Elevated Homologous Recombination Induces Karyotypic Changes and Predicts Poor Clinical Outcome In Multiple Myeloma

Abstract 1924

Homologous recombination (HR), by inducing DNA rearrangements, plays an important role in cancer cell proliferation and progression via induction of oncogene activation, and/or anti-oncogene inactivation (or loss of heterozygosity at tumor suppressor loci), as well as telomere-expansion. We have observed that recombinase (RAD51) expression and homologous recombination (HR) activity are constitutively elevated in multiple myeloma (MM) as well as other cancers, and the suppression of recombinase (hsRAD51) reduces HR and significantly inhibits genomic instability and development of drug resistance in MM. We have further extended these observations to investigate whether elevated HR in myeloma is also implicated in karyotypic instability and if prominent HR genes can be used to predict clinical outcome in MM. Myeloma cells, transduced with control and RAD51 shRNAs, were cultured for 30 days and evaluated for karyotypic changes using “day 0” cells as reference. G-band karyotype of baseline control cells showed number of chromosomal abnormalities including three copies of chromosome 7; and three copies of chromosome 14 each with different aberrations: add(14)(q32), add(14)(q24.3), and der(14)t(3;14)(p13;p11.2)add(14)(q24.3). We observed acquisition of new karyotypic change in the control shRNA transduced cells after 30 days. Besides retaining the same stemline karyotype as baseline, it showed a sideline (3 of 20 cells) with additional aberrations in chromosomes 7 and 14. In the sideline, one chromosome 7 showed additional material on the distal short arm, add(7)(p22), while the other abnormal chromosome 7 showed a deletion of the short arm, del(7)(p12). Only a single change was identified in the chromosomes 14 involving the loss of the 3p material from the short arm of the der(14)t(3;14). Interestingly, the recombinase-shRNA transduced cells showed the same stemline aberrations as the baseline reference cells, without acquisition of new change. We have confirmed similar results with spectral karyotyping as well as by analyzing copy number change using high-density SNP array. To further analyze the impact of HR on outcome in MM, we have analyzed, gene expression data from 170 uniformly treated patients using expression levels of 155 HR-related genes. We observed that several important HR-related genes including recombinase (HsRAD51), XRCC2, ERCC1, and endonucleases are significantly upregulated in MM patients (P<0.05). Unsupervised hierarchical clustering using these HR related genes divided the patients into two groups; patients with higher HR related gene expression had significantly poor overall survival compared to those with lower expression. These data confirm that elevated HR is implicated in both the mutational as well as karyotypic changes in MM, and suggest that suitable inhibitors of HR may reduce or prevent genomic instability and progression of disease.