TH-302, a hypoxia-activated prodrug with broad in vivo preclinical combination therapy efficacy: optimization of dosing regimens and schedules.

PURPOSE: Subregional hypoxia is a common feature of tumors and is recognized as a limiting factor for the success of radiotherapy and chemotherapy. TH-302, a hypoxia-activated prodrug selectively targeting hypoxic regions of solid tumors, delivers a cytotoxic warhead to the tumor, while maintaining relatively low systemic toxicity. The antitumor activity, different dosing sequences, and dosing regimens of TH-302 in combination with commonly used conventional chemotherapeutics were investigated in human tumor xenograft models. METHODS: Seven chemotherapeutic drugs (docetaxel, cisplatin, pemetrexed, irinotecan, doxorubicin, gemcitabine, and temozolomide) were tested in combination with TH-302 in eleven human xenograft models, including non-small cell lung cancer (NSCLC), colon cancer, prostate cancer, fibrosarcoma, melanoma, and pancreatic cancer. RESULTS: The antitumor activity of docetaxel, cisplatin, pemetrexed, irinotecan, doxorubicin, gemcitabine, and temozolomide was increased when combined with TH-302 in nine out of eleven models tested. Administration of TH-302 2-8 h prior to the other chemotherapeutics yielded superior efficacy versus other sequences tested. Simultaneous administration of TH-302 and chemotherapeutics increased toxicity versus schedules with dosing separations. In a dosing optimization study, TH-302 administered daily at 50 mg/kg intraperitoneally for 5 days per week in the H460 NSCLC model showed the optimal response with minimal toxicity. CONCLUSIONS: TH-302 enhances the activity of a wide range of conventional anti-neoplastic agents in a broad panel of in vivo xenograft models. These data highlight in vivo effects of schedule and order of drug administration in regimen efficacy and toxicity and have relevance to the design of human regimens incorporating TH-302.

Selective tumor hypoxia targeting by hypoxia-activated prodrug TH-302 inhibits tumor growth in preclinical models of cancer.

PURPOSE: Tumor hypoxia underlies treatment failure and yields a more aggressive, invasive, and metastatic cancer phenotype. TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide mustard (Br-IPM). The purpose of this study is to characterize the antitumor activity of TH-302 and investigate its selective targeting of the hypoxic cells in human tumor xenograft models. EXPERIMENTAL DESIGN: Antitumor efficacy was assessed by tumor growth kinetics or by clonogenic survival of isolated cells after tumor excision. Hypoxic fractions (HF) were determined by immunohistochemistry and morphometrics of pimonidazole staining. Tumor hypoxia levels were manipulated by exposing animals to different oxygen concentration breathing conditions. The localization and kinetics of TH-302 induced DNA damage was determined by γH2AX immunohistochemistry. RESULTS: TH-302 antitumor activity was dose-dependent and correlated with total drug exposure. Correlation was found between antitumor activity and tumor HF across 11 xenograft models. Tumor-bearing animals breathing 95% O(2) exhibited attenuated TH-302 efficacy, with whereas those breathing 10% O(2) exhibited enhanced TH-302 efficacy, both compared with air (21% O(2)) breathing. TH-302 treatment resulted in a reduction in the volume of the HF 48 hours after dosing and a corresponding increase in the necrotic fraction. TH-302 induced DNA damage as measured by γH2AX was initially only present in the hypoxic regions and then radiated to the entire tumor in a time-dependent manner, consistent with TH-302 having a "bystander effect." CONCLUSIONS: The results show that TH-302 has broad antitumor activity and selectively targets hypoxic tumor tissues.

Inhibition of both thioredoxin reductase and glutathione reductase may contribute to the anticancer mechanism of TH-302.

Selenium-containing thioredoxin reductase (TrxR) is an important target of cancer therapy. Many useful anticancer agents including bis-alkylating agents, cisplatin, and arsenic trioxide are known to interact with the selenocysteine dipeptide in the carboxy terminal region of thioredoxin reductase and inactivate its ability to reduce thioredoxin. Some investigators have postulated that the inactivation of TrxR may add to the cytotoxic potential of these anticancer agents. TH-302 is a newly developed antineoplastic drug which represents a potential new class of tumor selective hypoxia-activated prodrugs (HAPs). TH-302 is an inactive prodrug created by the covalent conjugation of 2-nitroimidazole as an oxygen sensor to bromo-isophosphoramide (Br-IPM). In the presence of severe hypoxia and near anoxia, the two imidazole sensor moiety undergoes reduction and the Br-IPM is released in situ. Bromo-IPM is a more potential analog of Chloro-IPM, the active alkylating moiety that is derived by activation of ifosfamide (IFO). We previously demonstrated that IFO could inhibit tumor TrxR activity and chloro-IPM is known to bind covalently to the seleno-cysteine dipeptide in thioredoxin reductase. The present study assessed the ability of TH-302 to activate in the tumors of mice-bearing hepatoma 22 (H22) and inactivate the tumor TrxR. In mice-bearing hepatoma 22 (H22) solid tumors, intraperitoneal (i.p.) injection with TH-302 at the dose of 200 mg/kg administered twice, a regimen which was well tolerated by the mice, significantly inhibited tumor growth. Also in this mice model, i.p. TH-302 at the dose of 300 mg/kg, which would be the maximum single i.p. administration dose tolerated by mice, and which induced only 2% body weight loss, significantly inhibited both TrxR and glutathione reductase (GR) activities by 46% (P < 0.001) and 60% (P < 0.001) as compared with the controls, respectively, at 3 h after the injection. Since TrxR is a key player in thioredoxin system and GR is the major reductase for the reduction of oxidized glutathione in glutathione system, the present results imply the anticancer effect of TH-302 is associated concurrently with modulation of TrxR and GR. These findings suggest that the anticancer activity of TH-302 in this model system may associate with both DNA alkylation and the modulation of TrxR and GR. In addition, they suggest that, by inhibition of these two critical reductases, with less glutathione available to intercept the reactive intermediates involved in DNA alkylation, the antitumor effects of the chemotherapy would be enhanced.

C-reactive protein as a prognostic marker for men with androgen-independent prostate cancer: results from the ASCENT trial.

BACKGROUND: Studies of cancer risk and molecular carcinogenesis suggest a role for inflammation in cancer development and progression. The authors sought to determine whether specific blood proteins associated with inflammation predict for outcomes in men with metastatic androgen-independent prostate cancer (AIPC) who are initiating docetaxel-based chemotherapy. METHODS: Baseline plasma samples were stored (-80 degrees C) from 160 of 250 patients enrolled in the AIPC Study of Calcitriol ENhancing Taxotere (ASCENT) trial, a randomized, placebo-controlled trial comparing weekly docetaxel plus high-dose calcitriol with weekly docetaxel. Multiplex immunoassays measured 16 cytokine, chemokine, cardiovascular, or inflammatory markers. The Cox proportional hazards model was used to assess associations between baseline biomarkers, clinical characteristics, and survival. Logistic regression was used for analyses of associations with prostate-specific antigen (PSA) decline. RESULTS: C-reactive protein (CRP) was found to be significantly predictive of a shorter overall survival (hazards ratio [HR] of 1.41 for each natural logarithm [ln] [CRP] increase; 95% confidence interval [95% CI], 1.20-1.65 [P < .0001]). When CRP (continuous) was entered into a multivariate model using 13 baseline clinical variables, only elevated CRP remained a significant predictor (P < .0001) of shorter overall survival. When categorized as normal (8 mg/L), elevated CRP was found to be a significant predictor of shorter overall survival (HR of 2.96; 95% CI, 1.52-5.77 [P = .001]), as was hemoglobin (P = .007). Elevated CRP was also associated with a lower probability of PSA decline (odds ratio of 0.74 for each ln(CRP) increase; 95% CI, 0.60-0.92 [P = .007]). CONCLUSIONS.: Elevated plasma CRP concentrations appear to be a strong predictor of poor survival and lower probability of PSA response to treatment in patients with AIPC who are receiving docetaxel-based therapy.

High dose calcitriol may reduce thrombosis in cancer patients.

The incidence of venous and arterial thrombosis in a placebo-controlled randomised trial of DN-101 (high dose calcitriol) with docetaxel versus docetaxel was compared. Of the 13 thrombotic events observed in the 250 patients enroled in this study, two occurred in DN-101 and 11 in placebo-treated patients (P = 0.01). This difference remained significant after adjustment for baseline history of thrombosis, atrial fibrillation and use of anti-thrombotic agents. In vitro and vitamin D receptor (VDR) knockout mouse studies predict that nanomolar concentrations of calcitriol may act as an antithrombotic agent. We report the first clinical observation that supports this hypothesis in humans.