A screen for inducers of p21waf1/cip1 identifies HIF prolyl hydroxylase inhibitors as neuroprotective agents with antitumor properties

Preventing neuronal death is a priority for treating neurological diseases. However, therapies that inhibit pathological neuron loss could promote tumorigenesis by preventing the physiological death of cancerous cells. To avert this, we targeted the transcriptional upregulation of p21waf1/cip1 (p21), an endogenous tumor suppressor with neuroprotective and pro-regenerative activity. We identified potential p21 indcuers by screening a FDA-approved drug and natural product small molecule library against hippocampal HT22 cells stably expressing a luciferase reporter driven by the proximal 60 bp of the p21 promoter, and tested them for neuroprotection from glutathione depletion mediated oxidative stress, and cytotoxicity to cancer cell lines (DLD-1, Neuro-2A, SH-SY5Y, NGP, CHLA15, CHP212, and SK-N-SH) in vitro. Of the p21 inducers identified, only ciclopirox, a hypoxia-inducible factor prolyl-4-hydroxylase (HIF-PHD) inhibitor, simultaneously protected neurons from glutathione depletion and decreased cancer cell proliferation at concentrations that were not basally toxic to neurons. We found that other structurally distinct HIF-PHD inhibitors (desferrioxamine, 3,4-dihydroxybenzoate, and dimethyloxalyl glycine) also protected neurons at concentrations that killed cancer cells. HIF-PHD inhibitors stabilize HIF transcription factors, mediating genetic adaptation to hypoxia. While augmenting HIF stability is believed to promote tumorigenesis, we found that chronic HIF-PHD inhibition killed cancer cells, suggesting a protumorigenic role for these enzymes. Moreover, our findings suggest that PHD inhibitors can be used to treat neurological disease without significant concern for cell-autonomous tumor promotion.

► Targets for chronic neuroprotection should not promote cancer/tumor formation. ► We screened for transcriptional inducers of p21waf1/cip1 (p21), a CDK inhibitor. ► p21 inducers protect neurons from cell death and prevent cancer cell proliferation. ► HIF-PHD inhibitors induce p21waf1/cip1 and are both neuroprotective and antitumor. ► HIF-PHD inhibitors should not promote tumor formation despite stabilizing HIF.