Our understanding of the biological mechanism of the development of myeloma in particular and hematologic malignancies in general will help us discover new drugs and design novel therapeutic strategies to provide a better treatment.
We are interested in understanding the biological mechanisms of proliferation and metastasis in cancer, including multiple myeloma, lymphoma and others. We are interested in understanding the mechanism involved in cell trafficking of cancer cells during proliferation metastasis. Particularly we are interested in the role of hypoxia and adhesion-molecules in promoting metastasis and drug resistance in these cancers. Our understanding of these mechanisms will help us design and develop novel drugs and therapeutic strategies which will be translated from-bench-to-bed.
We have different approaches to discover novel therapeutic strategies:
(1) Targeting the interaction between cancer cells and their microenvironment
The progression of hematologic malignancies(such as multiple myeloma, Waldenstrom’s macroglubolinemia, and CML) involves a continuous re-circulation of the cancer cells in the peripheral blood and re-entrance into the BM. The interaction of the cancer cells cells with extracellular matrix (ECM) proteins and bone marrow (BM) cells, as well as factors in the BM milieu (cytokines, chemokines, angiogenesis) plays a crucial role in cancer pathogenesis and drug resistance.
We have previously studied the mechanisms by which progression of MM cells occur through interaction with the BM microenvironment. We have previously showed that by blocking CXCR4/SDF1 we were able to disrupt the interaction of MM cells with the BM microenvironment, which in turn enhanced the efficacy of cytotoxic agents against MM cells. Mechanistically, we have also shown the inhibition of either the receptor-ligand interaction or inhibition of proteins downstream of CXCR4, such as Rho GTPases and PI3K, interrupted the interaction of MM cells with the BM microenvironment. Similarly, we found that inhibition of the interaction of MM cells with the BM by inhibition of interaction of P-Selectin ligand in the MM cells and the P-Selectin in endothelial cells and stromal cells in the bone marrow sensitized the MM cells to therapy.
(2) Studying the mechanisms of metastasis and spread
We studied the driving force that causes MM metastasis from one niche to another in the BM. We found that MM tumor progression induces hypoxia in the MM cells and other cells in the BM microenvironment. Hypoxia activates EMT-related machinery in MM cells, decreases expression of E-cadherin, decreases adhesion of MM cells to the BM, decrease the secretion of SDF1 from the stromal cells and enhances egress of MM cells to the circulation. In parallel, hypoxia increases the expression of CXCR4, and consequently increases the migration and homing of circulating MM cells to new BM niches in which they recover and display normoxic behavior. Further studies to manipulate hypoxia in order to regulate tumor dissemination as a therapeutic strategy are warranted. Please see the summary of the mechanism for the role of hypoxia in the dissemination of MM .
(3) The role of RTK’s in Waldenstrom’s Macroglobulinemia
Similarly, we investigated the role of receptor tyrosine kinases in Waldenström’s macroglobulinemia (low grade lymphoma), and found that FGFR3 was over-expressed and important for the proliferation of the Waldenström’s cells. In addition, he found over-activation of EPH-B2, plays a vital role in the interaction between Waldenström’s cells and the bone marrow microenvironment, and in the progression of the disease.
(4) Endothelial progenitor cells (EPCs) as a therapeutic target for prevention of angiogenesis in hematologic malignancies
Blood vessel formation plays an essential role in many physiologic and pathologic processes, including normal tissue growth and healing, as well as tumor progression. Endothelial progenitor cells (EPC) are a subtype of stem cells with high proliferative potential that are capable of differentiating into mature endothelial cells, thus contributing to neovascularization in tumors. In response to tumor-secreted cytokines, EPCs mobilize from the bone marrow to the peripheral blood, home to the tumor site, and differentiate to mature endothelial cells and secrete proangiogenic factors to facilitate vascularization of tumors. We study the expression of surface markers, cytokines, receptors, adhesion molecules, proteases, and cell signaling mechanisms involved in the different steps (mobilization, homing, and differentiation) of EPC trafficking from the bone marrow to the tumor site. Understanding the biologic mechanisms of EPC cell trafficking opens a window for new therapeutic targets in cancer.
(5) The role of P-Glycoproteins in drug resistance in myeloma
The majority of patients with MM initially respond to chemotherapy, but they become resistant to later drug therapy. One reason for drug resistance in MM patients is efflux transporters. P-gp is the most studied of the multidrug resistance proteins, and is up-regulated in response to many chemotherapeutic drugs. This up-regulation of P-gp decreases in the intracellular accumulation of drugs limiting their therapeutic efficacy.
In this review, we focused on the role of P-gp in drugs used for MM patients. P-gp has been shown to be an important factor in drug resistance in many of the drug classes used in the treatment of MM (proteasome inhibitors, anthracyclines, alkylating agents, and immunomodulators are examples); thus our further understanding of its mechanism and inhibitory effects will help us decrease drug resistance in MM patients.
(6) Development of novel biomarkers for detection of circulating tumor cells (CTCs), cancer-stem cells, and minimal residual disease (MRD) in multiple myeloma.
CD138 is the gold-standard marker for detecting MM cells using immunohistochemistry (IHC) and multi-parametric flow cytometry analysis of BM biopsies. A major concern for detection of MM cells using CD138 is that patients contain a sub-population of cells which is CD138-negative. This sub-population is clonotypic, drug resistant, exhibits stem cell-like properties, expresses drug efflux pumps and displays higher clonogenic potential than CD138+ sub-population in vivo. We developed a new method to detect MM cells, in the BM and in the circulation, using flow cytometry independent of the CD138 expression on these cells.
we explored the approach to detect MM cells as CD38-positive and (CD3, 14, 16, 19 and 123)-negative by a two-color flow cytometry, in which case CD38 was detected with an APC-labeled antibody while all the other antibodies used for exclusion were detected with the corresponding antibodies conjugated to FITC (and in some cases BV421).
We have shown that MRD cells after drug treatment are hypoxic, and that hypoxia and drug treatment downregulate the expression of the main surface marker (CD138) used to identify MM cells, which makes this marker unsuitable for detecting MM cells. Thus, we developed an alternative biomarker-set which detects myeloma cells independent of their hypoxic and CD138 expression status in vitro, in vivo and in primary MM patient samples. The new markers were able to identify a clonal CD138-negative population as MRD in the marrow and circulation of MM patients.