Targeting tumour hypoxia to prevent cancer metastasis. From biology, biosensing and technology to drug development: the METOXIA consortium

Abstract

The hypoxic areas of solid cancers represent a negative prognostic factor irrespective of which treatment modality is chosen for the patient. Still, after almost 80 years of focus on the problems created by hypoxia in solid tumours, we still largely lack methods to deal efficiently with these treatment-resistant cells. The consequences of this lack may be serious for many patients: Not only is there a negative correlation between the hypoxic fraction in tumours and the outcome of radiotherapy as well as many types of chemotherapy, a correlation has been shown between the hypoxic fraction in tumours and cancer metastasis. Thus, on a fundamental basis the great variety of problems related to hypoxia in cancer treatment has to do with the broad range of functions oxygen (and lack of oxygen) have in cells and tissues. Therefore, activation-deactivation of oxygen-regulated cascades related to metabolism or external signalling are important areas for the identification of mechanisms as potential targets for hypoxia-specific treatment. Also the chemistry related to reactive oxygen radicals (ROS) and the biological handling of ROS are part of the problem complex. The problem is further complicated by the great variety in oxygen concentrations found in tissues. For tumour hypoxia to be used as a marker for individualisation of treatment there is a need for non-invasive methods to measure oxygen routinely in patient tumours. A large-scale collaborative EU-financed project 2009-2014 denoted METOXIA has studied all the mentioned aspects of hypoxia with the aim of selecting potential targets for new hypoxia-specific therapy and develop the first stage of tests for this therapy. A new non-invasive PET-imaging method based on the 2-nitroimidazole [(18)F]-HX4 was found to be promising in a clinical trial on NSCLC patients. New preclinical models for testing of the metastatic potential of cells were developed, both in vitro (2D as well as 3D models) and in mice (orthotopic grafting). Low density quantitative real-time polymerase chain reaction (qPCR)-based assays were developed measuring multiple hypoxia-responsive markers in parallel to identify tumour hypoxia-related patterns of gene expression. As possible targets for new therapy two main regulatory cascades were prioritised: The hypoxia-inducible-factor (HIF)-regulated cascades operating at moderate to weak hypoxia (<1% O(2)), and the unfolded protein response (UPR) activated by endoplasmatic reticulum (ER) stress and operating at more severe hypoxia (<0.2%). The prioritised targets were the HIF-regulated proteins carbonic anhydrase IX (CAIX), the lactate transporter MCT4 and the PERK/eIF2α/ATF4-arm of the UPR. The METOXIA project has developed patented compounds targeting CAIX with a preclinical documented effect. Since hypoxia-specific treatments alone are not curative they will have to be combined with traditional anti-cancer therapy to eradicate the aerobic cancer cell population as well.

Down-regulating HIF-1α by lentivirus-mediated shRNA for therapy of triple negative breast cancer

“…In response to hypoxia, cancer cells undergo a variety of adoptive changes, including activation of signaling involve in cancer cells survival, proliferation, apoptosis, invasion, chemoresistance, and angiogenesis. 8,9 HIF-1 is one of the major transcription factors that mediate this adaptive process of cancer cells to the hypoxic environment. HIF-1 is a heterodimer composed of the rate limiting factor HIF1a and the constitutively expressed HIF-1b; 10 the latter is also called the aryl hydrocarbon receptor nuclear translocator and heterodimerises with several other factors, such as the Ahr transcription factor.…”

The extravascular penetration of tirapazamine into tumours: a predictive model of the transport and efficacy of hypoxia specific cytotoxic analogues and the potential use of cucurbiturils to facilitate delivery

“…A quantum mechanical study has shown that TPZ can form stable complexes with cucurbit [7]uril as a precursor to proof of principle of improved TPZ delivery to tumours.…”

“…7 [Pettersen 2014] Wardman 2007 8 has shown that electron-affinic compounds which react with DNA free radicals have the potential to be universally active in combating hypoxia related radiosensitizers, and hypoxia specific cytotoxins such as tirapazamine (TPZ) is particularly active. Drugs can be selectively delivered to hypoxic tumours using either reductive enzymes or radiation produced free radicals to activate drug release from electron-affinic prodrugs such as TPZ.…”

“…Keywords: Tirapazamine analogues, intra-tumoural diffusion, anti-cancer, hypoxia, cytotoxicity, DNA binding, cucurbiturils, quantum mechanics Abbreviations Tirapazamine TPZ, free energy of water desolvation ΔG desolv,CDS , lipophilicity free energy ΔG lipo,CDS , cavity dispersion solvent structure of the first solvation shell CDS, multicellular layers MCL, extracellular matrix ECM, diffusion through support membrane D s , diffusion through multicellular layer D MCL , cucurbit[n]urils CB, cucurbit [7]urils, CB [7], highest occupied molecular orbital HOMO, lowest unoccupied molecular orbital LUMO, density functional molecular orbital theory DFT, adiabatic electron affinity AEA, cisplatin CisPt, ratio aerobic property:hypoxic property HCR, aerobic aer, hypoxic hyp, DNA binding equilibrium constant K DNA, multiple correlation coefficient R 2 , the F test of significance, standards errors for the estimate (SEE) and standard errors of the variables SE(ΔG desolCDS ), SE(ΔG lipoCDS ), SE(Dipole Moment), SE (Molecular Volume), SE(AEA).…”

“…Application of the model to the DNA binding equilibrium constants of TPZ analogues with acridine or acridine-like moieties show that ligand water desolvation and lipophilicity are the dominant processes governing the DNA intercalation of TPZ analogues. This conclusion is consistent with DFT modelling of the complexes formed by TPZ analogues with neutral and N-protonated acridine moieties which intercalate with the guanine DNA nucleobases.A quantum mechanical study has shown that TPZ can form stable complexes with cucurbit [7]uril as a precursor to proof of principle of improved TPZ delivery to tumours.Keywords: Tirapazamine analogues, intra-tumoural diffusion, anti-cancer, hypoxia, cytotoxicity, DNA binding, cucurbiturils, quantum mechanics Abbreviations Tirapazamine TPZ, free energy of water desolvation ΔG desolv,CDS , lipophilicity free energy ΔG lipo,CDS , cavity dispersion solvent structure of the first solvation shell CDS, multicellular layers MCL, extracellular matrix ECM, diffusion through support membrane D s , diffusion through multicellular layer D MCL , cucurbit[n]urils CB, cucurbit [7]urils, CB [7], highest occupied molecular orbital HOMO, lowest unoccupied molecular orbital LUMO, density functional molecular orbital theory DFT, adiabatic electron affinity AEA, cisplatin CisPt, ratio aerobic property:hypoxic property HCR, aerobic aer, hypoxic hyp, DNA binding equilibrium constant K DNA, multiple correlation coefficient R 2 , the F test of significance, standards errors for the estimate (SEE) and standard errors of the variables SE(ΔG desolCDS ), SE(ΔG lipoCDS ), SE(Dipole Moment), SE (Molecular Volume), SE(AEA). …”