Detection of free light chain monoclonal proteins co-migrating with intact monoclonal proteins in patients with monoclonal gammopathy.

BACKGROUND: In a small, but potentially significant proportion of patients with a monoclonal gammopathy, patients show the existence of an intact monoclonal (M-) protein co-migrating with a free light chain (FLC) M-protein. Using traditional methods for detection of monoclonal immunoglobulins, only the intact M-protein may be detectable, and hence the FLC M-proteins may be missed. METHODS: Immunofixation electrophoresis (IFE) using two different sets of antisera were compared (one detecting both free and bound FLC epitopes, and one detecting only the free FLC epitopes), alongside urine protein electrophoresis and the Freelite assay in order to ascertain the best methods of detecting both types of M-proteins in this subset of patients. RESULTS: A total of 2% of the patient population tested were shown to have a FLC M-protein migrating coincidentally with an intact M-protein. These were not detected by IFE using the widely utilised antisera to both free and bound FLC epitopes, and hence may have been missed during routine testing, but were detectable using the other methods. CONCLUSIONS: This study highlights the important finding that in some patients with both an intact and a FLC M-protein, the FLC M-protein may be missed during routine testing. In incidences where no corresponding urine sample is sent to the laboratory alongside the serum sample, we would suggest testing for the presence of FLC M-proteins in this subset of patients using the Freelite assay, if no urine sample can be obtained, to ensure all FLC M-proteins are appropriately detected.

An unusual DNA binding compound, S23906, induces mitotic catastrophe in cultured human cells.

The biochemical pathways that lead cells to mitotic catastrophe are not well understood. To identify these pathways, we have taken an approach of treating cells with a novel genotoxic compound and characterizing whether cells enter mitotic catastrophe or not. S23906 is a novel acronycine derivative that forms adducts with the N2 residue of guanine in the minor groove of the DNA helix and destabilizes base pairing to cause helix opening. We observed, in HeLa and HT-29 cells, that S23906 induced gamma-H2AX and activated checkpoint kinase 1, as did bleomycin, camptothecin, and cisplatin, when tested under equi-toxic conditions. S23906 also induced cyclin E1 protein, although this activity was not required for cytotoxicity because knock down of cyclin E1 by RNA interference did not affect the number of dead cells after treatment. Cyclin B1 levels first decreased and then increased after treatment with S23906. Cyclin B1 was associated with Cdk1 kinase activity, which correlated with an increase in the number of mitotic cells. By 32 h after treatment, at least 20% of the cells entered mitotic catastrophe as determined by microscopy. Suppression of the DNA checkpoint response by co-treatment with caffeine increased the number of cells in mitosis. These results suggest that mitotic catastrophe is one of the cellular responses to S23906 and that mitotic catastrophe may be a common cellular response to many different types of DNA damage.