Despite new available therapies, including immunomodulatory drugs such as thalidomide and lenalidomide in multiple myeloma (MM), about 20-25% of patients are still considered at high risk for treatment failure. The emergence of therapeutically recalcitrant cases and disease relapse even under intensive treatment regimens suggests the existence of a dormant myeloma-initiating population within the bone marrow (BM) that is capable of drug escape. These myeloma-initiating cells are defined by the lack of the plasma cell marker CD138, while they express several hematopoietic stem (CD38) and B cell markers such as CD27 and CD19; however, the molecular and cellular mechanisms that regulate myeloma-initiating cell generation and maintenance are so far poorly understood. Recently, we and other groups showed that both NOTCH signaling and inflammation- responsive ADAR1 activation are crucial events regulating malignant stem cell maintenance in the bone marrow microenvironment, characterized by enhanced survival and self-renewal and cell cycle alterations of dormant progenitor cells. In this context, the central hypothesis of this proposal is that MM niche-derived pro- inflammatory signals induce aberrant human-specific RNA editing driven by adenosine deaminase acting on dsRNA-1 (ADAR1) in dormant myeloma-initiating cells that is accentuated by lenalidomide resistance. This project will: 1) determine whether ADAR1 activity is enhanced in myeloma-initiating cells and investigate the effects of lenalidomide treatment on ADAR1-dependent RNA editing in therapeutic resistance and relapse; 2) identify the NOTCH-regulated pro-inflammatory cytokines that activate ADAR1-dependent RNA editing in myeloma-initiating cells; and 3) determine whether direct inhibition of ADAR1 activity in MM initiating cells, or blocking microenvironmental signals that activate ADAR1, sensitizes myeloma-initiating cells to lenalidomide and prevents myeloma-initiating cell maintenance.
These aims will address PQC2: What molecular or cellular events establish tumor dormancy after treatment and what leads to recurrence? We will utilize both in vitro and in vivo measures of myeloma-initiating cell function using multicolor flow cytometry and fluorescent RNA probe-based strategies to purify and profile primary MM cellular constituents, coupled with a novel diagnostic qPCR-based assay to detect endogenous RNA editing, and gene knockout (CRISPR) or lentiviral shRNA- knockdown strategies to modulate NOTCH-dependent ADAR1 activation. A fluorescent ubiquitination cell cycle indicator (FUCCI) bi-cistronic lentiviral reporer will facilitate investigations of dormant live cells, in robust bone marrow stromal co-culture models and bioluminescent humanized MM mouse models. The ultimate goal is to investigate niche-dependent ADAR1 activation as a novel mechanism driving transcriptome recoding and molecular evolution of dormant myeloma-initiating cells, laying the groundwork for targeted therapeutics with potential applications in an array of other therapeutically recalcitrant malignancies.

Public Health Relevance

Multiple myeloma is an incurable and prevalent blood cancer, and in this disease rare myeloma-initiating cells within the bone marrow acquire drug resistance to standard of care therapies such as immunomodulatory drugs, promoting disease recurrence. The proposed study will examine the so far poorly-defined molecular and cellular mechanisms that drive myeloma-initiating cell maintenance and therapeutic resistance in multiple myeloma through activation of niche-responsive RNA editing by the stem cell self-renewal agonist ADAR1, and will lay the groundwork for development of targeted therapeutic strategies. The bone marrow microenvironment provides a pro-inflammatory supportive niche for malignant stem cells that can drive disease relapse after periods of tumor dormancy under treatment in a variety of hematological malignancies, and thus represents a novel therapeutic target that may have broader relevance to other cancers.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21CA194679-01
Application #
8877200
Study Section
Special Emphasis Panel (ZCA1-RPRB-M (J1))
Program Officer
Howcroft, Thomas K
Project Start
2015-05-01
Project End
2017-04-30
Budget Start
2015-05-01
Budget End
2016-04-30
Support Year
1
Fiscal Year
2015
Total Cost
$204,772
Indirect Cost
$72,661
Name
University of California San Diego
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
Colombo, Michela; Mirandola, Leonardo; Chiriva-Internati, Maurizio et al. (2018) Cancer Cells Exploit Notch Signaling to Redefine a Supportive Cytokine Milieu. Front Immunol 9:1823
Lazzari, Elisa; Mondala, Phoebe K; Santos, Nathaniel Delos et al. (2017) Alu-dependent RNA editing of GLI1 promotes malignant regeneration in multiple myeloma. Nat Commun 8:1922
Jiang, Qingfei; Crews, Leslie A; Holm, Frida et al. (2017) RNA editing-dependent epitranscriptome diversity in cancer stem cells. Nat Rev Cancer 17:381-392
Colombo, Michela; Galletti, Serena; Bulfamante, Gaetano et al. (2016) Multiple myeloma-derived Jagged ligands increases autocrine and paracrine interleukin-6 expression in bone marrow niche. Oncotarget 7:56013-56029
Zipeto, Maria Anna; Court, Angela C; Sadarangani, Anil et al. (2016) ADAR1 Activation Drives Leukemia Stem Cell Self-Renewal by Impairing Let-7 Biogenesis. Cell Stem Cell 19:177-191
Pineda, Gabriel; Lennon, Kathleen M; Delos Santos, Nathaniel P et al. (2016) Tracking of Normal and Malignant Progenitor Cell Cycle Transit in a Defined Niche. Sci Rep 6:23885
Zipeto, Maria Anna; Jiang, Qingfei; Melese, Etienne et al. (2015) RNA rewriting, recoding, and rewiring in human disease. Trends Mol Med 21:549-59