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E Boven

Publications and source records attributed to E Boven.

At least 37 records · Page 2Linked to original sources
PubMed2000

New highly lipophilic camptothecin BNP1350 is an effective drug in experimental human cancer.

BNP1350, 7-[(2-trimethylsilyl)ethyl]-20(S)-camptothecin, is a novel semi-synthetic, highly lipophilic, silicon-containing camptothecin and an inhibitor of topoisomerase I. It has been supercomputer engineered for superior oral bioavailability, superior lactone stability, broad anti-tumor activity, increased potency and insensitivity to Pgp/MRP/LRP drug resistance. We determined the efficacy of BNP1350 in experimental human colon cancer and compared its anti-tumor effects with those of CPT-11/SN-38. We also determined a possible influence of Pgp, MRP and LRP on the efficacy of BNP1350. The in vitro anti-proliferative capacity of the compounds using various exposure times was assessed in five colon cancer cell lines and indicated that BNP1350 was similarly effective or slightly more potent than SN-38. Four cell lines of other origin with sublines expressing Pgp, MRP and/or LRP showed that BNP1350 was significantly more effective than SN-38 (p < 0.05) and that the activity of BNP1350 was not reduced in multidrug-resistant cells. For in vivo experiments, BNP1350 was given 1.0 mg/kg i.p. or 1.5 mg/kg p.o. daily x 5 and CPT-11 20 mg/kg i.p. daily x 5 being equitoxic schedules in nude mice bearing s.c. human tumor xenografts. The schedules were studied in colon cancer xenografts COLO320, COLO205 or WiDr as well as in two Pgp-positive xenografts 2780AD and BRO/mdr1.1 and the parental Pgp-negative A2780 ovarian cancer xenografts and BRO melanoma xenografts. Growth inhibition of >50% was obtained for BNP1350 given i.p. in six out of the seven xenografts studied. BNP1350 was similarly effective when given i.p. or p.o. CPT-11 was as effective as BNP1350, except in BRO and BRO/mdr1.1 xenografts. Pgp expression in xenografts in vivo confirmed that there was no negative influence on the efficacy of BNP1350. In conclusion, BNP1350 shows a broad spectrum of activity in experimental human tumors and is a suitable candidate for oral treatment of cancer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Development of a panel of 15 human ovarian cancer xenografts for drug screening and determination of the role of the glutathione detoxification system.

OBJECTIVES: We have established a panel of 15 human ovarian cancer xenografts grown subcutaneously in the flank of the nude mouse. Similar to the clinic, the xenografts show differences in histological subtype and volume doubling time. We determined whether the panel is useful for drug screening by testing the sensitivity to six conventional anticancer agents. In addition, we investigated whether the glutathione detoxification system affects sensitivity to cisplatin and cyclophosphamide, major drugs in the treatment of ovarian cancer. METHODS: Mice bearing well-established tumors were treated at maximum tolerated doses as defined by a reversible weight loss up to 15% of their initial weight: cisplatin 5 mg/kg iv weekly x2, cyclophosphamide 150 mg/kg ip 2-weekly x2, doxorubicin 8 mg/kg iv weekly x2, hexamethylmelamine ip 150 mg/kg every other day x4, methotrexate ip 150 mg/kg weekly x2, and 5-fluorouracil 60 mg/kg ip weekly x4. Glutathione levels and the activities of three different glutathione-dependent enzymes were measured in untreated xenograft tissues. RESULTS: Growth inhibition >75% was reached for cisplatin in 40%, for cyclophosphamide in 27%, and for doxorubicin in 20% of the xenografts. Methotrexate and 5-fluorouracil did not induce growth inhibition of importance. Hexamethylmelamine showed >75% growth inhibition in 53% of the xenografts, which may have been caused by the favorable metabolism of the drug in mice when compared with that in patients. Glutathione levels varied 3.6-fold in the xenografts and did not show a relation with sensitivity to cisplatin, cyclophosphamide, or doxorubicin. No relation was found between the activities of glutathione S-transferase and glutathione peroxidase and the sensitivities to the three anticancer agents. Glutathione reductase activity, however, showed a weak, inverse relation with the efficacy of cisplatin and cyclophosphamide (r values of -0.55 and -0.58, respectively). CONCLUSIONS: The sensitivity to the six anticancer agents of our panel of 15 human ovarian cancer xenografts reflects the response rates known for similar drugs in ovarian cancer patients. In that respect, the panel may be useful for drug screening as well as studies on the relevance of drug resistance features in vivo. The various components of the glutathione detoxification system did not predict for primary drug resistance which confirms clinical data in ovarian cancer.

Animals↗
PubMed2000

Drug resistance features and S-phase fraction as possible determinants for drug response in a panel of human ovarian cancer xenografts.

Multidrug resistance (MDR) and more specifically the expression of P-glycoprotein (Pgp) have been studied extensively in vitro. Unfortunately, it appears that the predictive value of MDR recognized in vitro is mostly an incorrect measure to determine the responsiveness of a particular tumour in the clinic. This misunderstood or overvalued role of MDR might explain the failure of strategies to reverse Pgp function by the use of modulators in solid tumours. To obtain more insight in in vivo drug resistance we investigated a panel of 15 human ovarian cancer xenografts consisting of the most common histological subtypes known in ovarian cancer patients. The response rate to cisplatin, cyclophosphamide and doxorubicin in the xenografts resembled the results of phase II trials with these agents in ovarian cancer patients. This resemblance justifies drug resistance studies in this experimental in vivo human tumour system. We determined the expression levels of MDR 1, MRP 1, LRP and topoisomerase IIalpha mRNA by the RNase protection assay and the presence of MRP1 and LRP proteins by immunohistochemistry. The S-phase fraction was investigated as a separate parameter by flow cytometry. In none of the 15 ovarian cancer xenografts was MDR 1 expression detectable. The expression levels of MRP 1 and LRP were low to moderate and resembled the presence of the MRP1 and LRP proteins. There was a weak, inverse relationship between the expression levels of LRP and sensitivity to cisplatin and cyclophosphamide (r = -0.44 and -0.45), but not to doxorubicin. The levels of topoisomerase IIalpha varied among the xenografts (0.73-2.66) and failed to correlate with doxorubicin resistance (r = 0.14). The S-phase fraction, however, showed a relation with the sensitivity to cisplatin (r = 0.66). Among the determinants studied in ovarian cancer in vivo, LRP mRNA and the S-phase fraction were the best predictive factors for drug response and most specifically for the activity of cisplatin.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Mitochondrial and microsomal peripheral benzodiazepine receptors in human ovarian cancer xenografts.

To investigate whether the density of peripheral benzodiazepine receptors (PBR) in human ovarian tumors is related to the degree of histological differentiation and possibly elucidate their pathophysiology, PBR were measured in mitochondrial (m) and microsomal (p) fractions isolated from six different human ovarian carcinomas heterotransplanted into nude mice. A specific ligand PK11195 for PBR was employed and the density of binding sites and binding affinity (KD) were computed from Scatchard analysis. The PBR density in m-fractions was 3- to 4-fold higher than in p-fractions from all tumors. PBR density in both m- and p-fractions was highest in mucinous tumors with mid-high degree of differentiation. The density in serous tumor with mid-high differentiation was significantly lower than the mucinous tumor, but higher than the serous tumor with low degree of differentiation (OVCAR-3) in both m- and p-fractions. However, the PBR density in the undifferentiated tumor (IGROV1) was higher than in OVCAR-3. The KD values for PBR were very low ranging from 5.8 to 14.0 nM in all preparations. The KD values for p-fractions were generally lower than m-fractions and highly significant differences were observed in three of the six tumors. These data suggest two separate classes of PBR pertaining to m- and p-fractions and indicate that there is no clear relationship between PBR density and degree of differentiation.

Animals↗
PubMed1999

Distribution and pharmacokinetics of the prodrug daunorubicin-GA3 in nude mice bearing human ovarian cancer xenografts.

N-[4-daunorubicin-N-carbonyl (oxymethyl)phenyl] O-beta-glucuronyl carbamate (DNR-GA3) is a glucuronide prodrug of daunorubicin (DNR) which induced a better tumor growth delay than DNR when studied at equitoxic doses in three human ovarian cancer xenografts. These results suggested that the prodrug DNR-GA3 was selectively activated by human beta-glucuronidase present in tumor tissue. We determined the pharmacokinetics and distribution of DNR-GA3 in nude mice bearing human ovarian cancer xenografts (OVCAR-3, FMa, A2780, and MRI-H-207). Administration of DNR at 10 mg/kg i.v. (maximum tolerated dose) to OVCAR-3-bearing mice resulted in a peak plasma concentration of the drug of 12.18 microM (t = 1 min). DNR-GA3 at 100 mg/kg i.v. (approximately 50% of the maximum tolerated dose [MTD]) resulted in a peak plasma concentration of DNR that was 28-fold lower than that after DNR itself; in normal tissues, prodrug injection resulted in 5- to 23-fold lower DNR concentrations. DNR showed a relatively poor uptake into OVCAR-3 tumors with a peak concentration of 2.05 nmol x g(-1) after injection. In the same xenograft, DNR-GA3 resulted in a significantly higher DNR peak concentration of 3.45 nmol x g(-1) (P < 0.05). The higher area under the curve of DNR in tumor tissue after DNR-GA3 than after DNR itself would be the result of prodrug activation by beta-glucuronidase. In this respect, a considerably higher beta-glucuronidase activity was found in tumor tissue when compared to plasma. The specific activation of DNR-GA3 by beta-glucuronidase at the tumor site relative to normal organs leads to a more tumor-selective therapy, resulting in greater efficacy without increased toxicity.

Animals↗
PubMed1999

The influence of P170-glycoprotein modulators on the efficacy and the distribution of vincristine as well as on MDR1 expression in BRO/mdr1.1 human melanoma xenografts.

Multidrug resistance modulators may increase the antitumour efficacy of drugs affected by P170-glycoprotein (Pgp) in Pgp-positive tumours in vivo. Inhibition of Pgp function in normal tissues, however, may enhance side-effects. Dexniguldipine-HCl, its analogues B9203-009 and B9303-036, and the dipyridamole derivative BIBW22BS could reverse vincristine (VCR) resistance in BRO/mdr1.1 cells (transfected with full-length MDR1 cDNA) and 2780AD cells (selected for doxorubicin resistance) in vitro. VCR resistance in BRO/mdr1.1 xenografts grown subcutaneously (s.c.) in the nude mouse was not or only slightly affected by the Pgp modulators. VCR concentrations in normal mouse tissues increased with the dose of the Pgp modulator administered and this was most pronounced in liver, kidney, small gut and colon. Dexniguldipine 40 mg/kg intraperitoneally (i.p.) given once 4 h before VCR 1 mg/kg intravenously (i.v.) resulted in increased VCR concentrations in BRO/mdr1.1 xenograft tissue. Surprisingly, when dexniguldipine 40 mg/kg i.p. was administered daily x3 before VCR, tumour VCR concentrations were not affected. This phenomenon was not observed in normal mouse tissues. Upregulation of MDR1 mRNA to 2.7- to 3.8-fold higher levels than control mRNA in BRO/mdr1.1 xenograft tissue occurred after VCR or dexniguldipine at 4-8 h and up to 1.7-fold at 24-28 h after injection. The combination showed 3.6- to 3.7-fold increased levels at 4 h after VCR injection. The lower VCR concentrations measured in BRO/mdr1.1 xenograft tissue after pretreatment with dexniguldipine for 3 days relative to animals treated with dexniguldipine only once will likely be caused by a gradual increase of Pgp expression as a response to the upregulation of MDR1.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Novel anthracycline-spacer-beta-glucuronide,-beta-glucoside, and -beta-galactoside prodrugs for application in selective chemotherapy.

A series of anthracycline prodrugs containing an immolative spacer was synthesized for application in selective chemotherapy. The prodrugs having the general structure anthracycline-spacer-beta-glycoside were designed to be activated by beta-glucuronidase or beta-galactosidase. Prodrugs with -chloro, -bromo or -n-hexyl substituents on the spacer were synthesized as well as prodrugs containing a -beta-glucuronyl, -beta-glucosyl or -beta-galactosyl carbamate specifier. The key step in the synthesis of all prodrugs is the highly beta-diastereoselective addition reaction of the anomeric hydroxyl of a glycosyl donor to a spacer isocyanate resulting in the respective beta-glycosyl carbamate pro-moieties. The resulting protected pro-moieties were coupled to an anthracycline. Prodrugs were evaluated with respect to activation rate by the appropriate enzyme and additionally, their IC50 values were determined. Optimal prodrugs in this study were at least 100- to 200-fold less toxic than their corresponding drug in vitro and were activated to the parent drug in a half-life time of approximately 2 h.

Antibiotics, Antineoplastic↗
PubMed1999

Prolonged neoadjuvant chemotherapy with GM-CSF in locally advanced breast cancer.

BACKGROUND: Neoadjuvant chemotherapy improves survival in patients with locally advanced breast cancer (LABC). Usually three to four cycles of conventional-dose neoadjuvant chemotherapy are administered prior to local therapy, and another three cycles thereafter. In an attempt to improve results, we increased the dosages and applied GM-CSF, which, besides being a hematopoietic growth factor, has become increasingly known for its immunostimulatory effects, which might enhance the antitumor effect. METHODS: Forty-two patients with stage IIIA or IIIB breast cancer were treated with doxorubicin (A) (90 mg/m2) and cyclophosphamide (C) (1,000 mg/m2) at three-weekly intervals. In the second and fourth cycle a 10% dose reduction of both agents was applied. On the second day GM-CSF 250 micrograms/m2/day was started and given for 10 days. Initially, some patients were treated with < or = four cycles, but as the study progressed and toxicity appeared tolerable, six cycles were given whenever possible. After the chemotherapy, patients underwent surgery and postoperative radiotherapy. RESULTS: The response rate for the whole group to AC was 98% (95% confidence interval 94%-100%), with a clinical complete response rate of 50% (95% confidence interval 35%-65%). Six patients had a pathological complete response. Median follow-up from the start of chemotherapy is 49 months (range 10-100). The disease-free survival (DFS) at three years is 57% and the overall survival (OS) at three years is 79%. There is a significant trend for improved DFS (p = 0.0000) and OS (p = 0.0002) with increasing number of cycles. CONCLUSION: The results of the present study with neoadjuvant dose-intensive AC chemotherapy and GM-CSF compare favorably with previous studies in patients with LABC. This is most apparent in patients who received six cycles of neoadjuvant chemotherapy. We hypothesize that these encouraging results are probably related to the prolonged presence of the primary tumor, and to the long-term administration of GM-CSF with the primary tumor and axillary lymph nodes in situ. Therefore, a randomized study is warranted. We already initiated an international randomized trial in patients with LABC in order to answer two questions. First, does prolonged neoadjuvant chemotherapy result in an improved DFS and OS in comparison with the conventional approach, and secondly, what is the effect of GM-CSF in this approach in comparison with G-CSF?

Adult↗
PubMed1999

Pharmacokinetics and pharmacodynamics of lobaplatin (D-19466) in patients with advanced solid tumors, including patients with impaired renal of liver function.

The purpose of this study was to determine the influence of impaired renal and liver function on the pharmacokinetics and pharmacodynamics of lobaplatin in cancer patients. A total of 25 patients with advanced solid tumors not amenable for standard treatment entered the study. Patients had normal organ function or an impaired liver or renal function (two levels). The starting dose of lobaplatin was 50 mg/m2 i.v. given every 3 weeks. The blood and urine of all patients were sampled for the determination of (ultrafilterable) platinum, intact lobaplatin, creatinine, and blood cell counts. No objective responses were recorded. Five patients experienced no change and received 4-10 cycles (median, 6 cycles) of lobaplatin. The extent and duration of hematological toxicity were worse in patients with impaired renal function. Thrombocytopenia was most prominent; grade 4 toxicity was observed in 15 patients in the first two cycles of treatment. The concentration-time curves of ultrafilterable platinum and intact lobaplatin revealed almost identical patterns. The elimination of ultrafilterable platinum [final half-life (t1/2 final) = 131+/-15 min; clearance (Cl) = 125+/-14 ml/min/1.73 m2] was much faster than that of total platinum (t1/2 final = 6.8+/-4.3 days, CI = 34+/-11 ml/min/1.73 m2). No pharmacokinetic differences were observed between patients with normal organ function and those with an impaired liver function within the investigated range. An impaired renal function resulted in an increase of the t1/2 final due to a decrease of the total body Cl that resulted in a higher exposure of the body to the drug. The calculated creatinine Cl was linearly correlated with the total body clearance of ultrafilterable platinum (r = 0.91), which resulted in the dosage formula D = AUCinfinity (1.1 Cl(CrU) + 16), in which D represents dose, AUC represents area concentration-time curve, and Cl(CrU) represents creatinine Cl. The thrombocyte surviving fraction correlated well with the AUC value of ultrafilterable platinum (r = 0.72). It can be concluded that the hematological toxicity and the pharmacokinetics of lobaplatin are strongly affected by renal function. The total body Cl of ultrafilterable platinum correlated well with the creatinine Cl and the thrombocyte surviving fraction. In patients with renal function, represented by a creatinine clearance > or =30 ml/min/1.73 m2, the derived dosage formula will enable us to calculate the dose that is expected to lead to an acceptable extent of thrombocytopenia in a patient with a given renal function. Prospective studies with larger groups of patients are needed to prove the value of this dosage formula.

Adult↗
PubMed1999

American Association for Cancer Research--90th annual meeting. 10-14 April 1999, Philadelphia, PA, USA.

A major focus of this year's American Association for Cancer Research (AACR) meeting was the microenvironment of the tumor and tumor angiogenesis, as well as the development of drugs that affect tumor growth by use of extratumoral targets. Other areas of interest were advances in chemoprevention, cancer vaccines, gene therapy approaches and drug-resistance features. As before, many novel compounds affecting tumor cells were introduced, either being analogs of standard cytostatic agents or directed against new cellular targets. Mechanisms of action were further unraveled and emphasis was put on the various signals within a tumor cell to enter cell death through apoptosis. Molecular biology technology was dedicated to the development of tests to measure gene expression in small tissue samples.

Journal Article↗
PubMed1999

American Society of Clinical Oncology--35th annual meeting. 15-18 May 1999, Atlanta, GA, USA.

A major focus of this year's meeting was the plenary session on the use of high-dose chemotherapy for the treatment of metastatic breast cancer and the incorporation of adjuvant treatment for poor prognosis primary breast cancer. Four abstracts on large randomized collaborative trials in the US, Scandinavian countries and South Africa were presented in this plenary session and discussed by Dr R Livingston (University of Washington, USA), Dr G Hortobagyi (University of Texas/MD Anderson Cancer Center, USA) and Dr K Antman (Columbia University, USA). In general, high-dose chemotherapy followed by (autologous bone marrow) stem cell support has not yet shown improvement in overall survival and has contributed to substantial side-effects when compared to standard chemotherapy in breast cancer. In most trials, however, follow-up was short and long-term analysis may change the current conclusions. Other issues of interest included early clinical trials on agents affecting angiogenesis, signal transduction inhibitors, gene therapy and cancer vaccines.

Journal Article↗
PubMed1998

Construction and characterization of a fusion protein of single-chain anti-CD20 antibody and human beta-glucuronidase for antibody-directed enzyme prodrug therapy.

The CD20 antigen is an attractive target for specific treatment of B-cell lymphoma. Antibody-directed enzyme prodrug therapy (ADEPT) aims at the specific activation of a nontoxic prodrug at the tumor site by an enzyme targeted by a tumor-specific antibody such as anti-CD20. We constructed a fusion protein of the single-chain Fv anti-CD20 mouse monoclonal antibody (MoAb) 1H4 and human beta-glucuronidase for the activation of the nontoxic prodrug N-[4-doxorubicin-N-carbonyl(-oxymethyl) phenyl] O-beta-glucuronyl carbamate to doxorubicin at the tumor site. The cDNAs encoding the light- and heavy-chain variable regions of 1H4 were cloned, joined by a synthetic sequence encoding a 15-amino acid linker and fused to human beta-glucuronidase by a synthetic sequence encoding a 6-amino acid linker. An antibody-enzyme fusion protein-producing cell line was established by transfection of the construct into human embryonic kidney 293/EBNA cells. The yield of active fusion protein was 100 ng/mL transfectoma supernatant. Antibody affinity, antibody specificity, and enzyme activity were fully retained by the fusion protein. Immunoprecipitation and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the fusion protein has a relative molecular weight (Mw) of 100 kD under denaturing conditions. Gel filtration analysis indicated that the enzymatically active form of the fusion protein is a tetramer with an Mw of approximately 400 kD. The nontoxic prodrug N-[4-doxorubicin-N-carbonyl(-oxymethyl) phenyl] O-beta-glucuronyl carbamate was hydrolyzed by the fusion protein at a hydrolysis rate similar to that of human beta-glucuronidase. When the fusion protein was specifically bound to Daudi lymphoma cells, the prodrug induced similar antiproliferative effects as doxorubicin. Thus, it is feasible to construct a eukaryotic fusion protein consisting of a single-chain anti-CD20 antibody and human beta-glucuronidase for future use in the activation of anticancer prodrugs in B-cell lymphoma.

Amino Acid Sequence↗
PubMed1998

Construction and characterization of a fusion protein of single-chain anti-carcinoma antibody 323/A3 and human beta-glucuronidase.

We report the construction and expression of a fusion protein between a single-chain antibody specific for human carcinomas and human beta-glucuronidase by recombinant DNA technology. The sequences encoding the murine monoclonal antibody 323/A3 light- and heavy-chain variable genes were joined by a synthetic sequence encoding a 15-amino-acid linker and combined with human beta-glucuronidase by a synthetic sequence encoding a 6-amino-acid linker. The construct was placed under the control of the cytomegalovirus promotor and expressed in COS-7 cells. The yield of active fusion protein was 10 ng/ml transfectoma supernatant. Antibody affinity, antibody specificity and enzyme activity were fully retained by the fusion protein. Biochemical characterization of the fusion protein by sodium dodecyl sulfate/polyacrylamide gel electrophoresis showed a molecular mass of 100 kDa under denaturing conditions. Gel-filtration analysis indicated that the enzymatically active form is a tetramer of approximately 400 kDa. The non-toxic prodrug N-[4-doxorubicin-N-carbonyl(oxymethyl)phenyl]-O-beta-glucuronyl carbamate was activated to the cytotoxic drug doxorubicin by the fusion protein with a hydrolysis rate similar to that of human beta-glucuronidase. The growth inhibition of tumor cells coated with the fusion protein and exposed to prodrug was similar to that obtained with doxorubicin. This study shows the feasibility of constructing eukaryotic fusion proteins consisting of a single-chain antibody and human beta-glucuronidase for use in the specific activation of anticancer prodrugs.

Animals↗
PubMed1998

Pharmacokinetics of cisplatin with and without amifostine in tumour-bearing nude mice.

Amifostine (Ethyol, WR-2721) is in use in the clinic as a protector against platinum-induced toxicities. We have previously reported that amifostine induced a potentiation of the antitumour activity of carboplatin in human ovarian cancer xenografts. An influence of amifostine on the pharmacokinetics of carboplatin, resulting in higher platinum concentrations in plasma and tissues of the tumour-bearing nude mice, was thought to be the cause of enhancement of the antitumour activity. Therefore, the pharmacokinetics of cisplatin were investigated in tumour-bearing nude mice treated with cisplatin alone or in combination with amifostine. A significant increase in the area under the curve (AUC) of the total platinum concentration in mice treated with amifostine was only observed in the kidney (from 355 to 398 nmol h/g), whereas in the other tissues and plasma no significant changes were measured. The selective protection of normal tissues by amifostine was confirmed by a decrease in the AUC of the cisplatin-DNA adduct levels in normal tissues. The decrease was only significant in the liver (282-240 fmol h/microgram DNA), whereas in tumour tissue a slight increase in the AUC of the cisplatin-DNA adducts could be detected (91.3-110.1 fmol h/microgram DNA). The minor influence of amifostine on the pharmacokinetics of cisplatin may be the reason why amifostine did not potentiate the antitumour activity of cisplatin. The influence of amifostine on cisplatin-DNA adduct levels in normal tissues versus tumour tissues is further evidence for the usefulness of this toxicity modulator in cancer patients.

Amifostine↗
PubMed1998

[186Re]-labeled mouse and chimeric monoclonal antibody 323/A3: a comparison of the efficacy in experimental human ovarian cancer.

We have investigated whether [186Re]-labeled chimeric monoclonal antibody 323/A3 (MAb c-323/A3) is as effective as [186Re]-labeled mouse 323/A3 (m-323/A3) in the growth inhibition of human ovarian cancer xenografts OVCAR-3 and FMa. [186Re] was conjugated to MAbs with the use of the chelate S-benzoylmercaptoacetyltriglycine (S-benzoyl-MAG3). The maximum number of metal-MAG3 groups that could be conjugated to one MAb molecule accepting a minimal initial increase of the blood clearance (15%) was 8.5 and 2.9 for c-323/A3 and m-323/A3, respectively. With these molar ratios the immunoreactivity of both MAbs was maintained. An inverse relationship was observed between the protein dose of c-323/A3 and its blood clearance. Both [186Re]-c-323/A3 and [186Re]-m-323/A3 were comparable in the inhibition of the tumor growth when higher protein doses were used. Together with the expected lower immunogenicity, our results imply that c-323/A3 is preferable for use in [186Re]-radioimmunotherapy in ovarian cancer patients.

Animals↗
PubMed1998

Determinants of CPT-11 and SN-38 activities in human lung cancer cells.

Irinotecan (CPT-11) is a semisynthetic camptothecin derivative with a broad spectrum of anti-tumour activity. Carboxylesterase (CE) catalyses the conversion of CPT-11 to SN-38 (7-ethyl-10-hydroxycamptothecin), the active form of CPT-11. The antiproliferative effects of CPT-11 and SN-38, CE-activity and topoisomerase I protein expression were investigated in five human small-cell lung cancer (SCLC) cell lines and four human non-small-cell lung cancer (NSCLC) cell lines. Antiproliferative activity, expressed as IC50 values, was determined using the MTT assay. CPT-11 was significantly more active in SCLC than in NSCLC cell lines (P = 0.0036), whereas no significant difference between histological types was observed with SN-38. A significant correlation (r2 = 0.52, P = 0.028) was observed between CE activity and chemosensitivity to CPT-11 but not to SN-38, and significantly higher CE activity was observed in SCLC compared with NSCLC cell lines (P = 0.025). Western blotting experiments showed topoisomerase I protein expressions within a factor of 2, and a granular nuclear staining was detectable in all cell lines by immunocytochemistry of cytospins. No correlation was observed between protein expression and sensitivity to CPT-11 or SN-38. Cellular and medium concentrations of CPT-11 and SN-38 were measured by high-performance liquid chromatography (HPLC) in one SCLC cell line with high CE activity and high sensitivity to CPT-11, and one NSCLC cell line with low sensitivity to CPT-11 and CE activity. Intracellular concentrations of CPT-11 and SN-38 were higher in the SCLC cell line, and this was associated with an increase in cellular uptake of CPT-11 compared with the medium, and an increased intracellular formation of SN-38. In conclusion, CE activity appears to be associated with higher sensitivity to CPT-11 in human lung cancer cell lines and may partly explain the difference in the in vitro sensitivity to CPT-11 between SCLC and NSCLC cells. The assessment of CE activity in clinical material of lung cancer patients undergoing treatment with CPT-11 may be warranted. However, other mechanisms may influence sensitivity to CPT-11, possibly including drug transport.

Antineoplastic Agents, Phytogenic↗
PubMed1998

CPT-11 sensitivity in relation to the expression of P170-glycoprotein and multidrug resistance-associated protein.

The relevance of P170-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) for the sensitivity to CPT-11 was investigated in human malignant cell lines as well as in human tumour xenografts. In vitro, the P-gp-positive sublines BRO/mdr1.1 (transfected with MDR1) and 2780AD were slightly cross-resistant against carboxylesterase-activated CPT-11. Cross-resistance against SN-38 was present in 2780AD cells, but not in BRO/mdr1.1 cells. The P-gp modulators BIBW22BS, verapamil and dexniguldipine partly reversed the resistance against CPT-11 in the P-gp-positive sublines. BIBW22BS was the most effective modulator in the reversal of the resistance against carboxylesterase-activated CPT-11 as well as against SN-38 in the 2780AD subline. In contrast to doxorubicin and vincristine, the BRO/mdr1.1 xenografts were at least as sensitive to CPT-11 as the BRO xenografts. The 2780AD xenografts were slightly less sensitive than the parent tumours, but there was no difference in topoisomerase I DNA unwinding activity. Therefore, the high retention of the multidrug-resistant phenotype of 2780AD cells in vivo may be the cause of the low cross-resistance against CPT-11. The MRP-positive subline GLC4/ADR was cross-resistant against carboxylesterase-activated CPT-11 and SN-38. GLC4/ADR cells, however, demonstrated a twofold lower topoisomerase I activity than GLC4 cells. Cross-resistance against the camptothecin derivatives was not apparent in the MRP-transfected subline of SW1573/S1. In conclusion, P-gp-positive cells show a low cross-resistance against CPT-11/SN38, which is only apparent with high P-gp expression in vivo. MRP does not seem to play a role in the sensitivity to CPT-11.

ATP Binding Cassette Transporter, Subfamily B, Mem↗