Multiple myeloma (MM) is a clonal B cell malignancy characterized by an excess of mature plasma cells in the bone marrow. MM progression is enabled by tumor cells interacting within the bone marrow with different cell types that directly promote tumor cell proliferation and survival and contribute to a progressive impairment of anti-tumor immune response. Natural Killer (NK) cells represent a subset of innate lymphoid cells that play a key role in the immunosurveillance of MM. Relevant NK cell alterations resulting in poor disease control have been reported in MM patients. In the last years, a better understanding of MM biology and its role in immune dysregulation has led to an increasing interest in the clinical potential of immunotherapy for the treatment of this disease. Accumulating evidence suggests that type I interferon (IFN) production within the tumor microenvironment is important in shaping the anti tumor-immune response including the promotion of NK cell-mediated effector functions. In this regard, cyclic GMP-AMP synthase (cGAS)/Stimulator of interferon genes (STING) pathway that leads to type I interferon production has recently emerged as nodal player in cancer immunity and is currently being explored as potential therapeutic target. The main objective of our proposal relies on the activation of cGAS/STING pathway either in cancer and in bone marrow stromal cells by using different approaches including the usage of cyclic nucleotides, the synthesis on new lipid nanoparticles carrying cGAMP and the treatment with therapeutic DNA damaging agents. Moreover, the development of new models aimed at culturing primary myeloma, NK cells and bone marrow stromal cells in a three-dimensional (3D) environment will be pursued. We envisage that these experiments will provide the rationale for the combined use of cGAMP nanoparticles, checkpoint inhibitor drugs or therapeutic drugs for cancer treatment in order to overcome tumor immune evasion.
Appealing new strategies for effective cancer therapy are based on increasing the immunogenic potential of cancer cells to overcome the tumor immunoevasive phenotype (Zingoni, Frontiers in Immunol, 2017). In regard to multiple myeloma cancer model, accumulating evidence indicates that microenvironment transformation may significantly impair the immune system including NK cells (Pittari, Frontiers in Immunol, 2017). Thus, our project is aimed at reverse the tumor-mediated immune paralysis potentiating the NK cell mediated functions against malignant MM cells. Because IFNs can prime strong effector activity in NK cells, the GAS-STING pathway is an attractive candidate. We propose to improve this pathway directly in cancer cells but also in the bone marrow stromal cells by using DNA damaging agents or the STING agonist cGAMP.
In order to improve cell to cell transfer in multiple myeloma microenvironment, we propose to synthesize novel lipid nanoparticles carrying cGAMP to efficiently deliver this molecule directly in the tumor microenvironment. We will employ fluorescence microscopy-based methods to identify the most appropriate lipid composition of nanoparticles (i.e. the specific lipid composition that will allow lipid vesicles to avoid metabolic degradation and will result in massive intracellular release of cGAMP).
Several immunotherapies aimed at boosting immune response have recently been proposed that have revolutionized the clinical oncology (Fridman, Nature Rev Clin Onc 2017). Our proposal has a clear focus in exploring the immunological implications of cGAMP nanoparticle-based cancer therapy. Cancer cells in somehow find the way to use the immune checkpoints to avoid being attacked by the immune system, and drugs that target these checkpoints are now available for cancer treatment (Fritz and Lenardo, J Exp Med 2019). The effects of the cGAMP-modified bone marrow microenvironment on the immune checkpoint expression by NK cells are unknown and will be investigated. We will also explore whether cGAMP nanoparticles can be used in combination with other genotoxic agents that sustain the STING pathway. These experiments will provide the rationale for the combined use of cGAMP nanoparticles, checkpoint inhibitor drugs or therapeutic drugs for cancer treatment in order to overcome tumor immune evasion.
Another objective of our project is based on the development of new models aimed at culturing primary myeloma cells in vitro, in a 3D environment mimicking the human BM. One of the most prevalent challenges in cancer research is the current limitation of in vitro models, somewhat due to their inability to adequately reflect the tumor microenvironment and mimic the complex interactions between cancer cells and their surrounding native environment. This is even more important in MM, considering the evidences that BM microenvironment supports disease progression and chemoresistance. The establishment of novel, biologically relevant, human-derived artificial tissue models can open new routes not only in the research areas, but also in the clinics. In fact, the development of a patient-specific model supporting primary MM cell growth could be of great value in order to design and test new immunotherapeutic treatment strategies and to better elucidate NK cell subset functions against primary malignant plasmacells.