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 4

SMAP DT-061 in combination with TKI has an enhanced effect on apoptosis in vitro and tumor growth inhibition in vivo.

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SMAP DT-061 in combination with TKI has an enhanced effect on apoptosis ...
(A) H1975 and (B) H1650 cell lines were treated with vehicle control, 20 μM SMAP DT-061, 1 μM erlotinib, 100 nM afatinib, a combination of SMAP DT-061 and erlotinib, or a combination of SMAP DT-061 and afatinib. Annexin positivity at 24 hours in H1975 and H1650 cells treated with indicated concentrations of DT-061. Three independent experiments are represented as mean ± SD. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. BID: twice daily. (C and D) Western blot analysis of major PP2A and afatinib targets in H1975 treated with 20 μM SMAP DT-061, 100 nM afatinib, or a combination of SMAP DT-061 and afatinib at 24 hours. Results represent 3 independent experiments. (E) H1975 cells (5 million cells per injection) were subcutaneously injected in the right flank of nude mice. Once the tumor volumes reached approximately 100 mm3, mice were randomized and treated with vehicle control (n = 7), SMAP DT-061 (5 mg/kg) (n = 7) twice daily or afatinib (5 mg/kg) (n = 7) twice daily, or a combination of both SMAP DT-061 and afatinib (n = 7). The results are represented as mean ± SEM, with *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. The P values were calculated using a 2-tailed t test. (F) Body weights of mice throughout treatment. (G) Proposed model for enhanced effect of SMAP and TKI treatment of EGFR-driven LUAD. The black asterisks compare the different treatments with the vehicle control. The green asterisks compare the combination of Afatinib and DT-061 group with the vehicle control group, while the purple asterisks compare the DT-061 (5 mg/kg) group with the vehicle control group.