**3.4 Repurposed drugs for HMTs**

Given the diverse roles of the two classes of HMTs, KMTs, and PRMTs, in different diseases, there have been increasing efforts towards developing/repurposing drugs that affect HMTs for the treatment of diseases. Under the class of KMT enzymes, EZH2 is one of the highly pursued targets for epigenetic therapy. For example, Astemizole (**Table 1**), an antihistamine drug used to treat allergies, disrupts the proliferation of lymphoma cells *via* inhibition of EZH2 methyltransferase activity [84]. Also, a pilot HTS identified 4 out of 1600 FDA-approved drugs as putative EZH2 inhibitors, with apomorphine hydrochloride being the most potent inhibitor [103]. Apomorphine hydrochloride, under the brand name Kynmobi, is FDA approved for the treatment of PD Off episodes [104]. A separate review has suggested the repurposing of apomorphine hydrochloride in AD, ALS, HD, and multiple cancers considering the mounting evidence that demonstrates its neuroprotective and anti-cancer effects [85]. However, whether this drug exerts its protective properties *via* EZH2 remains to be investigated. The anti-malaria drug, hydroxychloroquine, inhibits EZH2 and has been reported to be effective for the treatment of multiple myeloma (MM) [86]. Furthermore, there are about 10 clinical trial studies investigating PRMT inhibitors for both solid and hematological malignancies on clinicaltrial.gov. Given the lack of investigation on market approved drugs for targeting PRMTs in diseases, our lab has taken considerable efforts to address this important gap. Currently, we have a provisional patent on repurposing the FDA-approved drugs for cough (Cloperastine) and for hypertension (Candersatan) to target PRMT5 in tumors (PCT/US2020/067694) [87, 88].
