Abstract 1350: Regulation of pH by growth factors is dependent on the expression of the calcineurin homologous protein-2 in human bone sarcoma cells
Authors: Chang Tiffany , Luong Serena S. , Zobel Adam P. , Ananieva Elitsa , Babich Victor , Di Sole Francesca 
Published: July 2021

Abstract
Bone sarcoma is a malignant tumor that includes multiple subtypes. The osteosarcoma is the sixth most common malignancy in adolescents, while chondrosarcoma is primarily a disease of adults. Current treatments for both osteosarcoma and chondrosarcoma have not demonstrated improvement in patients' survival over the past three decades. Extracellular acidosis affects osteoblast and chondrocyte function by reducing bone mineralization and increasing production of cartilage matrix, respectively. Thereby, it weakens bone matrix and expands cartilage matrix, and may play a role in the development of bone characteristics seen in patients with osteosarcoma or chondrosarcoma. Development of extracellular acidosis in cancer is due to dysregulation of pH dynamics mediated by constitutive activation of Na+/H+ exchanger-1 (NHE1) activity, the main transporter responsible for pH regulation. Current therapeutic agents that target inhibition of NHE1 activity are ineffective due to broad inhibitory effects. The calcineurin homologous protein (CHP) family binds to and regulates NHE1 activity. CHP isoform 1 (CHP1) is expressed in non-cancerous cells and forms a dynamic complex with NHE1. On the other hand, CHP isoform 2 (CHP2) is expressed primarily in cancerous cells and has a stronger binding affinity to NHE1 compared with CHP1. We hypothesize that CHP2 binding to NHE1 in cancer cells induces the over-activity of NHE1, making the extracellular pH of cancer cells more acidic than non-cancerous cells. We measured CHP1 or CHP2 protein expression levels in human osteoblast (hFOB), osteosarcoma (143B), and chondrosarcoma (SW1353) cells and studied whether the levels of CHP2 protein expression affected NHE activity in these cell lines. We determined that: 1. hFOB, 143B, and SW1353 cells expressed mainly NHE1; NHE activity measured using spectrofluorometry was completely blocked by a highly selective NHE1 inhibitor (zoniporide, 10-8 M); 2. NHE1 activity was increased by serum-nutrient deprivation, used to mimic a cancerous microenvironment and NHE1 over-activity was associated with increased levels of CHP2 protein expression; 3. silencing of CHP2 by shRNA inhibited NHE1 activity in response to serum-nutrient deprivation in 143B or SW1353 cells and restored the NHE1 response inducted by serum-deprivation in non-cancerous cells. Regulation of NHE1 through CHP2 is proposed as a promising novel target in sarcoma treatment and to overcome the wide range of side effects induced by inhibitors of NHE1 activity.
Citation Format: Tiffany Chang, Serena S. Luong, Adam P. Zobel, Elitsa Ananieva, Victor Babich, Francesca Di Sole. Regulation of pH by growth factors is dependent on the expression of the calcineurin homologous protein-2 in human bone sarcoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1350.