DDO-3733 is a specific, small molecule, allosteric activator of serine/threonine protein phosphatase 5 (PP5) with potency of 2.9-fold PP5 activation at 50 uM, inhibits HSP90 inhibitor-induced heat shock protein expression both in cells and in vivo.
DDO-3733 not affect the binding of the TPR-dependent PP5 activator to immobilized PP5 with a verified TPR-independent mechanism.
DDO-3733 shows ITC Kd of 1.14 uM for full-length PP5 binding, and ITC Kd of 0.811 uM of the phosphatase domain, but not to the TPR domain.
DDO-3733 activates PP5 with an EC50 value of 52.8 μM and an Emax value of 4.3-fold.
DDO-3733 does not affect the enzymatic activity of a small panel of phosphatases has been measured, including protein phosphatase 1 α and β (PP1A, PP1B), protein phosphatase 2A (PP2A), protein tyrosine phosphatase nonreceptor type 2 (PTPN2), low molecular weight protein tyrosine phosphatase A (LMPTP-A), dual-specificity phosphatase 3 (DUSP3), and SH2-containing protein tyrosine phosphatase-2 (SHP2).
DDO-3733 induces PP5 substrate dephosphorylation in vitro.
DDO-3733 enhances the antitumor activity of AT13387 and inhibits AT13387 induced expression of heat shock proteins.
AT13387 (20 mg/kg) and DDO-3733 (30 or 60 mg/kg) exhibited slightly stronger antitumor activities than the AT13387-alone group.