The role of MDR-1 in refractory lymphoma

Determinants of Drug Resistance in B-Cell Non-Hodgkin Lymphomas: The Case of Lymphoplasmacytic Lymphoma/Waldenström Macroglobulinemia

Lymphoplasmacytic lymphoma (LPL) is a rare subtype of B cell-derived non-Hodgkin lymphoma characterized by the abnormal growth of transformed clonal lymphoplasmacytes and plasma cells. This tumor almost always displays the capability of secreting large amounts of monoclonal immunoglobulins (Ig) of the M class (Waldenström Macroglobulinemia, WM). The clinical manifestations of WM/LPL may range from an asymptomatic condition to a lymphoma-type disease or may be dominated by IgM paraprotein-related symptoms. Despite the substantial progresses achieved over the last years in the therapy of LPL/WM, this lymphoma is still almost invariably incurable and exhibits a propensity towards development of refractoriness to therapy. Patients who have progressive disease are often of difficult clinical management and novel effective treatments are eagerly awaited. In this review, we will describe the essential clinical and pathobiological features of LPL/WM. We will also analyze some key aspects about the current knowledge on the mechanisms of drug resistance in this disease, by concisely focusing on conventional drugs, monoclonal antibodies and novel agents, chiefly Bruton’s Tyrosine Kinase (BTK) inhibitors. The implications of molecular lesions as predictors of response or as a warning for the development of therapy resistance will be highlighted.

The frequency and clinical relevance of multidrug resistance protein expression in patients with lymphoma

Objective: Multidrug resistance is a cause of treatment failure in patients with malignant lymphoma; however, the frequency and clinical relevance of multidrug resistance protein expression are unclear. The present study aimed to investigate expression of the most common multidrug resistance proteins in a group of lymphoma patients.

Material and Methods: The study included 44 previously untreated lymphoma patients (non-Hodgkin’s lymphoma [n = 21], non-malignant lymphadenopathy [n = 13], and Hodgkin’s lymphoma [n = 10]). MDR1, MRP, and LRP expression was assessed via quantitative PCR of lymph node biopsy specimens.

Results: In the non-Hodgkin’s lymphoma group MDR1 was positive in 23.8% (5/21) of the patients, MRP was positive in 57.14% (12/21), and LRP was positive in 90.47% (19/21). In the non-malignant lymphadenopathy group, MDR1 was positive in 46.15% (6/13) of the patients, MRP was positive in 84.61% (11/13), and LRP was positive in 100% (13/13). In the Hodgkin’s lymphoma group MDR1 was positive in 50% (5/10) of the patients, MRP was positive in 50% (5/10), and LRP was positive in 80% (8/10). MDR1, MRP, and LRP expression did not differ between the 3 groups. Furthermore, MDR1, MRP, and LRP expression wasn’t associated with tumor stage, response to first-line therapy, the erythrocyte sedimentation rate, or C reactive protein, beta 2 microglobulin, serum lactate dehydrogenase, and albumin levels. Additionally, survival time in the MDR1- and MRP-positive, and MDR1- and MRP-negative patients did not differ (comparison of LRP was not possible due to the small number of LRP-negative patients).

Conclusion: According to the present findings, future studies should investigate alternative pathways of multidrug resistance in order to arrive at a better understanding of treatment failure in lymphoma patients.

Future perspectives for the development of P-glycoprotein modulators

Resistance to chemotherapeutic agents constitutes one of the major obstacles to the successful treatment of cancer. While several mechanisms underlying drug resistance have been elucidated, the most widely studied mechanism involves the efflux of antineoplastic drugs from cancer cells by P-glycoprotein, the 170 kD glycoprotein product of the MDR-I gene. The observation that several compounds are able to inhibit P-glycoprotein in vitro created optimism that the problem of multidrug resistance in cancer could be quickly resolved by moving these compounds into the clinic. However, despite a large number of clinical trials with several different putative Pgp modulators, the value of Pgp modulation in clinical oncologic practice remains unresolved. While these initial trials have not answered the question of whether Pgp is an important mechanism of resistance in human cancers, or whether modulation of Pgp is likely to positively impact on the treatment of cancer, they have provided insights regarding the problems inherent in conducting trials of this nature. These clinical insights, along with knowledge gained from continued basic research on drug resistance mediated by Pgp and related transporters, will form a strong foundation for future research into the role of Pgp and Pgp modulation in the treatment of cancer. The ubiquitous nature of transporters and the high prevalence of transporter substrates among antineoplastic drugs, compel the development of modulators that can be used to prevent or reverse drug resistance.

Tariquidar (XR9576): a P-glycoprotein drug efflux pump inhibitor

P-glycoprotein actively transports structurally unrelated compounds out of cells, conferring the multidrug resistance phenotype in cancer. Tariquidar is a potent, specific, noncompetitive inhibitor of P-glycoprotein. Tariquidar inhibits the ATPase activity of P-glycoprotein, suggesting that the modulating effect is derived from the inhibition of substrate binding, inhibition of ATP hydrolysis or both. In clinical trials, tariquidar is tolerable and does not have significant pharmacokinetic interaction with chemotherapy. In patients, inhibition of P-glycoprotein has been demonstrated for 48 h after a single dose of tariquidar. Studies to assess a possible increase in toxicity of chemotherapy and the impact of P-glycoprotein inhibition on tumor response and patient outcome are ongoing. Tariquidar can be considered an ideal agent for testing the role of P-glycoprotein inhibition in cancer.

Phase I/II Trial of Nonpegylated Liposomal Doxorubicin, Cyclophosphamide, Vincristine, and Prednisone in the Treatment of Newly Diagnosed Aggressive Non-Hodgkin's Lymphoma

BACKGROUND

The toxicity and efficacy of nonpegylated liposomal doxorubicin (TLC D-99) when substituted for conventional doxorubicin in the CHOP (doxorubicin/cyclophosphamide/vincristine/prednisone) regimen were evaluated in the treatment of newly diagnosed patients with aggressive non-Hodgkin's lymphoma. Liposomal doxorubicin at doses of 40 mg/m2, 50 mg/m2, 60 mg/m2, and 80 mg/m2 was given with fixed doses of cyclophosphamide, vincristine, and prednisone. Chemotherapy cycles were repeated every 21 days.

PATIENTS AND METHODS

Forty-seven patients with a median age of 55 years (range, 25-83 years) were studied.

RESULTS

No dose-limiting toxicities were observed at any level. Reversible grade 3/4 neutropenia was the most common toxicity (95.8%). Most nonhematologic side effects were grade 1/2 in severity. Complete remissions were documented in 31 of 46 evaluable patients (67.4%) and partial remissions in 7 (15.2%), for an overall major response rate of 82.6%. The median duration of complete remission is > or = 27.7 months (range, 2.4 months to > or = 59.8 months). An exploratory objective was to correlate multidrug resistance-1 (MDR-1) expression with outcome. Immunohistochemistry for MDR-1-related p-glycoprotein was assessed in lymphoma tissues from 27 patients. Of the 27 lymphoma tissues studied, 8 (30%) were MDR-1 positive at diagnosis. The complete response rate was 63% in MDR-1-positive lymphomas and 74% in the MDR-1-negative cases (P = 0.66).

CONCLUSION

Nonpegylated liposomal doxorubicin in combination with cyclophosphamide, vincristine, and prednisone is an active regimen for patients with newly diagnosed, aggressive non-Hodgkin's lymphoma. The regimen is relatively well tolerated, with hematologic suppression as the major toxicity. Liposomal encapsulation might evade resistance caused by MDR-1 expression.

Cellular and molecular signal transduction pathways modulated by rituximab (rituxan, anti-CD20 mAb) in non-Hodgkin's lymphoma: implications in chemosensitization and therapeutic intervention

The clinical application of rituximab (chimeric mouse anti-human CD20 mAb, Rituxan, IDEC-C2B8), alone and/or combined with chemotherapy, has significantly ameliorated the treatment outcome of patients with relapsed and refractory low-grade or follicular non-Hodgkin's lymphoma (NHL). The exact in vivo mechanisms of action of rituximab are not fully understood, although antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis have been suggested. We have proposed that modifications of the cellular signaling pathways by rituximab may be crucial for its clinical response. The B-cell restricted cell surface phosphoprotein CD20 is involved in many cellular signaling events including proliferation, activation, differentiation, and apoptosis upon crosslinking. Monomeric rituximab chemosensitizes drug-resistant NHL cells via selective downregulation of antiapoptotic factors through the type II mitochondrial apoptotic pathway. Several signaling pathways are affected by rituximab which are implicated in the underlying molecular mechanisms of chemosensitization. ARL (acquired immunodeficiency syndrome (AIDS)-related lymphoma) and non-ARL cell lines have been examined as in vitro model systems. In ARL, rituximab diminishes the activity of the p38MAPK signaling pathway resulting in inhibition of the interleukin (IL)-10/IL-10R autocrine/paracrine cytokine autoregulatory loop leading to the inhibition of constitutive STAT-3 activity and subsequent downregulation of Bcl-2 expression leading to chemosensitization. Rituximab upregulates Raf-1 kinase inhibitor protein (RKIP) expression in non-ARL cells. Through physical association with Raf-1 and nuclear factor kappaB (NF-kappa B)-inducing kinase (NIK), RKIP negatively regulates two major survival pathways, namely, the extracellular signal-regulated kinase1/2 (ERK1/2) and the NF-kappa B pathways, respectively. Downmodulation of the ERK1/2 and NF-kappa B pathways inhibits the transcriptional activity of AP-1 and NF-kappa B transcription factors, respectively, both of which lead to the downregulation of Bcl-(xL) (Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene)) transcription and expression and sensitization to drug-induced apoptosis. Bcl-(xL)-overexpressing cells corroborated the pivotal role of Bcl-(xL) in chemosensitization. The specificity of rituximab-mediated signaling and functional effects were corroborated by the use of specific pharmacological inhibitors. Many patients do not respond and/or relapse and the mechanisms of unresponsiveness are unknown. Rituximab-resistant B-NHL clones were generated to investigate the acquired resistance to rituximab-mediated signaling, and chemosensitization. Resistant clones display different phenotypic, genetic and functional properties compared to wild-type cells. This review summarizes the data highlighting a novel role of rituximab as a signal-inducing antibody and as a chemosensitizing agent through negative regulation of major survival pathways. Studies presented herein also reveal several intracellular targets modified by rituximab, which can be exploited for therapeutic and prognostic purposes in the treatment of patients with rituximab- and drug-refractory NHL.

T-cell lymphoma as a model for the use of histone deacetylase inhibitors in cancer therapy: impact of depsipeptide on molecular markers, therapeutic targets, and mechanisms of resistance

Depsipeptide (FK228) is a novel histone deacetylase inhibitor currently in clinical trials and the first to demonstrate clinical activity in patients. Responses have been observed in patients with T-cell lymphomas, despite prior treatment with multiple chemotherapeutic agents. To better understand the effects of histone deacetylase inhibitors on T-cell lymphoma, the human T-cell lymphoma cell line HUT78 was tested for sensitivity and molecular response to depsipeptide. Treatment with depsipeptide, as well as other histone deacetylase inhibitors, caused induction of histone acetylation, induction of p21 expression, and substantial apoptosis without significant cell cycle arrest. Treatment with the caspase inhibitor z-VAD-fmk significantly inhibited depsipeptide-induced apoptosis, enabling detection of cell cycle arrest. Treatment with depsipeptide increased expression of the interleukin-2 (IL-2) receptor, and combination with the IL-2 toxin conjugate denileukin diftitox resulted in more than additive toxicity. Cells selected for resistance to depsipeptide overexpressed the multidrug resistance pump, P-glycoprotein (Pgp). However, cells selected for resistance to depsipeptide in the presence of a Pgp inhibitor had a Pgp-independent mechanism of resistance. These studies confirm the activity of depsipeptide in a T-cell lymphoma model and suggest a general sensitivity of T-cell lymphoma to histone deacetylase inhibitors, an emerging new class of anticancer agents. (Blood. 2004;103:4636-4643)

Increased myelotoxicity of idarubicin: is there a pharmacological basis? Results of a pharmacokinetic and an in vitro cytotoxicity study

BACKGROUND

Clinical trials evaluating idarubicin (IDA) in acute myeloid leukemia, multiple myeloma and non-Hodgkin's lymphoma (NHL) have provided some evidence for an increased myelotoxicity of IDA compared to other anthracyclines. IDA is known to be less sensitive towards multidrug resistance mediated by P-glycoprotein (P-gp). This phenotype is a major impediment to successful antineoplastic treatment, but P-gp is also expressed on hematopoietic stem cells (HSC).

METHODS

We investigated the pharmacokinetics of IDA and etoposide (ETO) in seven previously untreated patients with aggressive NHL. The patients received a CHOP-derived protocol (CIVEP) in which doxorubicin (DOX) was substituted by IDA 11-16 mg/m(2) and ETO 3 x 100 mg/m(2) was added. Furthermore, we evaluated in vitro the impact of P-gp expression on the cytotoxicity of DOX and IDA in cells from three parental chemosensitive leukemia and lymphoma cell lines (HL60, U937, CCRF) and their resistant sublines, as well as in CD34-positive HSC.

RESULTS

The peak plasma levels (C(max)), terminal elimination half-life (t(1/2)) and area under the concentration curve (AUC) both for IDA and for ETO did not differ from published data. In cell line models the numbers of viable cells in a P-gp-expressing resistant CCRF-VCR100 subline were significantly more reduced by IDA ( P<0.001), but there was no difference in the cytotoxicities of IDA and DOX in chemosensitive CCRF cells and in the (non-P-gp-expressing) resistant U937 and HL60 sublines. Cytotoxicity against HSC was more pronounced after incubation with IDA than after treatment with DOX ( P=0.014), even when a tenfold higher concentration of DOX than of IDA was used. The addition of cyclosporin A increased the cytotoxic effect of DOX but not that of IDA in HSC.

CONCLUSIONS

The pharmacokinetics of IDA and its main metabolite idarubicinol in CHOP-derived protocols were not different from data obtained with other combinations or monotherapy. The increased myelotoxicity of IDA may be a consequence of P-gp expression in CD34-positive HSC.

Resveratrol modifies the expression of apoptotic regulatory proteins and sensitizes non-Hodgkin's lymphoma and multiple myeloma cell lines to paclitaxel-induced apoptosis

Resveratrol (trans-3,4,5-trihydroxystilbene) has received attention for its potential chemopreventive and antitumor effects in experimental systems. Recent evidence suggests that paclitaxel, alone or in combination with other drugs, can be effectively used in the treatment of non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). This study investigated whether resveratrol can sensitize NHL and MM cell lines to paclitaxel-mediated apoptosis and to delineate the underlying molecular mechanism of sensitization. Both resveratrol and paclitaxel negatively modulated tumor cell growth by arresting the cells at the G2-M phase of the cell cycle. Low concentrations of resveratrol exerted a sensitizing effect on drug-refractory NHL and MM cells to apoptosis induced by paclitaxel. Resveratrol selectively down-regulated the expression of antiapoptotic proteins Bcl-xL and myeloid cell differentiation factor-1 (Mcl-1) and up-regulated the expression of proapoptotic proteins Bax and apoptosis protease activating factor-1 (Apaf-1). Paclitaxel down-regulated the expression of Bcl-xL, Mcl-1, and cellular inhibitor of apoptosis protein-1 antiapoptotic proteins and up-regulated Bid and Apaf-1. Combination treatment resulted in apoptosis through the formation of tBid, mitochondrial membrane depolarization, cytosolic release of cytochrome c and Smac/DIABLO, activation of the caspase cascade, and cleavage of poly(adenosine diphosphate-ribose) polymerase. Combination of resveratrol with paclitaxel had minimal cytotoxicity against quiescent and mitogenically stimulated human peripheral blood mononuclear cells. Inhibition of Bcl-xL expression by resveratrol was critical for chemosensitization and its functional impairment mimics resveratrol-mediated sensitization to paclitaxel-induced apoptosis. Inhibition of Bcl-xL expression by resveratrol was due to the inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway and diminished activator protein-1-dependent Bcl-xL expression. The findings by resveratrol were corroborated with inhibitors of the ERK1/2 pathway. This study demonstrates that in resistant NHL and MM cell lines resveratrol and paclitaxel selectively modify the expression of regulatory proteins in the apoptotic signaling pathway and the combination, via functional complementation, results in synergistic apoptotic activity.

The role of rituximab and chemotherapy in aggressive B-cell lymphoma: A preliminary report of dose-adjusted EPOCH-R

Accumulating evidence suggests that the ability to activate apoptotic pathways may be an important determinant of chemotherapy sensitivity and presents a potentially important new therapeutic strategy. Monoclonal antibodies against the CD20 antigen directly induce apoptosis and may serve to modulate the threshold for chemotherapy-induced apoptosis. Rituximab (Rituxan; Genentech, Inc, South San Francisco, CA, and IDEC Pharmaceuticals, San Diego, CA), a monoclonal antibody against CD20, was combined with dose-adjusted EPOCH (infusional etoposide/vincristine/doxorubicin/bolus cyclophosphamide/prednisone) chemotherapy and tested in 38 untreated or relapsed poor-prognosis aggressive lymphomas. Twenty-three patients were untreated. Of these patients, all had large B-cell histologies, a median age of 52 years, Eastern Cooperative Oncology Group performance status ≥ 2 in 30%, and high-intermediate or high International Prognostic Index scores in 61%. Fifteen patients had relapsed or refractory lymphomas. These patients had received a median of two (range, one to four) prior regimens, 67% had aggressive histologies, and 60% had high-intermediate or high International Prognostic Index scores. Complete remissions were achieved in 85% and 64% of untreated and previously treated patients, respectively; additionally 42% of patients with disease refractory before therapy achieved complete remission. At a median follow-up of 12 months, progression-free and overall survival in the previously untreated group was 85% and 79%, respectively, and no patient in complete remission has relapsed. These results suggest that rituximab may modulate the sensitivity of B-cell lymphomas to chemotherapy. Semin Oncol 29 (suppl 2):41-47. This is a US government work. There are no restrictions on its use.

Activity of infusional etoposide, vincristine, and doxorubicin with bolus cyclophosphamide (EPOCH) in relapsed Hodgkin's disease

INTRODUCTION

A phase II study of EPOCH chemotherapy in relapsed Hodgkin's disease was performed in 14 patients in a multicenter community setting. Patients and Methods. A total of 14 patients (9 males and 5 females) were included in the study. Ages ranged from 21-72 with a median age of 33. Eleven out of 14 patients had advanced (stage III or IV) disease, but all patients had good performance status. All 14 patients had received prior chemotherapy with ABVD, MOPP, or MOPP/ABVD hybrid.

RESULTS

A total of 57 cycles of EPOCH were administered during this trial. Patients received a median of four cycles of chemotherapy. An overall response rate of 86% was seen among the 14 patients with one patient achieving a complete response. Following EPOCH chemotherapy, 7 of 12 patients who responded underwent high-dose chemotherapy with stem cell support. Six out of 14 patients are currently alive, and three had no evidence of disease at the time of last follow-up. Toxicity with EPOCH chemotherapy consisted mainly of myelosuppression, and most patients were managed on an outpatient basis.

CONCLUSION

This multicenter community study confirms the activity of EPOCH chemotherapy in the treatment of patients with relapsed Hodgkin's disease.

Comparison of the uptake and clearance of Tc-99m MIBI, Tl-201 and Ga-67 in drug-resistant lymphoma cell lines

Tc-99m sestamibi (MIBI) has been used as a tumor-seeking agent. However, its role in detecting lymphomas has not been widely investigated. The aim of the present study was to determine the uptake and clearance characteristics of Tc-99m MIBI in vincristine-resistant lymphoma cell lines. In addition, thallium-201 (Tl-201) and gallium-67 (Ga-67) uptake and clearance characteristics were evaluated for comparison with Tc-99m MIBI. Drug-resistant lymphoma cell lines (monocyte-like, histiocytic lymphoma, human; B-lymphoma cell line, American Burkitt lymphoma, lymphoblastoid, human; Hodgkin's disease, lymphoid, human) were selected by multistep vincristine treatment up to 50 nM. After incubation of the radiotracers, Tc-99m MIBI, Tl-201 and Ga-67, in medium for 0, 10, 20, 30, 60 or 120 min, the uptake and clearance of each radiotracer were measured in the drug-resistant lymphoma cell lines. In addition, P-glycoprotein expression was determined by immunohistochemical study. In a comparison of the three radiotracers, the uptake of Tc-99m MIBI was the greatest in the studied wild-type lymphoma cell lines. Tc-99m MIBI uptake was much lower in drug-resistant tumor cell lines than in non-resistant cell lines. On the other hand, the uptake characteristics of Tl-201 did not differ between drug-resistant and non-resistant cells. Immunohistochemistry analyses of Ab-1 or JSB indicated that tumor cells expressed MDR-1 protein in all three cell lines. Tc-99m MIBI is a good radiotracer for detecting drug resistance in lymphoma cell lines.

High expression of MDR-1 gene and P-glycoprotein in initial and re-biopsy specimens of relapsed B-cell lymphoma

AIMS

Multidrug resistance (MDR) is a major obstacle in the treatment of lymphoma. The expression of MDR-1 mRNA and P-glycoprotein (MDR-1/P-gp) has been linked to MDR. We aimed to investigate the expression of MDR-1/P-gp in B-cell lymphoma.

METHODS AND RESULTS

Samples at diagnosis and relapse from 10 patients with B-cell lymphoma were obtained. We also obtained 14 unselected control cases of B-cell lymphoma at diagnosis. The expression of mRNA and protein were determined semiquantitatively by RT-PCR and immunohistochemistry. High MDR-1 and P-gp expressions were found in seven and seven of 10 samples obtained at diagnosis, eight and eight of 10 samples obtained at relapse, and three and four of 14 control cases at diagnosis, respectively. The results of RT-PCR paralleled those of immunohistochemistry. Concordance of high MDR-1/P-gp expression was noted in 27 of 34 samples (r = 0.73, P = 0.001). There were no significant changes in MDR-1/P-gp expression in all cases at relapse and during the clinical course following chemotherapy. In the 14 control cases, the average survival time was 12.7 months in MDR-1/P-gp positive cases and 29.0 months in the MDR-1/P-gp negative cases (P = 0.20).

CONCLUSIONS

Our results showed that at least some B-cell lymphomas express MDR-1/P-gp, which could be detected by different methods, and suggested that high MDR-1/P-gp expression in tumour cells may be associated with a high probability of relapse and poor prognosis.

A multicenter trial of infusional etoposide, doxorubicin, and vincristine with cyclophosphamide and prednisone (EPOCH) in patients with relapsed non-Hodgkin's lymphoma

A phase II study was performed in a multicenter community setting of EPOCH (etoposide/doxorubicin/vincristine/cyclophosphamide/prednisone) chemotherapy in 93 patients with relapsed non-Hodgkin's lymphoma. Patients included 41 females and 52 males, ranging in age from 31-81 years (median, 63 years). Lymphoma histologies included diffuse large-cell (56), follicular (21), mantle cell (11), peripheral T-cell (3), and small lymphocytic (2) lymphomas. Patients had received a median of two previous chemotherapy combinations (range, 1-9). Most patients had received the drugs in EPOCH with their previous chemotherapy regimens (vincristine 97%, cyclophosphamide 97%, doxorubicin 87%, and etoposide 28%). A total of 350 cycles of EPOCH were administered. EPOCH chemotherapy gave a response rate of 51% in the entire cohort of 93 patients. Among the 83 evaluable patients, a response rate of 57% was observed (24% complete response, 33% partial response). Seven of the 47 responders remain in clinical remission at 3 years after EPOCH chemotherapy alone. Additionally, 11 patients are alive after further salvage chemotherapy (four patients) or bone marrow transplantation (seven patients). Myelosuppression was common, with 36% of all cycles resulting in an absolute neutrophil count nadir < 500/microL. This study confirms the activity of infusional chemotherapy with EPOCH in patients with relapsed non-Hodgkin's lymphoma.

Phase I study of cinchonine, a multidrug resistance reversing agent, combined with the CHVP regimen in relapsed and refractory lymphoproliferative syndromes

Overexpression of P-glycoprotein (P-gp) in cancer cells reduces intracellular accumulation of various anticancer drugs including anthracyclines and vinca alkaloids. This multidrug resistance (MDR) phenotype can be reversed in vitro by a number of non-cytotoxic drugs. We have identified the quinine's isomer cinchonine as a potent MDR reversing agent, both in vitro and in animal models. Here, we report an open phase I dose escalation trial in patients with refractory or relapsed malignant lymphoid diseases. Cinchonine dihydrochloride was administered by continuous i.v. infusion for 48 h and escalated over five dose levels ranging from 15 to 35 mg/kg/d. Cinchonine infusion started 24 h before i.v. doxorubicin (25 mg/m2), vinblastine (6 mg/m2), cyclophosphamide (600 mg/m2) and methylprednisolone (1 mg/kg/d) (CHVP regimen) and lasted for 24 h after chemotherapy infusion. Thirty-four patients received 87 cycles of CHVP/cinchonine. The MTD of cinchonine administered by continuous i.v. infusion was 30 mg/kg/d. Prolonged cardiac repolarization was the main dose-limiting toxicity. No ventricular arrhythmia including 'torsade de pointes' was observed. An MDR reversing activity was identified in the serum from every patient and correlated with cinchonine serum level. When infused at 30 mg/kg/d, cinchonine demonstrated a limited influence on doxorubicin pharmacokinetic. We conclude that i.v. infusion of cinchonine might be started 12 h before MDR-related chemotherapy infusion and requires continuous cardiac monitoring but no reduction of cytotoxic drug doses.

PSC833, cyclosporin A, and dexniguldipine effects on cellular calcein retention and inhibition of the multidrug resistance pump in human leukemic lymphoblasts

A convenient functional assay of the multidrug resistance (MDR) pump is useful for the diagnosis of MDR-1 cancers and the quantitative determination of the potency of inhibitors of the pump. Calcein-AM, a substrate of the MDR pump, was used to determine the concentration of SDZ PSC833 needed to completely inhibit the pump in CEM/VLB100 drug-resistant cells. The initial rates (in percent) for calcein retention by these MDR-1 cells were used to calculate values for the percent initial efflux of calcein-AM through the MDR pump in the presence of the inhibitors PSC833, cyclosporinA, and dexniguldipine. The percent efflux values at 250 and 60 nM calcein-AM were used to calculate the required concentration of each inhibitor to produce half-inhibition (I50) of initial efflux through the pump. These results are consistent with a noncompetitive inhibition of the MDR pump by each of the three inhibitors.