Wu-Ming Qin, Kun Wang, Jia-Rong Huang, Xiao-Long Mei, and Zhi Shi, “Sildenafil Induces Cell Cycle Arrest and Apoptosis in Human Colorectal Cancer HT-29 Cells”, J. Can. Res. Updates, vol. 7, no. 2, pp. 59–63, Aug. 2021.