Proof-of-concept validation of the mechanism of action of Src tyrosine kinase inhibitors in dystrophic mdx mouse muscle: in vivo and in vitro studies

Src tyrosine kinase (TK), a redox-sensitive protein overexpressed in dystrophin-deficient muscles, can contribute to damaging signaling by phosphorylation and degradation of β-dystroglycan (β-DG). We performed a proof-of-concept preclinical study to validate this hypothesis and the benefit-safety ratio of a pharmacological inhibition of Src-TK in Duchenne muscular dystrophy (DMD). Src-TK inhibitors PP2 and dasatinib were administered for 5 weeks to treadmill-exercised mdx mice. The outcome was evaluated in vivo and ex vivo on functional, histological and biochemical disease-related parameters. Considering the importance to maintain a proper myogenic program, the potential cytotoxic effects of both compounds, as well as their cytoprotection against oxidative stress-induced damage, was also assessed in C2C12 cells. In line with the hypothesis, both compounds restored the level of β-DG and reduced its phosphorylated form without changing basal expression of genes of interest, corroborating a mechanism at post-translational level. The histological profile of gastrocnemius muscle was slightly improved as well as the level of plasma biomarkers. However, amelioration of in vivo and ex vivo functional parameters was modest, with PP2 being more effective than dasatinib. Both compounds reached appreciable levels in skeletal muscle and liver, supporting proper animal exposure. Dasatinib exerted a greater concentration-dependent cytotoxic effect on C2C12 cells than the more selective PP2, while being less protective against H₂O₂ cytotoxicity, even though at concentrations higher than those experienced during in vivo treatments. Our results support the interest of Src-TK as drug target in dystrophinopathies, although further studies are necessary to assess the therapeutic potential of inhibitors in DMD.

Synergistic antiproliferative and antiangiogenic effects of EGFR and mTOR inhibitors

Single-agent therapy with molecularly targeted agents has shown limited success in tumor growth control, mainly because escape or resistance mechanisms are activated once a signalling molecule is inhibited. Rational combinations of target-specific agents could counteract this response providing a useful strategy in cancer treatment. In this regard, the EGFR and mTOR inhibitors have been used together to generate a synergistic effect and maximize the efficacy of each individual agent. Overall, the in vivo and in vitro evidences support the utilization of combinations targeting EGFR and mTOR, for malignancies characterized by deregulated EGFR/PI3K/Akt/ mTOR signalling cascade; whereas the clinical experience points out that the assessment of the therapeutic value of such combination awaits further investigations.

Synthetic lethality to overcome cancer drug resistance

A large body of evidence point out that the onset of synthetic lethality may provide a useful tool for amplifying the efficacy of drugs in anticancer regimens, to uncover interdependence between genes and to identify predictive factors that would be extremely useful to guide in the selection of more effective targeted drugs and drug combinations for each patient. Here, we provide an overview on the exploitation of synthetic lethality to overcome drug resistance to conventional chemotherapy in several types of solid tumors. We report recent findings on cellular markers and gene mutations which are specifically essential for the viability of cancer cells and for resistance to chemotherapeutics. In addition, new molecularly targeted strategies to overcome drug resistance are suggested.