ABCB1 and osteosarcoma: Previous studies demonstrated that methotrexate-resistant, vincristine-resistant, multidrug resistant phenotypes of gastric cancer cells could be regulated by the inhibition of ZNRD1/Inosine monophosphate dehydrogenase 2 (IMPDH2), upregulated DARPP-32/downregulated ZNRD1, overexpressed miR-508-5p/ZNRD1/ABCB1 activities, respectively [26–28], but further researches of ZNRD1 in osteosarcoma chemoresistance remained to be conducted.