Cyclophosphamide treatment evoked side effect on skeletal muscle actin, monitored by DSC

Several kind of drugs—used in cancer treatments—such as cyclophosphamide (CP) can also trigger a disease classified as toxic polyneuropathy. Polyneuropathy is a simultaneous malfunction of several peripheral nerves, typical side effect of a cancer therapy. In our previous study, we used CP treated in vitro animal model (Guinea pig) with a comparable dosage and time handling of human protocol to show evidences of this drug-induced effects. We could show a dose-dependent difference between in Tm and ΔHcal of untreated and treated samples assigned to their intact muscle and nerve, blood plasma and red blood cells. In our current study we analyze this side effect on skeletal muscle actin (prepared from m. psoas of rabbit) by DSC (differential scanning calorimetry), to follow the possible consequence of drug treatment on the “activator” of muscle contraction. We have demonstrated that run of DSC curves, Tms together with the ΔHcal exhibit clear CP effect. In case of Ca2+ G actin it is manifested in a well separated second high denaturing temperature as a consequence of CP binding into the cleft. This way the nucleotide binding cleft with subdomains 1 and 3 becomes less flexible, indicating clear sensitivity to CP treatment. In F-actin samples, the main peak represents the thermal denaturation of subdomains 1 and 3, and the increased calorimetric enthalpy administrating Ca2+ as well as CP refers to a more rigid structure. These alterations can be the molecular background in the malfunction of muscle in case of polyneuropathy after CP treatment.