Is multidrug resistance (P-glycoprotein) an intrinsic characteristic of plasma cells in patients with monoclonal gammopathy of undetermined significance, plasmacytoma, multiple myeloma and amyloidosis?

The role of P-glycoprotein in drug resistance in multiple myeloma

Multiple myeloma (MM) is a malignant neoplastic cancer of the plasma cells that involves the bone marrow. The majority of patients with MM initially respond to chemotherapy, but they eventually become resistant to later drug therapy. One of the reasons for drug resistance in patients with MM is efflux transporters. P-glycoprotein (P-gp) is the most studied of the multidrug resistance proteins, and is up-regulated in response to many chemotherapeutic drugs. This up-regulation of P-gp causes a decrease in the intracellular accumulation of these drugs, limiting their therapeutic efficacy. In this review, we focus on the role of P-gp in drugs used for patients with MM. P-gp has been found to be an important factor with regard to drug resistance in many of the drug classes used in the treatment of MM (proteasome inhibitors, anthracyclines, alkylating agents and immunomodulators are examples). Thus, our further understanding of its mechanism and inhibitory effects will help us decrease drug resistance in patients with MM.

Functional Imaging of Multidrug Resistant Phenotype by 99mTc-MIBI Scan in Patients with Multiple Myeloma

Overexpression of P-glycoprotein (Pgp) is one of the primary mechanisms of multidrug resistance (MDR) in several diseases, including multiple myeloma. The aim of this study was to investigate whether the washout of 99mTc-MIBI, a transport substrate of Pgp, is enhanced in the bone marrow of patients with multiple myeloma overexpressing Pgp. Seventeen (17) patients were i.v. injected with 555 MBq of 99mTc-MIBI, and whole-body scans were performed at 10 and 60 minutes. A region of interest (ROI) was drawn over the thoracic spine of each scan, and the washout of 99mTc-MIBI was calculated, after decay correction, as: (10-minute counts/pixel minus 60-minute counts/pixel) divided by 10-minute counts/pixel. Pgp expression was determined in 17 bone marrow samples obtained from the same patients immediately before the 99mTc-MIBI scan. Following centrifugation over the Ficoll-Hypaque gradient, cytospins were obtained and immunostained with C219 monoclonal antibody. The immunostaining of Pgp was graded as 1, 2, or 3 when a faint, moderate, or intense reaction, respectively, was observed in infiltrating plasma cells. Washout of 99mTc-MIBI ranged between 5% and 26%. A statistically significant direct correlation was found between the washout of the tracer and Pgp expression (Spearman rank correlation coefficient r = 0.74, p < 0.001). A partial overlap of washout values was observed in different classes of Pgp expression, thus preventing the discrimination of individual patients. Washout of 99mTc-MIBI, expressed as the percentage of radioactivity cleared from the bone marrow over a 1-hour period, may be used as a noninvasive tool for in vivo whole-body imaging of Pgp expression and function in multiple myeloma patients.

Comparative whole-body 201Tl and bone scintigraphies for the detection of bone marrow involvement in multiple myeloma

The objectives of this study were to investigate the role of whole-body 201Tl-chloride scintigraphy in comparison with bone scintigraphy in the detection of bone marrow involvement in patients with multiple myeloma and to assess the follow-up evaluation using 201Tl-chloride. Twenty-one patients with untreated multiple myeloma were evaluated. 201Tl-chloride images were acquired 10 min (early) and 2 h (delayed) after the injection of 111 MBq 201Tl-chloride. Bone images were acquired 3 h after the intravenous injection of 740 MBq 99mTc-hydroxymethylene diphosphonate (HMDP). The 201Tl-chloride scan patterns were classified as normal, diffuse (presence of bone marrow), focal (localized areas of uptake) and diffuse+focal. The bone scan patterns were classified as normal and abnormal. Eight of the 21 patients also underwent 201Tl-chloride scintigraphy after chemotherapy for the evaluation of the therapeutic response. On the early 201Tl-chloride image, two patients showed a normal, 13 a diffuse, two a focal and four a diffuse + focal pattern. On the delayed 201Tl-chloride image, nine patients showed a normal, six a diffuse, four a focal and two a diffuse + focal pattern. Bone scintigraphy showed an abnormal accumulation in only five of the 21 patients. Of the eight patients who underwent follow-up 201Tl-chloride studies, the abnormal diffuse pattern was changed to a normal pattern on post-treatment scintigraphy in three, and the degree of abnormal 201Tl-chloride accumulation decreased in comparison with the pre-treatment scan in three. These six patients were considered to be in clinical remission. In the two remaining patients, the degree of abnormal 201Tl-chloride accumulation increased in comparison with the pre-treatment scan, and they were considered to be in clinical progression. 201Tl-chloride scintigraphy is a non-invasive tool, which may be more useful than bone scintigraphy for the diagnosis of multiple myeloma, and may be helpful in the follow-up of multiple myeloma.

Immunophenotypic Aberrations, DNA Content, and Cell Cycle Analysis of Plasma Cells in Patients with Myeloma and Monoclonal Gammopathies

We describe the immunophenotypic and gross DNA defects in 55 patients with myeloma and 50 patients with monoclonal gammopathy and review the literature on this subject (MedLine, 1994-2000). Our data confirmed previous reports indicating that in myeloma nearly all marrow plasma cells are abnormal (98.7 +/- 8.1%). In monoclonal gammopathy the fraction of abnormal plasma cells was 35.0 +/- 32.8%. In both myeloma and monoclonal gammopathy, the most frequent aberrant phenotypic features consisted of absence of expression of CD19, strong expression of CD56, and decreased intensity of expression of CD38; aberrant expression of CD10, CD20, CD22, or CD28 was observed in less than one-third of myeloma cases. The vast majority of cases had two or more phenotypic aberrations. In the DNA studies, 7% of myeloma cases were biclonal and 93% of cases were monoclonal. In those studies with only one plasma cell mitotic cycle, 37% had normal DNA content and 63% were aneuploid (hyperploid, 61%; hypoploid, 2%). The mean percentages of plasma cells in S- and G2M phases were 4.9 +/- 8.5 and 4.4 +/- 6.9%, respectively. Thirty-eight percent of cases had more than 3% of plasma cells in S phase. In monoclonal gammopathy, the DNA index of abnormal plasma cells ranged from 0.89 to 1.30 and the percentage of diploid (31%) and aneuploid (69%) cases was not different from the results found in myeloma. The differences in percentage of abnormal plasma cells in S- (7.4 +/- 8.6%) and G2M-phases (2.4 +/- 1.7%) in patients with monoclonal gammopathy were not statistically significant.