Inductively coupled plasma mass spectrometric analysis of the total amount of platinum in DNA extracts from peripheral blood mononuclear cells and tissue from patients treated with cisplatin.

We present a highly sensitive method for the determination of platinum (Pt) in DNA extracts of peripheral blood mononuclear cells (PBMCs) and tissue samples from patients treated with cisplatin. The method is based on the measurement of Pt by inductively coupled plasma mass spectrometry (ICP-MS) and allows quantification of Pt-DNA adducts in PBMCs isolated from 10 mL blood and 1 mg tissue. The lower limit of quantification is 0.75 pg Pt or 7.5 fg Pt µg(-1) DNA when using 100 µg DNA. The method proved to be accurate and precise. The results obtained using the ICP-MS method were in good agreement with results from the alternative (32)P-postlabelling assay. The ICP-MS method was, however, more sensitive and proved to be less laborious. The advantages of the presented ICP-MS technique were demonstrated by the analysis of PBMCs, normal gastric tissue, and gastric tumour tissue of patients treated with cisplatin.

Cisplatin-DNA adduct formation in patients treated with cisplatin-based chemoradiation: lack of correlation between normal tissues and primary tumor.

PURPOSE: In this study, the formation of cisplatin-DNA adducts after concurrent cisplatin-radiation and the relationship between adduct-formation in primary tumor tissue and normal tissue were investigated. METHODS: Three intravenous cisplatin-regimens, given concurrently with radiation, were studied: daily low-dose (6 mg/m(2)) cisplatin, weekly 40 mg/m(2), three-weekly 100 mg/m(2). A (32)P-postlabeling technique was used to quantify adducts in normal tissue [white blood cells (WBC) and buccal cells] and tumor. RESULTS: Normal tissue samples for adduct determination were obtained from 63 patients and tumor biopsies from 23 of these patients. Linear relationships and high correlations were observed between the levels of two guanosine- and adenosine-guanosine-adducts in normal and tumor tissue. Adduct levels in tumors were two to five times higher than those in WBC (P<0.001). No significant correlations were found between adduct levels in normal tissues and primary tumor biopsies, nor between WBC and buccal cells. CONCLUSIONS: In concurrent chemoradiotherapy schedules, cisplatin adduct levels in tumors were significantly higher than in normal tissues (WBC). No evidence of a correlation was found between adduct levels in normal tissues and primary tumor biopsies. This lack of correlation may, to some extent, explain the inconsistencies in the literature regarding whether or not cisplatin-DNA adducts can be used as a predictive test in anticancer platinum therapy.

Phase I and pharmacological study of the farnesyltransferase inhibitor tipifarnib (Zarnestra, R115777) in combination with gemcitabine and cisplatin in patients with advanced solid tumours.

This phase I trial was designed to determine the safety and maximum tolerated dose (MTD) of tipifarnib in combination with gemcitabine and cisplatin in patients with advanced solid tumours. Furthermore, the pharmacokinetics of each of these agents was evaluated. Patients were treated with tipifarnib b.i.d. on days 1-7 of each 21-day cycle. In addition, gemcitabine was given as a 30-min i.v. infusion on days 1 and 8 and cisplatin as a 3-h i.v. infusion on day 1. An interpatient dose-escalation scheme was used. Pharmacokinetics was determined in plasma and white blood cells. In total, 31 patients were included at five dose levels. Dose-limiting toxicities (DLTs) consisted of thrombocytopenia grade 4, neutropenia grade 4, febrile neutropenia grade 4, electrolyte imbalance grade 3, fatigue grade 3 and decreased hearing grade 2. The MTD was tipifarnib 200 mg b.i.d., gemcitabine 1000 mg m(-2) and cisplatin 75 mg m(-2). Eight patients had a confirmed partial response and 12 patients stable disease. No clinically relevant pharmacokinetic interactions were observed. Tipifarnib can be administered safely at 200 mg b.i.d. in combination with gemcitabine 1000 mg m(-2) and cisplatin 75 mg m(-2). This combination showed evidence of antitumour activity and warrants further evaluation in a phase II setting.

In vitro pharmacokinetic study of the novel anticancer agent E7070: red blood cell and plasma protein binding in human blood.

E7070 is a novel sulfonamide anticancer agent that arrests the G(1)/S phase of the cell cycle. Preclinical and phase I studies have demonstrated non-linear pharmacokinetics (PK) of the drug. A population PK analysis revealed that the human plasma concentration-time data were best described by a three-compartment model with non-linear distribution. We have studied the in vitro interaction of 14C-radiolabeled E7070 with red blood cells (RBC) and its binding to plasma proteins in the concentration range where non-linearity in disposition was observed in humans to get more insight into the behavior of the drug. After the addition of E7070 to whole blood at 37 degrees C, the drug is taken up or binds to RBC in a concentration-dependent manner. The addition of sodium azide, however, did not result in a decrease of drug uptake by RBC, indicating passive diffusion processes. A non-linear increase in drug uptake was observed at incubation concentrations above 4 microg/ml E7070 in whole blood. This non-linearity was confirmed by lower partition coefficients between RBC and plasma at higher incubation concentrations (from 2.37 at 4 microg/ml to 0.31 at 200 microg/ml). The plasma protein binding of E7070 was high (98-99%) and linear in the concentration range studied (20-200 microg/ml). In conclusion, E7070 in whole blood is preferentially bound to RBC and exhibits high plasma protein binding. The non-linear distribution of E7070 in humans can be caused, in part at least, by saturable binding of E7070 to RBC.

Circumvention of breast cancer resistance protein (BCRP)-mediated resistance to camptothecins in vitro using non-substrate drugs or the BCRP inhibitor GF120918.

This study was aimed at characterizing the role of BCRP/MXR/ABCP (BCRP) in resistance of the human ovarian tumor cell lines T8 and MX3 to camptothecins more extensively and investigating whether resistance can be reversed by inhibiting BCRP by GF120918. Camptothecins studied were topotecan, CPT-11, and its active metabolite SN-38, 9-aminocamptothecin, and the novel experimental camptothecins NX211, DX8951f, and BNP1350. Notably, DX8951f and BNP1350 appeared to be very poor substrates for BCRP, with much lower resistance factors observed both in T8 and MX3 cells than observed for the other camptothecins tested. In the presence of a nontoxic dose level of GF120918, the intracellular accumulation of topotecan in the T8 and MX3 cells was completely restored to the intracellular levels observed in the sensitive IGROV1 parental cell line. This resulted in almost complete reversal of drug resistance to topotecan and to most of the other topoisomerase I drugs tested in the T8 cell line and to complete reversal in the MX3 cells. However, coincubation of DX8951f or BNP1350 with GF120918 did not affect the cytotoxicity of either of these drugs significantly. From the combined data, we conclude that the affinities of topoisomerase I drugs for BCRP are, in decreasing order: SN-38 > topotecan > 9-aminocamptothecin approximately CPT-11 > NX211 > DX8951f > BNP1350. Furthermore, GF120918 appears to be a potent reversal agent of BCRP-mediated resistance to camptothecins, with almost complete reversal noted at 100 nM. Potential BCRP-mediated resistance to topoisomerase I inhibitors can also be avoided by using the BCRP-insensitive drugs DX8951f or BNP1350. This observation may have important clinical implications for future development of novel camptothecins.

32P-postlabeling assay for the quantification of the major platinum-DNA adducts.

To allow more sensitive, selective, and routine analyses of platinum(Pt)-GG and -AG intrastrand cross-links we have significantly improved our quantitative (32)P-postlabeling assay (M. J. P. Welters et al. Carcinogenesis 18, 1767-1774, 1997). Instead of off-line scintillation counting we introduced an on-line flow radioisotope detector into the HPLC system. Furthermore, the isolation protocol for the adducts was significantly modified and optimized to reduce interfering background peaks that prevented quantification of low levels of the cisplatin-DNA adducts in white blood cells obtained from patients. Reduction of background signals was obtained by boiling the samples, followed by phenol/chloroform/isoamylethanol extraction after the DNA digestion step. The labeling efficiency for the adducts was increased by 40% by using Na-formate instead of NH(4)-formate for elution of the adducts from the strong cation-exchange columns. Finally, a calibration curve and quality controls were implemented. The labeling efficiencies were not different between the dinucleotides. The between- and within-run precision for the Pt-GG and Pt-AG adducts measured at the lower limit of quantification of 87 and 53 amol/microg DNA, respectively, was less than 20% CV. The adducts were stable in DNA stored for a 2-month time period at -80 degrees C. The assay is now routinely used for high-precision analyses of patient and cell line samples containing very low adduct levels.

Overexpression of the BCRP/MXR/ABCP gene in a topotecan-selected ovarian tumor cell line.

Topotecan- or mitoxantrone-selected cell lines (T8 and MX3, respectively), derived from the human IGROV1 ovarian cancer cell line, were resistant to the topoisomerase I inhibitors topotecan, SN-38 (the active metabolite of irinotecan), and 9-aminocamptothecin, as well as to the topoisomerase II drug mitoxantrone. In both resistant cell lines, decreased accumulation of topotecan and mitoxantrone was observed, caused by enhanced energy-dependent efflux of the drugs involved. In both cell lines, we found that the breast cancer resistance protein/mitoxantrone resistance/placenta-specific ATP binding cassette (BCRP/MXR/ABCP) gene was overexpressed. Furthermore, BCRP/MXR/ABCP expression levels in various partially revertant T8 cells correlated with the levels of resistance to topotecan, SN-38, and mitoxantrone, strongly suggesting BCRP/MXR/ABCP to be the transporter responsible for the enhanced efflux. Pharmacodynamic analysis demonstrated that BCRP/MXR/ABCP is a very efficient transporter of topotecan; in vitro, 70% of the intracellular topotecan pool was transported out of the T8 or MX3 cells within 30 s. In conclusion, we report for the first time that BCRP/MXR/ABCP can also be up-regulated upon exposure of tumor cells to the clinically important drug topotecan, and that BCRP-mediated efflux of topotecan is very efficient. This highly efficient efflux of topotecan by BCRP/MXR/ABCP may have clinical relevance for patients being treated with topotecan.

In vitro antagonistic cytotoxic interactions between platinum drugs and taxanes on bone marrow progenitor cell CFU-GM.

We have designed and used an in vitro bone marrow cell culturing system for investigating pharmacodynamic interactions between platinum anti-cancer drugs and taxanes. With this system, in which the bone marrow progenitor cell CFU-GM is proliferating and differentiating into granulocytes and monocytes, we could show a strong antagonistic cytotoxicity of the combination carboplatin and Taxotere, in three different schedules, and of the combination cisplatin and Taxol, in two out of the three schedules tested. Modulation of intracellular platinum drug accumulation in granulocytes and monocytes does not seem to be a plausible explanation for the observed antagonism. In vitro co-incubation of granulocytes/monocytes with the combination carboplatin and Taxotere did not reveal an effect of Taxotere on intracellular platinum accumulation. Although Taxol reduced intracellular cisplatin levels by 12%, this effect was not significantly different from the co-incubation of cisplatin with Cremophor EL, the solvent for paclitaxel in Taxol. The toxicity data obtained in this study seem to be in accordance with recent clinical trials where combination therapies with platinum drugs and taxanes resulted in marked reductions in myelosuppression in patients. Therefore, these types of assays could be useful as to the assessment of bone marrow toxicities of clinically important drug combinations.

Catabolite inactivation of wild-type and mutant maltose transport proteins in Saccharomyces cerevisiae.

The maltose transporter of Saccharomyces cerevisiae is subject to rapid, irreversible inactivation in the presence of glucose. Loss of transport function was paralleled by a decrease in amount of transporter protein and most likely involves endocytosis and degradation of the protein in the vacuole. This (catabolite) inactivation of Mal61p was triggered not only by glucose but also by 2-deoxy-D-glucose, which cannot be metabolized beyond 2-deoxy-D-glucose phosphate. The signal that targets membrane proteins specifically for catabolite inactivation is unknown. To investigate whether or not specific modification of Mal61p triggers the inactivation, putative protein kinase A and C phosphorylation sites were removed, and the transport activities and levels of the mutant proteins upon addition of glucose were followed in time. Three Mal61p mutants, i.e. S295A, T363A, and S487A, exhibited significantly reduced rates of inactivation in the presence of glucose. Likewise, in wild-type Mal61p the rate of inactivation and degradation of the protein paralleled each other in the case of T363A. On the contrary, for the S295A and S487A mutants the rates of protein degradation were slowed down more profoundly than was the loss of transport activity. These observations indicate that (i) some form of modification (e.g. phosphorylation) of the protein precedes breakdown, (ii) the modification inactivates Mal61p, and (iii) the inactivation of Mal61p is not necessarily followed by proteolytic degradation.

The N-terminus of amine oxidase of Hansenula polymorpha contains a peroxisomal targeting signal.

Here we describe the identification of the targeting sequence of peroxisomal amine oxidase (AMO) of H. polymorpha. Deletion analysis revealed that essential targeting information is located within the extreme N-terminal 16 amino acids. Moreover, this sequence can direct a reporter protein to the peroxisomal matrix of H. polymorpha. The N-terminal 16 amino acids of AMO contain a sequence with strong homology to the conserved PTS2 sequence. Therefore, AMO is considered to be a PTS2 protein.