CXCR4 Monoclonal Antibody, BMS-936564 (MDX-1338), Modulates Epithelial to Mesenchymal Transition (EMT) in Multiple Myeloma Cells
Authors: Roccaro Aldo M , Sacco Antonio , Kuhne Michelle R. , Azab Abdel Kareem , Maiso Patricia , Azab Feda , Manier Salomon , Aljaway Yosra , Reagan Michaela R , Cohen Lewis , Cardarelli Pina M , Ghobrial Irene M. 
Published: October 2019

Abstract
Abstract 4009

Background.
The SDF1/CXCR4 axis plays a major role in homing and trafficking of multiple myeloma (MM) to the bone marrow (BM), and disruption of the interaction of tumor cells with the BM leads to enhanced sensitivity to therapeutic agents. Also, hypoxia leads to EMT activation as well as CXCR4 up-regulation in MM cells. We therefore hypothesized that CXCR4 may represent a crucial regulator of EMT in MM and an important target for preventing MM disease dissemination.

Methods.
Primary MM cells (CD138+); MM cell lines (MM.1S, RPMI.8226); and primary MM bone marrow stromal cells (BMSCs) were used. Dissemination of MM.1S/GFP+ cells to distant bone marrow niches was evaluated in vivo, by using in vivo confocal microscopy. CXCR4-loss of function studies were performed by transfecting MM cells with either a scrambled probe or CXCR4-siRNA. A novel HuMAb anti-CXCR4 (BMS-936564; Bristol Myers Squibb, NY) was used. Migration towards SDF-1 and BMSCs was evaluated. Cytotoxicity and DNA synthesis were measured by MTT and 3H-thymidine uptake, respectively. Cell signaling, apoptotic- and EMT-related pathways were studied by Western Blot. Synergism was calculated by using the Chou-Talalay method. In vivo, MM tumor growth was evaluated by using xenograft mouse models and a melanoma xenograft mouse model was used to validate the effect of anti-CXCR4 antibody on modulating tumor cell metastasis.

Results.
We demonstrated down-regulation of Twist, Snail and Slug, together with up-regulation of E-Cadherin in CXCR4-siRNA-transfected cells, compared to scrambled probe-transfected cells. These findings were next validated by using the new selective CXCR4 antibody (BMS-936564); and confirmed that BMS-936564-dependent inhibition of CXCR4 led to inhibition of Twist, Snail, and Slug; with up-regulation of E-Cadherin. These data were further corroborated in vivo, by using in vivo confocal microscopy: mice treated with BMS-936564 presented with less MM cell dissemination to distant bone marrow niches, compared to vehicle-treated mice, supporting the hypothesis that CXCR4 may represent a crucial modulator of tumor cell dissemination. These data were also confirmed in vivo, by using a xenograft melanoma model, where BMS-936564-treated mice presented with a reduced number of metastasis, compared to vehicle-treated mice. These in vivo data were supported by in vitro evidence showing the ability of BMS-936564 to functionally target MM cells in terms of migration, adhesion and survival. BMS-936564 inhibited migration of MM cells towards SDF-1a and primary MM BMSCs, in a dose-dependent manner. In addition, survival and adhesion of primary MM cells to BMSCs were inhibited by BMS-936564 in a dose-dependent manner. BMS-936564 targeted MM cells in the context of BM milieu, by overcoming BMSCs-induced proliferation of tumor cells. Moreover, BMS-936564 synergistically enhanced bortezomib-induced cytotoxicity in MM cells. BMS-936564-dependent activation of apoptotic pathways in MM cells was documented, as shown by cleavage of caspase-9 and PARP. SDF-1a-induced ERK-, Akt-, and Src-phosphorylation were inhibited by BMS-936564 in a dose-dependent manner. Importantly, BMS936564 inhibited MM cell proliferation in vivo in xenograft mouse models.

Conclusion.
These findings indicate that CXCR4 represents a valid therapeutic target due to its ability to modulate EMT, and that BMS-936564 functionally targets MM cell migration, adhesion and survival; thus providing evidence for using the anti-CXCR4 antibody, BMS-936564, as a therapeutic modality for MM.

Disclosures:
Kuhne: Bristol-Myers Squibb: Employment. Cohen:Bristol-Myers Squibb: Employment. Cardarelli:Bristol-Myers Squibb: Employment. Ghobrial:Novartis: Advisory Board Other; Onyx: Advisory Board, Advisory Board Other; Millennium: Advisory Board, Advisory Board Other; Bristol Myers Squibb: Advisory Board, Advisory Board Other.