Selective Protection Of Normal Tissues Research Articles

Selenium targets resistance biomarkers enhancing efficacy while reducing toxicity of anti-cancer drugs: preclinical and clinical development.

Selenium (Se)-containing molecules exert antioxidant properties and modulate targets associated with tumor growth, metastasis, angiogenesis, and drug resistance. Prevention clinical trials with low-dose supplementation of different types of Se molecules have yielded conflicting results. Utilizing several xenograft models, we earlier reported that the enhanced antitumor activity of various chemotherapeutic agents by selenomethione and Se-methylselenocysteine in several human tumor xenografts is highly dose- and schedule-dependent. Further, Se pretreament offered selective protection of normal tissues from drug-induced toxicity, thereby allowing higher dosing than maximum tolerated doses.These enhanced therapeutic effects were associated with inhibition of hypoxia-inducible factor 1- and 2-alpha (HIF1α, HIF2α) protein, nuclear factor (erythyroid-derived 2)-like 2 (Nrf2) and pair-related homeobox-1 (Prx1) transcription factors, downregulation of oncogenic- and upregulation of tumor suppressor miRNAs. This review provides: 1) a brief update of clinical prevention trials with Se; 2) advances in the use of specific types, doses, and schedules of Se that selectively modulate antitumor activity and toxicity of anti-cancer drugs; 3) identification of targets selectively modulated by Se; 4) plasma and tumor tissue Se levels achieved after oral administration of Se in xenograft models and cancer patients; 5) development of a phase 1 clinical trial with escalating doses of orally administered selenomethionine in sequential combination with axitinib to patients with advanced clear cell renal cell carcinoma; and 6) clinical prospects for future therapeutic use of Se in combination with anticancer drugs.

A PPAR gamma agonist protects against oral mucositis induced by irradiation in a murine model

BackgroundDue to its anti-inflammatory, antifibrotic and antineoplastic properties, the PPAR gamma agonist rosiglitazone is of interest in prevention and therapy of radiation-induced toxicities. We aimed to evaluate the radioprotective effect of rosiglitazone in a mouse model of radiation-induced oral mucositis. Material and methodsOral mucositis was obtained by irradiation of the oral region of C57BL/6J mice, pretreated or not with rosiglitazone. Mucositis was assessed by macroscopic scoring, histology and molecular analysis. Tumor xenograft was obtained by s.c. injection of Hep-2 cells in CD1 mice. Tumor volume was measured twice a week to evaluate effect of rosiglitazone alone and combined with radiotherapy. ResultsIrradiated mice showed typical features of oral mucositis, such as oedema and reddening, reaching the peak of damage after 12–15days. Rosiglitazone markedly reduced visible signs of mucositis and significantly reduced the peak. Histological analysis showed the presence of an inflammatory cell infiltrate after irradiation; the association with rosiglitazone noticeably reduced infiltration. Rosiglitazone significantly inhibited radiation-induced tnfα, Il-6 and Il-1β gene expression. Rosiglitazone controlled the increase of TGF-β and NF-kB p65 subunit proteins induced by irradiation, and enhanced the expression of catalase. Irradiation and rosiglitazone significantly reduced tumor volume as compared to control. Rosiglitazone did not protect tumor from the therapeutic effect of radiation. ConclusionRosiglitazone exerted a protective action on normal tissues in radiation-induced mucositis. Moreover, it showed antineoplastic properties on head-neck carcinoma xenograft model and selective protection of normal tissues. Thus, PPAR gamma agonists should be further investigated as radioprotective agents in head and neck cancer.

Improvement of the in vitro safety profile and cytoprotective efficacy of amifostine against chemotherapy by PEGylation strategy

Amifostine, an organic thiophosphate prodrug, has been clinically utilized for selective protection of normal tissues with high expression of alkaline phosphatase from oxidative damage elicited by chemotherapy or radiotherapy. However, the patients receiving amifostine suffer from severe dose-dependent adverse effects. Strategies for improvement of the protective efficacy and toxicity profile of amifostine are urgently required. Here we constructed a PEGylated amifostine (PEG-amifostine) through conjugation of amifostine to the 4-arm PEG (5000Da) by a mild one-step reaction. The relatively large PEG-amifostine molecules clustered into spherical nanoparticles, resulting in distinct hydrolysis properties, cell uptake profile and antioxidative activity compared with the free small molecules. PEGylation prolonged the hydrolysis time of amifostine, providing sustained transformation to its functional metabolites. PEG-amifostine could be internalized into cells and translocated to acidic organelles in a time-dependent manner. The intrinsic cytotoxicity of amifostine, which is related to the reductive reactivity of its metabolites and their ability to diffuse readily, was attenuated after PEGylation. This modification impeded the interaction between free sulfhydryls and functional biomolecules, providing PEG-amifostine with an improved safety profile in vitro. Moreover, PEG-amifostine showed higher efficiency in the elimination of reactive oxygen species and prevention of cisplatin-induced cytotoxicity compared with free amifostine. Overall, our study for the first time developed a PEGylated form of amifostine which significantly improved the efficacy and decreased the adverse effects of this antioxidant in vitro with great promise for clinical translation. In vivo study is urgently needed to confirm and redeem the cytoprotective effects of the PEG-amifostine in chemotherapy.

Abstract 4317: Low dose arsenic-induced transient p53 inhibition: A novel strategy for chemotherapy protection

Abstract Because of its effectiveness in killing cancer cells, chemotherapy remains to be one of the common modalities for cancer treatment, but the resulting severe side effects often pose a significant threat to cancer patients. Recognizing p53 activation in the sensitive tissues as the primary mechanism for chemotherapy-induced acute toxicity and the universal p53 inactivation in human cancers, we exploited the use of low dose arsenic to inhibit p53 for a selective protection of normal tissues from chemotherapeutics-induced damages. Colon carcinoma cell line SW-480 was used to generate a mouse xenograft model. Treatments were initiated three weeks after implantation when the tumor size reached approximately 100 mm3. Arsenic pretreatment was carried out by feeding sex-matched mice (4-6 weeks of age) with water (1.0 mg/L) for three days. As expected, treatment of tumor-bearing mice with 5FU for 7 days resulted in 77% decrease in tumor volume when compared with the untreated group. The brief treatment with low doses of arsenic did not affect the ability of 5FU to induce tumor regression as evidenced by an 80% reduction of tumor size. However, arsenic treatment was associated with a marked alleviation of 5FU-induced systemic toxicity as demonstrated by the finding that arsenic pretreatment reduced 5FU-induced body weight loss from 25% to 4%. The protecting effect of arsenic was also clearly evident in reducing 5FU-induced damage in gastrointestinal (GI) track and hematopoietic (HP) system, two of the most sensitive tissues. Using mutant p53 expressing mice, we demonstrate that arsenic-mediated protection primarily depends on functional p53. Our preclinical study implicates that the brief use of low doses arsenic to inhibit p53 is an effective approach of chemotherapy protection. If successfully validated in clinical studies, this strategy may not only minimize side effects, but would also allow escalated therapeutic doses to improve treatment efficacy in a safe and effective approach for cancer therapy protection. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4317. doi:10.1158/1538-7445.AM2011-4317

Selective protection of normal tissues from radiation damage by activation of Toll-like receptor 5 signaling

Selective protection of normal tissues from radiation damage by activation of Toll-like receptor 5 signaling

Targeting Molecular Determinants of Tumor Chemo-Radioresistance

Attempts to improve results of chemoradiotherapy by increasing the total dose of radiation or chemotherapy or by changing chemotherapeutic drugs have not been very successful. Additionally, some combinations have been associated with a high rate of unacceptable treatment-related morbidity, underscoring the need for new treatment strategies to combine with radiation to improve the therapeutic ratio. Potentially useful strategies include the selective protection of normal tissues, interference with resistance mechanisms, improved targeting of tumor stem cells, and dealing with residual tumor disease. Evidence is mounting that epidermal growth factor receptor (EGFR) overexpression or mutation, as well as dysregulation in cyclins and cyclin-dependent kinases represent major determinants in aggressive tumor growth and poor tumor response to standard treatment modalities, including radiotherapy. Two major approaches have been investigated, one consisting of blocking the extracellular domain of the receptor with anti-EGFR antibodies to prevent ligand-receptor binding, and the other consisting of small chemical compounds, tyrosine kinase inhibitors, which bind to the intracellular domain of the receptor preventing its phosphorylation. Clinical trials are evaluating whether or not quantifying EGFR expression in tumors can serve as a predictor of treatment outcome and if the incorporation of EGFR inhibitors into radiotherapy can improve treatment outcome.

Selective modulation of the therapeutic efficacy of anticancer drugs by selenium containing compounds against human tumor xenografts.

Studies were carried out in athymic nude mice bearing human squamous cell carcinoma of the head and neck (FaDu and A253) and colon carcinoma (HCT-8 and HT-29) xenografts to evaluate the potential role of selenium-containing compounds as selective modulators of the toxicity and antitumor activity of selected anticancer drugs with particular emphasis on irinotecan, a topoisomerase I poison. Antitumor activity and toxicity were evaluated using nontoxic doses (0.2 mg/mouse/day) and schedule (14-28 days) of the selenium-containing compounds, 5-methylselenocysteine and seleno-L-methionine, administered orally to nude mice daily for 7 days before i.v. administration of anticancer drugs, with continued selenium treatment for 7-21 days, depending on anticancer drugs under evaluation. Several doses of anticancer drugs were used, including the maximum tolerated dose (MTD) and toxic doses. Although many chemotherapeutic agents were evaluated for toxicity protection by selenium, data on antitumor activity were primarily obtained using the MTD, 2 x MTD, and 3 x MTD of weekly x4 schedule of irinotecan. Selenium was highly protective against toxicity induced by a variety of chemotherapeutic agents. Furthermore, selenium increased significantly the cure rate of xenografts bearing human tumors that are sensitive (HCT-8 and FaDu) and resistant (HT-29 and A253) to irinotecan. The high cure rate (100%) was achieved in nude mice bearing HCT-8 and FaDu xenografts treated with the MTD of irinotecan (100 mg/kg/week x 4) when combined with selenium. Administration of higher doses of irinotecan (200 and 300 mg/kg/week x 4) was required to achieve high cure rate for HT-29 and A253 xenografts. Administration of these higher doses was possible due to selective protection of normal tissues by selenium. Thus, the use of selenium as selective modulator of the therapeutic efficacy of anticancer drugs is new and novel. We demonstrated that selenium is a highly effective modulator of the therapeutic efficacy and selectivity of anticancer drugs in nude mice bearing human tumor xenografts of colon carcinoma and squamous cell carcinoma of the head and neck. The observed in vivo synergic interaction is highly dependent on the schedule of selenium.

Nitroxides as Radiation Protectors

Selective protection of normal tissues from the damaging effects of ionizing radiation is an important objective in cancer treatment research. Likewise, radioprotective agents may be useful in protecting the human population in the event of radiation-related accidents or military conflicts. Over the past decade, we have identified stable nitroxide compounds as a unique class of antioxidants with demonstrated radioprotective properties. We have shown that nitroxides at nontoxic concentrations are effective as in vitro and in vivo antioxidants when oxidation is induced by superoxide, hydrogen peroxide, organic hydroperoxides, ionizing radiation, or specific DNA-damaging anticancer agents. Studies have shown that nitroxides protect against radiation-induced DNA damage, chromosome aberrations, mutation induction, cell killing, and lethality in mice that receive whole-body irradiation. Whether these agents provide radioprotection for low-level radiation doses remains to be determined.

Pharmacokinetics of cisplatin with and without amifostine in tumour-bearing nude mice.

Amifostine (Ethyol, WR-2721) is in use in the clinic as a protector against platinum-induced toxicities. We have previously reported that amifostine induced a potentiation of the antitumour activity of carboplatin in human ovarian cancer xenografts. An influence of amifostine on the pharmacokinetics of carboplatin, resulting in higher platinum concentrations in plasma and tissues of the tumour-bearing nude mice, was thought to be the cause of enhancement of the antitumour activity. Therefore, the pharmacokinetics of cisplatin were investigated in tumour-bearing nude mice treated with cisplatin alone or in combination with amifostine. A significant increase in the area under the curve (AUC) of the total platinum concentration in mice treated with amifostine was only observed in the kidney (from 355 to 398 nmol h/g), whereas in the other tissues and plasma no significant changes were measured. The selective protection of normal tissues by amifostine was confirmed by a decrease in the AUC of the cisplatin-DNA adduct levels in normal tissues. The decrease was only significant in the liver (282-240 fmol h/microgram DNA), whereas in tumour tissue a slight increase in the AUC of the cisplatin-DNA adducts could be detected (91.3-110.1 fmol h/microgram DNA). The minor influence of amifostine on the pharmacokinetics of cisplatin may be the reason why amifostine did not potentiate the antitumour activity of cisplatin. The influence of amifostine on cisplatin-DNA adduct levels in normal tissues versus tumour tissues is further evidence for the usefulness of this toxicity modulator in cancer patients.

The need for cytoprotection

The toxicity associated with chemotherapy is significant and dose limiting. Multiple organ systems can be affected, with both acute and chronic side effects producing adverse effects. The concept of cytoprotection, or the selective protection of normal tissues is a strategy now being investigated in preclinical and clinical models. Systemic approaches have included the use of compounds such as sodium thiosulphate, diethyldithiocarbamate and amifostine. The most promising results have been obtained with the organic thiophosphate compound amifostine (Ethyol, WR-2721).

Exploration of platinum-based dose-intensive chemotherapy strategies with amifostine (Ethyol ®)

The preclinical evaluation of amifostine confirms selective protection of normal tissues against toxicity due to cisplatin therapy while maintaining the antitumour effects. The mechanism of protection relates to the selective uptake of the free thiol, amifostine, into normal tissue compared with tumour tissue, intracellular binding and therefore detoxification of anticancer drugs, as well as through the scavenging of oxygen free radicals. Although vigorous hydration schedules have helped to alleviate nephrotoxicity, ototoxicity and cumulative dose-related peripheral neuropathy, these side effects remain important dose-limiting toxicities related to cisplatin therapy. The preclinical and clinical results to date demonstrate that amifostine can protect against cisplatin toxicities, in particular nephrotoxicity. Recent studies have demonstrated that higher single and cumulative cisplatin doses have an important impact on survival outcome; however, the improvement in survival comes at the cost of increased acute and cumulative haematological, renal and neurological toxicities that can result in serious morbidity. The role of amifostine as a unique supportive measure to reduce these toxicities offers the possibility of improving the quality of life of patients receiving chemotherapy.

Amifostine: potential for clinically useful cytoprotection.

The ability to target malignant cells for cytotoxicity while sparing normal host tissues has proven to be limited. These limitations have resulted in unacceptable toxicity or insufficiently effective therapy. Continuing investigation of new, potentially useful cytotoxic agents must continue. An alternative approach, also worthy of study, is the selective protection of normal tissues. This approach, used in conjunction with available therapeutic agents, may open the therapeutic window and incrementally enhance the effectiveness of cytotoxic therapy. A variety of methods have been used to protect normal tissues selectively. Regional protection can be used for certain organ systems, such as the oral mucosa. Selective protection on a systemic level is more difficult but agents that seem to protect normal but not malignant tissues selectively are being developed. Among these is amifostine, which was originally selected by the U.S. defense department for study as a radioprotectant. Pre-clinical studies have suggested that amifostine is differentially concentrated in normal tissues but not in malignant tissues. Tissue-specific differences in the activity of alkaline phosphatase, which dephosphorylates amifostine to its active metabolite WR-1065, and in pH are thought to be involved in this relative specificity. Clinical studies indicate that amifostine can reduce the myelosuppression produced by cyclosphosphamide, the combination of cyclophosphamide and cisplatin, and, perhaps, carboplatin. The protective effects of amifostine on nonhematopoietic toxicities are being investigated. Future trials will investigate the integration of amifostine with cytokine-based supportive care in order to define the role of this potentially clinically useful cytoprotectant agent.

Phase I clinical trials of WR-2721 with alkylating agent chemotherapy

WR-2721 is an organic thiophosphate which in the animal model provides selective protection of normal tissues against the toxicity of radiation and alkylating agent chemotherapy. Phase I trials of WR-2721 in man have been initiated to establish the dose modification factors for this agent when used in combination with escalating doses of alkylating agents beyond the level currently tolerated, and to determine whether protection of normal tissues and tumors occurs. Three Phase I trials are in progress. Initially, we used a fixed 450 mg/M 2 dose of WR-2721 prior to escalating doses of either cyclophosphamide (CYC) or cis-platinum (PL) as single agents. More recently, the current maximum tolerated dose of WR-2721(740 mg/M 2) was administered prior to PL and to nitrogen mustard (HN 2). Ten patients received 19 courses of CYC after 450 mg/M 2 of WR-2721. At the 1800 mg/M 2 LV. dose level of CYC, moderate leukopenia was noted with a median WBC nadir of 1800/mm 3 on day 10. Twenty-two courses of PL were administered to 13, patients after 450–740 mg/M 2 of WR-2721. Hydration was used, but no mannitol diuresis was employed. Transient nephrotoxicity was noted in five courses at PL doses between 80–120 mg/M 2. Mild to moderate leukopenia has been noted with HN 2 at 10–16 mg/M 2 following WR-2721 (450–750 mg/M 2). Objective anti-tumor responses have been observed. These preliminary results suggest that WR-2721 may provide normal tissue protection when administered prior to cyclophosphamide or nitrogen mustard, although the level of protection is not yet of clinical benefit. However, using a 450–740 mg/M 2 dose of WR-2721 did not provide protection against platinum-induced nephrotoxicity. WR-2721 does not appear to protect against the anti-tumor activity of alkylating agents (objective tumor responses were noted), nor does there appear to be increased acute toxicity when it is combined with alkylating agent chemotherapy.

The Selective Protection of Normal Tissues by Irradiation of Tumor-Bearing Mice in Hypoxic Hypoxia

YARMONENKO, S. P., WAINSON, A. A., BEREZNOVA, L. I., KRIMKER, V. M., OVAKIMOV, V. G., PETROSIAN, E. P., AND SHMAKOVA, N. L. The Selective Protection of Normal Tissues by Irradiation of Tumor-Bearing Mice in Hypoxic Hypoxia. Radiat. Res. 67, 447458 (1976). The possibility of selective protection of normal tissues was demonstrated when mice with solid tumors were irradiated in an atmosphere of 95% N2 and 5% 02. Irradiation of animals in this gas mixture increased their survival with a dose-modifying factor (DMF) = 2.5, decreased the number of cells with chromosomal aberration in bone marrow (DMF, 2) and the degree of hair follicle damage (DMF, 1.6). The protective effect of hypoxia drastically diminished 40 min after its application. Local irradiation of allogeneic tumors under hypoxic conditions, on the other hand, resulted in an increased rate of their regression in comparison with irradiation in air. The mechanism of the observed phenomenon is under investigation.