisteal effects . "
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ABSTRACT: The popular theory six degrees of separation is used in this review as an analogy to relate all radiosensitization to oxygen. As the prime mover of all radiosensitizers, the pervasive influence of oxygen has consciously or unconsciously influenced the direction of research and development and provided the benchmark against which all other compounds and approaches are measured. It is the aim of this review to develop the six degrees of separation from oxygen analogy as a unifying framework for conceptually organizing the field and for giving context to its varied subspecializations and theories. Under such a framework, it would become possible for one area to consider questions and problems found in other areas of radiosensitization, using a common analogy, that would allow for further development and unification of this multifaceted discipline. In this review, approaches to the development of radiosensitizers and the current state of research in this field are discussed, including promising new agents in various stages of clinical development.
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