Search PubMed⌕ Search

Biomedical subjects

C Dumontet

Publications and source records attributed to C Dumontet.

At least 55 records · Page 3Linked to original sources
PubMed1999

Profiles and prognostic values of LDH isoenzymes in patients with non-Hodgkin's lymphoma.

Serum lactic dehydrogenase (LDH) is an important prognostic factor in patients with non-Hodgkin's lymphoma (NHL). We have examined the LDH isoenzyme content in serum and CSF of patients with NHL, at diagnosis and at relapse. In patients with increased serum LDH at diagnosis, the percentage of isoenzyme 2 was increased in 52% of patients and the absolute value of isoenzyme 3 was increased in 64% of patients. In relapsing patients these values were respectively 69% and 65%. Conversely in patients with increased serum LDH due to myeloid regeneration after chemotherapy, isoenzymes 4 and 5, but not isoenzymes 2 or 3, were increased. High absolute values of isoenzyme 3 were correlated with an altered performance status, advanced tumor stage, and aggressive histology whereas high isoenzyme 2 percentages were correlated with altered performance status only. Among patients with high total serum LDH, a high content of isoenzyme 2 and a high absolute value of isoenzyme 3 were correlated with high serum levels of TNFalpha and TNF receptor p75. Analysis of total LDH and LDH isoenzyme profiles in CSF did not reveal any correlation with meningeal involvement by lymphoma. High isoenzyme 2 percentages and high absolute values of isoenzyme 3 in serum were both significantly associated with a shorter freedom-from-progression and overall survival. Isoenzyme 3 remained a prognostic factor for survival even when considering only patients with high total serum LDH at diagnosis. We conclude that there are some characteristic serum LDH isoenzyme profiles in patients with NHL and that some of these specific alterations may help refine the prognostic value of total serum LDH.

Adolescent↗
PubMed1999

Common resistance mechanisms to deoxynucleoside analogues in variants of the human erythroleukaemic line K562.

Resistant variants of the human leukaemic line K562 were developed using selection with the deoxynucleoside analogues cytosine arabinoside, 2-chlorodeoxyadenosine, fludarabine and gemcitabine. The resistant lines displayed a high degree of cross resistance to all deoxynucleoside analogues, with little or no cross resistance to other agents. There was a profound accumulation defect of all nucleoside analogues in the resistant variants but no significant defect in nucleoside transport in any of the variants. 5' nucleotidase activity was strongly increased and deoxycytidine kinase activity was moderately reduced in all of the resistant variants, resulting in reduced accumulation of triphosphate analogues. In addition a deletion in one of the alleles of the deoxycytidine kinase was detected in the fludarabine-resistant line. Ribonucleotide reductase activity was found to be strongly increased in the gemcitabine-selected line and purine nucleoside phosphorylase was increased in the 2-chlorodeoxyadenosine-selected line. Free nucleotide pools were increased in the 2-chlorodeoxyadenosine-selected line. There was no expression of the mdr1 gene by the resistant lines. Karyotypic analysis and FISH experiments using a 6q21 specific probe showed alterations in the 6(q16-q22) region which contains the 5'-nucleotidase gene. Early events in the activation and degradation of deoxynucleoside analogues appear to constitute common mechanisms of resistance to these compounds.

Antineoplastic Agents↗
PubMed1999

Giant cell arteritis and polymyalgia rheumatica: are pregnancies a protective factor? A prospective, multicentre case-control study. GRACG (Groupe de Recherche sur l'Artérite à Cellules Géantes).

OBJECTIVE: To assess the potential role of allo-immunization, either by former pregnancies, or by a history of blood transfusion, in the pathogenesis of giant cell arteritis and polymyalgia rheumatica. METHODS: Two hundred and eighty-five incident female cases and 186 age-matched, population-based female controls were prospectively included in a multicentre case-control study. RESULTS: The number of pregnancies was significantly lower in cases than in controls (nulliparous: 21.55% vs 12.90%; > or =4 pregnancies: 16.25% vs 27.42%; Wilcoxon rank sum test: P = 0.0019) in biopsy-proven or negative temporal arteritis and, to a lesser extent, in polymyalgia rheumatica. No difference was found for history of blood transfusion. Pregnancies remained negatively associated with the disease in a multivariate analysis including cardiovascular risk factors such as smoking or a pre-existing peripheral vascular disease. CONCLUSION: Former pregnancies are not a risk factor for giant cell arteritis. Pregnancies may be protective thanks to an effect of the associated hyperoestrogenic state against alterations of the artery wall, as suggested in animal models.

Aged↗
PubMed1999

Biopsy proven and biopsy negative temporal arteritis: differences in clinical spectrum at the onset of the disease. Groupe de Recherche sur l'Artérite à Cellules Géantes.

OBJECTIVES: To assess the clinical features of biopsy proven and negative biopsy temporal arteritis at the time of diagnosis and during a three year follow up. METHODS: Newly diagnosed cases of giant cell arteritis were included in a prospective, multicentre study. Initial clinical and biological features, season of diagnosis, and cardiovascular events occurring during the follow up were recorded. Biopsy proven and negative biopsy cases were compared. RESULTS: Two hundred and seven biopsy proven, and 85 negative biopsy cases were included from 1991 to 1997. Fifty eight per cent of the biopsy proven cases, compared with 39.29% of the negative biopsy cases, were diagnosed during the autumn or winter (p = 0.003). Visual problems (31.5%, v 19.1%, p = 0.031), blindness (9.7% v 2.38%, p = 0.033), jaw claudication (40.8%, v 28.243%, p = 0.044), and temporal artery palpation abnormalities (61.3% v 29.5%, p = 7.10(-7)) were more frequent in the biopsy proven than in the negative biopsy group. Less specific symptoms, such as headache (82.5% v 92. 9%, p = 0.021), or associated polymyalgia rheumatica (40.1% v 65.9%, p = 9 x 10(-5)) were more prevalent in the negative biopsy cases. Biological markers of inflammation were significantly more increased in the biopsy proven group. All cases of blindness occurring after treatment belonged to the biopsy proven group. CONCLUSION: Biopsy proven cases seem to be more severe than biopsy negative cases at the time of diagnosis and during follow up. Seasonal difference at diagnosis may suggest a different aetiological pattern.

Aged↗
PubMed1999

Transient acute myopia induced by antilymphocyte globulins.

Acute onset of transient myopia may be induced by several drugs, different mechanisms having been described. We report the occurrence of such an event after intravenous administration of equine antilymphocyte globulins in a patient treated for aplastic anemia. Clinical ocular examination revealed no other abnormality, and ultrasonography disclosed no swelling of the ciliary body. The drug-induced myopia resolved completely after instillation of topical cyclopentolate, suggesting that its mechanism was the occurrence of a ciliary spasm. Acute myopia is a rare event and, to the authors' knowledge, this represents the first case described as being induced by antilymphocyte globulins.

Acute Disease↗
PubMed1999

Mechanisms of action of and resistance to antitubulin agents: microtubule dynamics, drug transport, and cell death.

PURPOSE: To analyze the available data concerning mechanisms of action of and mechanisms of resistance to the antitubulin agents, vinca alkaloids and taxanes, and more recently described compounds. DESIGN: We conducted a review of the literature on classic and recent antitubulin agents, focusing particularly on the relationships between antitubulin agents and their intracellular target, the soluble tubulin/microtubule complex. RESULTS AND CONCLUSION: Although it is widely accepted that antitubulin agents block cell division by inhibition of the mitotic spindle, the mechanism of action of antitubulin agents on microtubules remains to be determined. The classic approach is that vinca alkaloids depolymerize microtubules, thereby increasing the soluble tubulin pool, whereas taxanes stabilize microtubules and increase the microtubular mass. More recent data suggest that both classes of agents have a similar mechanism of action, involving the inhibition of microtubule dynamics. These data suggest that vinca alkaloids and taxanes may act synergistically as antitumor agents and may be administered as combination chemotherapy in the clinic. However, enhanced myeloid and neurologic toxicity, as well as a strong dependence on the sequence of administration, presently exclude these combinations outside the context of clinical trials. Although the multidrug resistance phenotype mediated by Pgp appears to be an important mechanism of resistance to these agents, alterations of microtubule structure resulting in altered microtubule dynamics and/or altered binding of antitubulin agents may constitute a significant mechanism of drug resistance.

Amino Acid Sequence↗
PubMed1999

Giant cell arteritis, polymyalgia rheumatica, and viral hypotheses: a multicenter, prospective case-control study. Groupe de Recherche sur l'Artérite à Cellules Géantes.

OBJECTIVE: Although suspected, a viral etiology has never been proven in giant cell arteritis (GCA). We tested for viruses known to induce multinucleated giant cells in human pathology, which include the parainfluenza viruses (HPIV), respiratory syncytial virus, measles virus, herpesviruses type 1 and 2, and the Epstein-Barr virus. METHODS: A multicenter case-control study on incident cases of temporal arteritis (TA) and polymyalgia rheumatica (PMR). Population based age and sex matched controls were randomly selected. Serological tests for IgG and IgM directed against the viruses listed above were performed, on blood samples taken at the time of clinical diagnosis. RESULTS: Three hundred five new patients were included over a 5 year period, of whom 159 presented with positive biopsy TA, 70 with negative biopsy TA, and 76 with negative biopsy PMR. Thirty-eight percent of cases versus 20.9% of controls were positive for IgM directed against HPIV (p = 0.00005). The association was stronger in the positive TA subgroup [positivity rate 43.31%; odds ratio with controls 2.89 (95% CI 1.82-4.60, p = 0.000006)] than in the PMR or negative biopsy TA subgroups. Only HPIV type 1 was associated with the disease, regardless of the season or the geographical origin of the cases. Positivity rates for HPIV types 2 and 3 and for the other viruses tested were similar in cases and controls. CONCLUSION: Our findings suggest that reinfection with HPIV type 1 is associated with the onset of GCA in a subset of patients, particularly in cases with positive TA biopsy.

Aged↗
PubMed1998

High CD34(+) cell counts decrease hematologic toxicity of autologous peripheral blood progenitor cell transplantation.

Optimal numbers of CD34(+) cells to be reinfused in patients undergoing peripheral blood progenitor cell (PBPC) transplantation after high-dose chemotherapy are still unknown. Hematologic reconstitution of 168 transplantations performed in patients with lymphoproliferative diseases was analyzed according to the number of CD34(+) cells reinfused. The number of days from PBPC reinfusion until neutrophil recovery (>1.0 x 10(9)/L) and unsustained platelet recovery (>50 x 10(9)/L) were analyzed in three groups defined by the number of CD34(+) cells reinfused: a low group with less than or equal to 2.5 x 10(6) CD34(+) cells/kg, a high group with greater than 15 x 10(6) CD34(+) cells/kg, and an intermediate group to which the former two groups were compared. The 22 low-group patients had a significantly delayed neutrophil (P < .0001) and platelet recovery (P < .0001). The 41 high-group patients experienced significantly shorter engraftment compared with the intermediate group with a median of 11 (range, 8 to 16) versus 12 (range, 7 to 17) days for neutrophil recovery (P = .003), and a median of 11 (range, 7 to 24) versus 14 (range, 8 to 180+) days for platelet recovery (P < .0001). These patients required significantly less platelet transfusions (P = .002). In a multivariate analysis, the amount of CD34(+) cells reinfused was the only variable showing significance for neutrophil and platelet recovery. High-group patients had a shorter hospital stay (P = .01) and tended to need fewer days of antibotic administration (P = .12). In conclusion, these results suggest that reinfusion of greater than 15 x 10(6) CD34(+) cells/kg after high-dose chemotherapy for lymphoproliferative diseases further shortens hematopoietic reconstitution, reduces platelet requirements, and may improve patients' quality of life.

Adolescent↗
PubMed1998

Frequency and significance of anemia in non-Hodgkin's lymphoma patients.

OBJECTIVES: Retrospective evaluation of anemia frequency and its prognostic value in patients with different subtypes of non-Hodgkin's lymphoma and comparison with other clinical characteristics. PATIENTS AND METHODS: Anemia was defined as a hemoglobin value less than or equal to 12 g/dl for all men and women over 50 years of age, and less than or equal to 11 g/dl for women under 50 years of age. The study included 1077 adult lymphoma patients treated between 1980 and 1995 with the following histologic subtypes: 127 patients with small lymphocytic or lymphoplasmacytoid, 62 with marginal zone, 50 with mantle-cell, 208 with follicular, 104 with T-cell lymphoma, 426 with diffuse large-cell and, finally, 73 patients with other high-grade lymphomas. RESULTS: Anemia was present in 341 patients (32%). It was an adverse prognostic factor (P < 0.0001) for overall survival (OS) and progression-free survival (PFS) but not for relapse-free survival (RFS). When patients with and those without bone marrow involvement were considered separately, anemia remained an adverse factor. Anemia was significantly associated with shorter PFS in small lymphocytic or lymphoplasmacytoid, mantle cell, diffuse large cell and high-grade lymphomas and with shorter OS in all histologic subgroups except marginal zone lymphoma. In multivariate analysis, anemia was a significant prognostic factor for OS and PFS for the population as a whole (P = 0.0001 and P = 0.0048, respectively) and in patients with bone marrow involvement (P = 0.007 and P = 0.005, respectively) but not in patients without bone marrow involvement. Finally, the addition of anemia to the International Prognostic Index led to an improvement for OS (P = 0.0004) and PFS (P = 0.0004). CONCLUSIONS: Anemia is an important adverse prognostic factor for the outcome of lymphoma patients, particularly in some histologic subgroups and in patients with bone marrow involvement.

Adult↗
PubMed1998

Plasma levels of tumour necrosis factor and its soluble receptors correlate with clinical features and outcome of Hodgkin's disease patients.

A prospective study was performed to assess the use of plasma measurement of tumour necrosis factor (TNF), lymphotoxin alpha (LT alpha) and their soluble receptors (p55 and p75) for prognostic risk assignment in 61 patients with Hodgkin's disease. Plasma levels of TNF, p55 and p75, but not of LT alpha, were higher in Hodgkin's disease patients than in healthy controls. Plasma levels of TNF, p55 and p75 were associated with several prognostic factors for Hodgkin's disease, including those related to the host (age, performance status) and to the tumour (disease stage, extranodal site involvement, bulky tumour, serum levels of LDH and beta2-microglobulin, histology). Elevated plasma levels of TNF, p55 and p75 were also associated with several parameters reflecting an immune activation, including the presence of B symptoms, elevated serum levels of gammaglobulins, alkaline phosphatase and fibrinogen, as well as peripheral monocytosis, anaemia and low serum albumin levels. Finally, elevated TNF ligand receptor plasma markers were associated with a lower incidence of complete response to therapy and predicted shorter free-from-progression survival and overall survival of the patients. These results indicate that the plasma levels of TNF and its soluble receptors correlate with clinical features and outcome of patients with Hodgkin's disease.

Adolescent↗
PubMed1998

Reduced progression-free survival in elderly patients receiving intensification with autologous peripheral blood stem cell reinfusion for multiple myeloma.

Between 1990 and 1997, 55 patients with high risk multiple myeloma underwent high-dose therapy with peripheral blood stem cell transplantation. Intensification consisted of high-dose L-PAM in 54 patients, and 15 patients underwent a second high-dose treatment. Thirty patients received total body irradiation. Twenty patients were more than 60 years old. Thirty-five patients were intensified during first response. The overall response rate was 78%. There were four toxic deaths. The median overall survivals after intensification and after first treatment of myeloma were greater than 48 months and 71 months, respectively. Conversely freedom from progression after intensification was short, with a median of 22 months. Freedom from progression was significantly shorter in patients older than 60 (12 months), and in patients who had received more than 75 mg/m2 of L-PAM before intensification (16 months). Although intensification is feasible in elderly patients the benefit appears to be reduced in this subgroup of patients. Prior therapy with high cumulative doses of L-PAM should be avoided in patients who will receive high-dose L-PAM for therapeutic intensification.

Adult↗
PubMed1998

Mantle cell lymphoma: a retrospective study of 121 cases.

Mantle cell lymphoma (MCL) patients represent a difficult problem, sometimes to establish the diagnosis but mostly because of their refractoriness to standard lymphoma treatments. Which treatments to apply and to whom is not yet defined. In this study, we attempted to analyze the clinical features, to identify the major prognostic factors, and to evaluate the outcome of 121 MCL patients treated in our institution between 1979 and 1997. Clinical data, treatment modalities, and International Prognostic Index (IPI) score were evaluated. Median age was 63 years. Patients usually presented with advanced stage disease (87%), disseminated lymph nodes (57%), bone marrow involvement (79%), but with a good performance status (PS) (81%). Lymphocytosis >4000/microl and/or peripheral blood involvement was present in 36% of cases, and gastrointestinal disease in 18%. The t(11;14)(q13;q32) and/or bcl-1 rearrangement was detected in 47/57 studied cases. Median overall survival (OS) was 3.12 years and a longer survival was significantly associated with younger age (<70 years), good PS (<2), localized disease (stage I-II), fewer than two extra-nodal sites, absence of spleen or peripheral blood involvement, normal serum LDH and beta2-microglobulin levels, and hemoglobin level greater than 12 g/dl. However, the IPI failed to identify patients with longer OS and in a multiparametric analysis, only older age, hemoglobin less than 12 g/dl, poor PS, and blood involvement were associated with a poorer outcome. Treatment modalities had no impact on survival with 75% of patients relapsing or progressing. Our data showed that the poor outcome of MCL patients is mainly related to adverse patient characteristics, a highly disseminated tumor, and some unknown parameters associated with the refractoriness to standard therapy.

Adult↗
PubMed1998

Factors associated with successful mobilization of peripheral blood progenitor cells in 200 patients with lymphoid malignancies.

Peripheral blood progenitor cells (PBPC) were mobilized and harvested in 200 patients treated for non-Hodgkin's lymphoma (n = 148), Hodgkin's disease (n = 22) and multiple myeloma (n = 30). The variables predicting the collection of a minimal (>2.5 x 10(6)/kg) or a high (>10 x 10(6)/kg) CD34+ cell count were analysed. Patients were mobilized with haemopoietic growth factors following either standard chemotherapy (n = 49) or high-dose cyclophosphamide, given alone (n = 55) or combined with high-dose VP16 (n = 86). 10 patients received haemopoietic growth factors only. The first mobilization resulted in a PBPC harvest with enough CD34+ cells in 179/200 patients (90%). High-dose cyclophosphamide, with or without VP16, did not mobilize a higher progenitor cell yield than standard chemotherapy. When performing multiple regression analysis in the 190 patients who received chemotherapy-containing mobilization, only the number of previous chemotherapy regimens and the exposure to fludarabine predicted for a failure to collect a minimal PBPC count (P=0.06 and 0.0008 respectively). The target to collect a high CD34+ cell count was negatively associated with the number of previous chemotherapy regimens (P=0.002). When only non-Hodgkin's lymphoma patients were considered for multivariate analysis, low-grade histology with fludarabine appeared to be associated with poor PBPC cell yield (P=0.08 and 0.005 respectively). This data confirms that PBPC harvest should be planned early in the disease course in transplant candidates, and can be obtained after a standard course of chemotherapy.

Adolescent↗
PubMed1998

Potential interactions between antitubulin agents and temperature: implications for modulation of multidrug resistance.

We analyzed the effect of high temperature (a 1-h incubation at 43 degrees C) on the accumulation and cytotoxicity of vinblastine and docetaxel in two model cell lines, K562 and MESSA, and their multidrug resistance (MDR) counterparts, K562/R7 and MESSA/Dx5. High temperature increased the amount of intracellular vinblastine and docetaxel significantly in MESSA cell and, to a much lesser extent, in K562 cells. MDR-positive cells retained a profound drug accumulation defect at 43 degrees C. Hyperthermia enhanced the cytotoxic effect of vinblastine (but not docetaxel) in both K562 and MESSA cells, but not in the MDR-positive variants. PSC833, a potent modulator of P-glycoprotein, induced high levels of drug accumulation in the two MDR-positive cell lines at both 37 degrees C and at 43 degrees C. PSC833 also significantly reduced the resistance levels of the two MDR-positive lines at both 37 degrees C and at 43 degrees C. The effect of hyperthermia on drug accumulation thus seems to depend on the cell line, whereas the effect on cytotoxicity depends on the type of compound. The MDR phenotype remains a therapeutic obstacle at 43 degrees C but is accessible to modulation.

Antineoplastic Agents, Phytogenic↗
PubMed1997

Primary anaplastic large-cell lymphoma in adults: clinical presentation, immunophenotype, and outcome.

Anaplastic, CD30+, large-cell lymphoma is now a well-recognized pathologic entity that accounts for 2% to 8% of all lymphomas. Recent progress has been made in the understanding of certain biologic features found in anaplastic large-cell lymphoma, but information about its clinical behavior, in comparison to other large-cell lymphomas, is limited. The pathologic review of a large multicenter study of the treatment of aggressive lymphoma identified 146 cases of anaplastic large-cell lymphoma (ALCL) on the basis of morphology and CD30 expression. We compared initial presentation, immunophenotype, and clinical outcome of these cases with those of the 1,695 nonanaplastic diffuse large-cell lymphomas (non-ALCL) included in the same trial. Patients with ALCL were more likely to be male (P = .018) and were younger (P < .0001) than those with non-ALCL. B symptoms were more frequent in ALCL (P = .006). Skin (P < .0001) and lung (P < .05) involvement was also more frequent in ALCL, but frequency of bone marrow involvement was identical (P = . 5). Tumor cell phenotype was B in 56 cases (38%), T in 49 cases (34%), and null in 33 cases (22%). Response to chemotherapy (P = . 001), event-free survival (P = .006), and overall survival (P = . 0004) were better for ALCL than for non-ALCL. Multivariate analyses identified anaplastic character as an independent factor that predicted a longer survival. Tumor cell phenotype did not influence event-free survival (P = .72) or overall survival (P = .83). ALCL in adults is a clinicopathologic entity which, independent of its phenotypic characteristics, has a better outcome than other diffuse large-cell lymphomas.

Adult↗
PubMed1997

Very low density lipoproteins and interleukin 2 enhance the immunogenicity of 9-O-acetyl-GD3 ganglioside in BALB/c mice.

Gangliosides expressed by tumor cells constitute potential targets for immunotherapy. A major limitation of protocols aiming to immunize patients against tumor gangliosides is the weak immunogenicity of these molecules. We have previously shown that exogenous gangliosides are essentially bound to serum lipoproteins. In this study we have analyzed the influence of human serum lipoproteins on the immunogenicity of purified human ganglioside 9-O-acetyl-GD3 in BALB/c mice. Although expressed at very low levels in mice, this ganglioside was not immunogenic when administered in the form of micelles. However 9-O-acetyl-GD3 adsorbed onto Very Low Density Lipoproteins (VLDL) was strongly and reproducibly immunogenic, inducing both an IgM and an IgG response, with higher titers than those obtained with total serum. The IgM antibody response appeared after a single injection whereas the IgG response was observed after 3 weeks but was stronger and more durable. The antibody response to 9-O-acetyl-GD3 bound to other serum fractions was weak or absent. The addition of recombinant interleukin 2 (IL-2) enhanced weak antibody responses to 9-O-acetyl-GD3 thereby facilitating responses to ganglioside in micelles and in protein-free Very Low Density Particles. Using in vitro assays, we demonstrated that VLDL-bound ganglioside 14C-GM3 was more sensitive to the effect of neuraminidase than gangliosides bound to other lipoprotein fractions, suggesting greater accessibility of VLDL-bound gangliosides. These results indicate that VLDL-bound gangliosides are the most immunologically active fraction of serum gangliosides. VLDL or similar particles and recombinant IL-2 may be useful adjuvants for immunization with gangliosides.

Adjuvants, Immunologic↗
PubMed1997

Multidrug-resistant human sarcoma cells with a mutant P-glycoprotein, altered phenotype, and resistance to cyclosporins.

A variant of the multidrug-resistant human sarcoma cell line Dx5 was derived by co-selection with doxorubicin and the cyclosporin D analogue PSC 833, a potent inhibitor of the multidrug transporter P-glycoprotein. The variant DxP cells manifest an altered phenotype compared with Dx5, with decreased cross-resistance to Vinca alkaloids and no resistance to dactinomycin. Resistance to doxorubicin and paclitaxel is retained. The multidrug resistance phenotype of DxP cells is not modulated by 2 microM PSC 833 or cyclosporine. DxP cells manifest a decreased ability to transport [3H]cyclosporine. DNA heteroduplex analysis and sequencing reveal a mutant mdr1 gene (deletion of a phenylalanine at amino acid residue 335) in the DxP cell line. The mutant P-glycoprotein has a decreased affinity for PSC 833 and vinblastine and a decreased ability to transport rhodamine 123. Transfection of the mutant mdr1 gene into drug-sensitive MES-SA sarcoma cells confers resistance to both doxorubicin and PSC 833. Our study demonstrates that survival of cells exposed to doxorubicin and PSC 833 in a multistep selection occurred as a result of a P-glycoprotein mutation in transmembrane region 6. These data suggest that Phe335 is an important binding site on P-glycoprotein for substrates such as dactinomycin and vinblastine and for inhibitors such as cyclosporine and PSC 833.

ATP Binding Cassette Transporter, Subfamily B, Mem↗