Direct activation of PP2A for the treatment of tyrosine kinase inhibitor–resistant lung adenocarcinoma
Rita Tohmé, … , Jaya Sangodkar, Goutham Narla
Rita Tohmé, … , Jaya Sangodkar, Goutham Narla
Published February 21, 2019
Citation Information: JCI Insight. 2019;4(4):e125693. https://doi.org/10.1172/jci.insight.125693.
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Research Article Oncology Therapeutics

Direct activation of PP2A for the treatment of tyrosine kinase inhibitor–resistant lung adenocarcinoma

Abstract

Although tyrosine kinase inhibitors (TKIs) have demonstrated significant efficacy in advanced lung adenocarcinoma (LUAD) patients with pathogenic alterations in EGFR, most patients develop acquired resistance to these agents via mechanisms enabling the sustained activation of the PI3K and MAPK oncogenic pathways downstream of EGFR. The tumor suppressor protein phosphatase 2A (PP2A) acts as a negative regulator of these pathways. We hypothesize that activation of PP2A simultaneously inhibits the PI3K and MAPK pathways and represents a promising therapeutic strategy for the treatment of TKI-resistant LUAD. After establishing the efficacy of small molecule activators of PP2A (SMAPs) in a transgenic EGFRL858R model and TKI-sensitive cell lines, we evaluated their therapeutic potential in vitro and in vivo in TKI-resistant models. PP2A activation resulted in apoptosis, significant tumor growth inhibition, and downregulation of PI3K and MAPK pathways. Combination of SMAPs and TKI afatinib resulted in an enhanced effect on the downregulation of the PI3K pathway via degradation of the PP2A endogenous inhibitor CIP2A. An improved effect on tumor growth inhibition was observed in a TKI-resistant xenograft mouse model treated with a combination of both agents. These collective data support the development of PP2A activators for the treatment of TKI-resistant LUAD.

Authors

Rita Tohmé, Sudeh Izadmehr, Sai Gandhe, Giancarlo Tabaro, Sanjay Vallabhaneni, Ava Thomas, Neal Vasireddi, Neil S. Dhawan, Avi Ma’ayan, Neelesh Sharma, Matthew D. Galsky, Michael Ohlmeyer, Jaya Sangodkar, Goutham Narla

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Figure 2

PP2A activation induces apoptosis in TKI-resistant LUAD cell lines.

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PP2A activation induces apoptosis in TKI-resistant LUAD cell lines. (A) ...
(A) Mechanisms of acquired resistance in LUAD. The most common mechanism of acquired resistance to TKIs is through the gatekeeper mutation T790M (tyrosine amino acid changed into a methionine at position 790), which alters the affinity of the drug to EGFR and leads to a sustained activation of both PI3K and MAPK pathways. Another common mechanism of resistance is through bypassing EGFR and sustainably activating the PI3K and MAPK pathways via modifications at the level of the downstream effectors themselves or by inactivating regulators of the pathways, such as PTEN. RAF, rapidly accelerated fibrosarcoma. (B) Proposed model for PP2A activation in EGFR-driven LUAD. SMAP treatment activates PP2A and leads to the downregulation of both PI3K and MAPK pathways that are commonly upregulated in TKI-resistant LUAD. (C) H1650 and H1975 were treated with DMSO vehicle control or increasing concentrations of SMAP DT-061 for 48 hours. Drug treatment resulted in decreased cell viability in both cell lines, with IC50 of 10.6 μM. (D) The ability of H1975 and H1650 cell lines to form colonies when treated with vehicle control or 5, 7.5, or 10 μM SMAP DT-061 every 72 hours for 14 days. (E) Quantification of colony formation assay for H1975. (F) Quantification of colony formation assay for H1650. (G) PARP cleavage at 24 hours in H1975 and H1650 cells treated with indicated concentrations of DT-061. Annexin positivity at 24 hours in (H) H1975 and (I) H1650 cells treated with indicated concentrations of DT-061. Three independent experiments represented as mean ± SD are shown. **P < 0.01; ***P < 0.001; ****P < 0.0001.