Abstract 3401: The natural products, parthenolide and andrographolide, exhibit anti-cancer stem cell activity in multiple myeloma

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Multiple myeloma (MM) is an incurable plasma cell malignancy where even patients in remission succumb to an inevitable relapse. Pre-clinical testing of emerging therapeutics is hindered by the failure of the standard models to sustain the ex vivo growth of the MM clone. We have recently described a 3-D culture system where the extracellular matrix and cellular compartments of the bone marrow (BM) are reconstructed in vitro, recapitulating the native microenvironment of the human BM where cells occupy distinct niches. Cells from the BM aspirates are grown in a fibronectin, laminin, and collagen rich extracellular matrix designed to reconstruct endosteal and central marrow compartments of the BM (rBM). In the rBM model, the MM undergoes up to 15-fold expansion of malignant cells harboring the clonotypic IgH VDJ. The currently used MM pre-clinical models only target the plasma cells, comprising the bulk of the tumor, leaving the cancer stem cells (CSCs) to repopulate the tumor and trigger the relapse. The localization of non-proliferating, drug resistant CD20+ B cells to the reconstructed endosteum, in contact with N-cadherin and osteocalcin positive osteoblastic cells, suggests the presence of MM-cancer stem cells (MM-CSC) in the endosteal niche of rBM; the niche known to harbor the hematopoietic stem cells. MM-CSCs exhibit tumorigenic and self-renewal potential, measured by their ability to generate clonotypic colonies and differentiate into plasma cells in colony forming unit assays. Thus, the rBM model provides biologically relevant pre-clinical paradigm enabling the evaluation of therapeutic vulnerabilities of all compartments of the MM clone, including the drug-resistant MM-CSC. We have previously demonstrated that melphalan, dexamethasone, vincristine, and bortezomib therapies are not curative because these drugs target CD138+CD56+ MM plasma cells, thus failing to eliminate the MM-CSC. Utilizing the rBM culture system, we tested anti-MM-CSC potential of two natural product inhibitors of NFkB, parthenolide and andrographolide. Here we show that parthenolide and andrographolide are potent anti-MM-CSC agents (LC50=1.5-3.5μM), inducing apoptosis in MM-CSCs through the activation of caspases 8 and 3. Both natural products showed preferential toxicity toward MM-CSCs over non-tumorigenic MM cells. Addition of bone marrow stromal compartment abrogated andrographolide activity while having no effect on parthenolide cytoxicity. This is a first report of a natural product with anti-CSC activity in myeloma, suggesting that it has the potential to improve the survival of patients with MM by eliminating the relapse-causing MM-CSCs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3401. doi:10.1158/1538-7445.AM2011-3401