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Acute myeloid leukemia (AML) is a largely incurable disease, for which new treatments are urgently needed. While leukemogenesis occurs in the hypoxic bone marrow, the therapeutic tractability of the hypoxia-inducible factor (HIF) system remains undefined. Given that inactivation of HIF-1α/HIF-2α promotes AML, a possible clinical strategy is to target the HIF-prolyl hydroxylases (PHDs), which promote HIF-1α/HIF-2α degradation. Here, we reveal that genetic inactivation of Phd1 / Phd2 hinders AML initiation and progression, without impacting normal hematopoiesis. We investigated clinically used PHD inhibitors and a new selective PHD inhibitor (IOX5), to stabilize HIF-α in AML cells. PHD inhibition compromises AML in a HIF-1α-dependent manner to disable pro-leukemogenic pathways, re-program metabolism and induce apoptosis, in part via upregulation of BNIP3. Notably, concurrent inhibition of BCL-2 by venetoclax potentiates the anti-leukemic effect of PHD inhibition. Thus, PHD inhibition, with consequent HIF-1α stabilization, is a promising nontoxic strategy for AML, including in combination with venetoclax.

As part of the cellular adaptation to limiting oxygen availability in animals, the expression of a large set of genes is activated by the upregulation of the hypoxia-inducible transcription factors (HIFs). Therapeutic activation of the natural human hypoxic response can be achieved by the inhibition of the hypoxia sensors for the HIF system, i.e. the HIF prolyl-hydroxylases (PHDs). Here, we report studies on tricyclic triazole-containing compounds as potent and selective PHD inhibitors which compete with the 2-oxoglutarate co-substrate. One compound (IOX4) induces HIFα in cells and in wildtype mice with marked induction in the brain tissue, revealing that it is useful for studies aimed at validating the upregulation of HIF for treatment of cerebral diseases including stroke.

Hypoxia Inducible Factors (HIF) functions are master regulators of oxygen homeostasis and have a key role in the physiological responses to hypoxia including angiogenesis and erythropoiesis. Under hypoxia, levels of HIF-α subunits increase, they hetereodimerise with HIF-1β sub unit and promote the initiation of transcription of target genes. Under normoxia, oxygen dependent HIF-α degradation is promoted by hydroxylation of either of two proline residues (Pro402 and Pro564). The interaction of prolylhydroxylated HIF-α with the Von Hippel-Lindau protein (pVHL) promotes hydrolytic degradation of HIFα through an E3 ubiquitin ligase proteasomal pathway. HIF prolyl hydroxylation is catalysed by three 2-oxoglutarate (2OG)-dependent oxygenases known as prolyl hydroxylase domain (PHD 1-3) proteins, through an Fe(II) mediated catalytic process using 2OG, and oxygen. The PHDs are part of the family of Fe(II) bound 2OG dependent oxygenases. There are approximately 70 human 2OG oxygenases many of which have biologically important roles. Small-molecule inhibitors have reached advanced clinical trials; however, many clinical candidates inhibit other structurally similar 2OG oxygenases (OGFOD1 and vCPH) potentially altering the therapeutic effect. This thesis describes the design and synthesis of potent and 2OG oxygenase selective inhibitors for the PHDs. The 1,3,8-triazaspiro[4.5]decane-2,4-dione and 4-hydroxy-2-(pyrazole)pyrimidine-5-amide series were chosen as initial 'hits' (reported in the patent literature). The main analogues of the series were characterised in vitro and in cells as potent and selective PHD inhibitors over structurally similar 2OG oxygenases (Chapter 2). Broad structure activity relationship (SAR) of both initial series demonstrated the sensitivity for PHD2 inhibition (Chapter 3). Combination of SAR work described in Chapters 2 and 3 lead to the development of the novel 4-hydroxy pyridine series. In-depth SAR resulted in optimised analogues including 1 (IC50 69 nM) and highly selective over structurally similar 2OG oxygenases including OGFOD1. The completed SAR work led to the development of two novel pharmacophores 2 and 3. Both pharmacophores displayed potent PHD inhibition and selectivity over OGFOD1. Analogues including 1 and 3 displayed on target cellular activity stabilising HIF-1α at 20 μM (Chapter 4). The 4-dimethylamine pyridine analogue displayed an increase in substrate hydroxylation on PHD2 in contrast to the DMSO control (Chapter 3). SAR and cellular characterisation indicated that the effect observed was not an assay artifact (Chapter 5). Fenofibrate was used as a starting point for the development of novel inhibitors of the oxygen consumption rate (OCR) via mitochondrial inhibition (Chapter 6). Analogues were synthesised in order to conduct broad SAR and on-target cellular activity was observed in a Seahorse XF assay (50% reduction in the OCR at 1 μM). A selection of amino and amide analogues warrant further investigation.

As part of the cellular adaptation to limiting oxygen availability in animals, the expression of a large set of genes is activated by the upregulation of the hypoxia-inducible transcription factors (HIFs). Therapeutic activation of the natural human hypoxic response can be achieved by the inhibition of the hypoxia sensors for the HIF system, i.e. the HIF prolyl-hydroxylases (PHDs). Here, we report studies on tricyclic triazole-containing compounds as potent and selective PHD inhibitors which compete with the 2-oxoglutarate co-substrate. One compound (IOX4) induces HIF alpha in cells and in wildtype mice with marked induction in the brain tissue, revealing that it is useful for studies aimed at validating the upregulation of HIF for treatment of cerebral diseases including stroke.