Glioblastoma multiforme (GBM): An overview of current therapies and mechanisms of resistance.

Glioblastoma multiforme (GBM) is a WHO grade IV glioma and the most common malignant, primary brain tumor with a 5-year survival of 7.2%. Its highly infiltrative nature, genetic heterogeneity, and protection by the blood brain barrier (BBB) have posed great treatment challenges. The standard treatment for GBMs is surgical resection followed by chemoradiotherapy. The robust DNA repair and self-renewing capabilities of glioblastoma cells and glioma initiating cells (GICs), respectively, promote resistance against all current treatment modalities. Thus, durable GBM management will require the invention of innovative treatment strategies. In this review, we will describe biological and molecular targets for GBM therapy, the current status of pharmacologic therapy, prominent mechanisms of resistance, and new treatment approaches. To date, medical imaging is primarily used to determine the location, size and macroscopic morphology of GBM before, during, and after therapy. In the future, molecular and cellular imaging approaches will more dynamically monitor the expression of molecular targets and/or immune responses in the tumor, thereby enabling more immediate adaptation of tumor-tailored, targeted therapies.

Metabolic effects of antiangiogenic drugs in tumors: therapeutic implications.

Antiangiogenic therapy has become a mainstay of cancer therapeutics, but clinical responses are generally short-term owing to the development of secondary resistance. Tumor starvation by antiangiogenic drugs is largely attributed to increased hypoxia and impaired nutrients supply, suggesting that angiogenesis inhibition causes remarkable metabolic perturbations in the tumor microenvironment. We review here recent acquisitions concerning metabolic effects of angiogenesis blockade in tumors and discuss the possibility that some metabolic features of tumor cells - i.e. their dependency from glucose as primary energy substrate - might affect tumor responses to anti-vascular endothelial growth factor treatment. Moreover, we discuss the hypothesis that anti-angiogenic therapy might foster metabolic evolution of tumors. The therapeutic implications of this hypothesis will be discussed further here.

The multikinase inhibitor axitinib is a potent inhibitor of human CYP1A2.

The tyrosine kinase inhibitors (TKIs) and multikinase inhibitors (MKIs) are oncology drugs of increasing importance that have improved the treatment of multiple tumors types. In some patients these agents produce adverse effects, including pharmacokinetic drug-drug interactions, due to cytochrome P450 (CYP) inhibition. Information on the propensity of the drugs to elicit such effects often only becomes evident as the drugs enter clinical use. The present study assessed 18 kinase inhibitors (1 and 50 µM) for the inhibition of major drug metabolizing CYPs 1A2, 2C9, 2D6 and 3A4 in human liver microsomes. Most TKIs and MKIs inhibited CYP reactions at the higher concentration but axitinib also potently inhibited CYP1A2-dependent 7-ethoxyresorufin O-deethylation activity at the lower concentration. Kinetic analyses of CYP1A2 inhibition by axitinib were undertaken in microsomes and found a Ki of 0.11 ± 0.01 µM, which was 7.5-fold lower than the Km for 7-ethoxyresorufin oxidation (0.83 ± 0.06 µM); the inhibition mechanism was linear-mixed. From computational modeling two potential binding modes for axitinib were identified in the active site of CYP1A2: one in which the oxidizable axitinib thioether sulfur atom is within ~4.45 Å of the CYP1A2 heme, and is likely to favor biotransformation of the drug, and a second in which the pyridine moiety is in proximity to the heme, which may contribute to inhibition. The applicability of these findings to potential pharmacokinetic interactions in patients during axitinib treatment should now be assessed.