PPM1H Regulates the Response to Paclitaxel in Triple Negative Breast Cancer.

Abstract

There has been an increasing interest in patient-derived tumor xenograft (PDX) models for cancer research. Since these models mostly retain histological and genetic characteristics of patients, they are also useful for studies that elucidates the cancer cell survival during cytotoxic chemotherapy. Paclitaxel is one of the well-known chemotherapeutic agents for breast cancer patients, but most advanced cases often develop resistance to the paclitaxel during the treatment. To understand the molecular adaptation of cancer cells during the paclitaxel treatment, we performed in vivo paclitaxel experiment using a patient-derived xenograft model. We established two triple negative breast cancer (TNBC) PDX models separately derived from single patient's primary and recurrent tumor. For each TNBC PDX model, ten mice were intraperitoneally (IP) injected with either PBS or paclitaxel (15mg/kg) for 4 weeks. Both PDX models showed statistically significant tumor growth inhibition after paclitaxel treatment and we obtained transcriptome and exome sequencing data from both groups. Transcriptome data identified thirteen genes that were commonly upregulated after paclitaxel treatment in both PDX models (p ≤ 0.05, 2-fold ≥ 0.5) and four genes (CXCL10, FMO2, PPM1H and RNF150) showed differential expression with the adjusted p value of less than 0.1. Whole-exome sequencing data were used to identify the fluctuations of somatic mutations in paclitaxel-treated tumors. Interestingly, PPM1H, one of the genes that were upregulated in transcriptome data analysis, had changes in the prevalence of somatic mutations in paclitaxel-treated tumors. We further observed that the paclitaxel treatment increased PPM1H gene expression levels in both TNBC PDX tumors and breast cancer cells. PPM1H gene expression was also upregulated by short-term in vitro paclitaxel treatment using various breast cancer cell lines. We established a breast cancer cell line (MDA-MB-231) that stably overexpressed PPM1H and tested various phenotypic aspects. MDA-MB-231 cells overexpressing PPM1H had no substantial effects on cell proliferation, migration, and invasion, but were more sensitive to paclitaxel in both 2D and 3D cell cultures. Increased PPM1H expression levels also elevated tumor suppressor p27 protein levels. Our data demonstrate that breast cancer cells undergo diverse genomic changes during paclitaxel treatment and PPM1H may regulate the paclitaxel sensitivity in breast cancer cells. Further studies are needed to clarify the mechanistic pathways of PPM1H.