A drug screening assay on cancer cells chronically adapted to acidosis

Abstract

BackgroundDrug screening for the identification of compounds with anticancer activity is commonly performed using cell lines cultured under normal oxygen pressure and physiological pH. However, solid tumors are characterized by a microenvironment with limited access to nutrients, reduced oxygen supply and acidosis. Tumor hypoxia and acidosis have been identified as important drivers of malignant progression and contribute to multicellular resistance to different forms of therapy. Tumor acidosis represents an important mechanism mediating drug resistance thus the identification of drugs active on acid-adapted cells may improve the efficacy of cancer therapy.MethodsHere, we characterized human colon carcinoma cells (HCT116) chronically adapted to grow at pH 6.8 and used them to screen the Prestwick drug library for cytotoxic compounds. Analysis of gene expression profiles in parental and low pH-adapted cells showed several differences relating to cell cycle, metabolism and autophagy.ResultsThe screen led to the identification of several compounds which were further selected for their preferential cytotoxicity towards acid-adapted cells. Amongst 11 confirmed hits, we primarily focused our investigation on the benzoporphyrin derivative Verteporfin (VP). VP significantly reduced viability in low pH-adapted HCT116 cells as compared to parental HCT116 cells and normal immortalized epithelial cells. The cytotoxic activity of VP was enhanced by light activation and acidic pH culture conditions, likely via increased acid-dependent drug uptake. VP displayed the unique property to cause light-dependent cross-linking of proteins and resulted in accumulation of polyubiquitinated proteins without inducing inhibition of the proteasome.ConclusionsOur study provides an example and a tool to identify anticancer drugs targeting acid-adapted cancer cells.Electronic supplementary materialThe online version of this article (10.1186/s12935-018-0645-5) contains supplementary material, which is available to authorized users.

The Encapsulation of Febuxostat into Emulsomes Strongly Enhances the Cytotoxic Potential of the Drug on HCT 116 Colon Cancer Cells

“…Overall, our results clearly depict the enhanced cytotoxic activity exerted by the FBX drug when encapsulated into the EMLs on the well-characterized human colorectal carcinoma (HCT 116) cells [ 26 , 27 , 28 , 29 ], making the base for the investigation of this optimized formula in vivo.…”

“…Based on the above evidence, we carried out in vitro cell experiments in which the encapsulation of FBX into EMLs was performed to enhance the toxic potential of the drug towards human colorectal carcinoma (HCT 116) cells, a well-known experimental model in cancer drug discovery to predict clinical efficacy of anti-cancer drugs [ 26 , 27 , 28 , 29 ]. As a first step, we determined the cytotoxic potential of the free drug (FBX-R) as well as of the optimized formula (FBX encapsulated into EMLs, FBX-EMLs) on HCT 116 cells, expressed as IC50, the concentration of the drug able to reduce the cell viability by 50%, an index frequently employed to compare the anti-proliferative activity and the toxic potential of different anti-cancer drugs [ 45 ].…”

“…Furthermore, EMLs are more stable compared with other well-known vesicular carriers such as liposomes, showing low toxicity profile, prolonged drug release, and improved drug efficacy [ 24 , 25 ]. These characteristics of EMLs make the base for the investigation of this nanocarriers to formulate FBX, with the aim to improve the cytotoxicity of this drug on HCT 116 colorectal cancer cells, a well-established in vitro human cell line model used in drug screenings and drug discovery programs in the field of cancer to predict clinical response to anti-cancer drugs [ 26 , 27 , 28 , 29 ].…”

The therapeutic importance of acid-base balance

“…Another example is the use of pH-sensitive vehicles such as micelles that could release cytotoxic chemotherapeutic agents only in the acidic tumor environment [470] . Similarly, as suggested by the disparity between the usefulness of an anticancer drug that was identified in an in vitro screening performed at neutral pH and its value in vivo in the acidic tumor microenvironment [471] , it is possible that some drugs may be inactive in circulation and may not be activated until they reach an acidic environment.…”

Cancer Cell Acid Adaptation Gene Expression Response Is Correlated to Tumor-Specific Tissue Expression Profiles and Patient Survival

“…The molecular mechanisms through which growth under chronic extracellular acidosis leads to this profound rewiring of cancer cells are poorly understood. While several studies have examined global changes in gene expression upon acidosis or lactic acidosis [15,21,22], the overlap between the changes induced by acidosis and those found in patient tumors, and the correlation of acidosis-responsive gene expression to overall patient survival, have to our knowledge never been comprehensively examined. Because acidic growth seems to drive at least some phenotypes akin to those found in highly aggressive cancers, an important question is whether there is a generic response to acid adaptation that is shared between cancer cells, and whether this response reflects the expression changes observed between tumors and normal tissues in patient samples.…”