Proteomic approach to the identification of early phase biomarker for anticancer peptides targeting thefolate pathway

Many efforts to improve survival of patients affected by Ovarian Cancer (OC) have focused on more effective systemic therapies and on the search for new therapeutic targets. One of the molecular targets for OC is human Thymidylate Synthase (hTS), a homodimeric enzyme essential for DNA biosynthesis. In order to investigate the effects of hTS-interface-mimicking peptides at a cellular level, we started a study in which the cellular behavior of the peptides was investigated in combination with the proteomic differential analysis of the cytoplasmatic proteins of treated vs. untreated OC cells. The same experiment was performed with pemetrexed (PTX), a well known antifolate, for control purposes. The bioinformatic analysis of the effects of our peptide drug candidate indicates that deregulations can be mainly assigned to modulation of translational initiation, termination of RNA Pol-II transcription, transport, and protein catabolic events. Although apparently folate pathway members are not directly altered at a protein level, as the selection of ions to be sequenced is stochastic and biased towards abundant peptides, the bioinformatic analysis of peptide-modulated proteins suggested cellular investigations on the proteins of the folate-associated genes showing the largest number of dependencies to the species of the core set, which is required for the phosphorylation of several deoxyribonucleosides and nucleoside analogues. Comparison with the PTX-modulated proteins shows that some proteins of the proteasome complex and ribonucleoproteins are involved in both cases. These differences suggest that the two compounds may show a different mechanism of action which is in agreement with the hypothesized pharmacological model. Detailed cellular proteins profile based on the inferred roles of the identified proteins will further clarify the biological effects.