Understanding the Mechanisms of ALA-induced Fluorescence in Malignant Gliomas - Exploring the Biological Basis of Tumoral Heterogeneity.

Malignant gliomas are the commonest malignant brain tumors but are extremely challenging to treat. Neuro-oncology has seen little progress in its treatment despite extensive research. Extent of resection remains a very important prognostic factor in these tumors. Better the resection, better the outcomes. However resecting these tumors is not very easy primarily due to their infiltrative nature and difficulty in discerning tumor boundaries intraoperatively. Fluorescence guided resection (FGR) has recently been shown to be a very important and useful adjunct in maximizing this goal. FGR involves administration of aminolevulinic acid (ALA) to the patient prior to surgery. The ALA is converted to protoporphyrin IX (PPIX) in glioma cells. The PPIX is a fluorophore and can be visualized intraoperatively using a suitably modified microscope. Neurosurgeons can then resect the tumor radically guided by this fluorescence which is superior to the conventional microscopic resection. Selective PPIX accumulation in glioma cells is the key to the accuracy of this technique. The biological basis of selectivity of PPIX accumulation within glioma cells is however poorly understood. Various mechanisms could be involved starting from variable transport (related to blood-brain barrier properties), differential uptake (governed by active transport mechanisms) and differential metabolism within the cell. Understanding these mechanisms can lead to refinements in this strategy, overcoming its present limitations and development of methods to extend its scope.