2D7 diabody bound to the α2 domain of HLA class I efficiently induces caspase-independent cell death against malignant and activated lymphoid cells

Concise review: Defining and targeting myeloma stem cell-like cells

Multiple myeloma (MM) remains incurable despite recent advances in the treatment of MM. Although the idea of MM cancer stem cells (CSCs) has been proposed for the drug resistance in MM, MM CSCs have not been properly defined yet. Besides clonotypic B cells, phenotypically distinct MM plasma cell fractions have been demonstrated to possess a clonogenic capacity, leading to long-lasting controversies regarding the cells of origin in MM or MM-initiating cells. However, MM CSCs may not be a static population and survive as phenotypically and functionally different cell types via the transition between stem-like and non-stem-like states in local microenvironments, as observed in other types of cancers. Targeting MM CSCs is clinically relevant, and different approaches have been suggested to target molecular, metabolic and epigenetic signatures, and the self-renewal signaling characteristic of MM CSC-like cells.

Small molecule antibody targeting HLA class I inhibits myeloma cancer stem cells by repressing pluripotency-associated transcription factors

Cancer stem cells have been proposed to be responsible for tumorigenesis and recurrence in various neoplastic diseases, including multiple myeloma (MM). We have previously reported that MM cells specifically express HLA class I at high levels and that single-chain Fv diabody against this molecule markedly induces MM cell death. Here we investigated the effect of a new diabody (C3B3) on cancer stem cell-like side population (SP) cells. SP fraction of MM cells highly expressed ABCG2 and exhibited resistance to chemotherapeutic agents; however, C3B3 induced cytotoxicity in both SP cells and main population (MP) cells to a similar extent. Moreover, C3B3 suppressed colony formation and tumorigenesis of SP cells in vitro and in vivo. Crosslinking of HLA class I by C3B3 mediated disruption of lipid rafts and actin aggregation, which led to inhibition of gene expression of β-catenin and pluripotency-associated transcription factors such as Sox2, Oct3/4 and Nanog. Conversely, knockdown of Sox2 and Oct3/4 mRNA reduced the proportion of SP cells, suggesting that these factors are essential in maintenance of SP fraction in MM cells. Thus, our findings reveal that immunotherapeutic approach by engineered antibodies can overcome drug resistance, and provide a new basis for development of cancer stem cell-targeted therapy.

Epithelial membrane protein-2 is a novel therapeutic target in ovarian cancer

PURPOSE

The tetraspan protein epithelial membrane protein-2 (EMP2) has been shown to regulate the surface display and signaling from select integrin pairs, and it was recently identified as a prognostic biomarker in human endometrial cancer. In this study, we assessed the role of EMP2 in human ovarian cancer.

EXPERIMENTAL DESIGN

We examined the expression of EMP2 within a population of women with ovarian cancer using tissue microarray assay technology. We evaluated the efficacy of EMP2-directed antibody therapy using a fully human recombinant bivalent antibody fragment (diabody) in vitro and ovarian cancer xenograft models in vivo.

RESULTS

EMP2 was found to be highly expressed in >70% of serous and endometrioid ovarian tumors compared with nonmalignant ovarian epithelium using a human ovarian cancer tissue microarray. Using anti-EMP2 diabody, we evaluated the in vitro response of nine human ovarian cancer cell lines with detectable EMP2 expression. Treatment of human ovarian cancer cell lines with anti-EMP2 diabodies induced cell death and retarded cell growth, and these response rates correlated with cellular EMP2 expression. We next assessed the effects of anti-EMP2 diabodies in mice bearing xenografts from the ovarian endometrioid carcinoma cell line OVCAR5. Anti-EMP2 diabodies significantly suppressed tumor growth and induced cell death in OVCAR5 xenografts.

CONCLUSIONS

These findings indicate that EMP2 is expressed in the majority of ovarian tumors and may be a feasible target in vivo.

Regulation of multiple myeloma survival and progression by CD1d

Down-regulation of conventional human leukocyte antigen (HLA) class I and II molecules from the surface of tumor cells is an important mechanism for tumor immune evasion, survival, and progression. Whether CD1d, a nonconventional, glycolipid-presenting HLA class I-like molecule instructing the function of the immunoregulatory invariant NKT cells can affect tumor cell survival is not known. Here we show that CD1d is highly expressed in premalignant and early myeloma, but with disease progression its expression is reduced and eventually in advanced stages and myeloma cell lines is lost altogether, suggesting that CD1d impacts negatively on myeloma cell survival. Consistent with this, engagement of CD1d by anti-CD1d monoclonal antibodies (mAbs) induces cell death of myeloma cell lines with restored CD1d expression and primary myeloma cells. Cell death induced by monoclonal antibody engagement of CD1d is associated with overexpression of proapoptotic Bax and mitochondrial membrane potential loss but it is caspase-activation independent; in addition, it requires the cytoplasmic tail but not the Tyr residue critical for lysosomal sorting of CD1d. Finally, anti-CD1d cooperates with antimyeloma agents in the killing of myeloma cells. Thus, this work provides evidence linking a novel function of CD1d in the regulation of cell death with tumor survival and progression in humans.

A single-chain Fv diabody against human leukocyte antigen-A molecules specifically induces myeloma cell death in the bone marrow environment

Cross-linked human leukocyte antigen (HLA) class I molecules have been shown to mediate cell death in neoplastic lymphoid cells. However, clinical application of an anti-HLA class I antibody is limited by possible side effects due to widespread expression of HLA class I molecules in normal tissues. To reduce the unwanted Fc-mediated functions of the therapeutic antibody, we have developed a recombinant single-chain Fv diabody (2D7-DB) specific to the alpha2 domain of HLA-A. Here, we show that 2D7-DB specifically induces multiple myeloma cell death in the bone marrow environment. Both multiple myeloma cell lines and primary multiple myeloma cells expressed HLA-A at higher levels than normal myeloid cells, lymphocytes, or hematopoietic stem cells. 2D7-DB rapidly induced Rho activation and robust actin aggregation that led to caspase-independent death in multiple myeloma cells. This cell death was completely blocked by Rho GTPase inhibitors, suggesting that Rho-induced actin aggregation is crucial for mediating multiple myeloma cell death. Conversely, 2D7-DB neither triggered Rho-mediated actin aggregation nor induced cell death in normal bone marrow cells despite the expression of HLA-A. Treatment with IFNs, melphalan, or bortezomib enhanced multiple myeloma cell death induced by 2D7-DB. Furthermore, administration of 2D7-DB resulted in significant tumor regression in a xenograft model of human multiple myeloma. These results indicate that 2D7-DB acts on multiple myeloma cells differently from other bone marrow cells and thus provide the basis for a novel HLA class I-targeting therapy against multiple myeloma.