Intravenous injection of bortezomib, melphalan and dexamethasone in refractory and relapsed multiple myeloma.

BACKGROUND: A combination of bortezomib (1.3 mg/m(2)), melphalan (5 mg/m(2)), and dexamethasone (40 mg) (BMD), with all three drugs given as a contemporary intravenous administration, was retrospectively evaluated. PATIENTS AND METHODS: Fifty previously treated (median 2 previous lines) patients with myeloma (33 relapsed and 17 refractory) were assessed. The first 19 patients were treated with a twice-a-week (days 1, 4, 8, 11, 'base' schedule) administration while, in the remaining 31 patients, the three drugs were administered once a week (days 1, 8, 15, 22, 'weekly' schedule). RESULTS: Side-effects were predictable and manageable, with prominent haematological toxicity, and a better toxic profile in 'weekly' schedule (36% versus 66% in 'base' schedule). The overall response rate was 62%. After median follow-up of 24.5 months (range 2.7-50 months), the median progression-free survival (PFS) was 21.6 with no difference between the two schedules and the median overall survival (OS) was 33.8 months. Independently from the adopted schedule, we found that also in a cohort of relapsed/refractory patients achieving at least partial remission improved PFS (35.2 versus 9 months) and OS (unreached median versus 18 months). CONCLUSION: Taken together, our observations suggest that BMD is an effective regimen in advanced myeloma patients with acceptable toxicity.

Cellular and molecular effects of protons: apoptosis induction and potential implications for cancer therapy.

Due to their ballistic precision, apoptosis induction by protons could be a strategy to specifically eliminate neoplastic cells. To characterize the cellular and molecular effects of these hadrons, we performed dose-response and time-course experiments by exposing different cell lines (PC3, Ca301D, MCF7) to increasing doses of protons and examining them with FACS, RT-PCR, and electron spin resonance (ESR). Irradiation with a dose of 10 Gy of a 26,7 Mev proton beam altered cell structures such as membranes, caused DNA double strand breaks, and significantly increased intracellular levels of hydroxyl ions, are active oxygen species (ROS). This modified the transcriptome of irradiated cells, activated the mitochondrial (intrinsic) pathway of apoptosis, and resulted in cycle arrest at the G2/M boundary. The number of necrotic cells within the irradiated cell population did not significantly increase with respect to the controls. The effects of irradiation with 20 Gy were qualitatively as well as quantitatively similar, but exposure to 40 Gy caused massive necrosis. Similar experiments with photons demonstrated that they induce apoptosis in a significantly lower number of cells and in a temporally delayed manner. These data advance our knowledge on the cellular and molecular effects of proton irradiation and could be useful for improving current hadrontherapy protocols.

G-CSF alone vs cyclophosphamide plus G-CSF in PBPC mobilization of patients with lymphoma: results depend on degree of previous pretreatment.

We performed a randomized study to compare 'G-CSF alone' (administered at dose of 10 mcg/kg/day) and 'cyclophosphamide plus G-CSF' (cyclophosphamide at dose of 4 g/m(2) and G-CSF at dose of 10 microg/kg/day), as PBPC mobilization schedules in 52 patients with NHL or HD. Randomization was stratified according to the amount of previous chemotherapy (< or =2 and >2 lines of previous chemotherapy). Mean CD34+ cell peak in P.B., mean 'Total CD34+ cells' harvested and percentage of patients successfully mobilized, in the group mobilized with 'G-CSF alone' vs the group mobilized with 'cyclophosphamide plus G-CSF', were: 35.3 x 10(6) vs 45.8 x 10(6)/l (P=0.3), 5.4 x 10(6) vs 6.8 x 10(6)/kg (P>0.9) and 50 vs 61% (P=0.4). No differences were observed in the stratum of less pretreated patients. However, in the stratum of patients who had previously received more than two lines of chemotherapy, CD34+cell peak (P=0.05) and percentage of successful mobilization (P=0.01) were higher when 'cyclophosphamide plus G-CSF' was used. Using logistic regression, both age and mobilization with 'G-CSF alone' were significantly associated with a low CD34+ cell peak in P.B. However, in the stratum of less pretreated patients, only age was significantly associated with this risk.

Cell-surface exposure of phosphatidylserine correlates with the stage of fludarabine-induced apoptosis in chronic lymphocytic leukemia and expression of apoptosis-regulating genes.

BACKGROUND: Programmed cell death (PCD) is characterized by a sequence of tightly regulated events that result in the activation of caspases and in internucleosomal DNA cleavage. Late apoptotic events such as DNA-strand breaks can be assayed by in situ end labeling (ISEL) and DNA measurement (sub G1) using flow cytometry. Phosphatidylserine (PS) redistribution from the inner plasma membrane leaflet to the outer leaflet, an early event in PCD, can be detected by annexin V (AxV) binding to PS. AxV-fluorescein isothiocyanate (FITC) fluorescence intensity is variable and characterizes different cell populations, denoted here as AxV-negative (AxV(neg)), AxV-low-positive (AxV(lo)), and AxV-high-positive (AxV(hi)). METHODS: We investigate the correlation of three methods (ISEL, sub G1 DNA content, and AxV assay) for detecting apoptosis with focus on differences between populations with different levels of PS. We also examined the expression of PCD-regulating Bcl-2 family members in these cell populations by reverse transcription-polymerase chain reaction (RT-PCR). Chronic lymphocytic leukemia (CLL) cells exposed to fludarabine (FAMP) were used as an in vitro model. Cells with different PS/AxV levels were separated using fluorescence-activated cell sorting (FACS). RESULTS: Only purified AxV(hi) cells had high positivity in the ISEL and sub G1 assays (94 +/- 0.6%, 88.6 +/- 6.6%, and 98.6 +/- 0.6%, respectively), indicating that late apoptotic cells are detected equally by all three methods. In the AxV(lo) population, ISEL was positive in 21% +/- 13% and DNA sub G1 in 20% +/- 6.6% of cells, suggesting that AxV identifies early apoptotic cells better than the other assays. Anti-apoptotic Bcl-2 and Bcl-X(L) were upregulated by FAMP when cells entered apoptosis (AxV(lo)), as was pro-apo- ptotic Bcl-X(S), which was undetectable in nonapoptotic AxV(neg) cells. Pro-apoptotic Bax was only expressed in AxV(neg) and AxV(lo) cells. Late apoptotic AxV(hi) cells did not express Bcl-X(S) or Bax. RESULTS: (1) AxV staining is more sensitive than sub G1 or ISEL in detecting early apoptotic cells; (2) only late apoptotic cells are equally detected by all assays; (3) AxV is a valuable tool in the detection and isolation of apoptotic cells at different stages of PCD; and (4) pro-apoptotic Bcl-X(S) and Bax are expressed at early, not late, stages of apoptosis.

Mitogenic effect of nerve growth factor (NGF) in LNCaP prostate adenocarcinoma cells: role of the high- and low-affinity NGF receptors.

We have investigated the effect of nerve growth factor (NGF) in the androgen-dependent, prostate adenocarcinoma LNCaP cell line. Exposure of LNCaP cells to NGF resulted in a significant increase of cell proliferation. The effect was concentration dependent and equally present in serum- or charcoal-stripped serum-supplemented and serum-deprived conditions. The mitogenic action of NGF was accompanied by an enhanced expression of prostate-specific antigen (PSA) and resulted additive to the proliferative effect of dihydrotestosterone. The proliferative effect of NGF appeared to be mediated by the high-affinity NGF receptor, p140trka. Only p140trka, but not the low-affinity NGF receptor, p75LNGFR, was expressed in LNCaP cells; both the proliferative response and the phosphorylation of p140trka upon NGF treatment were prevented by the tyrosine kinase inhibitor K252a. LNCaP cells transiently transfected with the cDNA encoding for p75LNGFR appeared more sensitive to NGF, as demonstrated by the increased number of p75LNGFR-transfected LNCaP cells exposed for 72 h to NGF compared with wild LNCaP cultures. However, p75LNGFR-transfected LNCaP cells rapidly underwent apoptotic death when deprived of NGF. Our study demonstrates the physiological relevance of NGF in the regulation of prostate cell proliferation and the relative contribution of the high- and low-affinity NGF receptors in this control.

In vitro apoptotic response of freshly isolated chronic myeloid leukemia cells to all-trans retinoic acid and cytosine arabinoside.

Chronic myeloid leukemia (CML) is a hematological malignancy resulting from clonal expansion and massive accumulation of leukemic myeloid cells that retain differentiation and maturation capacity. Since CML cell accumulation has been related to apoptosis inhibition by the product of the BCR-ABL gene, attempts to eradicate leukemic cells would require therapeutic drugs able to overcome this inherent resistance. Here, we investigated in vitro the apoptotic effect of all-trans retinoic acid (ATRA) and cytosine arabinoside (ARA-C), employed alone, in combination or in sequence, on freshly isolated cells from 10 patients with chronic-phase CML. Our cell cultures showed that both ATRA and ARA-C were able to induce apoptosis in CML cells, even if ARA-C resulted more effective than ATRA. The combined use of ATRA and ARA-C seemed to have only an additive effect while the sequential use did not show any advantage. These in vitro observations indicate that ATRA and ARA-C may be effective in reducing CML cells through apoptosis induction, suggesting that it could be worthwhile to examine ATRA and ARA-C combinations in the therapy of CML.

All-trans-retinoic-acid- and growth-factor- mediated induction of alkaline phosphatase activity in freshly isolated chronic myeloid leukemia cells.

Reduced or absent neutrophil alkaline phosphatase (NAP) activity is a common feature of neutrophilic granulocytes from patients with chronic myeloid leukemia (CML). In this study we examined whether NAP activity could be restored in vitro by stimulating CML cells with different promoters such as all-trans-retinoic acid (ATRA), granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF). The results obtained indicated that ATRA and G-CSF, either alone or in combination, were effective in inducing NAP activity in CML cells, whereas GM-CSF was not. Further, NAP restoration in ATRA- and G-CSF-treated cultures was accompanied by increased morphologic differentiation of the CML clone. It might be concluded that the CML clone could be driven in vitro by ATRA and G-CSF both to achieve granulocytic maturation and to correct functional NAP-related defects.

All-trans retinoic acid converts E2F into a transcriptional suppressor and inhibits the growth of normal human bronchial epithelial cells through a retinoic acid receptor- dependent signaling pathway.

Retinoids, including retinol and retinoic acid derivatives, maintain the normal growth and differentiation of human bronchial epithelial (HBE) cells and are under investigation as agents for lung cancer prevention. In this study, we examined the biologic effects of retinoids on normal HBE cells and the molecular mechanisms of retinoid actions. At a dose of 10(-6) M, all-trans retinoic acid (t-RA) suppressed the proliferation of normal HBE cells, which accumulated in the G0 phase. No evidence of programmed cell death was observed. The class of retinoid nuclear receptor that mediated the growth arrest was explored. Normal HBE cell growth was suppressed by a retinoid that selectively activates retinoic acid receptors but not by one that activates retinoid X receptors. The E2F transcription factor has demonstrated a role in G0 entry through transcriptional suppression of genes that induce cell cycle progression. To investigate the role of E2F in retinoid signaling, transient transfection assays were performed using reporter plasmids containing E2F-binding sites. Findings from these experiments suggested that t-RA treatment converted E2F into a transcriptional suppressor. Supporting this possibility, t-RA inhibited the expression of the E2F target genes B-myb, cyclin A, and cyclin E. Further, t-RA increased the levels of nuclear E2F-4, p107, and p130 and enhanced the binding of E2F-4 to p107, which have been associated with the conversion of E2F into a transcriptional suppressor in other cells. These findings point to retinoic acid receptor- and E2F-dependent pathways as potential mediators of retinoid-induced growth arrest in normal HBE cells and have implications for the use of retinoids in clinical trials on the prevention of lung cancer.

Differential induction of apoptosis by fludarabine monophosphate in leukemic B and normal T cells in chronic lymphocytic leukemia.

Fludarabine (F-ara-A), an adenine nucleoside analog with efficacy in B-cell chronic lymphocytic leukemia (B-CLL), has also been shown to have a long-lasting suppressive effect on T lymphocytes. In heterogeneous clinical samples, apoptosis cannot be detected by standard methods in small cellular subsets. We developed, therefore, a combined assay of in situ end-labeling of nicked DNA by terminal deoxynucleotide transferase, with measurements of cellular DNA content and surface antigens (CD3, CD4, CD8, and CD19) by multiparametric flow cytometry. This assay was used to determine F-ara-A-induced apoptosis in different lymphocyte subsets from CLL patients and normal controls treated with F-ara-A in vitro. Apoptosis was also correlated to bcl-2 protein levels. We observed a direct effect of F-ara-A on both B-CLL and T lymphocytes. The response to F-ara-A in B-CLL lymphocytes in vitro was Rai stage-dependent, the early-stages being more responsive (P = .01). Higher levels of spontaneous apoptosis were observed in B-CLL lymphocytes from early stage patients (P = .02). No difference was observed in spontaneous apoptosis of normal T cells in B-CLL, although T lymphocytes in late-stage disease were more sensitive to F-ara-A-induced apoptosis. Incubation with cyclosporin A did not affect B-CLL and T-lymphocyte survival compared with control cultures. Results suggested a direct apoptotic effect of F-ara-A on B-CLL lymphocytes that decreases with increasing clinical stage. No correlation was found between bcl-2 and spontaneous or F-ara-A-induced apoptosis. Apoptosis occurred at all cell-cycle stages and was not restricted to cells in S phase. The mechanisms of this stage-dependent apoptosis in CLL remain to be elucidated.

Rescue from apoptosis in early (CD34-selected) versus late (non-CD34-selected) human hematopoietic cells by very late antigen 4- and vascular cell adhesion molecule (VCAM) 1-dependent adhesion to bone marrow stromal cells.

Monoclonal antibodies to very late antigen 4 (VLA-4) recognize the alpha4beta1 integrin receptor. This monoclonal antibody blocks the adhesion between early hematopoietic progenitor cells (CD34-selected cells) and stromal cells when added to cultures of these cells. Addition of the VLA-4 monoclonal antibody to cultures of stromal cells and CD34-selected cells was shown to induce apoptosis of CD34-selected cells in these CD34-selected cell/stromal cell cocultures, as measured by the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling method. In contrast to these experiments with early hematopoietic progenitor cells (CD34+), the level of adhesion between more differentiated cells (unfractionated hematopoietic cells) and stromal cells was not significantly altered by addition of the anti-VLA-4 monoclonal antibody. Similarly, the level of apoptosis of unfractionated hematopoietic cells was not significantly increased by the addition of anti-VLA-4 monoclonal antibody to cultures of the latter cells with stromal cells. The binding of the unfractionated cells is less than that of the CD34-selected cells. Given that there is no difference between the alpha4beta1 integrin expression level of the early and late myeloid cells, there may be a difference in the functional state of the integrin between the early and late myeloid cells. We also show that CD34+-selected precursor cells proliferate at a higher rate when these cells are plated on recombinant vascular cell adhesion molecule 1 molecules. These data indicate that the alpha4beta1 integrin receptor (VLA-4) plays a central role in the apoptosis rescue function that results from the anchorage-dependent growth of the CD34-selected early hematopoietic cells on stromal cells. The data suggest that these apoptosis rescue pathways have less significance as the cells mature and become anchorage independent in their growth. These data should assist in the design of systems for the ex vivo proliferation and transduction of early hematopoietic cells for genetic therapy.

Accumulation of cyclin B1, activation of cyclin B1-dependent kinase and induction of programmed cell death in human epidermoid carcinoma KB cells treated with taxol.

Cyclin B1 plays a critical role in regulating cell-cycle progression from G2 through M phase (including exit from M phase). In this study, we investigated the relationship between taxol-induced M-phase arrest, disruption of the cyclin B1-regulation pathway and apoptosis in KB cells. Continuous exposure of KB cells to 0.5 microg/ml taxol caused mitotic arrest and >90% cell death at 48 hr. Mitotic blockade peaked at 24 hr, with 68% of cells in mitosis at that time compared with 3% at baseline, and decreased thereafter. Apoptosis assessed by morphological changes and DNA ladder fragmentation was a later event, peaking at 48 hr (later time points were not studied). Taxol also caused an increase in cyclin B1 accumulation, as assessed by Western blot analysis, and stimulated cyclin B1-dependent kinase. Cyclin B1 accumulation and kinase stimulation peaked at 12 and 24 hr, respectively, at which times they were 5-fold and 90-fold higher than in control untreated cells. These effects decreased thereafter. All taxol-induced cellular effects were abrogated by the protein and RNA synthesis inhibitors cycloheximide and actinomycin D. In contrast, the endonuclease inhibitors aurintricarboxilic acid and zinc markedly inhibited taxol-induced DNA ladder fragmentation without altering taxol-induced cell-cycle arrest, cyclin B1 accumulation, activation of cyclin B1 kinase activity and cytotoxicity. We conclude that taxol-induced stimulation of cyclin B1-dependent kinase activity parallels mitotic arrest, is more pronounced than mitotic arrest and precedes the induction of programmed cell death.

Elevated levels of biologically active soluble CD40 ligand in the serum of patients with chronic lymphocytic leukaemia.

Chronic lymphocytic leukaemia (CLL) is an indolent lymphoproliferative disorder manifested by low growth fraction and prolonged survival of the malignant cells. The mechanisms that enable CLL cells to live longer and to resist apoptosis remain unclear. Because the malignant CLL cells express CD40 and Fas receptors, which can transduce cell-survival and cell-death signals, we examined the role of CD40 in the growth regulation of CLL cells and its interaction with Fas-mediated and fludarabine-induced apoptosis in vitro. Primary CLL cells underwent spontaneous apoptosis in culture, which was enhanced by exogenous human Fas ligand (FasL) or fludarabine. Exogenous CD40L rescued CLL cells from spontaneous apoptosis in a dose-dependent manner, and caused CLL cells to resist apoptosis induced by FasL or fludarabine. Patients' autologous plasma rescued CLL cells from spontaneous apoptosis, an effect that could be reversed with anti-CD40 ligand (CD40L) antibodies. The levels of soluble CD40 ligand in the sera of 51 CLL patients and 55 healthy donors were determined by enzyme-linked immunosorbent assay. The mean soluble CD40L level in normal donors was 0.29 ng/ml compared to a mean value of 0.80 ng/ml in CLL patients (P < 0.001). CD40L up-regulated bcl-X(L) mRNA but not bcl-2 in CLL cells within 3-6 h in culture. Our results demonstrated that serum of patients with CLL contained elevated levels of biologically active soluble CD40L, and that CD40L can prolong survival of CLL cells and mediate their resistance to FasL and fludarabine in vitro.

Differential p53 phosphorylation and activation of apoptosis-promoting genes Bax and Fas/APO-1 by irradiation and ara-C treatment.

In this study, we examined the effects of radiation and ara-C on induction of apoptosis and on the apoptosis-promoting genes p53, Bax and Fas/APO-1, in BV173 human leukemia cells, which harbor the wild-type p53 gene. It has been reported that p53 upregulates Fas/APO-1 and Bax expression. Both irradiation and ara-C treatment resulted in apoptosis and induction of p53 proteins within hours. The Bax gene was activated in irradiated and ara-C-treated BV173 cells, but Fas/APO-1 was induced only in irradiated BV173 cells. Radiation and ara-C treatment did not induce Bax or Fas/APO-1 protein expression in p53-null HL60 cells. Radiation weakly induced Fas/APO-1 expression in KBM-7 cells, which harbor a partially defective p53 gene. Both HL60 and KBM-7 cells are more resistant to radiation- and ara-C-induced apoptosis than BV173 cells. These results suggest that functional p53 is necessary for the activation of Bax and Fas/APO-1 expression. However, elevated p53 protein is not sufficient to activate Fas/APO-1 gene expression in ara-C-treated cells. Using two-dimensional gel electrophoresis, we found that the p53 proteins in irradiated and ara-C-treated BV173 cells have different isoelectric points; they converged to a single isoelectric point after in vitro treatment with phosphatase. These results suggest that different genotoxic treatments cause different phosphorylations of p53, which may account for the different levels of activation of Fas/APO-1 expression.

CD30 ligand in lymphoma patients with CD30+ tumors.

PURPOSE: CD30 ligand (CD30L), which is expressed on resting B and activated T lymphocytes, can induce cell death in several CD30+ cell lines. Patients with CD30+ tumors (Hodgkin's disease and Ki-1+ non-Hodgkin's lymphoma) frequently have elevated soluble CD30 (sCD30) levels in their serum, which correlates with a poor prognosis. The role of sCD30 in protecting tumor cells from CD30L-mediated cell death and the pattern of CD30L expression on human peripheral-blood lymphocytes (PBLs) of normal donors and patients with CD30+ tumors are investigated. MATERIALS AND METHODS: CD30L surface protein expression was determined by two-color flow cytometry on PBLs of patients with CD30+ tumors and normal individuals. CD30L levels were determined on subsets of PBLs before and after stimulation with phytohemagglutinin (PHA), anti-CD3 antibody, or CD40L. sCD30 was measured by enzyme-linked immunosorbent assay (ELISA). The apoptotic activity of membrane-bound CD30L was tested in a CD30+ cell line by the annexin V-binding method. RESULTS: Unstimulated T lymphocytes of normal donors and patients with lymphoma rarely expressed CD30L surface protein, but were able to express it after stimulation with PHA or anti-CD3 antibody. Resting B cells of patients with CD30+ tumors had lower levels of detectable surface CD30L compared with normal donors (mean, 55% and 80.6%, respectively; P = .0008). Patients with high levels of serum sCD30 had lower detectable levels of CD30L on their PBLs (R2 = .72, P = .0008) and exogenous sCD30 blocked membrane-bound CD30L-mediated apoptosis in a CD30+ cell line. CONCLUSION: In patients with CD30+ tumors, sCD30 can decrease the availability of CD30L on PBLs. Blocking the apoptosis-inducing activity of CD30L by its soluble receptor may explain how CD30+ tumors escape immunosurveillance and may be related to the reported poor prognosis of patients who have elevated sCD30 levels.

2-Chlorodeoxyadenosine therapy for idiopathic hypereosinophilic syndrome.

Idiopathic hypereosinophilic syndrome (HES) is a rare disease with no established effective therapy. It has been reported that interleukin-5 (IL-5) produced by helper T cells plays a major role in the proliferation of eosinophils. The nucleotide analogue 2-chlorodeoxyadenosine (2-CdA), which induces excellent clinical responses in hairy cell leukemia, is known to suppress helper T cells; therefore, we used 2-CdA, alone or in combination with cytarabine, to treat patients with idiopathic HES. 2-CdA alone and combined with cytarabine resulted in a rapid and sustained decrease in circulating eosinophils in two patients with idiopathic HES that was refractory to steroids, hydroxyurea and cytarabine. The efficacy of 2-CdA alone and combined with cytarabine exceeded by far that of cytarabine alone. However, reverse transcription-polymerase chain reaction (RT-PCR) did not show production of IL-5 or granulocyte-macrophage colony-stimulating factor mRNA in T cells as previously reported, and multiple cytokine receptors were found on eosinophils in idiopathic HES, suggesting that IL-5 may not be the sole cytokine involved in the regulation of idiopathic HES. The clinical efficacy of 2-CdA in idiopathic HES needs to be established on a large group of patients.

Phase I study of mitoxantrone plus etoposide with multidrug blockade by SDZ PSC-833 in relapsed or refractory acute myelogenous leukemia.

PURPOSE: Expression of the multidrug resistance gene (MDR1) p170 protein is frequent in leukemic blasts from patients with relapsed acute myelogenous leukemia (AML). A phase I study using the nonimmunosuppressive MDR1 blocker SDZ PSC-833 (PSC) in combination with mitoxantrone (MITO) and etoposide (VP) was performed. PATIENTS AND METHODS: Starting doses (LVL0) of MITO (3.25 mg/m2/d on days 1 and 3 to 6) and VP (210 mg/m2/d on days 1 and 3 to 5) were 40% of the maximal-tolerated dose (MTD) from a prior study. A 1.5-mg/kg loading dose of PSC was followed by a 120-hour continuous infusion of 10 mg/kg/d on days 2 to 6. Blood samples for PSC, MITO, and VP pharmacokinetics (PK) were taken on days 1 and 3, and samples for MDR1 expression were taken on day 0. RESULTS: Severe mucositis developed in all patients at LVL0; therefore, MITO and VP doses were reduced to 2.5 and 170 mg/m2 (LVL-1) for the next seven patients, and this dose proved to be MTD. All LVL0 and three LVL-1 patients had transient elevations in the serum bilirubin level to > or = 4 mg/dL. Serum creatinine level increased to greater than 2 mg/dL in one case. There were no other grade 3 or 4 nonhematologic toxicities observed. The peripheral blood was cleared of leukemia in three LVL0 and four LVL-1 patients. The marrow was cleared of leukemic cells in one LVL0 and five LVL-1 patients, and a significant reduction in marrow leukemic infiltrate was observed in eight of 10. No patient achieved complete remission (CR), and all died of progressive disease (n = 8) or infection (n = 2). MDR1 expression was detected by fluorescent-activated cell sorter (FACS) analysis in five of seven cases. An elevated MDR1 mRNA level was detected by quantitative polymerase chain reaction (Q-PCR) in six of eight cases studied. Clearing of leukemia cells from the marrow occurred in four of six MDR1-positive and one of three MDR1-negative patients. Despite the fact that LVL0 doses had to be reduced due to toxicity, coadministration of PSC did not produce a consistent effect on MITO PK; however, it did repeatedly lead to increased levels of VP in the serum. CONCLUSION: We conclude that PSC-MITO-VP is a tolerable regimen with antileukemic activity. Addition of PSC necessitated a 66% reduction in MITO and VP doses from a prior study without PSC.