“Sildenafil Enhances the Anticancer Activity of Paclitaxel in an ABCB1-Mediated Multidrug Resistance Xenograft Mouse Model”. Journal of Cancer Research Updates, vol. 3, no. 3, July 2014, pp.  169-173, https://doi.org/10.6000/1929-2279.2014.03.03.7.