Mechanisms to Elevate Endogenous GLP-1 Beyond Injectable GLP-1 Analogs and Metabolic Surgery

Therapeutic engineering of glucagon-like peptide 1 (GLP-1) has enabled development of new medicines to treat type 2 diabetes. These injectable analogs achieve robust glycemic control by increasing concentrations of "GLP-1 equivalents" (∼50 pmol/L). Similar levels of endogenous GLP-1 occur after gastric bypass surgery, and mechanistic studies indicate glucose lowering by these procedures is driven by GLP-1. Therefore, because of the remarkable signaling and secretory capacity of the GLP-1 system, we sought to discover mechanisms that increase GLP-1 pharmacologically. To study active GLP-1, glucose-dependent insulinotropic polypeptide receptor (Gipr)-deficient mice receiving background dipeptidyl peptidase 4 (DPP4) inhibitor treatment were characterized as a model for evaluating oral agents that increase circulating GLP-1. A somatostatin receptor 5 antagonist, which blunts inhibition of GLP-1 release, and agonists for TGR5 and GPR40, which stimulate GLP-1 secretion, were investigated alone and in combination with the DPP4 inhibitor sitagliptin; these only modestly increased GLP-1 (∼5-30 pmol/L). However, combining molecules to simultaneously intervene at multiple regulatory nodes synergistically elevated active GLP-1 to unprecedented concentrations (∼300-400 pmol/L), drastically reducing glucose in Gipr null and Lepr^db/db mice in a GLP-1 receptor-dependent manner. Our studies demonstrate that complementary pathways can be engaged to robustly increase GLP-1 without invasive surgical or injection regimens.

Maytansinoid immunoconjugate IMGN901 is cytotoxic in a three-dimensional culture model of multiple myeloma

Environmental-mediated drug-resistance (EM-DR) presents a major challenge for therapeutic development. Tissue microenvironment in the form of extracellular matrix, soluble factors, and stroma contribute to EM-DR. In multiple myeloma (MM), drug-resistance has hindered treatment success with 5-year survival rates remaining <50%. Here we evaluated IMGN901, a maytansinoid immunoconjugate, for its ability to overcome EM-DR alone or in combination with lenalidomide or dexamethasone. We show that while adhesion of MM cells to the extracellular matrix reduces potency of IMGN901, it remains cytotoxic with an average LC50=43 nM. However, only a combination of IMGN901, lenalidomide, and dexamethasone was able to overcome drug-resistance arising from the direct contact between MM and stromal cells. We demonstrate that multi-drug resistance protein-1 (MDR-1) was upregulated in MM cells grown in contact with stroma, likely responsible for the observed resistance. This study emphasizes the importance of incorporating the elements of tumor microenvironment during preclinical testing of novel therapeutics.

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

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

Abstract 4292: Parthenolide and structurally related natural products as anti-cancer stem cell agents: A new era in treatment of multiple myeloma

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. Here we show that parthenolide and structurally related natural product inhibitors of NFkB are potent anti-MM-CSC agents (LC50=5μM), inducing apoptosis in MM-CSCs through the activation of caspases 8 and 3. Combination treatment with conventional chemotherapeutic agents melphalan or bortezomib and parthenolide were cytotoxic and eliminated both the plasma cell burden and the MM-CSC, implying that such combinations may have curative potential. We determined that an analog of parthenolide, 13-(3-trifluoromethyl-phenyl)-parthenolide, has MM-CSC activity (LC50=15μM). The lower cytotoxicity of the fluorinated analog makes it a candidate to be used as an imaging probe. Therefore, we plan to test this compound as a labeling reagent for PET detection of MM-CSCs. This is a first report of an anti-CSC agent in MM, suggesting that parthenolide and its analogs could improve the survival of patients with MM by eliminating the relapse causing MM-CSCs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4292.