Maria R. Baer

To report a case of serotonin syndrome associated with interaction between fentanyl and citalopram, as evidenced by medication history, clinical features and reversal following discontinuation of fentanyl. A 65-year-old patient chronically treated with the selective serotonin reuptake inhibitor (SSRI) citalopram developed confusion, agitation, tachycardia, tremors, myoclonic jerks and unsteady gait, consistent with serotonin syndrome, following initiation of fentanyl, and all symptoms and signs resolved following discontinuation of fentanyl. Based on the Naranjo probability scale, serotonin syndrome was a probable adverse reaction associated with co-administration of citalopram and fentanyl. Serotonin syndrome is a potentially lethal pharmacodynamic interaction between medications that increase serotonergic transmission at the synaptic junction. The development of new pharmacological agents with varied properties and actions has increased the risk of serotonin syndrome as a clinical diagnosis. SSRIs and fentanyl are commonly co-administered, especially in the setting of chronic or malignant pain, as underlying depression may contribute to the pathogenesis of pain. Healthcare professionals should be aware of the possible development of serotonin syndrome as a complication of initiation of fentanyl and other phenylpiperidine opioids in patients treated with SSRIs.

Background: The synthetic 4’-O-benzylated doxorubicin analog WP744 was designed to abrogate transport by the multidrug resistance (MDR)-associated ATP-binding cassette (ABC) proteins P-glycoprotein (Pgp) and multidrug resistance protein (MRP-1). We compared its uptake and cytotoxicity with those of doxorubicin and daunorubicin in cell lines overexpressing Pgp, MRP-1 or breast cancer resistance protein (BCRP) and in acute myeloid leukemia (AML) cells. Methods: Cellular uptake was studied by flow cytometry and cytotoxicity in 96-h 96-well cultures in cell lines overexpressing Pgp, MRP-1 or wild type (BCRP^R482) or mutant (BCRP^R482T, BCRP^R482G) BCRP and in pre-treatment AML marrow cells. Results: Uptake and cytotoxicity of WP744 were consistently greater than those of doxorubicin and daunorubicin at equimolar concentrations in all cell lines studied and in AML cells. Conclusion: WP744 overcomes transport by Pgp, MRP-1 and BCRP in cell lines and AML cells and is a promising agent for clinical development in AML and other malignancies with broad-spectrum multidrug resistance.

Purpose We sought to determine the effects of the immunosuppressants, cyclosporin A (CsA), tacrolimus and sirolimus, on drug transport by the ATP-binding cassette proteins, P-glycoprotein (Pgp; ABCB1), multidrug resistance protein-1 (MRP-1; ABCC1) and breast cancer resistance protein (BCRP; ABCG2), and the major vault protein lung resistance protein (LRP). Methods Cellular content of mitoxantrone, a Pgp, MRP-1 and BCRP substrate, was measured by flow cytometry in cells overexpressing these proteins following incubation with and without CsA, tacrolimus or sirolimus. Interaction of BCRP with these compounds was studied by photolabeling and ATPase assays. Nuclear–cytoplasmic distribution of doxorubicin was studied by confocal microscopy in cells overexpressing LRP. Results CsA increased cellular drug uptake in cells overexpressing Pgp, MRP-1 or BCRP and nuclear drug uptake in cells overexpressing LRP at the clinically achievable concentration of 2.5 μM. Tacrolimus enhanced cellular drug uptake at 1 μM, but not at 0.08 μM, its clinically achievable concentration, and did not enhance nuclear drug uptake. Sirolimus enhanced cellular drug uptake in cells overexpressing Pgp, MRP-1 and BCRP with optimal effects at 2.5 μM, but was effective at its clinically achievable concentration of 0.25 μM if cells were pre-incubated for at least 30 min before drug exposure, and also enhanced nuclear drug uptake at 0.25 μM. BCRP modulation by all three immunosuppressive agents was associated with competitive binding to the drug transport sites. Conclusions CsA, tacrolimus and sirolimus modulate drug transport by Pgp, MRP-1 and BCRP and CsA and sirolimus modulate drug transport by LRP at concentrations that differ from immunosuppressive concentrations and maximum tolerated concentrations.

Diagnostic evaluation of acute leukemia at Roswell Park Cancer Institute has routinely included immunophenotyping by multiparameter flow cytometry. In a retrospective analysis of 646 cases, morphology and cytochemistry established lineage in 612, but not in 34 (5%), of which 26, 5, and 3 were myeloid, undifferentiated, and lymphoid, respectively, based on immunophenotyping. In addition, immunophenotyping changed the lineage assigned based on morphology and cytochemistry in 11 cases (2%); 8 changed from lymphoid to myeloid, and 3 from myeloid to lymphoid. The data support routine inclusion of at least limited immunophenotyping in the diagnostic evaluation of acute leukemia. © 2006 International Society for Analytical Cytology

Summary: Drugs used in treatment of adult acute lymphoblastic leukaemia (ALL) are substrates for breast cancer resistance protein (BCRP, MXR, ABCG2), which may thus play a role in resistance in this disease. Pretreatment blasts from 30 adult ALL patients were studied for BCRP mRNA by quantitative reverse transcription polymerase chain reaction analysis, BCRP protein by immunophenotyping with three antibodies and BCRP function by fumitremorgin C modulation of intracellular mitoxantrone retention, measured by flow cytometry. BCRP mRNA in all cases encoded wild type protein (BCRP^R482), which mediates mitoxantrone and methotrexate resistance, but only low‐level anthracycline resistance. The BXP‐21, BXP‐34 and anti‐ABCG2 antibodies stained blasts in 13, 11 and 14 cases (43%, 37% and 47%); BXP‐21 correlated well with BXP‐34 and anti‐ABCG2, but BXP‐34 and anti‐ABCG2 did not correlate, and antibody staining did not correlate with mRNA levels. BCRP function was seen in 21 cases (70%), but correlated poorly with antibody staining. An exploratory statistical analysis indicated that BXP‐21 staining was predictive of shorter disease‐free survival (DFS) (P = 0·0374) in this small patient population. Poor correlations between mRNA, protein and function indicate the complex biology of BCRP in adult ALL, and the possible correlation of BCRP expression with DFS should be studied in larger series.

Data on breast cancer resistance protein (BCRP, MXR, ABCG2) expression in acute myeloid leukemia (AML) have been inconsistent, possibly due to use of different assays in different studies. BCRP mRNA was studied by the reverse-transcription polymerase chain reaction and BCRP protein expression (BXP-21, BXP-34 or anti-ABCG2 antibody, with anti-CD34 and anti-CD33) and function (fumitremorgin C modulation of mitoxantrone retention) by flow cytometry in eight cell lines and in pretreatment blasts from 31 AML patients. BCRP mRNA levels, antibody staining and function correlated strongly in cell lines (Pearson r values, 0.73–0.97), but not in AML samples. AML sample BCRP mRNA levels were between those in parental 8226 and 35-fold mitoxantrone-resistant 8226/MR20 cells in all but one case, and BCRP mRNA had the wild-type sequence at codon 482 in all. In AML, unlike in cell lines, BCRP protein expression or function, when present, was only detected in small subpopulations. BCRP mRNA and protein expression did not correlate, nor did staining with different BCRP antibodies, and function did not correlate with mRNA nor protein expression. Presence of BCRP only in subpopulations and discordance among BCRP measurements suggest complex biology of BCRP in AML and incomplete modeling by cell lines.

Purpose The taxanes paclitaxel and docetaxel are substrates for P-glycoprotein (Pgp), an ATP-binding cassette (ABC) transport protein associated with multidrug resistance (MDR). In contrast, the synthetic taxane ortataxel (BAY 59-8862, IDN-5109) is effective against Pgp-expressing cells by virtue of modulation of Pgp-mediated transport. The synthetic taxane tRA96023 also modulates Pgp and is noncytotoxic due to removal of the tubulin-binding side chain at the C-13 position of the taxane backbone. We studied the effects of ortataxel and tRA96023 on the other MDR-associated ABC transport proteins, multidrug resistance protein (MRP-1) and breast cancer resistance protein (BCRP, MXR, ABCG2). Methods Modulation of mitoxantrone, daunorubicin and doxorubicin retention and cytotoxicity by ortataxel and tRA96023 was studied in established cell lines overexpressing Pgp, MRP-1 and wild type (BCRP^R482) and mutant (BCRP^R482T) BCRP, and was compared with modulation by the established Pgp-, MRP-1- and BCRP-specific modulators PSC-833, probenecid and fumitremorgin C, respectively. Results Ortataxel effectively modulated drug retention and cytotoxicity in cell lines overexpressing MRP-1 and BCRP^R482, in addition to Pgp. tRA96023 modulated drug retention and cytotoxicity in cell lines overexpressing BCRP^R482 and Pgp, but not those overexpressing MRP-1. Neither ortataxel nor tRA96023 modulated BCRP^R482T. Conclusions The synthetic taxane derivatives ortataxel and tRA96023 are broad-spectrum ABC protein modulators. Further studies will seek to identify a noncytotoxic synthetic taxane that modulates Pgp, MRP-1 and BCRP.

Acute myeloid leukemia (AML) is a curable malignancy, but its cure rate remains disappointingly low. Accurate quantitation of residual AML cells would allow individualization of therapy and thereby increase the likelihood of cure for each patient. Techniques that are being studied for residual disease detection include molecular assays for abnormalities that are present in subsets of AML patients, and multiparameter flow cytometry, which has broader applicability. Although significant advances have been made in the development of assays for monitoring residual disease, and particularly in techniques for molecular quantitation, additional refinement and validation are needed before these assays can be applied routinely in clinical management.