Letters to the editor Eur J Nucl Med (2001) 28:1430–1431 DOI 10.1007/s002590100576 Published online: 10 July 2001 © Springer-Verlag 2001
Bone marrow uptake of 99mTc-MIBI in patients with multiple myeloma Dear Sir, We read with interest the paper by Fonti et al. entitled “Bone marrow uptake of 99mTc-MIBI in patients with multiple myeloma” (Eur J Nucl Med 2001; 28:214–220). In patients with multiple myeloma (MM) or monoclonal gammopathy of undetermined significance (MGUS), the authors found a significant correlation between in vitro uptake of 99mTc-MIBI by bone marrow mononuclear cells and both bone marrow plasma cell infiltration and in vivo uptake score on 99mTc-MIBI scintigraphy. Our personal approach has been to try to separate blood cells 10 min after in vivo intravenous injection of 99mTc-MIBI in MM patients selected for having a significant number of circulating plasma cells in blood, and we have discovered that radioactivity is associated with different cellular components, including erythrocytes. To concentrate on the mononuclear cell fraction separated on a Ficoll-Hypaque gradient obviously does not tell the whole story. In this cell subgroup it is, moreover, difficult to distinguish between lymphocytes and plasma cells without the use of specific monoclonal antibodies, and contamination by erythrocytes does occur, especially when biopsy is obtained at the sternum. Reading the paper by Fonti et al., we could not be sure that the in vitro cellular uptake of 99mTc-MIBI in the mononuclear cell fraction was only linked to the uptake by the malignant plasma cells and that this mechanism accounted quantitatively for the actual uptake in vivo. We acknowledge, however, that the authors made an interesting point by observing a correlation between the in vitro uptake of 99mTc-MIBI in the Ficoll-Hypaque cellular fraction and the activity in the bone marrow of the same patients. The observed correlation between the in vitro uptake of 99mTc-MIBI by mononuclear cells and bone marrow plasma cell infiltration seems to indicate that the malignant plasma cells of each investigated patient had a comparable level of 99mTc-MIBI uptake. We find such a relationship surprising as we observed that the 90-min 99mTc-MIBI uptake by three different human multiple myeloma cell lines (JJN3, L363, EJM) ranged from a coefficient of 1 to 4. Pgp could also play a role in the uptake level, similar to that observed in breast cancer cell lines [1].
The problem of 99mTc-MIBI uptake should be considered without focussing on plasma cells only. Bone marrow samples obtained rapidly after intravenous injection of the radionuclide should be sorted by monoclonal antibodies, allowing determination of the activity linked to each characterized cell type. The procedure is, however, hindered by two formidable difficulties. First, cell death leads to the extremely fast release of 99mTc-MIBI, precluding the use of fixation or staining or any form of washing in preparation for autoradiography. Up to now and in our hands, freeze-drying of bone marrow samples has not proven more successful. Second, lability of cell labelling is a problem even when taking care to maintain cell life. As cell washout of 99mTc-MIBI can be rapid and proceed at a rate dependent on the cell type and the prevailing extracellular conditions [2], it is far from accepted that the cellular distribution at the end of any separation procedure reflects the situation at the moment of sampling. We congratulate Fonti et al. for their interesting contribution regarding 99mTc-MIBI uptake by bone marrow cells in myeloma. We feel, however, that more has to be learnt. Plasma cells are not the sole cellular component of bone marrow that can accumulate 99mTc-MIBI, as is illustrated by the impressive and constant bone marrow uptake in patients with sickle cell anaemia (Fig. 1). Before 99mTc-MIBI scintigraphy is established as a tool for monitoring and prognostic purposes, one has to understand what 99mTc-MIBI actually labels in a complex situation where there is indeed proliferation of abnormal
Fig. 1. Impressive 99mTc-MIBI bone marrow uptake in a patient presenting with sickle cell anaemia. Posterior view
European Journal of Nuclear Medicine Vol. 28, No. 9, September 2001
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plasma cells, but also production of many cytokines, anaemia, renal insufficiency and interference with active pharmaceuticals. Didier Blocklet (✉), André Schoutens Department of Nuclear Medicine, ULB-Hôpital Erasme, Université Libre de Bruxelles, Route de Lennik 808, 1070 Brussels, Belgium e-mail: [email protected] Tel.: +32-2-5553300, Fax: +32-2-5556800 Alain Kentos, Walter Feremans Department of Haematology, ULB-Hôpital Erasme, Université Libre de Bruxelles, Brussels, Belgium
References 1. Cordobes MD, Duran M, Starzec A, Delmon-Moingeon L, Blanchot C, Kouyoumdjian J-C, Prévost G, Caglar M, Moretti J-L. Technetium-99m-sestamibi uptake by human benign and malignant breast tumor cells : correlation with mdr gene expression. J Nucl Med 1996; 37:286–289. 2. Delmon-Moingeon LI, Piwnica-Worms D, Van den Abbeele AD, Holman BL, Davison A, Jones AG. Uptake of the cation hexakis(2-methoxyisobutylisonitrile)-technetium-99m by human carcinoma cell lines in vitro. Cancer Res 1990; 50:2198–2202.
Eur J Nucl Med (2001) 28:1431–1432 DOI 10.1007/s002590100577 Published online: 10 July 2001 © Springer-Verlag 2001
Reply Dear Sir, We appreciated the comments made by D. Blocklet et al. on our previously published article [1]. We totally agree with them that infiltrating plasma cells are not the sole cellular component of bone marrow that can accumulate 99mTc-MIBI in certain pathological conditions. 99mTcMIBI is, indeed, reported to enter both normal and malignant cells and to reversibly accumulate within mitochondria in response to high negative transmembrane potentials. Therefore, it is not surprising that pathological conditions inducing metabolic activation and/or increased cellular density due to proliferative expansion of specific cellular compartments may cause increased 99mTc-MIBI uptake independently of neoplastic transformation. In this respect, increased bone marrow uptake of 99mTc-MIBI has been reported in Gaucher’s disease, an autosomal recessive metabolic disorder characterized by accumulation of glucocerebroside in cells of the reticulo-
endothelial system [2]. In our experience, patients with myelofibrosis show intense and diffuse bone marrow uptake of 99mTc-MIBI (unpublished observations). Once the diagnosis of multiple myeloma has been made, the percentage of infiltrating plasma cells is subsequently an important index of disease activity, and our results provide a rational basis for monitoring of multiple myeloma patients with 99mTc-MIBI scan since the latter reflects changes in plasma cell infiltration. Blocklet et al. claim that other possible factors such as cytokines, anaemia, renal insufficiency and interference with active pharmaceuticals may affect bone marrow uptake of 99mTc-MIBI in multiple myeloma patients. In our study, none of the patients had received chemotherapy in the 6 months preceding the study and no correlation was found between serum creatinine levels and in vivo 99mTcMIBI uptake. Although in this study we did not address the issue of cytokines, we determined interleukin-6 in the serum of the majority of our patients and no correlation could be found with either in vitro or in vivo 99mTcMIBI uptake. However, a weak and inverse correlation was found between haemoglobin levels and in vivo 99mTc-MIBI uptake, which confirmed the ability of 99mTc-MIBI scan to reflect disease stage and activity. The approach of Blocklet et al. in separating blood cells 10 min after in vivo intravenous injection of 99mTcMIBI may be heavily affected by the impossibility of discriminating between specific and non-specific binding. In these conditions the association of radioactivity with different cellular components, including erythrocytes, cannot be defined as specific and any quantitation is not reliable. Our technical approach allowed the determination of radioactivity specifically associated to the cells, and our experimental conditions were set to maintain non-specific binding at an acceptable level. Purification of bone marrow mononuclear cells by Ficoll-Hypaque density gradient centrifugation has been extensively used to study abnormal plasma cells. We agree with Blocklet et al. that it may be difficult to distinguish lymphocytes and plasma cells in mononuclear cell fractions. However, in our study mononuclear cell fractions of healthy donors showed no specific accumulation of 99mTc-MIBI and this was in agreement with previous reports showing no specific uptake of 99mTc-MIBI in human peripheral blood mononuclear cells [3]. Furthermore, the microautoradiographic study confirmed the localization of the tracer within plasma cells. However, we cannot exclude the possibility that 99mTc-MIBI uptake may occur in abnormal monoclonal B lymphocytes which are considered part of the malignant clone in these patients [4]. The observed correlation between the in vitro uptake of 99mTc-MIBI by mononuclear cells and the percentage of infiltrating plasma cells does not indicate that the malignant plasma cells of each investigated patient have a comparable level of 99mTc-MIBI uptake. This can be easily assessed by calculating the absolute number of plas-
European Journal of Nuclear Medicine Vol. 28, No. 9, September 2001
Bone marrow uptake of 99mTc-MIBI in patients with multiple myeloma Dear Sir, We read with interest the paper by Fonti et al. entitled “Bone marrow uptake of 99mTc-MIBI in patients with multiple myeloma” (Eur J Nucl Med 2001; 28:214–220). In patients with multiple myeloma (MM) or monoclonal gammopathy of undetermined significance (MGUS), the authors found a significant correlation between in vitro uptake of 99mTc-MIBI by bone marrow mononuclear cells and both bone marrow plasma cell infiltration and in vivo uptake score on 99mTc-MIBI scintigraphy. Our personal approach has been to try to separate blood cells 10 min after in vivo intravenous injection of 99mTc-MIBI in MM patients selected for having a significant number of circulating plasma cells in blood, and we have discovered that radioactivity is associated with different cellular components, including erythrocytes. To concentrate on the mononuclear cell fraction separated on a Ficoll-Hypaque gradient obviously does not tell the whole story. In this cell subgroup it is, moreover, difficult to distinguish between lymphocytes and plasma cells without the use of specific monoclonal antibodies, and contamination by erythrocytes does occur, especially when biopsy is obtained at the sternum. Reading the paper by Fonti et al., we could not be sure that the in vitro cellular uptake of 99mTc-MIBI in the mononuclear cell fraction was only linked to the uptake by the malignant plasma cells and that this mechanism accounted quantitatively for the actual uptake in vivo. We acknowledge, however, that the authors made an interesting point by observing a correlation between the in vitro uptake of 99mTc-MIBI in the Ficoll-Hypaque cellular fraction and the activity in the bone marrow of the same patients. The observed correlation between the in vitro uptake of 99mTc-MIBI by mononuclear cells and bone marrow plasma cell infiltration seems to indicate that the malignant plasma cells of each investigated patient had a comparable level of 99mTc-MIBI uptake. We find such a relationship surprising as we observed that the 90-min 99mTc-MIBI uptake by three different human multiple myeloma cell lines (JJN3, L363, EJM) ranged from a coefficient of 1 to 4. Pgp could also play a role in the uptake level, similar to that observed in breast cancer cell lines [1].
The problem of 99mTc-MIBI uptake should be considered without focussing on plasma cells only. Bone marrow samples obtained rapidly after intravenous injection of the radionuclide should be sorted by monoclonal antibodies, allowing determination of the activity linked to each characterized cell type. The procedure is, however, hindered by two formidable difficulties. First, cell death leads to the extremely fast release of 99mTc-MIBI, precluding the use of fixation or staining or any form of washing in preparation for autoradiography. Up to now and in our hands, freeze-drying of bone marrow samples has not proven more successful. Second, lability of cell labelling is a problem even when taking care to maintain cell life. As cell washout of 99mTc-MIBI can be rapid and proceed at a rate dependent on the cell type and the prevailing extracellular conditions [2], it is far from accepted that the cellular distribution at the end of any separation procedure reflects the situation at the moment of sampling. We congratulate Fonti et al. for their interesting contribution regarding 99mTc-MIBI uptake by bone marrow cells in myeloma. We feel, however, that more has to be learnt. Plasma cells are not the sole cellular component of bone marrow that can accumulate 99mTc-MIBI, as is illustrated by the impressive and constant bone marrow uptake in patients with sickle cell anaemia (Fig. 1). Before 99mTc-MIBI scintigraphy is established as a tool for monitoring and prognostic purposes, one has to understand what 99mTc-MIBI actually labels in a complex situation where there is indeed proliferation of abnormal
Fig. 1. Impressive 99mTc-MIBI bone marrow uptake in a patient presenting with sickle cell anaemia. Posterior view
European Journal of Nuclear Medicine Vol. 28, No. 9, September 2001
1431
plasma cells, but also production of many cytokines, anaemia, renal insufficiency and interference with active pharmaceuticals. Didier Blocklet (✉), André Schoutens Department of Nuclear Medicine, ULB-Hôpital Erasme, Université Libre de Bruxelles, Route de Lennik 808, 1070 Brussels, Belgium e-mail: [email protected] Tel.: +32-2-5553300, Fax: +32-2-5556800 Alain Kentos, Walter Feremans Department of Haematology, ULB-Hôpital Erasme, Université Libre de Bruxelles, Brussels, Belgium
References 1. Cordobes MD, Duran M, Starzec A, Delmon-Moingeon L, Blanchot C, Kouyoumdjian J-C, Prévost G, Caglar M, Moretti J-L. Technetium-99m-sestamibi uptake by human benign and malignant breast tumor cells : correlation with mdr gene expression. J Nucl Med 1996; 37:286–289. 2. Delmon-Moingeon LI, Piwnica-Worms D, Van den Abbeele AD, Holman BL, Davison A, Jones AG. Uptake of the cation hexakis(2-methoxyisobutylisonitrile)-technetium-99m by human carcinoma cell lines in vitro. Cancer Res 1990; 50:2198–2202.
Eur J Nucl Med (2001) 28:1431–1432 DOI 10.1007/s002590100577 Published online: 10 July 2001 © Springer-Verlag 2001
Reply Dear Sir, We appreciated the comments made by D. Blocklet et al. on our previously published article [1]. We totally agree with them that infiltrating plasma cells are not the sole cellular component of bone marrow that can accumulate 99mTc-MIBI in certain pathological conditions. 99mTcMIBI is, indeed, reported to enter both normal and malignant cells and to reversibly accumulate within mitochondria in response to high negative transmembrane potentials. Therefore, it is not surprising that pathological conditions inducing metabolic activation and/or increased cellular density due to proliferative expansion of specific cellular compartments may cause increased 99mTc-MIBI uptake independently of neoplastic transformation. In this respect, increased bone marrow uptake of 99mTc-MIBI has been reported in Gaucher’s disease, an autosomal recessive metabolic disorder characterized by accumulation of glucocerebroside in cells of the reticulo-
endothelial system [2]. In our experience, patients with myelofibrosis show intense and diffuse bone marrow uptake of 99mTc-MIBI (unpublished observations). Once the diagnosis of multiple myeloma has been made, the percentage of infiltrating plasma cells is subsequently an important index of disease activity, and our results provide a rational basis for monitoring of multiple myeloma patients with 99mTc-MIBI scan since the latter reflects changes in plasma cell infiltration. Blocklet et al. claim that other possible factors such as cytokines, anaemia, renal insufficiency and interference with active pharmaceuticals may affect bone marrow uptake of 99mTc-MIBI in multiple myeloma patients. In our study, none of the patients had received chemotherapy in the 6 months preceding the study and no correlation was found between serum creatinine levels and in vivo 99mTcMIBI uptake. Although in this study we did not address the issue of cytokines, we determined interleukin-6 in the serum of the majority of our patients and no correlation could be found with either in vitro or in vivo 99mTcMIBI uptake. However, a weak and inverse correlation was found between haemoglobin levels and in vivo 99mTc-MIBI uptake, which confirmed the ability of 99mTc-MIBI scan to reflect disease stage and activity. The approach of Blocklet et al. in separating blood cells 10 min after in vivo intravenous injection of 99mTcMIBI may be heavily affected by the impossibility of discriminating between specific and non-specific binding. In these conditions the association of radioactivity with different cellular components, including erythrocytes, cannot be defined as specific and any quantitation is not reliable. Our technical approach allowed the determination of radioactivity specifically associated to the cells, and our experimental conditions were set to maintain non-specific binding at an acceptable level. Purification of bone marrow mononuclear cells by Ficoll-Hypaque density gradient centrifugation has been extensively used to study abnormal plasma cells. We agree with Blocklet et al. that it may be difficult to distinguish lymphocytes and plasma cells in mononuclear cell fractions. However, in our study mononuclear cell fractions of healthy donors showed no specific accumulation of 99mTc-MIBI and this was in agreement with previous reports showing no specific uptake of 99mTc-MIBI in human peripheral blood mononuclear cells [3]. Furthermore, the microautoradiographic study confirmed the localization of the tracer within plasma cells. However, we cannot exclude the possibility that 99mTc-MIBI uptake may occur in abnormal monoclonal B lymphocytes which are considered part of the malignant clone in these patients [4]. The observed correlation between the in vitro uptake of 99mTc-MIBI by mononuclear cells and the percentage of infiltrating plasma cells does not indicate that the malignant plasma cells of each investigated patient have a comparable level of 99mTc-MIBI uptake. This can be easily assessed by calculating the absolute number of plas-
European Journal of Nuclear Medicine Vol. 28, No. 9, September 2001
