Chromosomal instability is a defining feature of clonal myeloma plasma cells that results in the perpetual accumulation of genomic aberrations. In addition to its role in protein homeostasis, the ubiquitinproteasome system is also involved in the regulation of DNA damage-repair proteins. In the present study, we show that proteasome inhibition induces a "BRCAness" state in myeloma cells (MM), with depletion of their nuclear pool of ubiquitin and abrogation of H2AX polyubiquitylation, an essential step for the recruit- IntroductionGenomic integrity is continuously challenged by both exogenous and endogenous stressors. 1 To counteract DNA damage, cells have evolved repair mechanisms specific for many types of lesions. [2][3][4][5][6] Single-strand DNA breaks (SSBs) are repaired through the nucleotide excision repair or the base excision repair machinery, which require the activation of poly-ADP-ribose polymerase (PARP). PARP1, and to a lesser extent PARP2, bind DNA SSBs and catalyze the synthesis and addition of large chains of poly-ADP-ribose (PAR) polymers on target proteins, including the histones H1 and H2B and PARP1 itself. These polymers serve to recruit variable proteins needed to activate DNA-damage repair (DDR). [7][8][9] If persistent or left unrepaired, SSBs encountered by replication forks lead to the formation of potentially lethal double-strand DNA breaks (DSBs). These genomic DSBs encountered in the S/G 2 phases are predominantly repaired by the homologous recombination (HR) pathway, in which the MRN (MRE11-RAD50-NBS1) complex senses the DSBs and initiates a dynamic protein recruitment to DNA-repair foci. 10,11 MRN first recruits the ATM kinase to the vicinity of the lesions, with resulting ATM-mediated phosphorylation of the histone variant H2AX that leads to the accumulation of the MDC1 protein and its binding partners. These include the MRN complex and RNF8 and RNF168, 2 ubiquitin ligases that initiate histone H2AX Lys63 mono-and polyubiquitylation at sites of DNA damage. This histone ubiquitylation allows for a second wave of protein accumulation, including factors such as 53BP1 and the BRCA1 A complex that are critically important for DSB repair and for the maintenance of genomic integrity. [12][13][14] Deregulation of the DDR machinery fuels the genomic instability needed to drive cancer-cell development and clonal evolution. Recognition of these deregulated DDR pathways has led to the discovery of novel therapeutics that result in synthetic lethality in transformed cells. Recent studies have demonstrated the efficacy of targeting PARP1 in tumors with impaired HR resulting from the homozygous loss of the BRCA1 or BRCA2 genes. [15][16][17] Furthermore, genetic screens have identified a host of HR-related genes (including RAD51, ATR, and PCNA) that upon deletion or silencing render cells hypersensitive to PARP inhibitors. 18 Therefore, tumor cells with any HR deficiency or "BRCAness" are likely to be particularly sensitive to PARP inhibitors because they are unable to cope effectively with the ...

Integrin-␤7 (ITGB7) mRNA is detected in multiple myeloma (MM) cells and its presence is correlated with

As the current efficacy of oncolytic viruses (OVs) as monotherapy is limited, exploration of OVs as part of a broader immunotherapeutic treatment strategy for cancer is necessary. Here, we investigated the ability for immune checkpoint blockade to enhance the efficacy of oncolytic reovirus (RV) for the treatment of breast cancer (BrCa). In vitro, oncolysis and cytokine production were assessed in human and murine BrCa cell lines following RV exposure. Furthermore, RV-induced upregulation of tumor cell PD-L1 was evaluated. In vivo, the immunocompetent, syngeneic EMT6 murine model of BrCa was employed to determine therapeutic and tumor-specific immune responses following treatment with RV, anti-PD-1 antibodies or in combination. RV-mediated oncolysis and cytokine production were observed following BrCa cell infection and RV upregulated tumor cell expression of PD-L1. In vivo, RV monotherapy significantly reduced disease burden and enhanced survival in treated mice, and was further enhanced by PD-1 blockade. RV therapy increased the number of intratumoral regulatory T cells, which was reversed by the addition of PD-1 blockade. Finally, dual treatment led to the generation of a systemic adaptive anti-tumor immune response evidenced by an increase in tumor-specific IFN-γ producing CD8+ T cells, and immunity from tumor re-challenge. The combination of PD-1 blockade and RV appears to be an efficacious immunotherapeutic strategy for the treatment of BrCa, and warrants further investigation in early-phase clinical trials.

The ability to repurpose sunitinib for augmentation of reovirus' immunotherapeutic efficacy positions this novel combination therapy as an attractive strategy ready for clinical testing against a range of histologies, including RCC and NSCLC. Clin Cancer Res; 22(23); 5839-50. ©2016 AACR.