Anticancer Properties for 4,4′-Dihydroxybenzophenone-2,4-dinitrophenylhydrazone (A-007)/3,7-Diaminophenothiazin-5-ium Double Salts

4,4′-Dihydroxybenzophenone-2,4-dinitrophenylhydrazone (A-007) formed stable double salts with phenothiazin-5-ium salts (2a–d), which have improved in vitro anticancer activities, as compared to A-007 alone. The stable salt between methylene blue (2a) and A-007 allowed the latter to diffuse into the dermis layers of skin. It is anticipated that these new salts will allow A-007 to penetrate into the deep lymphatic/vascular channels of the dermis, which contain metastatic cancer cells, and improve in vivo anticancer activities.