Influence of SDZ-PSC833 on daunorubicin intracellular accumulation in bone marrow specimens from patients with acute myeloid leukaemia

Immunosuppressors as multidrug resistance reversal agents

Multidrug-resistance (MDR) is the major reason for failure of cancer therapy. ATP-binding cassette (ABC) transporters contribute to drug resistance via ATP-dependent drug efflux. P-glycoprotein (Pgp), which is encoded by MDR1 gene, confers resistance to certain anticancer agents. The development of agents able to modulate MDR mediated by Pgp and other ABC transporters remained a major goal for the past 20 years. The calcium blocker verapamil was the first drug shown to be a modulator of Pgp, and since many different chemical compounds have been shown to exert the same effect in vitro by blocking Pgp activity. These included particularly immunosuppressors. Cyclosporin A (CSA) was the first immunosuppressor that have been shown to modulate Pgp activity in laboratory models and entered very early into clinical trials for reversal of MDR. The proof of reversing activity of CSA was found in phase II studies with myeloma and acute leukemia. In phase III studies, the results were less convincing regarding the response rate, progression-free survival, and overall survival, which were detected in advanced refractory myeloma. The non-immunosuppressive derivative PSC833 (valspodar) was subsequently developed. This compound showed tenfold higher potency in reversal of MDR mediated by Pgp. However, pharmacokinetic interactions required reductions in the dose of the concurrently administered anticancer agents. The pharmacokinetic interactions were likely because of decreased clearance of the anticancer agents, possibly as a result of Pgp inhibition in organs such as the gastrointestinal tract and kidney, as well as inhibition of cytochrome P450. Finally, CSA and PSC833 have been shown also to modulate the ceramide metabolism which stands as second messenger of anticancer agent-induced apoptosis. In fact, CSA and PSC833 are also able to respectively inhibit ceramide glycosylation and stimulate de novo ceramide synthesis. This could enhance the cellular level of ceramide and potentiate apoptosis induced by some anticancer agents.

Immunosuppressors and reversion of multidrug-resistance

Drug resistance is the major reason for failure of cancer therapy. When one drug elicits a response in tumour cells resulting in resistance to a large variety of chemically unrelated drugs, this is called multidrug-resistance (MDR). ATP-binding cassette (ABC) transporters contribute to drug resistance via ATP-dependent drug efflux. P-glycoprotein (Pgp) encoded by MDR1 gene, confers resistance to certain anticancer agents. The development of agents able to modulate MDR mediated by Pgp and ABC transporters remained a major goal for the past 10 years. Immunosuppressors, cyclosporin A (CSA) in particular, were shown to modulate Pgp activity in laboratory models and entered very early into clinical trials for reversal of MDR. The proof of reversing activity of CSA was found in phase II studies with myeloma and acute leukaemia. In phase III studies, the results were less convincing regarding the response rate, progression-free survival and overall survival were detected in advanced refractory myeloma. The non-immunosuppressive derivative PSC833 was then extensively studied. This compound shows 10-fold higher potency in reversal of MDR mediated by Pgp. Results from clinical trials with this modulator are still emerging and the notable finding was the need to reduce the dose of anticancer agent used in combination with it. Other effects of CSA and PSC833 on MDR have been described. These two molecules have been shown to have an action on the metabolism of ceramide which stands as second messenger of anticancer agents-induced apoptosis. PSC833 stimulates de novo ceramide synthesis and enhances cell death induced by anticancer agents, such as camptothecins and anthracyclines. In addition, ceramide glycosylation and storage in some cell lines have been described to play a crucial role in resistance to anticancer drugs. CSA is able to inhibit ceramide glucosylation and modulate MDR phenotype. The emergence of other modulators with several ABC protein targets like VX710 are of clinical interest in malignancies expressing several efflux pumps.

Dose escalation studies of cytarabine, daunorubicin, and etoposide with and without multidrug resistance modulation with PSC-833 in untreated adults with acute myeloid leukemia younger than 60 years: final induction results of Cancer and Leukemia Group B Study 9621

PURPOSE

P-glycoprotein (Pgp) is strongly inhibited by PSC-833. A chemotherapy dose-escalation study was performed with PSC-833 in patients younger than 60 years with untreated acute myeloid leukemia. Clinical rather than pharmacokinetic end points were used to develop two induction therapies containing drugs susceptible to Pgp-mediated efflux and associated with comparable toxicities at the maximum-tolerated doses.

PATIENTS AND METHODS

A total of 410 patients were enrolled. Fifteen induction regimens containing variable doses of daunorubicin (DNR) and etoposide (ETOP) and fixed doses of cytarabine were evaluated with (ADEP) or without (ADE) a fixed dose of PSC-833.

RESULTS

Doses selected for phase III testing were DNR 90 mg/m(2) and ETOP 100 mg/m(2) in ADE, and DNR and ETOP each 40 mg/m(2) in ADEP. Intolerable mucosal toxicity occurred at higher doses of ADEP. Although the design of this study precludes direct comparisons, there was an apparent advantage for receiving ADEP with respect to disease-free and overall survival in patients < or = 45 years old, despite the significantly lower doses of DNR and ETOP given in ADEP compared with ADE.

CONCLUSION

A large clinical data set was used to develop induction regimens containing two drugs susceptible to Pgp-mediated efflux, with and without an inhibitor of Pgp function. The chosen doses have comparable antileukemia activity and toxicity, making them suitable for use in a phase III comparative study of induction chemotherapy for patients with acute myeloid leukemia younger than 60 years. That trial will also clarify whether patients < or = 45 years old are especially likely to benefit from Pgp inhibition during induction therapy.

A phase I/II study of the MDR modulator Valspodar (PSC 833) combined with daunorubicin and cytarabine in patients with relapsed and primary refractory acute myeloid leukemia

The cyclosporine analog Valspodar (PSC 833, Novartis Pharma) is a strong inhibitor of the mdr1 gene product p-glycoprotein (pgp). A phase I/II study was conducted in order to evaluate if addition of Valspodar to treatment with daunorubicin and cytarabine, given to patients with primary refractory or relapsed acute myeloid leukemia, could increase the complete remission rate.Fifty-three patients were treated in cohorts of three to six patients. Twelve patients reached a complete remission in bone marrow, five of whom also normalized their peripheral blood values. Three patients experienced treatment-related deaths from pneumonia, liver failure and cerebral hemorrhage, respectively. It is concluded that Valspodar 10 mg/kg per 24 h in combination with daunorubicin 45 mg/m(2) for 3 days and cytarabine 1 g/m(2) twice daily for 4 days is tolerable in this heavily pre-treated group of patients. Due to the moderate treatment results, the phase II part of the study was ended prematurely. The modulation of only pgp did not give an obvious improvement of the treatment results in this group of patients.

Reduced effect of gemtuzumab ozogamicin (CMA-676) on P-glycoprotein and/or CD34-positive leukemia cells and its restoration by multidrug resistance modifiers

Gemtuzumab ozogamicin (CMA-676), a calicheamicin-conjugated humanized anti-CD33 mouse monoclonal antibody, has recently been introduced clinically as a promising drug for the treatment of patients with acute myeloid leukemia (AML), more than 90% of which express CD33 antigen. However, our recent study suggested that CMA-676 was excreted by a multi- drug-resistance (MDR) mechanism in P-glycoprotein (P-gp)-expressing leukemia cell lines. We analyzed the in vitro effects of CMA-676 on leukemia cells from 27 AML patients in relation to the amount of P-gp, MDR-associated protein 1 (MRP1), CD33 and CD34, using a multi-laser-equipped flow cytometer. The cytocidal effect of CMA-676, estimated by the amount of hypodiploid portion on cell cycle, was inversely related to the amount of P-gp estimated by MRK16 monoclonal antibody (P = 0.004), and to the P-gp function assessed by intracellular rhodamine-123 accumulation in the presence of PSC833 or MS209 as a MDR modifier (P = 0.0004 and P = 0.002, respectively). In addition, these MDR modifiers reversed CMA-676 resistance in P-gp-expressing CD33(+) leukemia cells (P = 0.001 with PSC833 and P = 0.0007 with MS209). In CD33(+) AML cells from 13 patients, CMA-676 was less effective on CD33(+)CD34(+) than CD33(+)CD34(-) cells (P = 0.002). PSC833 partially restored the effect of CMA-676 in CD33(+)CD34(+) cells. These results suggest that the combined use of CMA-676 and a MDR modifier will be more effective on CD33(+) AML with P-gp-related MDR.

Calcein assay for multidrug resistance reliably predicts therapy response and survival rate in acute myeloid leukaemia

In this study, we evaluated the suitability of the calcein assay as a routine clinical laboratory method for the identification of multidrug-resistant phenotype in acute leukaemia. This study presents the results of the calcein tests obtained in two large haematological centres in Hungary. Assays were performed with blast cells of 93 de novo acute leukaemia patients, including 65 patients with acute myeloid leukaemia (AML). Results were expressed as multidrug resistance activity factor (MAF) values. AML patients were divided into responders and non-responders and MAF values were calculated for each group. In both centres, responder patients displayed significantly lower MAF values than non-responders (P = 0.0045 and P = 0.0454). Cut-off values were established between the MAFR + SEM and MAFNR - SEM values. On the basis of these cut-off levels, multidrug resistance (MDR) negativity showed a 72% predictive value for the response to chemotherapy, whereas MDR positivity was found to have an average predictive value of 69% for therapy failure. MDR activity was a prognostic factor for survival rate and the test was suitable for detecting patients at relapse. The calcein assay can be used as a quantitative, standardized, inexpensive screening test in a routine clinical laboratory setting. The assay detects both P-glycoprotein and multidrug resistance-associated protein activities, and identifies AML patients with unfavourable therapy responses.

Drug resistance mechanisms in acute leukemia

Markers of anticancer drug resistance are predictive of treatment response and outcome in patients with acute myeloid leukemia. Immunologic detection of the drug efflux pumps, P-glycoprotein (Pgp) and multidrug resistance-associated protein 1 (MRP1), correlate with functional assays of drug resistance. These accumulation defects also appear operable in acute lymphoblastic leukemia. Many of the efflux pumps identified share significant structural homology with the large superfamily of ATP-binding cassette transporters. Other markers such as lung-resistance protein, bcl-2, and breast cancer-resistance protein, have been described in acute myeloid leukemia patients although their pathophysiology and clinical relevance are less clear and the methodology for their quantification are not well standardized. Preclinical studies have shown that small molecules capable of reversing efflux can restore drug sensitivity in resistant tumor models. Although initial clinical studies were limited by both potency and specificity of the reverser, later studies with more effective reversers have in many instances been limited by pharmacokinetic interactions exacerbating the clinical toxicities of chemotherapy. Although one large randomized study has demonstrated a proven survival advantage without increased toxicity using cyclosporine, the inconsistent results with other modulators raise doubt as to the utility and overall strategy of using drug efflux blockers in patients with established Pgp overexpression. Many of these patients have additional resistance mechanisms, and achieving meaningful clinical responses will likely require more complex clinical strategies. Preventing or delaying development of drug resistance in chemosensitive patients represents another therapeutic strategy to be tested.

Modulation of daunorubicin cellular resistance by combination of P-glycoprotein blockers acting on drug efflux and intracellular drug sequestration in Golgi vesicles

BACKGROUND

S9788 and PSC833 were developped as P-glycoprotein (Pgp) blockers and found to act additionally on daunorubicin subcellular distribution, involving different putative targets. On this basis, combinations of S9788 and PSC833 were evaluated in Pgp-expressing MCF7(DXR) cells in which we recently demonstrated that daunorubicin was sequestered in Golgi vesicles (Bour-Dill et al.: Cytometry, 39: 16-25, 2000).

METHODS

Combinations of S9788 and PSC833 consisted in complementary fractions of iso-effective concentrations (IEC) leading to 90% (IEC90) and median (IEC50) reversion of daunorubicin resistance. Resistance modulation was assessed using cytotoxicity assays, flow cytometry determination of intracellular daunorubicin, and fluorescence microscopy analysis of daunorubicin subcellular distribution.

RESULTS

Individually, both S9788 and PSC833 were found to be very potent with IEC90 of 5 and 15 micromol/l, and IEC50 of 0.1 and 0.2 micromol/l, respectively, for S9788 and PSC833. When combined, synergistic cytotoxicity was observed for both IEC90 and IEC50 combinations while intracellular daunorubicin fluorescence was only synergistically increased for IEC90 combinations. For IEC50 combinations, no increase in intracellular fluorescence was observed, and fluorescence microscopy examination of the cells suggested that daunorubicin sequestration in Golgi vesicles could be modulated at concentrations that do not significantly increase daunorubicin cellular concentration. Using immunofluorescence and reverse transcription-polymerase chain reaction analyses, multidrug resistance-associated protein, major vault lung-resistance protein, and anthracycline-resistance associated protein were not found to be implicated.

CONCLUSIONS

Synergistic combinations of S9788 and PSC833 might offer alternative ways to decrease the toxicity generated by high-dose Pgp-blockers without altering the efficacy of the resistance modulation.

SDZ PSC 833 the drug resistance modulator activates cellular ceramide formation by a pathway independent of P-glycoprotein

SDZ PSC 833 (PSC 833) is a new multidrug resistance modulator. Recent studies have shown that the principal mechanism of action of PSC 833 is to bind P-glycoprotein (P-gp) and prevent cellular efflux of chemotherapeutic drugs. We previously reported that PSC 833 increases cellular ceramide levels. The present study was conducted to determine whether the impact of PSC 833 on ceramide generation is dependent on P-gp. Work was carried out using the drug-sensitive P-gp-deficient human breast adenocarcinoma cell line, MCF-7, and drug resistant MCF-7/MDR1 clone 10.3 cells (MCF-7/MDR1), which show a stable MDR1 P-gp phenotype. Overexpression of P-gp in MCF-7/MDR1 cells did not increase the levels of glucosylceramide, a characteristic which has been associated with multidrug resistant cells. Treatment of MCF-7 and MCF-7/MDR1 cells with PSC 833 caused similar ceramide elevation, in a dose-responsive manner. At 5.0 microM, PSC 833 increased ceramide levels 4- to 5-fold. The increase in ceramide levels correlated with a decrease in survival in both cell lines. The EC50 (concentration of drug that kills 50% of cells) for PSC 833 in MCF-7 and MCF-7/MDR1 cells was 7.2 +/- 0.6 and 11.0 +/- 1.0 microM, respectively. C6-Ceramide exposure diminished survival of MCF-7 cells; whereas, MCF-7/MDR1 cells were resistant to this short chain ceramide analog. Preincubation of cells with cyclosporine A, which has high affinity for P-gp, did not diminish the levels of ceramide generated upon exposure to PSC 833. These results demonstrate that PSC 833-induced cellular ceramide formation occurs independently of P-gp. As such, these data indicate that reversal of drug resistance by classical P-gp blockers may be modulated by factors unrelated to drug efflux parameters.

Determination of intracellular organelles implicated in daunorubicin cytoplasmic sequestration in multidrug-resistant MCF-7 cells using fluorescence microscopy image analysis

BACKGROUND

Anthracycline resistance is known to be mediated by P-glycoprotein (P-gp) or multidrug-resistance related protein (MRP) as well as intracellular sequestration of drugs.

METHODS

The resistance phenotype of doxorubicin-selected MCF-7(DXR) human breast adenocarcinoma cell line was characterized by cellular and nuclear daunorubicin efflux, P-gp and MRP expression and apoptosis induction. Daunorubicin sequestration was investigated through organelle markers (lysosomes, endoplasmic reticulum and Golgi apparatus) and daunorubicin co-localization by dual-color image analysis fluorescence microscopy using high numerical aperture objective lenses to achieve the smallest field depth and the best lateral resolution. Signal to noise and specificity ratios were optimized for daunorubicin and organelle fluorescent probes labeling.

RESULTS

An original image analysis procedure was developed to investigate daunorubicin and organelles co-localization. The reliability of the image analysis was controlled through chromatic shift and intensity linearity measurement using calibrated microbeads. The main contribution (65%) of Golgi vesicles in daunorubicin sequestration was demonstrated. Although no rational relationship could be established between daunorubicin sequestration and apoptosis induction, no apoptosis was observed in MCF-7(DXR) cells.

CONCLUSIONS

In addition to P-glycoprotein mediated drug efflux and without MRP overexpression, MCF-7(DXR) daunorubicin resistance phenotype involves drug sequestration within intracellular vesicles identified as Golgi vesicles and resistance to apoptosis induction.