The therapy involving the restriction of glycine utilization through betaine has displayed promising treatment outcomes for MM, either individually or when combined with bortezomib.[50,55] Furthermore, the upregulation of pyrroline-5-carboxylate reductase 1-3 (PYCR1-3) and pyrroline-5-carboxylate synthase is induced by MYC, leading to the promotion of glutamine to proline biosynthesis.[44,57] Interfering with PYCR1 leads to a decrease in myeloma cell proliferation and survival by blocking the pathway of proline-rich akt substrate 40 kDa-mediated protein synthesis. Here, PYCR1 is linked to plasma cell myeloma.