Tumour vasculature targeting agents in hybrid/conjugate drugs

Tumour vasculature targeting has been a very active area of cancer drug discovery over the last decade. Growth of solid tumours beyond a certain point requires a sufficient blood supply in order for them to develop and metastasise. While novel anti-angiogenic and vascular disrupting agents represent an important contribution to the armoury of anti-cancer agents they nevertheless usually require combination with standard cytotoxic therapy in order to demonstrate positive clinical outcomes. In line with this consensus, a new concept has arisen, namely the design of functional hybrids where at least one component of the design targets a tumour angiogenic/vasculature pathway. This review will outline examples of such hybrid/conjugate-based approaches. Emphasis will be placed on their preclinical evaluation with particular focus on the RGD/NGR-conjugates, heparin-related hybrids and antibody-drug conjugates. In conclusion, the benefits and shortcomings of hybrids under development will be discussed in the context of future directions and applications.