Abstract LB-38: Zebrafish embryos provide a permissive environment for the growth and dissemination of primary human myeloma and its precursor cells

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Existing animal models do not support the growth and dissemination of purified patient myeloma cells, a significant obstacle to the study of their biological behavior and the identification of pathways that might be targeted therapeutically. We report here that zebrafish embryos do support the growth of myeloma cells. This study was designed to compare the host angiogenic response and the growth and dissemination of CD138+ plasma cells derived from the bone marrow of patients with primary and relapsed myeloma to CD138+ cells from patients with the pre-myelomatous conditions monoclonal gammopathy of uncertain significance (MGUS) and smoldering myeloma. Fifty to 100 primary myeloma or myeloma precursor cells suspended in Matrigel and labeled with the red fluorescent indocarbocyanine dye DiI were injected into the perivitelline space of zebrafish embryos 48 hours after fertilization and the embryos observed for up to 7 days after injection. We used Tg(fli1:GFP) zebrafish bred on a Casper (albino) background to monitor host angiogenesis. Cells from primary and relapsed myeloma patients induced intense angiogenesis with ventral migration of vascular sprouts from the ipsilateral sub-intestinal venous system into the Matrigel plug, as well as rapid growth of the injected cells. In 70% of the injected embryos, CD138+ cells from myeloma patients formed a large red fluorescent cell mass and some or all of the cells exited the Matrigel plug and disseminated throughout the embryo. In contrast, CD138+ cells from patients with MGUS or smoldering myeloma did not induce angiogenesis and did not grow or disseminate. When purified human or zebrafish VEGF was added to a Matrigel plug containing MGUS cells, they behaved like cells isolated from patients with myeloma - forming a tumor mass and exiting the Matrigel plug. In contrast, CD138+ cells from normal individuals did not proliferate or disseminate, even when exposed to exogenous VEGF. To the best of our knowledge, this is the first study to compare the behavior of plasma cells isolated from myeloma and pre-myeloma patients in zebrafish embryos, which allow for direct observation of cell behavior in real time. The most important finding is that there is an absolute requirement for VEGF which changes the behavior of clonal cells derived from MGUS patients and makes them indistinguishable from cells derived from patients with clinical myeloma. This finding challenges the prevailing dogma that conversion from MGUS to myeloma is due to the acquisition of one or more “driver” mutations that favor proliferation and dissemination of a previously indolent cell population. Our data suggest that exposure to a host humoral factor can also induce this transformation. To the best of our knowledge, this is the first demonstration of the conversion of a pre-malignant to a malignant cell in myeloma or any other tumor by in vivo manipulation of the host environment. This change in phenotype, may not be unique to MGUS and suggests a new paradigm for assessing the transformation of other pre-malignant disorders, like Barrett's esophagus or ductal carcinoma in situ (DCIS) of the breast. Our data provides evidence that it is possible to induce “primed” pre-malignant cells to acquire a “malignant” phenotype by delivering blood borne factors to dormant or slowly growing cells. Citation Format: Dongdong MA, Arinze Nwokeji, Jianhong Lin, Yu-Tzu Tai, Nikhil Munshi, Robert I. Handin. Zebrafish embryos provide a permissive environment for the growth and dissemination of primary human myeloma and its precursor cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-38. doi:10.1158/1538-7445.AM2014-LB-38