Quantitative analysis of protein expression for the evaluation of chemotherapy for colorectal carcinoma

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Anti-cancer agents are generally believed to affect particular parts of molecular networks, resulting in cell cycle arrest or apoptosis, but the molecular targets of most anti-cancer drugs in current use remain unclear. At the protein level, responses may vary depending on drug type, concentration, and mode of administration. To identify which molecular targets are crucial for responses to clinically used drugs, we developed a reverse-phase protein lysate microarray system (RPA) for measuring quantitative protein dynamics induced by drug exposure. For the preliminary experiment, three clinically used drugs, CDDP, 5-FU, and CPT-11, were administrated at four different concentrations and with two types of administration (sustained and tentative) to observe protein kinetics in a dose and time-dependent manner. Drug concentrations were at levels that would provide 0, 50, and 100% growth suppression, as determined by prior growth suppression assays. Among the proteins tested to date, p53, p … More 21, CyclinD3 showed a dose-dependent protein expression following 24h-sustained administration for each of these 3 drugs, whereas, in a time course experiment, p53 protein showed a higher expression in response to CDDP and 5-FU exposure in a time-dependent manner, and a fluctuating pattern in response to CPT-11. Tentative administration (3h) resulted in a similar pattern of fluctuation in p53 protein expression in response to 5-FU and CPT-11, whereas the p53 expression increased in extended period of time in response to CDDP. These results may suggest that protein signaling differs depending on the type of drug and its mode of administration, even if the same phenotypic consequences, such as growth suppression, are induced. We are currently performing a high-resolution dose escalation, as well as time-course studies, to monitor protein kinetics in detail, using RPAs. We believe that a combination of RPA and bioinformatics approaches will allow drug molecular targets to be reliably determined. Less