Pifithrin-μ

In addition to its transactivational functions, p53 mediates apoptosis by binding with the anti-apoptotic proteins Bcl-xL and Bcl-2 at the mitochondrial surface. Pifithrin-μ (PFT-μ) is an inhibitor of p53-mediated apoptosis, preventing p53 binding to Bcl-xL and Bcl-2 at the mitochondria without affecting p53 transactivational activities In vitro, PFT-μ binds both p53 (K_d = 0.82 mM) and Bcl-xL (K_d = 0.80 mM). PFT-μ reduces p53-mediated apoptosis induced by γ-radiation in mouse thymocytes in vitro and protects mice from doses of radiation that cause lethal hematopoietic syndrome. At 25 μM, PFT-μ reduces apoptosis triggered by nutlin-3, which inhibits MDM2/p53 binding and potentiates p53-mediated growth arrest and apoptosis. PFT-μ also interacts selectively with heat shock protein 70 (Hsp70), leading to disruption of the association between Hsp70 and many of its co-chaperones and substrate proteins.

Pifithrin-μ has been used:

• to treat microglial cell line to analyse its neuroprotective effect on M1-like and M2-like phenotype
• as heat shock protein (HSP)-70 inhibitor, to treat transfected Marc-145 cells
• to inhibit heat shock cognate 70 (Hsc70) to elucidate heat shock chaperones mouse embryonic stem cells

A cell-permeable sulfonamide that blocks p53 interaction with Bcl-xL and Bcl-2 proteins and selectively inhibits p53 translocation to mitochondria without affecting the transactivation function of p53. Effectively protects against γ radiation-induced cell death in vitro and animal lethality in vivo. Because Pifithrin-μ targets only the mitochondrial branch of the p53 pathway without affecting the important transcriptional functions of p53, it is superior to Pifithrin-α (Cat. No. 506132) in in vivo studies. Shown to selectively interact with inducible HSP70 and disrupt its functions.

Inhibits p53 binding to mitochondria by reducing its affinity for antiapoptotic proteins Bcl-2 and Bcl-XL. Displays no effect on the transactivational or cell cycle checkpoint control function of p53. Potentially increases reprogramming efficiency of human somatic cells to induced pluripotent stem cells (iPSCs) by silencing p53. Reduces cell death induced by γ -radiation in vitro and protects mice from doses of radiation that cause lethal hematopoietic syndrome. Selectively inhibits heat shock protein 70 (HSP70) activity.

This cell-permeable sulfonamide-based inhibitor and anti-apoptotic factor (FW = 181.20 g/mol; CAS 64984-31-2; Solubility: >10 mg/mL DMSO, <2 mg/mL H2O; pKa = 8; Symbol = PFTμ and PAS), also known as 2- phenylethynesulfonamide, targets p53 and Heat Shock Protein-70, or HSP 70. Because it only targets the mitochondrial branch of the p53 pathway without affecting the important transcriptional functions of p53, Pifithrin-μ is recommended over Pifithrin-α for in vivo studies. PFTμ exhibits high specificity for p53 and does not protect cells from apoptosis induced by overexpression of the proapoptotic protein Bax or by treatment with dexamethasone. With B-chronic lymphocytic leukemia (CLL) cells, Pifithrin-μ (5–20 μM) initiated apoptosis within 24 hours, with maximal death at 48 hours, as assessed by cell morphology, cleavage of poly(ADPribose) polymerase (PARP), caspase-3 activation, and annexin V staining.