Are MTT assays the right tool to analyze drug resistance caused by ABC-transporters in patient samples?

Drug resistance can be caused by ATP-binding-cassette (ABC)-transporters which function as outward pumps for chemotherapeutic drugs. The aim of the present study was to analyze the association between eight ABC-transporters (BCRP, MDR1, SMRP, MRP1, MRP2, MRP3, MRP4, and MRP5) and in vitro drug resistance. Leukemic cells from 52 children with previously untreated acute leukemia (ALL: n=37; AML: n=15) were analysed. The expression of the ABC-transporters was measured by TaqMan real-time PCR. In vitro drug resistance to cytarabine, vincristine, tioguanine, daunorubicin, etoposide, dexamethasone, and prednisone was analysed with methyl-thiazol-tetrazolium (MTT) assays.MDR1 was weakly associated with resistance to vincristine (p<0.05) in AML samples. No other correlation between an ABC-transporter and a higher in vitro drug resistance was found. In vitro drug resistance was not associated with the simultaneous expression of a larger number of ABC-transporters.MTT assays are a widely used and validated method to analyse in vitro drug resistance but they may not be a useful tool to detect resistance which is caused by drug efflux in patient samples. If that is the case, MTT assays and the expression of ABC-transporters could provide complementary information on the drug resistance profile of patients with acute leukemia.

[Procalcitonin as marker of systemic inflammatory reaction after isolated extremity perfusion]

The systemic side effects of isolated limb perfusion (ILP) with rhTNF alpha and melphalan are characterised by the induction of a systemic inflammatory response syndrome (SIRS). Procalcitonin (PCT), a serum marker of bacterial sepsis, was investigated with respect to its role in SIRS after TNF-ILP. Serum-PCT was analysed in 24 patients (12 male, 12 female), who treated by ILP for regionally metastasized melanoma (n = 8) or locally advanced soft tissue sarcoma (n = 16). Serum samples were analysed pre- and intraoperatively, and at defined intervals after reperfusion of the limb. In addition to PCT, serum IL-6 and IL-8 were analysed in 11 patients. PCT was significantly elevated over baseline after ILP with a maximum between 8 and 36 hours (p < 0.001). Even 96 hours after reperfusion, PCT was still significantly elevated as compared to baseline levels (p = 0.005). There was no correlation to the systemic leakage rate during the perfusion. IL-6 and IL-8 were also significantly increased after ILP (p = 0.001), but the maximum peaks of both cytokines were reached much earlier than for PCT (IL-8 max. at 1 hour and IL-6 max. at 4 hours after reperfusion). Serum procalcitonin is induced as part of the specific SIRS after ILP with rhTNF alpha and melphalan. It may be induced directly by rhTNF alpha or by different cytokines, as serum peaks of IL-6 and IL-8 are reached well before the peak of PCT. Determination of PCT prior to and after ILP with TNF might be useful to assess patients at risk of developing hyperdynamic shock.