BMS expects that Ixempra (ixabepilone) will be available to patients "within days", and although the drug's target isn't new, its structure is. The compound is an epothilone B analogue and is the first of this class of molecule to be approved.

The epothilones are derived from Sorangium cellulosum, a myxobacterium first discovered on the banks of the Zambezi River in Africa 20 years ago. The reason scientists are excited about this new class of drug is that, unlike taxanes, the epothilones appear not to be very susceptible to known tumour resistance mechanisms.

The drug works by binding to tubulin, a protein that is forms the basis of microtubules - the cell skeleton or scaffold. By binding to its target, ixabepilone stabilises the cell and prevents it from dividing (they stop in the G2-M phase of cell cycle). This, in turn, can prevent a tumour from growing.

Another BMS drug, Taxol (paclitaxel) binds to the beta subunit of tubulin but Ixempra interacts with different sub-types of microtubules. It is active against the Beta III tubulin isoform, high levels of which are associated with resistance and poor responses to taxanes. The drug also has low susceptibility to mechanisms that confer tumour resistance, such as overexpression of efflux transporters -P-glycoprotein (P-gp) and multidrug-resistance protein-1 (MRP1).

Ixempra has been approved as a monotherapy for the treatment of patients with metastatic or locally advanced breast cancer, in patients whose tumours are resistant or refractory to anthracyclines, taxanes, and Roche's Xeloda (capecitabine). The FDA has also granted approval of the drug in combination with Xeloda.

Breast cancer sufferers can also be treated with a choice of two targeted therapies. The first is Genentech and Roche's Herceptin (trastuzumab), which is a monoclonal antibody against the human epidermal growth factor receptor 2 (HER2). The second, only approved this year, is Tykerb (lapatinib), which was developed by GlaxoSmithKline (GSK). This small molecule drug also targets HER2 through binding to its tyrosine kinase domain. Unlike Herceptin, however, Tykerb also blocks HER1 (also called epidermal growth factor receptor, EGFR), which is the target of AstraZenenca's Iressa (gefitinib). Although Tykerb is approved in the US, GSK is still waiting on a decision from EU regulators, where the pharma giant plans to market it under the name Tyverb.