Selective Tumor Hypoxia Targeting by Hypoxia-Activated Prodrug TH-302 Inhibits Tumor Growth in Preclinical Models of Cancer

Threshold Pharmaceuticals, South San Francisco, California 94080, USA.
Clinical Cancer Research (Impact Factor: 8.19). 12/2011; 18(3):758-70. DOI: 10.1158/1078-0432.CCR-11-1980
Source: PubMed

ABSTRACT 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.
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.
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."
The results show that TH-302 has broad antitumor activity and selectively targets hypoxic tumor tissues.

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    • "This is exemplified by the development of highly active compounds that selectively target hypoxic regions within solid tumors [12]. TH-302 is a newly developed hypoxia-activated DNA crosslinking pro-drug that displays potent hypoxia-dependent cytotoxicity both in vitro and in preclinical cancer models [13] [14] [15]. TH-302 is currently being evaluated in phase I/II clinical trials for the treatment of solid tumors as a single agent and in combination with conventional therapies [16]. "
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    ABSTRACT: Tumor hypoxia is a major cause of treatment failure for a variety of malignancies. However, tumor hypoxia also offers treatment opportunities, exemplified by the development compounds that target hypoxic regions within tumors. TH-302 is a pro-drug created by the conjugation of 2-nitroimidazole to bromo-isophosphoramide (Br-IPM). When TH-302 is delivered to regions of hypoxia, Br-IPM, the DNA cross linking toxin, is released. In this study we assessed the cytotoxic activity of TH-302 against osteosarcoma cells in vitro and evaluated its anticancer efficacy as a single agent, and in combination with doxorubicin, in an orthotopic mouse model of human osteosarcoma (OS). In vitro, TH-302 was potently cytotoxic to osteosarcoma cells selectively under hypoxic conditions, whereas primary normal human osteoblasts were protected. Animals transplanted with OS cells directly into their tibiae and left untreated developed mixed osteolytic/osteosclerotic bone lesions and subsequently developed lung metastases. TH-302 reduced tumor burden in bone and cooperated with doxorubicin to protect bone from osteosarcoma induced bone destruction, while it also reduced lung metastases. TH-302 may therefore be an attractive therapeutic agent with strong activity as a single agent and in combination with chemotherapy against OS. Crown Copyright © 2014. Published by Elsevier Ireland Ltd. All rights reserved.
    Cancer Letters 11/2014; 357(1). DOI:10.1016/j.canlet.2014.11.020 · 5.62 Impact Factor
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    • "A Phase 3 trial is currently testing gemcitabine in combination with TH-302 in patients with locally advanced unresectable or metastatic pancreatic adenocarcinoma. As outlined above, pancreatic cancer is highly hypoxic and TH-302 is a chemotherapeutic agent which is selectively activated in a hypoxic tumor microenvironment (Sun et al., 2012). Angiotensin II type I receptor inhibitors have also been explored as potential therapeutics to inhibit PSC activity. "
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    ABSTRACT: Pancreatic cancer is highly chemoresistant. A major contributing factor is the characteristic extensive stromal or fibrotic reaction, which comprises up to 90% of the tumor volume. Over the last decade there has been intensive research into the role of the pro-fibrogenic pancreatic stellate cells (PSCs) and their interaction with pancreatic cancer cells. As a result of the significant alterations in the tumor microenvironment following activation of PSCs, tumor progression, and chemoresistance is enhanced. This review will discuss how PSCs contribute to chemoresistance in pancreatic cancer.
    Frontiers in Physiology 04/2014; 5:141. DOI:10.3389/fphys.2014.00141 · 3.50 Impact Factor
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    • "However, while elegant in concept, this approach has proved extremely difficult to translate into clinical efficacy. Novel compounds are still being developed (McKeage et al., 2011; Weiss et al., 2011; Sun et al., 2012) and are in clinical trial, but the fact remains that after 40 years of research and development , no hypoxia-selective bioreductive drugs have been approved for use in humans. The need to develop hypoxiaselective drugs is even more important today as our understanding of the effect that hypoxia has on tumour biology and therapy increases. "
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    ABSTRACT: Hypoxia in tumours is known to cause resistance to conventional chemotherapeutic drugs. In contrast, little is known about the effects of hypoxia on targeted anti-cancer drugs. This study evaluated the effect of hypoxia on a series of clinically approved tyrosine kinase inhibitors (TKIs). The effect of hypoxia (0.1% oxygen) on the activity of conventional cytotoxic drugs (5-fluorouracil, doxorubicin and vinblastine), the hypoxia activated pro-drug tirapazamine and 9 TKIs was determined in a panel of cell lines. Where hypoxia had a marked effect on chemosensitivity, western blot analysis to determine the effect of hypoxia on target expression and the effect of TKIs on cell signalling response under aerobic and hypoxic conditions was conducted. Three patterns of chemosensitivity were observed; resistance under hypoxia, equi-toxic activity against hypoxic and aerobic cells and preferential cytotoxicity to hypoxic cells. Significant hypoxia selectivity (independent of HIF1) was observed in the case of dasatinib and this correlated with the ability of dasatinib to inhibit phosphorylation of Src at tyrosine 530. Sorafenib was significantly less effective under hypoxic conditions but resistance did not correlate with hypoxia induced changes in RAF/MEK/ERK signalling. Hypoxia influences the activity of TKIs but in contrast to conventional cytotoxic drugs, preferential activity against hypoxic cells can occur. The search for hypoxia targeted therapies has been long and fruitless and this study suggests that some clinically approved TKIs could preferentially target the hypoxic fraction of some tumour types.
    British Journal of Pharmacology 10/2013; 171(1). DOI:10.1111/bph.12438 · 4.99 Impact Factor
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