Elevated serum GPI levels have been used as a prognostic biomarker for colorectal , breast , lung , kidney , gastrointestinal , and other cancers .   As AMF, GPI is attributed with regulating cell migration during invasion and metastasis .  One study showed that the external layers of breast tumor spheroids (BTS) secrete GPI, which induces epithelial–mesenchymal transition (EMT), invasion, and metastasis in BTS. The GPI inhibitors ERI4P and 6PG were found to block metastasis of BTS but not BTS glycolysis or fibroblast viability. In addition, GPI is secreted exclusively by tumor cells and not normal cells. For these reasons, GPI inhibitors may be a safer, more targeted approach for anti-cancer therapy.  GPI also participates in a positive feedback loop with HER2 , a major breast cancer therapeutic target, as GPI enhances HER2 expression and HER2 overexpression enhances GPI expression, and so on. As a result, GPI activity likely confers resistance in breast cancer cells against HER2-based therapies using Herceptin /Trastuzumab, and should be considered as an additional target when treating patients. 
c) Compare the lock and key and induced-fit models of enzyme activity. The lock-and-key model shows that the enzyme’s activity is limited to only one kind of substrate. The shape and charge of the active site doesn’t change for a lock-and-key model and the substrate immediately fits. The lock-and-key model is good to explain substrate specificity but the induced-fit model better explains the process of catalyzing a substrate – how the bonds are broken. The substrate enters the active site and then the active site will alter to fit the substrate in shape and charge. This model also helps to explain how activation energy is reduced as it breaks the bonds of the substrate (or creates it in the case of condensation synthesis). The induced-fit model better explains the wide variety of substrate specificity in enzymes.