Personalized medicine and pharmacogenetic biomarkers: progress in molecular oncology testing.

In the field of oncology, clinical molecular diagnostics and biomarker discoveries are constantly advancing as the intricate molecular mechanisms that transform a normal cell into an aberrant state in concert with the dysregulation of alternative complementary pathways are increasingly understood. Progress in biomarker technology, coupled with the companion clinical diagnostic laboratory tests, continue to advance this field, where individualized and customized treatment appropriate for each individual patient define the standard of care. Here, we discuss the current commonly used predictive pharmacogenetic biomarkers in clinical oncology molecular testing: BRAF V600E for vemurafenib in melanoma; EML4-ALK for crizotinib and EGFR for erlotinib and gefitinib in non-small-cell lung cancer; KRAS against the use of cetuximab and panitumumab in colorectal cancer; ERBB2 (HER2/neu) for trastuzumab in breast cancer; BCR-ABL for tyrosine kinase inhibitors in chronic myeloid leukemia; and PML/RARα for all-trans-retinoic acid and arsenic trioxide treatment for acute promyelocytic leukemia.

Arginine metabolism by macrophages promotes cardiac and muscle fibrosis in mdx muscular dystrophy.

BACKGROUND: Duchenne muscular dystrophy (DMD) is the most common, lethal disease of childhood. One of 3500 new-born males suffers from this universally-lethal disease. Other than the use of corticosteroids, little is available to affect the relentless progress of the disease, leading many families to use dietary supplements in hopes of reducing the progression or severity of muscle wasting. Arginine is commonly used as a dietary supplement and its use has been reported to have beneficial effects following short-term administration to mdx mice, a genetic model of DMD. However, the long-term effects of arginine supplementation are unknown. This lack of knowledge about the long-term effects of increased arginine metabolism is important because elevated arginine metabolism can increase tissue fibrosis, and increased fibrosis of skeletal muscles and the heart is an important and potentially life-threatening feature of DMD. METHODOLOGY: We use both genetic and nutritional manipulations to test whether changes in arginase metabolism promote fibrosis and increase pathology in mdx mice. Our findings show that fibrotic lesions in mdx muscle are enriched with arginase-2-expressing macrophages and that muscle macrophages stimulated with cytokines that activate the M2 phenotype show elevated arginase activity and expression. We generated a line of arginase-2-null mutant mdx mice and found that the mutation reduced fibrosis in muscles of 18-month-old mdx mice, and reduced kyphosis that is attributable to muscle fibrosis. We also observed that dietary supplementation with arginine for 17-months increased mdx muscle fibrosis. In contrast, arginine-2 mutation did not reduce cardiac fibrosis or affect cardiac function assessed by echocardiography, although 17-months of dietary supplementation with arginine increased cardiac fibrosis. Long-term arginine treatments did not decrease matrix metalloproteinase-2 or -9 or increase the expression of utrophin, which have been reported as beneficial effects of short-term treatments. CONCLUSIONS/SIGNIFICANCE: Our findings demonstrate that arginine metabolism by arginase promotes fibrosis of muscle in muscular dystrophy and contributes to kyphosis. Our findings also show that long-term, dietary supplementation with arginine exacerbates fibrosis of dystrophic heart and muscles. Thus, commonly-practiced dietary supplementation with arginine by DMD patients has potential risk for increasing pathology when performed for long periods, despite reports of benefits acquired with short-term supplementation.

Expression of the liver form of arginase in erythrocytes.

Arginase I (AI) has a critical function in mammalian liver as the final enzyme in the urea cycle responsible for the disposal of ammonia from protein catabolism. AI is also expressed in various extrahepatic tissues and may play a role in regulating arginine levels and in providing ornithine for biosynthetic reactions that generate various critical intermediary metabolites such as glutamate, glutamine, GABA, agmatine, polyamines, creatine, proline, and nitric oxide. AI is expressed in red blood cells (RBCs) only in humans and certain higher primates. Macaca fascicularis has been identified as an evolutionary transition species in which RBC-AI expression is co-dominantly regulated. The M. fascicularis AI gene was analyzed to understand AI expression in erythrocytes. Erythroid progenitor cells [nucleated red blood cells (nRBCs)] isolated from cord blood were utilized to demonstrate AI expression by immunocytochemical staining using anti-AI antibody. Introduction of EGFP reporter vectors into nRBC showed that the proximal 1.2 kbp upstream of the AI gene is sufficient for AI expression. Expression of a second arginase isoform, AII, in nRBCs was discovered by cDNA profiling. This contrasts with mature fetal or adult RBCs which contain only the AI protein. In addition, an alternatively spliced AI (AI(')) variant was observed from erythroid mRNA analysis with an alternative splice acceptor site located within intron 2, causing the insertion of eight additional amino acids yet retaining significant enzymatic activity.