Cancer Anti-angiogenic Therapy

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Abstract
Tumor angiogenesis affords new targets for cancer therapy, since inhibition of angiogenesis suppresses tumor growth by cutting out the supply of oxygen and nutrients. Anti-angiogenic therapy is thought to be free of the severe side effects that are usually seen with cytotoxic anticancer drugs. Furthermore, anti-angiogenic therapy is thought not only to eradicate primary tumor tissues, but also to suppress tumor metastases. However, it is uncertain whether this therapy causes tumor regression because it inhibits only angiogenic events. Recently, a novel anti-angiogenic therapy called anti-neovascular therapy (ANET) has become notable. This therapy inflicts indirect lethal damage on tumor cells by damaging newly formed blood vessels using anti-cancer drugs targeting the angiogenic vasculature, since cytotoxic anti-cancer drugs cause damage to proliferating neovascular endothelial cells as well as tumor cells. Moreover, neovascular endothelial cells would not be expected to acquire drug-resistance. Traditional chemotherapy, which directly targets tumor cells, has potential problems such as low specificity and severe side effects. On the contrary, in ANET, severe side effects may be suppressed, since traditional anti-cancer agents are delivered to the neovessels by DDS technology. Besides the usage of DDS technology, anti-neovascular scheduling of chemotherapy, or metronomic-dosing chemotherapy, has also been attempted in which anti-cancer drugs are administered on a schedule to damage neovessels. In this review, we describe traditional anti-angiogenic therapy and ANET. We also discuss anti-angiogenic cancer photodynamic therapy (PDT), since PDT is clinically applied to treat age-related macular degeneration (AMD), in which uncontrolled angiogenesis occurs.