The Drug Targeting and Delivery Approach Applied to Pt-Antitumour Complexes. A Coordination Point of View

Platinum-based anticancer chemotherapy is associated to severe side effects because of its poor specificity. In particular, the hydrolysis of Pt-based drugs generates cationic complexes with electrophylic properties able to target DNA. The effectiveness of this kind of chemotherapy relies solely on the proliferation index of tumour cells, which is higher than in healthy cells. In recent years, the “drug targeting and delivery” approach has been developed in an attempt to reduce chemotherapy-related systemic side effects by using vectors that selectively deliver the cytotoxic agent to tumour cells, thus sparing healthy cells. These vectors include bioactive substances, such as nutrients, that more readily enter metabolically active tumour cells, or hormones, folates and bile acids, that are selectively conveyed by receptors/transporters often over-expressed in cancer cells (active targeting). Alternatively, macromolecular vectors, exploiting the so-called EPR (enhanced permeability and retention) effect, can be used (passive targeting). The bioactive or macromolecular vector must contain a coordinating arm capable of binding the PtX2-unit, acting either as carrier or leaving group for the cytotoxic Pt-moiety. In both cases, the Pt-vector conjugate should be promptly cleaved to generate the active species. The release of platinum drugs from the pharmacophore is crucial for fine-tuning of the overall cytotoxic properties of the conjugates. The “drug targeting and delivery” method represents an exciting field of research for improving the therapeutic potential of the long established, very efficient, but intrinsically non-specific Pt-based drugs.