Nanocarriers as an Emerging Platform for Cancer Therapy

Nanotechnology has the potential to revolutionize cancer diagnosis and therapy. Advances in protein engineering and materials science have contributed to novel nanoscale targeting approaches that may bring new hope to cancer patients. Several therapeutic nanocarriers have been approved for clinical use. However, to date, there are only a few clinically approved nanocarriers that incorporate molecules to selectively bind and target cancer cells. This review examines some of the approved formulations and discusses the challenges in translating basic research to the clinic. We detail the arsenal of nanocarriers and molecules available for selective tumour targeting, and emphasize the challenges in cancer treatment. Cancer remains one of the world's most devastating diseases, with more than 10 million new cases every year 1. However, mortality has decreased in the past two years 2 owing to better understanding of tumour biology and improved diagnostic devices and treatments. Current cancer treatments include surgical intervention, radiation and chemotherapeutic drugs, which often also kill healthy cells and cause toxicity to the patient. It would therefore be desirable to develop chemotherapeutics that can either passively or actively target cancerous cells. Passive targeting exploits the characteristic features of tumour biology that allow nanocarriers to accumulate in the tumour by the enhanced permeability and retention (EPR) effect 2. Passively targeting nanocarriers first reached clinical trials in the mid-1980s, and the first products, based on liposomes and polymer–protein conjugates, were marketed in the mid-1990s. Later, therapeutic nanocarriers based on this strategy were approved for wider use (Table 1) and methods of further enhancing targeting of drugs to cancer cells were investigated. Active approaches achieve this by conjugating nanocarriers containing chemotherapeutics with molecules that bind to overexpressed antigens or receptors on the target cells. Recent reviews provide perspective on the use of nanotechnology as a fundamental tool in cancer research and nanomedicine 3,4. Here we focus on the potential of nanocarriers and molecules that can selectively target tumours, and highlight the challenges in translating some of the basic research to the clinic. PaSSive anD aCtive targeting Nanocarriers encounter numerous barriers en route to their target, such as mucosal barriers and non-specific uptake 5,6. To address the challenges of targeting tumours with nanotechnology, it is necessary to combine the rational design of nanocarriers with the fundamental understanding of tumour biology (Box 1). General features of tumours include leaky blood vessels and poor lymphatic drainage. Whereas free drugs may diffuse non-specifically, a nanocarrier can …