Retrospective Evaluation of Melanocortin Receptor 4 Polymorphisms in Patients With GBM Treated With Radiochemotherapy

Glioma is the most frequent malignant primary brain tumor and remains a lethal disease with a dismal prognosis. Glioblastoma (GBM) accounts approximately 50% of all glioma and among these tumors, are the most malignant. GBM are characterized by a higher cellular density and by the ample existence of atypia, mitotic cells, pseudopalisading necrosis and microvascular proliferations. The cells of origin of glioma are still undefined, but the most putative target cells include astrocytes, neural stem cells, and oligodendrocyte precursor cells. Despite therapeutic advances recorded over the last decade, treatment of GBM remains difficult and nowadays no available treatments have a curative attempt. Therefore, the treatment of patients with malignant gliomas still remains palliative. The current standard of care for patients with newly diagnosed GBM was established in 2005 by Stupp et al following the pivotal trial by the European Organisation for the Research and Treatment of Cancer/National Cancer Institute of Canada Clinical Trials Group. The final results of that randomized phase III trial for patients with newly GBM revealed that survival of patients who received temozolomide with radiotherapy for GBM is superior to radiotherapy alone across all clinical prognostic subgroups. On the contrary, the treatment of recurrent GBM is still controversy and continues to be a moving target as new therapeutic principles enrich the standards of care for newly diagnosed disease. After upfront therapy the recurrence rates remain high (≈90%) and the Median overall survival (OS) is 15-18 months in clinical trial populations, and less than 10% of patients are alive at 5 years.

Melanocortins are peptides with well-recognized anti-inflammatory and neuroprotective activity. Of the five known melanocortin receptors (MCRs), only subtype 4 is present in astrocytes. Melanocortin receptor 4 (MC4R) is expressed predominantly in the brain, although it was also detected in adipose tissue, in human skin melanocytes. MC4R has been shown to mediate melanocortin effects on energy homeostasis, reproduction, inflammation, and neuroprotection and, recently, to modulate astrocyte functions. The signaling pathway for MC4R involves G protein-mediated activation of adenylate cyclase and increased cAMP production; in astrocytes it also involves cAMP-protein kinase A (PKA)-cAMP response element binding protein and mitogen-activated protein kinase extracellular signal-regulated kinase -1/2 activation. A recent study showed that melanocyte-stimulating hormone (MSH) induces neurogenesis in the hippocampus of animals after global ischemia and this effect is mediated by MC4R. In an animal model of focal cerebral ischemia, delayed treatment with α-MSH or treatment with Afamelanotide but not with the melanocortin receptor 3 agonist reduced neuron death. This protection correlated with decreased tumor necrosis factor-α and NO production, and decreased expression of pro-apoptotic Bax and caspase-3 activation, and also with increased serum levels of interleukin-10 and Bcl2 expression induced by Afamelanotide. In cerebral ischemia, neuroprotection by Afamelanotide also involves activation of MC4R and Bcl2 upregulation .

Recently, in experimental brain ischemia, treatment with melanocortins acting at melanocortin receptors 4 induces neural stem/progenitor cell proliferation by triggering the canonicalWnt-3A/β-catenin and Shh signaling pathway. Caruso et al. demonstrated that MC4R activation by α-MSH protects astrocytes from apoptosis. Melanocortins prevent astrocyte death by decreasing caspase-3 activity and the expression of Bax and by increasing the expression of Bcl2. As melanocortins increase astrocyte survival, this can contribute to their neuroprotective effects . Moreover, the anti-inflammatory action of α-MSH, an MCR agonist, reduces the secretion of mediators such as cytokines, NO, and prostaglandins and impairs leukocyte activation and infiltration into damaged tissues. Moreover, proliferative effects of α-MSH were reported in 7-day-old cultured astrocytes.

The Single Nucleotide Polymorphisms (SNPs) rs17782313 of the MC4R gene have shown an effect on Body Mass Index (BMI) in different populations; and a direct role in the interaction between Fat Mass and Obesity Associated (FTO) and MC4R gene polymorphisms in breast cancer development has been recently demonstrated. However, no data are currently available on MC4R gene polymorphisms and gliomas or their relationship with radiotherapy/chemotherapy with or without antiangiogenic drugs.

Given the association between MC4R with antiinflammatory activity, neuroprotection, induction of neural stem/progenitor cell proliferation in brain hypoxia, and prevention of astrocyte apoptosis, the aim of this study is to evaluate, retrospectively, the possible prognostic/predictive role of the MC4R SNPs on glioblastoma therapy. Our hypothesis is that these SNPs could have a direct role in the modulation of the therapeutic effects of radiotherapy, chemotherapy and antiangiogenic drugs on glioblastoma and they could influence the prognosis of the disease through their effect on patient's brain.