Melinda S. Gordon

Somatic hypermutation of the B cell receptor genes B29 (Igβ, CD79b) and mb1 (Igα, CD79a)

Somatic hypermutation (SHM), coupled to selection by antigen, generates high-affinity antibodies during germinal center (GC) B cell maturation. SHM is known to affect Bcl6, four additional oncogenes in diffuse large B cell lymphoma, and the CD95/Fas gene and is regarded as a major mechanism of B cell tumorigenesis. We find that mutations in the genes encoding the B cell receptor (BCR) accessory proteins B29 (Igβ, CD79b) and mb1 (Igα, CD79a) occur as often as Ig genes in a broad spectrum of GC- and post-GC-derived malignant B cell lines, as well as in normal peripheral B cells. These B29 and mb1 mutations are typical SHM consisting largely of single nucleotide substitutions targeted to hotspots. The B29 and mb1 mutations appear at frequencies similar to those of other non-Ig genes but lower than Ig genes. The distribution of mb1 mutations followed the characteristic pattern found in Ig and most non-Ig genes. In contrast, B29 mutations displayed a bimodal distribution resembling the CD95/Fas gene, in which promoter distal mutations conferred resistance to apoptosis. Distal B29 mutations in the cytoplasmic domain may contribute to B cell survival by limiting BCR signaling. B29 and mb1 are mutated in a much broader spectrum of GC-derived B cells than any other known somatically hypermutated non-Ig gene. This may be caused by the common cis-acting regulatory sequences that control the requisite coexpression of the B29, mb1, and Ig chains in the BCR.

Antimyeloma effects of arsenic trioxide are enhanced by melphalan, bortezomib and ascorbic acid

Arsenic trioxide (ATO) induces apoptosis of malignant plasma cells through multiple mechanisms, including inhibition of DNA binding by nuclear factor kappa‐B, a key player in the development of chemoresistance in multiple myeloma (MM). This activity suggests that ATO may be synergistic when combined with other active antimyeloma drugs. To evaluate this, we examined the antimyeloma effects of ATO alone and in combination with bortezomib, melphalan and ascorbic acid (AA) both in vitro and in vivo using a severe combined immunodeficient (SCID)‐hu murine myeloma model. Marked synergistic antimyeloma effects were demonstrated when human MM Los Angeles xenograft IgG lambda light chain (LAGλ‐1) cells were treated in vitro with ATO and any one of these agents. SCID mice bearing human MM LAGλ‐1 tumours were treated with single‐agent ATO, bortezomib, melphalan, or AA, or combinations of ATO with either bortezomib or melphalan and AA. Animals treated with any of these drugs alone showed tumour growth and increases in paraprotein levels similar to control mice, whereas animals treated with ATO‐containing combinations showed markedly suppressed tumour growth and significantly reduced serum paraprotein levels. These in vitro and in vivo results suggest that addition of ATO to other antimyeloma agents may result in improved outcomes for patients with relapsed or refractory MM.

Serum pleiotrophin levels are elevated in multiple myeloma patients and correlate with disease status

Pleiotrophin (PTN), a tightly regulated angiogenic and mitogenic heparin‐binding protein, is markedly elevated in a variety of aggressive solid tumours. The role of PTN in haematological malignancies, however, has not been previously evaluated. This study demonstrated that PTN serum levels were elevated in multiple myeloma (MM) patients when compared with healthy subjects (P < 0·0001). Serum levels of this protein significantly increased during progression of disease, and decreased during response to anti‐MM therapy (P < 0·001). These results suggest that serum PTN may be a new biomarker for monitoring the disease status and therapeutic response of MM patients.