MRI for assessing antivascular cancer treatments.

Selective antiangiogenesis and vascular targeting drugs hold out the promise of improved efficacy and tolerability for anticancer treatments. Early phase 1 drug trials have shown good tolerability for antiangiogenesis agents with biological activity below the maximum tolerated dose. Advanced clinical trials have demonstrated that morphological assessments of tumour response are of limited value in gauging the efficacy of treatment. MRI is a versatile technique which is sensitive to contrast mechanisms that can be affected by antivascular treatments; this use for MRI has been validated in xenografts and humans. Dynamic contrast-enhanced MRI (DCE-MRI), which demonstrates tissue perfusion and permeability, is being used clinically as a pharmacodynamic indicator of biological activity for antivascular cancer drugs. Early data show that DCE-MRI studies can define the biologically active dose and predict the efficacy of treatment on the basis of changes observed. MRI with macromolecular contrast media (MMCM) depicts microvessel permeability and fractional plasma volume. Xenograft studies with MMCM have shown great promise for evaluating antivascular treatments but this has not been used clinically. Intrinsic susceptibility-weighted MRI, which is sensitive to blood oxygenation and flow, is emerging as a technique that may be able to monitor vascular targeting therapies.