Multiple myeloma: expression of nucleoside transporters on malignant plasma cells and their relationship to cellular proliferation

Analysis of human equilibrative nucleoside transporter 1 (hENT1) protein in non-Hodgkin's lymphoma by immunohistochemistry

The human equilibrative nucleoside transporter 1 (hENT1) is a member of the equilibrative nucleoside transporter family that mediates cellular entry of gemcitabine, cytarabine, and fludarabine. Deficiency in hENT1 confers resistance to toxicity of these drugs in a variety of model systems. Since some nucleoside analogs have a role in treating patients with non-Hodgkin's lymphoma (NHL), this study was undertaken to assess hENT1 abundance in NHL. A total of 115 cases of NHL of various subtypes and 15 reactive lymph nodes were evaluated for the presence of hENT1 protein using immunohistochemistry applied to frozen tissues. Samples were considered positive when >or=50% of neoplastic cells showed immunostaining. In reactive lymph nodes, hENT1 was confined to the germinal centers, whereas mantle zone B-cells and interfollicular T-cells were negative. In NHL, a relatively high frequency of hENT1 positivity was found in Burkitt lymphoma/leukemia (63%), diffuse large B-cell lymphoma (DLCL; 45%), and follicular lymphoma (40%). In DLCL, 26% of cases were positive for CD10, and CD10-positive DLCL cases were more likely to be hENT1 positive than CD10-negative cases (P=0.025). A lower frequency of hENT1 positivity was found in mantle cell lymphoma (13%) and peripheral T-cell lymphomas (37%). All marginal zone lymphomas (n=5), chronic lymphocytic leukemia small lymphocytic lymphomas (n=10), plasmacytoma (n=3), acute lymphoblastic lymphoma/leukemia, and anaplastic large-cell lymphomas (n=5) were negative. In conclusion, hENT1 was most frequently found in benign and malignant follicular center cells. Prospective studies to assess the value of hENT1 immunostaining in predicting resistance to nucleoside chemotherapy for NHL are warranted.

Dose escalation therapy in previously untreated patients with multiple myeloma following Z-Dex induction treatment

A phase I-II study of high-dose (HD) alkylating agents in newly diagnosed patients with multiple myeloma after maximum response to Z-Dex (idarubicin, dexamethasone) therapy and DHAP (cisplatin, HD cytosine arabinoside, dexamethasone), stem cell mobilization is reported. Twenty-six patients, median age 56 years (range 42-66), completed Z-Dex chemotherapy and peripheral blood stem cells (PBSC) were mobilized with DHAP. Patients then preceded to cyclophosphamide (HD Cy: 6 g/m(2)) with granulocyte colony-stimulating factor followed by busulphan-melphalan-conditioned PBSC autograft. Interferon alpha was introduced at 3 months post transplant as maintenance therapy. Six patients failed to complete the full protocol. Median time from diagnosis to transplantation was 8 months (range 6-12). Mean CD34+ cell dose collected was 15.8 x 10(6)/kg (CI 11.8, 19.8). Median time from DHAP to HD-Cy was 6 weeks (range 4-12) and from HD-Cy to transplant was 8 weeks (range 6-12). The median follow-up was 36 months (range 6-63). On an intent-to-treat basis, the response rates were three complete response (CR, 12%), 21 partial response (PR, 80%) and two stable disease (SD, 8%) post Z-Dex, five CR (19%) and 21 PR (81%) post HD-Cy, and 14 CR (54%) and 12 PR (46%) post transplant. The treatment-related mortality (TRM) was 4% (1 patient). Median overall survival (OS) and progression-free survival (PFS) have not been reached; estimated values were 60 and 48 months respectively. The 3-year OS and PFS were 72% and 62%. Actuarial 5-year OS and event-free survival were 49% and 32%. DHAP produces effective PBSC mobilization and sequential HD therapy, including autologous PBSCT, in patients who received Z-Dex; this offers significant durable disease response rates with acceptable TRM.

Nucleoside analogues: mechanisms of drug resistance and reversal strategies

Nucleoside analogues (NA) are essential components of AML induction therapy (cytosine arabinoside), effective treatments of lymphoproliferative disorders (fludarabine, cladribine) and are also used in the treatment of some solid tumors (gemcitabine). These important compounds share some general common characteristics, namely in terms of requiring transport by specific membrane transporters, metabolism and interaction with intracellular targets. However, these compounds differ in regard to the types of transporters that most efficiently transport a given compound, and their preferential interaction with certain targets which may explain why some compounds are more effective against rapidly proliferating tumors and others on neoplasia with a more protracted evolution. In this review, we analyze the available data concerning mechanisms of action of and resistance to NA, with particular emphasis on recent advances in the characterization of nucleoside transporters and on the potential role of activating or inactivating enzymes in the induction of clinical resistance to these compounds. We performed an extensive search of published in vitro and clinical data in which the levels of expression of nucleoside-activating or inactivating enzymes have been correlated with tumor response or patient outcome. Strategies aiming to increase the intracellular concentrations of active compounds are presented.

The functional phenotype of the primitive plasma cell in patients with multiple myeloma correlates with the clinical state

The malignant plasma cells from patients with multiple myeloma display considerable phenotypic heterogeneity. All plasma cells express high intensity CD38 (CD38++), cytoplasmic immunoglobulin and either kappa or lambda light chains. Subpopulations of mature (CD45-), immature (CD45+) and primitive (CD45++, CD19+) plasma cells can be defined but little is known about the functional differences and clinical significance of these subpopulations. Three colour flow cytometry and permeabilisation was used to determine the expression of functionally important antigens in plasma cell subpopulations. These antigens included the labelling index (LI, bromodeoxyuridine), number of nucleoside transporter per cell, p-glycoprotein (JSB-1), and oncoprotein expression (c-myc, c-fos, c-neu, bcl-2, p-ras, p53m, p-53w, and Rb). In progressive disease there was an increase in the absolute number but not the percentage of CD45++ plasma cells. There was a significant difference in the mean LI of the CD38++, CD45++ population in progressive disease compared with stable disease (9.2% vs 2.2%; z = 19.9, p < 0.001). The LI of CD45++ cells ranged up to 45% and provided a better correlation with disease status than the LI of the total cell population. Any increase in nucleoside transporters or p-glycoprotein expression was almost entirely attributable to an increase in the primitive plasma cell population. In 96% (n = 28) of samples from patients in progressive disease there was at least one abnormality in the functional phenotype of the primitive plasma cells. This is in contrast with 44% of samples from patients in stable disease (n = 58). These studies suggest that the functional phenotype of the primitive plasma cell determines the clinical phenotype of patients with myeloma.

Nucleoside transporters, bcl-2 and apoptosis in CLL cells exposed to nucleoside analogues in vitro

The purine nucleoside analogues fludarabine (F1) and chlorodeoxyadenosine (2-CdA) are considered to be cell cycle specific agents which require DNA synthesis for cytotoxicity. However, their efficacy in the treatment of CLL, an indolent lymphoid malignancy suggests additional mechanisms of action. Like cytosine arabinoside (AraC), F1 and 2-CdA gain access to the cell via a specific nucleoside transporter (NST) protein. To investigate the mode of action of these drugs in CLL, we used a fluorescent ligand for the NST (5'-(SAENTA- x8)-fluorescein) and 3-colour flow cytometry to determine NST expression on CD5+/CD19+ B-cells from the peripheral blood (PB) of patients with CLL. NST levels on these cells was found to be not significantly different from normal control lymphocytes (mean = 485 +/- 425) vs. (mean = 553 +/- 178). Exposure to varying concentrations (0, 3 microM and 30 microM) of F1 and 2-CdA, however, resulted in an upregulation of NST (mean = 1552 +/- 775 with 30 microM FL; mean = 3392 +/- 2197 with 30 microM 2-CdA) after 48. "Large" lymphoid cells (not present in normal PB) were found to express significantly more NST (mean = 2540 +/- 2861) and have a higher proliferative capacity than "small" cells (mean = 357 +/- 517 NST/cell). Incubation of CLL cells with F1 (n = 6) and 2-CdA (n = 8) in vitro over 48 h also resulted in an increase in the proportion of cells in S-phase (0 microM = 0.2 + 2 - 0.1; 30 microM FL = 2.4 +/- 2.0; 30 microM 2-CdA = 3.3 +/- 1.3) and a significant increase in morphologically identifiable apoptosis. Apoptosis was confirmed by flow cytometric DNA analysis (0 microM = 13 +/- 8%; 30 microM FL = 40 +/- 20%; 30 microM 2-CdA = 48 +/- 11%). In situ hybridization using a biotinylated cDNA bcl-2 probe demonstrated that bcl-2 mRNA expression was markedly decreased in treated cells after 24 h. These studies have demonstrated that: (1) NST expression on CLL lymphocytes is low; (2) in vitro exposure to the analogues increases both the level of NST expression and the % cells in S-phase; (3) exposure to the analogues downregulates bcl-2 expression and increases apoptosis.

Mechanisms of the escape phase of myeloma

In multiple myeloma the duration of plateau is an important clinical and biological determinant of quality of life and survival. During plateau phase, the tumour is in an indolent state, as manifested by a low labelling index of plasma cells and other proliferative markers, e.g. the thymidine kinase level. The mechanism by which plasma cells escape from this indolent phase to a more aggressive phase of this disease is unknown, but a number of possible mechanisms have been postulated. These include loss of immunoregulation, clonal evolution, cytokine dysfunction and oncogene activation or tumour suppressor gene dysfunction. As current chemotherapy protocols do not appear to be able to eradicate the malignant clone, understanding the nature of the indolent phase of the malignant clone and the reasons for its escape from this phase are very important and may provide new options for disease control.