Orally available selective melanocortin-4 receptor antagonists stimulate food intake and reduce cancer-induced cachexia in mice.

BACKGROUND: Cachexia is among the most debilitating and life-threatening aspects of cancer. It represents a metabolic syndrome affecting essential functional circuits involved in the regulation of homeostasis, and includes anorexia, fat and muscle tissue wasting. The anorexigenic peptide alpha-MSH is believed to be crucially involved in the normal and pathologic regulation of food intake. It was speculated that blockade of its central physiological target, the melanocortin (MC)-4 receptor, might provide a promising anti-cachexia treatment strategy. This idea is supported by the fact that in animal studies, agouti-related protein (AgRP), the endogenous inverse agonist at the MC-4 receptor, was found to affect two hallmark features of cachexia, i.e. to increase food intake and to reduce energy expenditure. METHODOLOGY/PRINCIPAL FINDINGS: SNT207707 and SNT209858 are two recently discovered, non peptidic, chemically unrelated, orally active MC-4 receptor antagonists penetrating the blood brain barrier. Both compounds were found to distinctly increase food intake in healthy mice. Moreover, in mice subcutaneously implanted with C26 adenocarcinoma cells, repeated oral administration (starting the day after tumor implantation) of each of the two compounds almost completely prevented tumor induced weight loss, and diminished loss of lean body mass and fat mass. CONCLUSIONS/SIGNIFICANCE: In contrast to the previously reported peptidic and small molecule MC-4 antagonists, the compounds described here work by the oral administration route. Orally active compounds might offer a considerable advantage for the treatment of cachexia patients.

Mammalian animal models for Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disease that affects boys and leads to early death. In the quest for new treatments that improve the quality of life and in the search for a possible definitive cure, the use of animal models plays undoubtedly an important role. Therefore, a number of different mammalian models for DMD have been described. Much knowledge on the molecular mechanisms underlying the disease has arisen from studies in these animals. However, the use of different models does not often allow a direct comparison of results obtained in preclinical trials and therefore hinders a straightforward translational research. In the frame of "TREAT-NMD", a European Network of Excellence addressing the fragmentation in the assessment and treatment of neuromuscular diseases, we compare here the currently used mammalian animal models for DMD with the aim of selecting and recommending the most appropriate ones for preclinical efficacy testing of new therapeutic strategies.

Effect of calpain and proteasome inhibition on Ca2+-dependent proteolysis and muscle histopathology in the mdx mouse.

Dystrophin deficiency is the underlying molecular cause of progressive muscle weakness observed in Duchenne muscular dystrophy (DMD). Loss of functional dystrophin leads to elevated levels of intracellular Ca(2+), a key step in the cellular pathology of DMD. The cysteine protease calpain is activated in dystrophin-deficient muscle, and its inhibition is regarded as a potential therapeutic approach. In addition, previous work has shown that the ubiquitin-proteasome system also contributes to muscle protein breakdown in dystrophic muscle and, therefore, also qualifies as a potential target for therapeutic intervention in DMD. The relative contribution of calpain- and proteasome-mediated proteolysis induced by increased Ca(2+) levels was characterized in cultured muscle cells and revealed initial Ca(2+) influx-dependent calpain activity and subsequent Ca(2+)-independent activity of the ubiquitin-proteasome system. We then set out to optimize novel small-molecule inhibitors that inhibit both calpain as well as the 20S proteasome in a cellular system with impaired Ca(2+) homeostasis. On administration of such inhibitors to mdx mice, quantitative histological parameters improved significantly, in particular with compounds strongly inhibiting the 20S proteasome. To investigate the role of calpain inhibition without interfering with the ubiquitin-proteasome system, we crossed mdx mice with transgenic mice, overexpressing the endogenous calpain inhibitor calpastatin. Although our data show that proteolysis by calpain is strongly inhibited in the transgenic mdx mouse, this calpain inhibition did not ameliorate muscle histology. Our results indicate that inhibition of the proteasome rather than calpain is required for histological improvement of dystrophin-deficient muscle. In conclusion, we have identified novel proteasome inhibitors that qualify as potential candidates for pharmacological intervention in muscular dystrophy.