Imatinib cancer drug, molecular model. This drug, marketed as Gleevac or Glivac, is used to treat several cancers, including chronic myelogenous leukaemia and gastrointestinal stromal tumours. It inhibits a form of tyrosine kinase enzyme, which is responsible for promoting the growth of certain tumours. By blocking the enzyme's active site, it prevents the proliferation of tumour cells. It also encourages the enzyme to enter the cell nucleus, where it cannot prevent the suicide (apotosis) of cancer cells. In this model, atoms are represented by coloured spheres; carbon is green, hydrogen is white, nitrogen is blue, and oxygen is red.