Mechanisms for high methoxymorpholino doxorubicin cytotoxicity in doxorubicin-resistant tumor cell lines

Methoxymorpholino doxorubicin (MMRDX) is an anthracycline analogue that is able to overcome tumor cell resistance to classical anthracyclines. Mechanisms for increased MMRDX cytotoxicity were analyzed in a small cell lung carcinoma cell line (GLC(4)), its 300-fold doxorubicin-resistant and multidrug resistance-associated protein (MRP)-over-expressing subline (GLC(4)/ADR), an ovarian carcinoma cell line (A2780) and its 100-fold doxorubicin resistant and P-glycoprotein (P-gp)-over-expressing subline A2780AD. Cross-resistance, measured with the MTT assay at MMRDX concentration resulting in 50% growth inhibition, was 1.8-fold in GLC(4)/ADR and 4.5-fold in A2780AD compared to their respective parental cell lines. Cellular MM RDX accumulation was equal in GLC(4) and GLC(4)/ADR and 2-fold lower in A2780AD compared to A2780. Doxorubicin fluorescence was analyzed with confocal laser scan microscopy. Fluorescence was nuclear in sensitive, and cytoplasmic in resistant, cell lines, while MMRDX fluorescence was found in the nucleus in all cell lines. Pre-incubation with the MRP blocker MK571 restored in GLC(4)/ADR cells the nuclear doxorubicin fluorescence pattern, as observed in GLC(4) cells. MMRDX, thus, can largely overcome cross-resistance in these P-gp- and MRP-overexpressing doxorubicin-resistant cell lines. Our results suggest that MMRDX is not a substrate for MRP-mediated resistance. (C) 1997 Wiley-Liss, Inc

Method-dependent increase in lipoprotein(a) in insulin-dependent diabetes mellitus during pregnancy

The current prevalent view is that plasma lipoprotein(a) [Lp(a)] concentrations are under strong genetic control. Most dietary and drug interventions seem to have little or no effect on plasma Lp(a) levels. However, evidence for a possible regulatory role of hormones is accumulating, for instance, fluctuations of Lp(a) levels during pregnancy have been reported. Also, in insulin-dependent diabetes mellitus (IDDM) patients, elevated Lp(a) levels have been reported. In the present longitudinal study, plasma lipid concentrations, including Lp(a), were determined in IDDM women before pregnancy, during pregnancy, and 3 months postpartum. In our study population, Lp(a) concentration was not significantly correlated with either hemoglobin A(1c) (HbA(1c)) levels or apolipoprotein(a) [apo(a)] phenotype. Changes in other lipid parameters observed during pregnancy in our IDDM population were similar to those reported during normal pregnancy. Lp(a) concentrations were quantified using two different immunochemical methods that possess different sensitivities and specificities: an immunoradiometric assay (IRMA) using two different anti-apo(a) antibodies, and an enzyme-linked immunosorbent assay (ELISA) using an anti-apo(a) and an anti-apo B antibody. Median prepregnancy Lp(a) concentrations were 118 mg/L (range, 15 to 672) as determined with the IRMA and 107 mg/L (range, 21 to 451) as determined with the ELISA. Women with IDDM showed, in general, no significant change in Lp(a) concentration during pregnancy when it was assayed with the IRMA, although a tendency to increased values was observed. When Lp(a) concentrations were determined with the ELISA, a strong and significant increase in Lp(a) from weeks 17 to 24 of pregnancy onward was found. The latter results confirm the prevalent view that during pregnancy Lp(a) levels are increased. However, the present results and those of others on Lp(a) in normal pregnancy strongly emphasize the importance of method selection when determining Lp(a) concentrations. Copyright (C) 1995 by W.B. Saunders Compan