Mechanism of hypoxia-specific cytotoxicity of procaspase-3 fused with a VHL-mediated protein destruction motif of HIF-1alpha containing Pro564

Under normoxic conditions the alpha-subunit of hypoxia-inducible factor (HIF-1alpha) protein is targeted for degradation by the von Hippel-Lindau (VHL) tumor suppressor protein acting as an E3 ubiquitin ligase. Recently, we developed a hypoxia-targeting protein, TOP3, which consisted of procaspase-3 with the VHL-mediated protein destruction motif of HIF-1alpha. This design enables procaspase-3 to be regulated similarly with HIF-1alpha, being degraded under normoxia while stabilized under hypoxia. Furthermore, stabilized TOP3 was cleaved by the hypoxic stress-induced endogenous caspases and thus the procaspase-3 was converted to active caspase-3 specifically under hypoxic conditions. These data demonstrated that the VHL-mediated protein destruction motif of HIF-1alpha endowed procaspase-3 with hypoxia-specific cytotoxicity.     

Identification of LEM-14 inhibitor of the oncoprotein NSD2

The NSD family (NSD1, NSD2/MMSET/WHSC1, and NSD3/WHSC1L1) are histone lysine methyltransferases (HMTases) essential for chromatin regulation. The NSDs are oncoproteins, drivers of a number of tumors and are considered important drug-targets but the lack of potent and selective inhibitors hampers further therapeutic development and limits exploration of their biology. In particular, MMSET/NSD2 selective inhibition is being pursued for therapeutic interventions against multiple myeloma (MM) cases, especially in multiple myeloma t(4;14)(p16.3;q32) translocation that is associated with a significantly worse prognosis than other MM subgroups. Multiple myeloma is the second most common hematological malignancy, after non-Hodgkin lymphoma and remains an incurable malignancy.Here we report the discovery of LEM-14, an NSD2 specific inhibitor with an in vitro IC₅₀ of 132?μM and that is inactive against the closely related NSD1 and NSD3. LEM-14-1189, a LEM-14 derivative, differentially inhibits the NSDs with in vitro IC₅₀ of 418?μM (NSD1), IC₅₀ of 111?μM (NSD2) and IC₅₀ of 60?μM (NSD3). We propose LEM-14 and derivative LEM-14-1189 as tools for studying the biology of the NSDs and constitute meaningful steps toward potent NSDs therapeutic inhibitors.