Cell Specific Recognition and Capture of Ctdna in Multiple Myeloma

Multiple myeloma (MM) is a heterogeneous malignant plasma cell disorder with complex molecular and genetic abnormalities. Clonal evolution in MM is a hallmark of treatment failure. The origin of clonal evolution seems to result from the pressure induced by treatment, microenvironmental factors and immune response. In this work we identified that ctDNA may reshape tumor genetic landscape by horizontal gene transfer similar to what is seen in prokaryotes and some Eukaryotes. Our work demonstrated that ctDNA from treatment resistant patients can transmit the phenotype to MM cell lines. Using in vitro microscopy assays and whole genome sequencing methods, we identified that ctDNA preferentially target cells that resemble their MM cell of origin compared to other cancer cell types. The tropism for MM ctDNA to target MM cells was validated in in vivo xenograft mouse models, where ctDNA targeted tumor cells and spared other tissues or other tumor xenografts. To further understand, whether cell targeting was produced via a direct interaction of ctDNA with a receptor protein, we treated ctDNA with anti-DNA antibodies derived from lupus patients prior adding it to cell culture. Our results showed a significant reduction of ctDNA incorporation. Then, we treated cells with trypsin after 30 minutes incubation with ctDNA and showed a significant reduction of CY5-ctDNA cellular signal suggesting that ctDNA incorporation is mediated by a direct interaction of ctDNA with a receptor protein. Based on these findings, we performed mass spectrometry on proteins pulled from coculture of biotin labelled ctDNA and cell lysates derived from 3 different tumor types. Results identified eight proteins bound to ctDNA that were enriched compared to biotin or a CMV-GFP linearized control vector (HLA-A, CD41, Cd97, Integrin αVβ5, P14K2A, TMEM and PTK7A). The role of these proteins in ctDNA incorporation was evaluated by culturing cells with antibodies against these proteins prior to adding ctDNA. Integrin αVβ5 followed by PTK7A, P14K2A, TMEM and HLA-A were able to reduce ctDNA cell incorporation. These results are being confirmed using shRNA methods and results will be available at the time for the meeting. In summary, we have identified a novel mechanism by which MM cells share genetic material altering their genetic landscape and elucidated potential receptors mediating ctDNA recognition.