ApoptoSENS - Senolytic CAR-NK cells
Over time, a subset of cells in our body experience damage and enter a state of senescence. Cellular senescence is the irreversible arrest of proliferation accompanied by proinflammatory factors that lead to tissue dysfunction. Selective elimination of these senescent cells has been shown to ameliorate hallmarks of aging in both mice and humans. However, current methods to eliminate senescent cells are non-specific and may have off-target effects. As a result, we are developing Chimeric Antigen Receptor Natural Killer (CAR-NK) cells to precisely and safely eliminate senescent cells in vivo.
When cells become damaged, they may enter a state of cellular senescence where they no longer function properly and secrete proinflammatory factors. The immune system’s ability to eliminate senescent cells diminishes with age, resulting in their accumulation throughout the body. This accumulation leads to dysfunction in many different tissue types and accelerates aging. Current approaches to eliminate senescent cells are non-specific and their mechanisms of action are largely unknown. Also, due to the highly heterogeneous nature of senescent cells, including the existence of senescent cells with beneficial effects, there is currently a lack of knowledge regarding cell surface markers to identify populations of harmful senescent cells. The current focus on senescence as a therapeutic target was prompted by the discoveries that markers of cellular senescence accumulate with aging and accumulation is delayed by interventions that increase healthspan and lifespan, removal of senescent cells increases healthspan in progeroid mouse models, and transplantation of a relatively small number of senescent cells into previously healthy animals provokes multisystem dysfunction similar to what is seen in aged animals. Furthermore, it has been shown that the correlation of senescent cell accumulation with disease extends to humans. Since senescent cells are highly heterogeneous in both their molecular biology and their physiological function, targeted strategies are needed that ideally preserve senescent cells in beneficial contexts while eliminating effects that are detrimental. Broadly speaking, current therapies can be broken down into the major categories of senomorphic (targeting SASP, i.e., senescence-associated secretory phenotype, components) and senolytic (targeting senescent cells) drugs. While the first senolytics were developed using a bioinformatically informed approach aimed at disrupting SCAPs and other pro-survival networks, the class has expanded to take advantage of additional senescence features and enhance immune-mediated clearance. Most notably, characterization of senescent cells has revealed unique markers that serve as senescence-associated self-antigens, and these can be co-opted for immune system-mediated senolytic activity and clearance. Despite the pre-clinical promises of targeting senescent cells and/or SASP, clinical trials in humans thus far have been less encouraging. Nevertheless, significant interest remains in the general approach. A recent study took advantage of this approach using chimeric antigen receptor (CAR) T cells targeted against the urokinase-type plasminogen activator receptor (uPAR) in a mouse model (doi: 10.1038/s41586-020-2403-9). Cytotoxic CAR T cells were able to selectively clear uPAR-expressing senescent cells in vitro and in vivo. CAR T cell-mediated clearance of senescent cells led to survival and histopathologic benefit in murine models of both carbon tetrachloride- and diet-induced liver fibrosis, suggesting the feasibility and potential of this clearance strategy. However, supratherapeutic CAR T cell dosing is associated with a proinflammatory cytokine profile, weight loss and hypothermia, suggesting that careful attention would need to be paid to initial dosing strategies, particularly in geriatric populations where a compromised immune system together with ongoing chronic inflammation may restrict the therapeutic window. Additionally, CAR T cell approaches in humans involve initial immune system suppression with considerable attendant morbidity and are expensive. Although senolytic CAR T cells appear to be self-limiting, their expansion and contraction occurs over a period of days, which is a risk in the case of an acute to subacute adverse reaction. Overall, this strategy is highly promising given its preclinical efficacy and senescent cell specificity, but future optimization and testing is necessary before clinical administration.
Given the success of CAR T cells, particularly in the cancer field, we have identified unique surface markers on senescent cells for targeted removal. Using a commercially available protocol, we have found several cell surface markers of IMR-90 cells made senescent by ionizing radiation or doxorubicin treatments that are not present on healthy cells. To date, we have focused on 5 top candidates, of which SENS-1, -2 and -3 have been further vetted, with SENS-3 perhaps looking the most promising. In the proposal here, priority senescent cell markers will be more extensively validated using additional cell model paradigms (stressors), as well as in mouse models (cross-species validation). Validated surface markers will be used to generate monoclonal antibodies, which will then be confirmed for specificity against the target antigen. Appropriate CAR NK cells will be created to further establish proof of concept for their approach of selective removal of senescent cells in their various model systems. Commercial Viability A patent regarding methods to develop the CAR-NK cells is intended to be filed. They already have filed patents for specific surface-marker antibodies and subsequent reagents that allow selective targeting of senescent cells.
Project BudgetRequired Funding$430,000