Endocrine Abstracts

Background: Mitotane (o,p’DDD) is the reference therapy for adrenocortical carcinoma (ACC) and should undergo metabolization in o,p’DDE and o,p’DDA to exert its anti-proliferative activity. We have previously shown that there is a link between RRM1 gene expression and o,p’DDD activity in an adjuvant setting. Aim of this study was to assess whether RRM1 gene expression is correlated to the bioavailability and cytotoxic activity of o,p’DDD and its metabolites in ACC cell lines.

Methods: The ACC cell lines SW-13 and H295R were incubated with o,p’DDD, o,p’DDE, o,p’DDA at therapeutic concentrations, and cell viability (evaluated using the WST-1 method) was correlated with RRM1 gene expression (evaluated using real time-PCR). The intracellular concentrations of o,p’DDD and o,p’DDE were evaluated in cells lysates using HPLC-UV method in both cell lines.

Results: In H295R cells, o,p’DDD, o,p’DDE and o,p’DDA showed a similar cytotoxic effect (IC50 of 32 μM, <1 μM, 292 μM, respectively) and RRM1 gene expression was not influenced by any drug. In SW-13 cells, o,p’DDD and o,p’DDE were effective at high concentrations only (IC50 of 829 μM, 122 μM, respectively), while o,p’DDA showed a greater cytotoxic activity (IC50 292 μM). An up-modulation of RRM1 mRNA was induced by o,p’DDD and o,p’DDE, whose intracellular concentrations were lower in SW-13 than in H295R cells. The higher sensitivity of SW-13 cells to o,p’DDA was associated with the loss of up-modulation of RRM1 mRNA. Moreover, RRM1 gene silencing in SW13 cells increased the intracellular concentrations of o,p’DDD and o,p’DDE, and their cytotoxic activity as well.

Conclusions: The present data suggest that RRM1 gene expression may affect both pharmacokinetic and anti-neoplastic activity of o,p’DDD in SW-13 cells.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.