Pharmacological Inhibition of PP2A Overcomes Nab-Paclitaxel Resistance by Downregulating MCL1 in Esophageal Squamous Cell Carcinoma (ESCC).

Herui Wang,Jieakesu Su,Jie Huang,Dongxian Jiang,Qi Song,Gen Sheng Wu,Chen Xu,Qi Zhang,Haixing Wang,Jing Cui,Yingyong Hou,Zhengping Zhuang

doi:10.3390/cancers13194766

Abstract

Simple SummaryPaclitaxel-based chemotherapy has been introduced to treat esophageal squamous cell carcinoma. While its initial efficacy has been clinically established, the development of resistance is inevitable. To understand the paclitaxel resistance mechanism, we developed nanoparticle albumin-bound paclitaxel (nab-PTX)-resistant esophageal squamous cell lines from their sensitive counterparts. We found that resistant cells express higher levels of protein phosphatase 2A (PP2A), oxidative phosphorylation, and anti-apoptotic protein MCL1 than their counterparts. Therapeutically, the PP2A inhibitor LB-100 synergistically sensitized resistant esophageal squamous cells to nab-PTX both in vitro and in vivo. Therefore, our data suggest that LB-100 may potentially overcome nab-PTX resistance in a clinical setting.Paclitaxel-based chemotherapy is a treatment option for advanced esophageal squamous cell carcinoma (ESCC). However, the development of chemoresistance leads to treatment failure, and the underlying mechanism remains elusive. We investigated the mechanisms of nanoparticle albumin-bound paclitaxel (nab-PTX) resistance by establishing three nab-PTX resistant ESCC cell lines. Proteomics analysis revealed higher oxidative phosphorylation (OXPHOS) in resistant cell line DR150 than in its parental cell line KYSE150, which is likely caused by stabilized anti-apoptotic protein MCL1. Additionally, we discovered the elevated activity of protein phosphatase 2A (PP2A), the phosphatase that dephosphorylates and stabilizes MCL1, in nab-PTX resistant cell lines. Pharmacological inhibition of PP2A with small molecule compound LB-100 decreased MCL1 protein level, caused more apoptosis in nab-PTX resistant ESCC cell lines than in the parental cells in vitro, and significantly inhibited the tumor growth of nab-PTX resistant xenografts in vivo. Moreover, LB-100 pretreatment partially restored nab-PTX sensitivity in the resistant cell lines and synergistically inhibited the tumor growth of nab-PTX resistant xenografts with nab-PTX. In summary, our study identifies a novel mechanism whereby elevated PP2A activity stabilizes MCL1 protein, increases OXPHOS, and confers nab-PTX resistance, suggesting that targeting PP2A is a potential strategy for reversing nab-PTX resistance in patients with advanced ESCC.

Highlights

Esophageal cancer (EC) is one of the most common digestive malignant tumors [1]
Our study showed that phosphatase 2A (PP2A) inhibition increases esophageal squamous cell carcinoma (ESCC) sensitivity to Nanoparticle albumin-bound paclitaxel (nab-PTX) by downregulating Myeloid cell leukemia-1 (MCL1) and oxidative phosphorylation (OXPHOS)
DR30, DR70 and DR150 cells continued to grow in media containing 10, 20 and 50 ng/mL nab-PTX, respectively, while the parental KYSE30, KYSE70, KYSE150 cells were very sensitive to nab-PTX treatment

Summary

Introduction

Esophageal cancer (EC) is one of the most common digestive malignant tumors [1]. Due to few symptoms at the early stage and the tumor’s aggressive nature, EC is often diagnosed at an advanced stage, and recurrent disease after surgical resection is common [2]. Emerging data has shown that nab-PTX has therapeutic benefits for various types of squamous cell carcinoma [14]. A combination of nab-PTX and cisplatin can be used as first-line therapy for metastatic ESCC [15] and as a neoadjuvant chemotherapy strategy for local advanced ESCC [16]. A recent study showed that MYC and MCL1 could cooperatively promote paclitaxel-resistant breast cancer stem cells by increasing mitochondrial OXPHOS [21]. Non-pharmacological inhibition of PP2A with okadaic acid, calyculin A, and PP2A/Aα knockdown all increased MCL1 Thr-163/Ser-159 phosphorylation and decreased MCL1 protein levels [26], indicating that pharmacologic inhibition of PP2A is a potential therapeutic option to disrupt stabilized MCL1 in paclitaxel-resistant tumors. Our study showed that PP2A inhibition increases ESCC sensitivity to nab-PTX by downregulating MCL1 and OXPHOS. Cancers 2021, 13, 4766 that increased PP2A activity drives nab-PTX resistance in ESCC cells and suggests that targeting PP2A could be a promising strategy for overcoming nab-PTX resistance

OXPHOS Is Elevated in Nab-PTX Resistant ESCC Cells

MCL1 Contributes to Nab-PTX Resistance in ESCC Cells

Cell Lines

Conclusions