TP53 mutations frequently occur in
head and neck squamous cell carcinoma (
HNSCC) patients without
human papillomavirus infection. The recurrence rate for these patients is distinctly high. It has been actively explored to identify agents that target TP53 mutations and restore wild-type (WT) TP53 activities in
HNSCC.
PRIMA-1 (p53-reactivation and induction of massive apoptosis-1) and its methylated analogue PRIMA-1Met (also called APR-246) were found to be able to reestablish the
DNA-binding activity of p53 mutants and reinstate the functions of WT p53. Herein we report that
piperlongumine (PL), an
alkaloid isolated from Piper longum L., synergizes with
APR-246 to selectively induce apoptosis and autophagic cell death in
HNSCC cells, whereas primary and immortalized mouse embryonic fibroblasts and spontaneously immortalized non-tumorigenic human skin keratinocytes (HaCat) are spared from the damage by the co-treatment. Interestingly, PL-sensitized
HNSCC cells to
APR-246 are TP53 mutation-independent. Instead, we demonstrated that
glutathione S-transferase pi 1 (GSTP1), a GST family member that catalyzes the conjugation of GSH with electrophilic compounds to fulfill its detoxification function, is highly expressed in
HNSCC tissues. Administration of PL and
APR-246 significantly suppresses GSTP1 activity, resulting in the accumulation of ROS, depletion of GSH, elevation of
GSSG, and DNA damage. Ectopic expression of GSTP1 or pre-treatment with
antioxidant N-acetyl-L-cysteine (NAC) abrogates the ROS elevation and decreases DNA damage, apoptosis, and autophagic cell death prompted by PL/APR-246. In addition, administration of PL and
APR-246 impedes UMSCC10A xenograft
tumor growth in SCID mice. Taken together, our data suggest that
HNSCC cells are selectively sensitive to the combination of PL and
APR-246 due to a remarkably synergistic effect of the co-treatment in the induction of ROS by suppression of GSTP1.