GLP1R and diabetes mellitus: Indeed, oral DPP-4 inhibitors, such as sitagliptin, were approved as second-line agents in 2007 (7), while a plethora of additional GLP-1 mimetics have since gained regulatory approval for diabetes in addition to exenatide, namely the longer-acting mimetics: liraglutide, semaglutide, albiglutide and dulaglutide (Table 2).