Cancer Cachexia (CC) is a complex syndrome compromising quality of life and survival, mainly characterised by weight loss attributed to a catastrophic loss of muscle and adipose tissue. Recent research by our lab shows that only tumours expressing Fn14 (tumour necrosis factor receptor superfamily member 12A; TNFRSF12A) can induce CC but tumours without Fn14 cannot and monoclonal antibodies against human Fn14 prevent cachexia (Johnson et al, Cell). Since these tumours cause cachexia in Fn14-/- and in Tweak-/- (the only known ligand for FN14) mice, we hypothesize that there must be factor(s) other than Tweak specifically secreted from the Fn14-expressing tumour cells inducing muscle atrophy and fat loss systemically. To identify these factor(s), we have generated reporter cell lines that are activated by pro-cachectic factors released by tumours.
MuRF1 (Muscle RING finger-containing protein 1) and CIDEA (Cell Death-Inducing DFFA-like Effector A) are two genes that are constitutively activated in muscle and adipose tissues of CC patients respectively. The promoters of the genes were cloned into a vector which drives the reporter genes, luciferase and GFP. Constructs were stably inserted into C2C12 myoblasts and 3T3-L1 pre-adipocytes, which, when differentiated into myotubules and white adipose adipocytes, express receptors for soluble factors released from cachexia inducing tumour cells. We show that Activin A and myostatin, two factors demonstrated to be involved in CC, can activate C2C12 myotubes reporter cells and their mRNAs are also up-regulated in Fn14-expressing tumours. Similarly, serum from mice with Fn14 induced cachexia is able to activate luciferase in the differentiated reporter cell lines.
We are now using these reporter cell lines to isolate and identify key soluble factor(s) involved in the cachectic process and will use the most promising of these factors as biomarkers for early detection and monitoring the outcomes of treatment of cachectic patients with our therapeutic antibody.