Inhibition of spontaneous metastases formation by amifostine

WR1065 conjugated to thiol-PEG polymers as novel anticancer prodrugs: broad spectrum efficacy, synergism, and drug resistance reversal

The lack of anticancer agents that overcome innate/acquired drug resistance is the single biggest barrier to achieving a durable complete response to cancer therapy. To address this issue, a new drug family was developed for intracellular delivery of the bioactive aminothiol WR1065 by conjugating it to discrete thiol-PEG polymers: 4-star-PEG-S-S-WR1065 (4SP65) delivers four WR1065s/molecule and m-PEG6-S-S-WR1065 (1LP65) delivers one. Infrequently, WR1065 has exhibited anticancer effects when delivered via the FDA-approved cytoprotectant amifostine, which provides one WR1065/molecule extracellularly. The relative anticancer effectiveness of 4SP65, 1LP65, and amifostine was evaluated in a panel of 15 human cancer cell lines derived from seven tissues. Additional experiments assessed the capacity of 4SP65 co-treatments to potentiate the anticancer effectiveness and overcome drug resistance to cisplatin, a chemotherapeutic, or gefitinib, a tyrosine kinase inhibitor (TKI) targeting oncogenic EGFR mutations. The CyQUANT®-NF proliferation assay was used to assess cell viability after 48-h drug treatments, with the National Cancer Institute COMPARE methodology employed to characterize dose-response metrics. In normal human epithelial cells, 4SP65 or 1LP65 enhanced or inhibited cell growth but was not cytotoxic. In cancer cell lines, 4SP65 and 1LP65 induced dose-dependent cytostasis and cytolysis achieving 99% cell death at drug concentrations of 11.2 ± 1.2 µM and 126 ± 15.8 µM, respectively. Amifostine had limited cytostatic effects in 11/14 cancer cell lines and no cytolytic effects. Binary pairs of 4SP65 plus cisplatin or gefitinib increased the efficacy of each partner drug and surmounted resistance to cytolysis by cisplatin and gefitinib in relevant cancer cell lines. 4SP65 and 1LP65 were significantly more effective against TP53-mutant than TP53-wild-type cell lines, consistent with WR1065-mediated reactivation of mutant p53. Thus, 4SP65 and 1LP65 represent a unique prodrug family for innovative applications as broad-spectrum anticancer agents that target p53 and synergize with a chemotherapeutic and an EGFR-TKI to prevent or overcome drug resistance.

Prophylactic administration of Amifostine protects vessel thickness in the setting of irradiated bone

Although often beneficial in the treatment of head and neck cancer (HNC), radiation therapy (XRT) leads to the depletion of vascular supply and eventually decreased perfusion of the tissue. Specifically, previous studies have demonstrated the depletion of vessel volume fraction (VVF) and vessel thickness (VT) associated with XRT. Amifostine (AMF) provides protection from the detrimental effects of radiation damage, allowing for reliable post-irradiation fracture healing in the murine mandible. The purpose of this study is to investigate the prophylactic ability of AMF to protect the vascular network in an irradiated field. Sprague-Dawley rats (n = 17) were divided into 3 groups: control (C, n = 5), radiated (XRT, n = 7), and radiated mandibles treated with Amifostine (AMF XRT, n = 5). Both groups receiving radiation underwent a previously established, human equivalent dose of XRT totaling 35 Gy, equally fractionated over 5 days. The AMF XRT group received a weight dependent (0.5 mg AMF/5 g body weight) subcutaneous injection of AMF 45 min prior to XRT. Following a 56-day recovery period, mandibles were perfused, dissected, and imaged with μCT. ANOVA was used for comparisons between groups and p < 0.05 was considered statistically significant. Stereologic analysis demonstrated a significant and quantifiable restoration of VT in AMF treated mandibles as compared to those treated with radiation alone (0.061 ± 0.011 mm versus 0.042 ± 0.004 mm, p = 0.027). Interestingly, further analysis demonstrated no significant difference in VT between control mandibles and those treated with AMF (0.067 ± 0.016 mm versus 0.061 ± 0.011 mm, p = 0.633). AMF treatment also showed an increase in VVF, however those results were not statistically significant from VVF values demonstrated by the XRT group. Our data support the contention that AMF therapy acts prophylactically to protect vessel thickness. Based on these findings, we support the continued investigation of this treatment paradigm in its potential translation for the prevention of vascular depletion after radiotherapy.

D-penicillamine and other low molecular weight thiols: review of anticancer effects and related mechanisms

Low molecular weight thiols (LMWTs) like N-acetyl cysteine, D-penicillamine, captopril, Disulfiram and Amifostine, etc. have been used as chemo-preventive agents. Recent studies have reported cell growth inhibition and cytotoxicity in several different types of cancer cells following treatment with several LMWTs. Cytotoxic and cytostatic effects of LMWTs may involve interaction of the thiol group with cellular lipids, proteins, intermediates or enzymes. Some of the mechanisms that have been proposed include a p53 mediated apoptosis, thiyl radical induced DNA damage, membrane damage through lipid peroxidation, anti-angiogenic effects induced by inhibition of matrix metalloproteinase enzymes and angiostatin generation. LMWTs are strong chelators of transition metals like copper, nickel, zinc, iron and cobalt and may cause metal co-factor depletion resulting in cytotoxicity. Oxidation of thiol group can also generate cytotoxic reactive oxygen species (ROS).

The cytoprotective drug amifostine modifies both expression and activity of the pro-angiogenic factor VEGF-A

BACKGROUND

Amifostine (WR-2721, delivered as Ethyol) is a phosphorylated aminothiol compound clinically used in addition to cis-platinum to reduce the toxic side effects of therapeutic treatment on normal cells without reducing their efficacy on tumour cells. Its mechanism of action is attributed to the free radical scavenging properties of its active dephosphorylated metabolite WR-1065. However, amifostine has also been described as a potent hypoxia-mimetic compound and as a strong p53 inducer; both effects are known to potently modulate vascular endothelial growth factor (VEGF-A) expression. The angiogenic properties of this drug have not been clearly defined.

METHODS

Cancer cell lines and endothelial cells were used in culture and treated with Amifostine in order to study (i) the expression of angiogenesis related genes and proteins and (ii) the effects of the drug on VEGF-A induced in vitro angiogenesis.

RESULTS

We demonstrated that the treatment of several human cancer cell lines with therapeutical doses of WR-1065 led to a strong induction of different VEGF-A mRNA isoforms independently of HIF-1alpha. VEGF-A induction by WR-1065 depends on the activation of the eIF2alpha/ATF4 pathway. This up-regulation of VEGF-A mRNA was accompanied by an increased secretion of VEGF-A proteins fully active in stimulating vascular endothelial cells (EC). Nevertheless, direct treatment of EC with amifostine impaired their ability to respond to exogenous VEGF-A, an effect that correlated to the down-regulation of VEGFR-2 expression, to the reduction in cell surface binding of VEGF-A and to the decreased phosphorylation of the downstream p42/44 kinases.

CONCLUSIONS

Taken together, our results indicate that amifostine treatment modulates tumour angiogenesis by two apparently opposite mechanisms - the increased VEGF-A expression by tumour cells and the inhibition of EC capacity to respond to VEGF-A stimulation.

Amifostine induces antioxidant enzymatic activities in normal tissues and a transplantable tumor that can affect radiation response

PURPOSE

To determine whether amifostine can induce elevated manganese superoxide dismutase (SOD2) in murine tissues and a transplantable SA-NH tumor, resulting in a delayed tumor cell radioprotective effect.

METHODS AND MATERIALS

SA-NH tumor-bearing C3H mice were treated with a single 400 mg/kg or three daily 50 mg/kg doses of amifostine administered intraperitoneally. At selected time intervals after the last injection, the heart, liver, lung, pancreas, small intestine, spleen, and SA-NH tumor were removed and analyzed for SOD2, catalase, and glutathione peroxidase (GPx) enzymatic activity. The effect of elevated SOD2 enzymatic activity on the radiation response of SA-NH cells was determined.

RESULTS

SOD2 activity was significantly elevated in selected tissues and a tumor 24 h after amifostine treatment. Catalase and GPx activities remained unchanged except for significant elevations in the spleen. GPx was also elevated in the pancreas. SA-NH tumor cells exhibited a twofold elevation in SOD2 activity and a 27% elevation in radiation resistance. Amifostine administered in three daily fractions of 50 mg/kg each also resulted in significant elevations of these antioxidant enzymes.

CONCLUSIONS

Amifostine can induce a delayed radioprotective effect that correlates with elevated levels of SOD2 activity in SA-NH tumor. If limited to normal tissues, this delayed radioprotective effect offers an additional potential for overall radiation protection. However, amifostine-induced elevation of SOD2 activity in tumors could have an unanticipated deleterious effect on tumor responses to fractionated radiation therapy, given that the radioprotector is administered daily just before each 2-Gy fractionated dose.

Chemical Warfare Agents Chemical Warfare Agents: Their Past and Continuing Threat and Evolving Therapies Part II of II

Chemical warfare agents are ideal weapons for terrorists and for use in military operations against both civilian populations and troops. Thus, there have been efforts by the United States in cooperation with other concerned nations to develop animal models to understand the pathophysiology of the injuries induced by these agents, and to develop suitable animal models for testing of pre-and post-exposure protectants and therapies. Sulfur mustard remains the most significant chemical warfare agent that produces cutaneous injuries. Institution of standard recommendations prior to threatened exposure or after exposure are something that we need to be aware of in the world we live in. In addition, pre-and post-exposure therapies now being studied offer hope for moderating the mortality and morbidity that can result from chemical exposure.

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

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

Delayed radioprotection by NFkappaB-mediated induction of Sod2 (MnSOD) in SA-NH tumor cells after exposure to clinically used thiol-containing drugs

The ability of thiol-containing reducing agents to activate transcription factors leading to changes in gene expression and enzyme activities provides an additional mechanism to potentially protect against radiation-induced cell killing. Manganese superoxide dismutase (Sod2) is one such gene whose expression levels have been shown to be elevated after exposure to the thiol compounds WR-1065 and N-acetyl-L-cysteine (NAC), resulting in an increase in radiation resistance. To further characterize this effect, SA-NH sarcoma cells, both wild-type and a clone stably transfected with a plasmid containing an IkappaBalpha gene mutated at serines 32 and 36, which prevents the inducible phosphorylation of these residues and the subsequent activation of NFkappaB (SA-NH+mIkappaBalpha1), were grown to confluence and then exposed to amifostine's free thiol WR-1065 at a concentration of 4 mM for 30 min. Effects of thiol exposure on NFKB activation in SA-NH+mIkappaBalpha1 cells were determined by a gel shift assay, and changes in Sod2 protein levels in these cells 24 h after exposure to 40 microM or 4 mM WR-1065 were measured by Western blot analysis and compared with wild-type cells exposed to the NFkappaB inhibitor BAY 11-7082. Changes in radiation response, measured immediately after thiol exposure or 24 h later, were determined using a colony-forming assay and were correlated with NFKB activation and Sod2 protein levels. The effects of captopril, mesna and NAC, each at a dose of 4 mM, on radiation response were also determined and contrasted with those of WR-1065. Only WR-1065 and captopril protected SA-NH cells when present during irradiation, i.e. 1.57 and 1.31 times increase in survival at 2 Gy, respectively. All four thiols were protective if irradiation with 2 Gy occurred 24 h later; i.e. increases in survival of 1.40, 1.22, 1.35, and 1.25 times were found for WR-1065, captopril, mesna and NAC, respectively. This delayed radioprotective effect correlated with elevated Sod2 protein levels in wild-type SA-NH tumor cells but was not observed in SA-NH+mIkappaBalpha1 cells, indicating that interference with thiol-induced NFKB activation abrogates this delayed radioprotective effect. Because the delayed radioprotective effect is readily demonstrable at a radiation dose of 2 Gy 24 h after exposure to clinically approved thiol-containing drugs such as amifostine, captopril, mesna and NAC, it suggests a new potential concern regarding the issue of tumor protection and the use of these agents in cancer therapy.

Amifostine has antiangiogenic properties in vitro by changing the redox status of human endothelial cells

Amifostine is a broad-spectrum cytoprotective agent, selective for normal tissues. It is a pro-drug metabolised to the free thiol WR-1065 that may act as a scavenger of free radicals, generated in tissues exposed to chemotherapeutic agents or radiation. WR-1065 can be further oxidized to its symmetric disulfide WR-33278 or degraded to hydrogen peroxide (H2O2). Both WR-1065 and WR-33278 resemble endogenous polyamines. Although amifostine is used in some cases in the clinic, there are only few studies concerning its actions at the cellular level. We have previously shown that amifostine inhibits angiogenesis in vivo, affecting the expression of several angiogenic genes. In the present work, we studied the effect of amifostine on human umbilical vein endothelial cell (HUVEC) functions in vitro, in order to further clarify its mechanism(s) of action. Amifostine increased HUVEC proliferation, an effect that was reversed by the intracellular H2O2 scavenger sodium pyruvate, agents that increase intracellular cAMP levels and L-valine. On the other hand, amifostine decreased HUVEC migration, an effect that was reversed by L-valine or L-arginine but not sodium pyrouvate. The decrease in migration was in line with decreased tube formation on matrigel and decreased amounts of metalloproteinase-2 released into the culture medium of HUVEC. Finally, amifostine reduced tyrosine nitration of the cytoskeletal proteins actin and alpha-tubulin in a time dependent manner. This last action could be due to the reduced production of nitric oxide (NO) or to other not yet identified mechanisms. Collectively, our results suggest that amifostine acts on endothelial cells through pathways that affect the redox status of the cells, either by producing H2O2 or by modulating NO production.

Amifostine: is there evidence of tumor protection?

A large body of experimental evidence suggests that amifostine (Ethyol, WR-2721; MedImmune, Inc, Gaithersburg, MD) is a selective cytoprotector of normal tissues. Nevertheless, several experimental studies, most of which were conducted in the early 1980s, suggest that amifostine may protect tumor tissues, although to a much lower degree than its protective effect on normal tissues. Based on a critical literature review, we conclude that any experimental evidence suggesting tumor protection is weak. The effects of anesthesia and hypotension on normal and tumor tissue oxygenation status of animals, the consequences of such events on amifostine activity, and the impact of this complex situation on host immunity and radiotherapy efficacy in the experimental setting do not reliably simulate the clinical setting. Analyses of radiobiologic and histologic results of the Canine Sarcoma Study show that, if any conclusion is to be made, amifostine protected normal tissues and preserved (or even enhanced) the antitumor activity of radiotherapy. The Ormaplatin Study clearly showed a 10-fold decreased concentration of platinum in tumor compared with normal tissues, and does not therefore support evidence of lack of amifostine selectivity. Finally, not one clinical study suggests tumor protection with amifostine. On the contrary, the majority of clinical data strongly suggest that patients who receive amifostine with radiotherapy and/or chemotherapy do better than controls. Rather than organizing large-scale, randomized clinical trials to exclude tumor protection by amifostine, it seems more useful to design trials that would measure amifostine benefits in terms of improved quality of life, tumor control, and survival rates in patients being treated with standard or novel chemotherapy/radiotherapy regimens.

Antitumor efficacy of reticulol from Streptoverticillium against the lung metastasis model B16F10 melanoma. Lung metastasis inhibition by growth inhibition of melanoma

Reticulol was isolated from the culture broth of the strain Streptoverticillium sp. NA-4803. Recticulol (M.W. 222.2) exhibited a potent in vitro cytotoxicity against A427, a human lung tumor cell line, and B16F10, a mouse melanoma cell line. In the trypan blue staining assay for B16F10 cells, the cell viability by reticulol treatment was significantly decreased in a dose-dependent manner. The in vivo assay for the lung metastasis-blocking effect showed that reticulol injected intravenously suppressed the increase in colonies on the lung in a dose-dependent manner. In addition, the survival rate of tumor-implanted mice treated with reticulol was closely associated with its antitumoral efficacy. Reticulol administered via the peritoneum of mice showed less metastasis inhibition than that injected intravenously. To demonstrate the mechanism for inhibition of metastasis, the inhibitory effect of reticulol for matrix metalloproteinase-2 or -9 involved in melanoma metastasis was investigated; however, they were not observed on zymogram gel. In addition, the antitumor efficacy of reticulol was not associated with cell cycle arrest or apoptosis. Therefore, it was inferred that reticulol known as a phosphodiesterase inhibitor directly inhibited the growth of B16F10 melanoma, showing necrotic response. These results suggest that reticulol protects its lung metastasis via the bloodstream by inhibiting the growth of B16F10 melanoma at the cellular level.

Amifostine inhibits angiogenesis in vivo

Amifostine (WR-2721) is an inorganic thiophosphate-cytoprotective agent developed to selectively protect normal tissues against the toxicity of chemotherapy and radiation. We have previously shown that amifostine protects both chicken embryo chorioallantoic membrane (CAM) vessels and cells from the effects of X-rays. In the present work, we studied the effect of amifostine on angiogenesis in vivo, using the CAM model. Amifostine decreased the number of CAM vessels in a dose-dependent manner, without being toxic for the tissue. It also decreased the mRNA levels of both vascular endothelial growth factor (VEGF) isoforms VEGF(165) and VEGF(190), 6 and up to 48 h after its application onto the CAM. Similarly, it decreased the mRNA levels of inducible nitric-oxide synthase, 24 and 48 h after drug application. Furthermore, amifostine decreased the deposited amounts of laminin and collagen I 24 h after its application, without affecting the expression of the corresponding genes. The protein amounts and activity of matrix metalloproteinase-2 were not affected, whereas the expression of the corresponding gene was decreased up to 48 h after drug application. Finally, the activity of plasmin was increased 6 h after amifostine application and remained increased at later time points. These findings suggest that amifostine alters the expression of several molecules implicated in the angiogenesis process and affects the composition of the extracellular matrix in a way that leads to inhibition of angiogenesis. Such an antiangiogenic action of amifostine, together with its radioprotective effects, further supports its use in combination with radiotherapy for increased therapeutic efficacy.

Delayed cytoprotection after enhancement of Sod2 (MnSOD) gene expression in SA-NH mouse sarcoma cells exposed to WR-1065, the active metabolite of amifostine

SA-NH mouse sarcoma cells were grown to confluence and then exposed to either 40 microM or 4 mM of WR-1065, i.e. the active thiol form of amifostine, for 30 min and then washed. Total RNA and protein were isolated at various times up to 24 h after exposure. Both concentrations of WR-1065 were equally effective in affecting Sod2 (also known as MnSOD) gene expression and protein levels. Northern blot analysis using a mouse cDNA probe revealed three Sod2 transcripts of 1, 4 and 6 kb. Expression of both the 4- and 6-kb transcripts increased by 20 and 60%, respectively, and remained elevated over a period of 4 to 20 h. Sod2 protein levels, as determined by Western blot analysis, increased 15-fold over background control levels over the same interval. Sod2 protein was evaluated using activity gels and was found to be active. SA-NH cells were irradiated with X rays either in the presence of 40 microM or 4 mM WR-1065 or 24 h later after its removal, when Sod2 protein levels were most elevated. No protection was observed for cells irradiated in the presence of 40 microM WR-1065. In contrast, survival after a dose of 2 Gy was elevated 1.27-, 1.14- and 1.20-fold in SA-NH cells irradiated in the presence of 4 mM WR-1065 or 24 h after exposure of the cells to 40 microM and 4 mM WR-1065, respectively. The increased survival levels observed 24 h after exposure to WR-1065 represents a delayed radioprotective effect of WR-1065 and corresponds to the time at which Sod2 protein levels are most elevated. These data demonstrate a novel mechanism for radioprotection by WR-1065 and suggest a new potential concern regarding the issue of tumor protection.

Activation of the nuclear transcription factor kappaB (NFkappaB) and differential gene expression in U87 glioma cells after exposure to the cytoprotector amifostine

PURPOSE

Amifostine has been approved as a therapy to decrease the incidence of moderate-to-severe xerostomia in patients undergoing postoperative radiation treatment for head-and-neck cancer. As a reducing agent capable of participating in intracellular reductive/oxidative processes, it has the potential to affect redox-sensitive transcription factors and gene expression. Amifostine's active free thiol WR-1065 was investigated to determine its effect on nuclear transcription factor kappaB (NFkappaB) activation and subsequent gene expression in U87 glioma cells.

METHODS AND MATERIALS

The human glioma cell line U87 was grown to confluency and then exposed to WR-1065 at a concentration of 40 microM for times ranging from 30 min to 24 h. Changes in cell cycle were monitored by flow cytometry. The effect of WR-1065 on NFkappaB activation was determined by a gel shift assay. Changes in gene expression as a function of time of exposure to WR-1065 were determined by Northern blot and the Atlas Human cDNA Expression Array (Clontech, Palo Alto, CA). Changes in gene expression using the Atlas Array were verified by reverse transcriptase-polymerase chain reaction (RT-PCR) with gene-specific primers.

RESULTS

Exposure of U87 cells to 40 microM WR-1065 resulted in a marked activation of NFkappaB between 30 min and 1 h after treatment. Expression of MnSOD, an NFkappaB-responsive gene, was enhanced by over 2-fold after 16 h of treatment and remained elevated at 24 h. During this period of time, no changes in cell cycle distribution were observed. To assess changes in the expression levels of NFkappaB-responsive genes as a function of WR-1065 exposure, cDNA arrays containing 49 genes identified as having DNA-binding motifs for NFkappaB were used. Only five genes were found to be significantly affected at 1, 4, and/or 16 h of treatment. GST-3 and c-myc were repressed up to 2- and 4-fold, respectively. The expression levels of IL-2Ra, RANTES, and c-myb, in contrast, were enhanced up to 14-, 3-, and 2-fold, respectively. The remaining genes having NFkappaB-responsive elements in their promoter regions were either not expressed (20 genes) or were not affected (24 genes) by exposure to WR-1065.

CONCLUSIONS

The redox-sensitive transcription factor NFkappaB can be activated in U87 glioma cells by the active thiol form of the cytoprotector amifostine. Activation of NFkappaB by the antioxidant WR-1065 is accompanied by a reduced expression of the oncogene c-myc and an enhanced expression of the antioxidant gene MnSOD, a gene whose expression in tumor cells is relatively low, but when overexpressed has been correlated with a suppression of the malignant phenotype. Activation of NFkappaB by WR-1065, however, results in selective rather than global changes in the expression of genes containing NFkappaB-responsive elements.

Inflammation dampened by gelatinase A cleavage of monocyte chemoattractant protein-3

Tissue degradation by the matrix metalloproteinase gelatinase A is pivotal to inflammation and metastases. Recognizing the catalytic importance of substrate-binding exosites outside the catalytic domain, we screened for extracellular substrates using the gelatinase A hemopexin domain as bait in the yeast two-hybrid system. Monocyte chemoattractant protein-3 (MCP-3) was identified as a physiological substrate of gelatinase A. Cleaved MCP-3 binds to CC-chemokine receptors-1, -2, and -3, but no longer induces calcium fluxes or promotes chemotaxis, and instead acts as a general chemokine antagonist that dampens inflammation. This suggests that matrix metalloproteinases are both effectors and regulators of the inflammatory response.