During the last decade, we have used PPRHs as gene silencing tools to inhibit genes related to cancer progression such as dihydrofolate reductase (DHFR) (de Almagro et al., 2009, 2011), telomerase (TERT) (de Almagro et al., 2009), BCL2, topoisomerase 1 (TOP1), mTOR, MDM2, C-MYC (Villalobos et al., 2015), CHK1, WEE1 (Aubets et al., 2020) and survivin (BIRC5) in vivo (Rodríguez et al., 2013). Here, DHFR is linked to cancer.