Activation of PP2A by Perphenazine Induces Apoptosis in T-ALL

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer that frequently harbors activating mutations in NOTCH1, which encodes a transcriptional regulator activated by gamma-secretase–mediated proteolytic cleavage. Gamma-secretase inhibitors (GSI) have shown only partial activity against T-ALL in clinical trials, suggesting that a combinatorial approach with additional NOTCH1-independent compounds may be more effective. To identify rapidly translatable therapies for T-ALL, Gutierrez and colleagues screened FDA-approved drugs for cytotoxic activity in a MYC-induced T-ALL zebrafish model and in a NOTCH1-dependent human T-ALL cell line in combination with GSIs. Both screens identified the antipsychotic dopaminergic antagonist perphenazine, which synergized with GSIs to induce NOTCH1-independent apoptosis of T-ALL cells. Because unrelated dopaminergic inhibitors had no effect on T-ALL cell growth, a quantitative mass spectrometry approach was used to identify perphenazine targets in T-ALL cells. Interestingly, binding of perphenazine to the Aα scaffolding subunit of the protein phosphatase PP2A, a known tumor suppressor, was correlated with perphenazine activity in T-ALL cells. Treatment of T-ALL cells with perphenazine induced the rapid dephosphorylation of multiple PP2A targets involved in oncogenic signaling, such as AKT and ERK, suggesting that perphenazine stimulates PP2A phosphatase activity. Consistent with these findings, shRNA knockdown of PP2A impaired perphenazine-induced target dephosphorylation and T-ALL cell apoptosis, further indicating that the antileukemic effects of perphenazine are PP2A dependent. Moreover, perphenazine treatment of primary human T-ALL cells suppressed growth and induced PP2A target dephosphorylation both in vitro and in in vivo xenograft mouse models. Although the development of more potent and selective PP2A-stimulating compounds is needed, these findings suggest that pharmacologic activation of PP2A in conjunction with GSIs may be an attractive therapeutic strategy for T-ALL and other NOTCH1-associated cancers.

Gutierrez A, Pan L, Groen RW, Baleydier F, Kentsis A, Marineau J, et al. Phenothiazines induce PP2A-mediated apoptosis in T cell acute lymphoblastic leukemia. J Clin Invest 2014 Jan 9 [Epub ahead of print].