No abstract

The genetics of myeloma has been increasingly elucidated in recent years. Recurrent genetic events, and also biologically distinct and clinically relevant genetic subtypes of myeloma have been defined. This has facilitated our understanding of the molecular pathogenesis of the disease. In addition, some genetic abnormalities have proved to be highly reproducible prognostic factors. With the expanding therapeutic armamentarium, it is time to include genetic assessment as part of clinical evaluation of myeloma patients to guide management. In this review we examine the role of various genetic abnormalities in the molecular pathogenesis of myeloma, and the use of such abnormalities in disease classification, prognosis and clinical management.

Translocations involving an MYC gene (c >> N >>L) are very late tumor progression events and provide a paradigm for secondary translocations in multiple myeloma. Using a combination of fluorescent in situ hybridization and comparative genomic hybridization arrays (aCGH), we have identified rearrangements of an MYC gene in 40 of 43 independent myeloma cell lines. A majority of MYC translocations involve an Ig locus (IgH > Iglambda >> Igkappa), but the breakpoints only infrequently occur near or within switch regions or V(D)J sequences. Surprisingly, about 40% of MYC translocations do not involve an Ig locus. The MYC translocations mostly are nonreciprocal translocations or insertions, often with the involvement of three chromosomes and sometimes with associated duplication, amplification, inversion, and other associated chromosomal abnormalities. High-density aCGH analyses should facilitate the cloning of MYC breakpoints, enabling the determination of their structures and perhaps elucidating how rearrangements not involving an Ig gene cause dysregulation of an MYC gene.

A rhodium(III) complex, rac-[Rh(bpy)2phzi] 3؉ (bpy, 2,2-bipyridine; phzi, benzo[a]phenazine-5,6-quinone diimine) has been designed as a sterically demanding intercalator targeted to destabilized mismatched sites in double-helical DNA. The complex is readily synthesized by condensation of the phenazine quinone with the corresponding diammine complex. Upon photoactivation, the complex promotes direct strand scission at singlebase mismatch sites within the DNA duplex. As with the parent mismatch-specific reagent, [Rh(bpy)2(chrysi)] 3؉ [chrysene-5,6-quinone diimine (chrysi)], mismatch selectivity depends on the helix destabilization associated with mispairing. Unlike the parent chrysi complex, the phzi analogue binds and cleaves with high affinity and efficiency. The specific binding constants for CA, CC, and CT mismatches within a 31-mer oligonucleotide duplex are 0.3, 1, and 6 ؋ 10 7 M ؊1 , respectively; site-specific photocleavage is evident at nanomolar concentrations. Moreover, the specificity, defined as the ratio in binding affinities for mispaired vs. well paired sites, is maintained. The increase in affinity is attributed to greater stability in the mismatched site associated with stacking by the heterocyclic aromatic ligand. The high-affinity complex is also applied in the differential cleavage of DNA obtained from cell lines deficient in mismatch repair vs. those proficient in mismatch repair. Agreement is found between photocleavage by the mismatch-specific probes and deficiency in mismatch repair. This mismatch-specific targeting, therefore, offers a potential strategy for new chemotherapeutic design.T he targeting of single-base mismatches in DNA represents a challenging problem in molecular recognition. The mismatched site may be of variable sequence and within a variable sequence context. What distinguishes such a site, instead, is the local destabilization in opposing bases because of the absence of Watson-Crick hydrogen bonding (1). Although challenging, however, the development of small molecules targeted to mismatches offers many applications. Site-specific mismatch probes could be used in discovery efforts to identify single-nucleotide polymorphisms. Moreover, such molecules could provide the basis for the development of novel chemotherapeutics. Many cancers are associated with a deficiency in mismatch repair (2, 3). Hence, by directing small molecules to the accumulated mismatches, a cancer-specific targeting strategy could be envisioned.In our laboratory, we have exploited the local helix destabilization associated with mispairing in the design of a metal complex targeted to mismatches (4, 5). Shown in Fig. 1 is a rhodium complex containing the benzo[a]phenazine-5,6-quinone diimine (phzi) ligand, as well as chrysene-5,6-quinone diimine (chrysi) and phenanthrene quinone diimine (phi) ligands (4). Octahedral rhodium(III) complexes containing the phi ligand bind avidly to double-helical DNA by intercalation (6); on photoactivation, direct DNA strand cleavage is also promoted at the bound site (7)...