Determination of the antiinfectious activity of RU 41740 (Biostim) as an example of an immunomodulator

The Synthetic Dipeptide Pidotimod Shows a Chemokine-Like Activity through CXC Chemokine Receptor 3 (CXCR3)

In recent years immunomodulators have gained a strong interest and represent nowadays an active expanding area of research for the control of microbial diseases and for their therapeutic potential in preventing, treating and reducing the morbidity and mortality of different diseases. Pidotimod (3-L-pyroglutamyl-L-thiaziolidine-4carboxylic acid, PDT) is a synthetic dipeptide, which possesses immunomodulatory properties and exerts a well-defined pharmacological activity against infections, but its real mechanism of action is still undefined. Here, we show that PDT is capable of activating tyrosine phosphorylation-based cell signaling in human primary monocytes and triggering rapid adhesion and chemotaxis. PDT-induced monocyte migration requires the activation of the PI3K/Akt signaling pathway and chemokine receptor CXCR3. Indeed, a mAb to CXCR3 and a specific receptor inhibitor suppressed significantly PDT-dependent chemotaxis, and CXCR3-silenced primary monocytes lost responsiveness to PDT chemoattraction. Moreover, our results highlighted that the PDT-induced migratory activity is sustained by the CXCR3A isoform, since CXCR3-transfected L1.2 cells acquired responsiveness to PDT stimulation. Finally, we show that PDT, as CXCR3 ligands, is also able to direct the migration of IL-2 activated T cells, which express the highest levels of CXCR3 among CXCR3-expressing cells. In conclusion, our study defines a chemokine-like activity for PDT through CXCR3A and points on the possible role that this synthetic dipeptide may play in leukocyte trafficking and function. Since recent studies have highlighted diverse therapeutic roles for molecules which activates CXCR3, our findings call for an exploration of using this dipeptide in different pathological processes.

Pidotimod: the past and the present

At the end of 1990s, acute respiratory tract infections (ARTIs) were called the 'forgotten pandemic’, with a clear dichotomy between developing and industrialised countries in mortality and morbidity, the main outcomes associated with ARTIs. This definition still applies 20 years later, when the introduction of new and safe antibiotics and vaccines has certainly contributed to controlling the most life-threatening ARTIs, but has not had a major impact on viral ARTIs in paediatric age. One functional approach to preventing and treating ARTIs is non-specifically increasing the immune response or enhancing the children’s innate defence mechanisms. Different kinds of biologically active substances – called immunostimulants – of natural and synthetic origins and with different mechanisms of action have been introduced in some countries for the prevention of ARTIs in children. Recently, research focused on one of these compounds, Pidotimod, has attempted to better clarify and define its mechanisms of action both in vitro and in vivo. In this paper, we critically examine the most recent findings on Pidotimod. Certainly the improvement of research methodology in the last 20 years and the acquired knowledge in various fields of clinical immunology should be the starting point for research on Pidotimod. Preclinical research will be essential to better understand the mechanisms of action of this compound. However, in vivo studies, especially randomised control trials, will be necessary to establish the real efficacy of Pidotimod in the prevention of ARTIs in paediatric age.