title: The Relationship between P-glycoprotein, Carbonic Anhydrase XII, and the Thioredoxin System in Bortezomib Resistant Multiple Myeloma Cells
Creators: name: Zhang, Yu
Publisher: name: Griffith University
Year: 2019
Subjects: subject: Multiple myeloma
subject: P-glycoprotein
subject: Carbonic anhydrase XII
subject: Thioredoxin system
subject: Bortezomib resistant

description: Multiple myeloma (MM), also known as plasma cell myeloma, is a hematological cancer. In 2003, the first proteasome inhibitor BTZ was approved by the U.S. Food and Drug Administration to treat MM. This dipeptide boronic acid analogue bortezomib (BTZ) is a proteasome inhibitor that targets the 26S proteasome complex and became an effective anti-MM drug. However, despite this encouraging progress, drug resistance remains a prominent challenge to myeloma therapy using BTZ. MM is still considered to be an incurable disease. Therefore, it is important to understand the mechanism of action of BTZ and the mechanism of BTZ resistance in MM. The essence of the mechanism of the action of BTZ is the inhibition of the proteasome, which inhibits the protein degradation of the ubiquitin-proteasome pathway. This inhibition results in the blocking of the degradation of abnormal proteins, thus triggering ER stress and apoptosis and the blocking of the degradation of key regulatory proteins, thus directly altering pro-survival or pro-apoptotic signalling cascades. The mechanisms of BTZ resistance is complicated, which include genetic abnormalities in the proteasome, use of an alternative protein degradation pathway, aberrant survival signalling pathways, metabolism, microenvironment, and drug efflux such as via P-glycoprotein (Pgp). The role of Pgp in BTZ resistant MM has been studied. It has been shown that BTZ is one of the substrates of Pgp. However, the correlation between Pgp and BTZ resistance in MM conflicts in different studies. This study found that the mRNA level and activity level of Pgp were upregulated, and the inhibition of Ppg by tariquidar overcame the BTZ resistance in both acquired and hypoxia-induced RPMI8226 and U266 myeloma cells. These results suggest that the Pgp indeed plays a role in the BTZ resistance in MM. Recent studies showed that carbonic anhydrase XII (CAXII) is overexpressed in the Pgp-positive chemoresistant lung, osteosarcoma, and colon cancer cells and its activity is necessary for the activity of Pgp, and the inhibition of CAXII overcomes the Pgp-mediated chemoresistance. This study showed that The CAXII inhibitor Psammaplin C reduced the Pgp activity and overcame the BTZ resistance in the acquired and hypoxia-induced RPMI8226 and U266 myeloma cells. These results support that CAXII plays a role in the BTZ resistance in MM. Previous structural studies showed that both Pgp and CAXII contain a disulfide bond, which allows the possibility that they may be regulated by the thioredoxin (Trx) system. This study showed that the inhibition of Trx system by auranofin reduced the Pgp expression levels in the hypoxia-induced BTZ resistant RMI8226 and MM cell and also reduced the mRNA levels of CAXII in the hypoxia-induced BTZ resistant RPMI8226 and U266 myeloma cells. These results support that the Trx system could be capable of regulating the expression of Pgp and CAXII in MM. Based on the results obtained with Pgp and CAXII, the expression levels of Pgp and CAXII in MM patients were also analysed using bioinformatics methods. Using publically available datasets this study showed Pgp and CAXII have higher expression in MM patients who respond to BTZ than the patients who do not respond to BTZ. These results support that CAXII and Pgp play an important role in BTZ resistance in MM. In addition, bioinformatics analysis highlighted 327 differently expressed genes in the relapsed MM patients. The interactions analysis by the Ingenuity Pathway Analysis program highlighted potential targets for BTZ resistance in the relapsed MM cells including NFκB, ElK1, HOXB9, CALM, and Fyn. In conclusion, this project highlights the role of Pgp and CAXII in the resistant MM cells. This project also showed that the Trx system could be capable of regulating the expression of Pgp and CAXII in MM. Bioinformatics analysis highlights 327 differently expressed genes in the relapsed MM patients compared to newly diagnosed MM patients and potential targets for BTZ resistance including nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), ETS Like-1 protein (ElK1), Homeobox B9 (HOXB9), calmodulin (CALM), and tyrosine-protein kinase (Fyn).