Can the selective removal of old cells
modify age-related conditions?
The impact of age is readily apparent at the cellular level, and a variety of alterations in the mechanisms which regulate normal cell division and function, including genetic stability; energy production, and cell-to-cell communication – collectively “cellular senescence” – have been identified. Ageing cells secrete a variety of pro-inflammatory proteins and are more abundant in failing hearts, joints and eyes. The relationship between senescence and organ dysfunction is misty, but animal studies in which an artificially-aged type of stem cell was transplanted into young mice resulted in a decrease in their physical capabilities and lifespan when compared to control animals.
Moreover, treatment with agents hypothesised to be capable of triggering programmed cell death (apoptosis) in senescent cells had a positive effect on physical function and lifespan in the stem cell-transplanted mice and on levels of secreted proteins associated with cellular senescence.
Drugs designed to selectively remove ageing cells- “senolytics”- are just beginning to make their way into clinical development. Unity Biotechnology’s strategy is the elimination of ageing cells in specific disease states. UBX0101 targets the interaction of the proteins MDM and p53, the latter being involved in cell-cycle arrest and apoptosis. A Phase I study is recruiting subjects with osteoarthritis, who will each receive a single intra-articular injection into the knee. A preclinical candidate, UBX1967 targets Bcl-2, another pro-apoptotic protein, and is intended for the treatment of age-related ophthalmological conditions.
Several other candidate senolytics are in preclinical evaluation. Two target the interaction between p53 and a DNA-binding protein: FOX04, a pro-apoptopic peptide (FOX04-DRI: Cleara Biotech), and an undisclosed small molecule (Antoxerene). Oisin Biotechnologies is developing a plasmid-based gene therapy to selectively ablate senescent cells.
Recently published results suggest that pharmaceutical intervention might be capable of bolstering ageing immune systems. RTB101, being developed by ResTORbio in partnership with Novartis has completed a Phase II study conducted in elderly volunteers. RTB101 is a combination of two drugs, both of which act on targets within a long-studied, multi-protein complex, “the mechanistic target of rapamycin” (TORC1), which is critical for the activation of protein translation.
The 264 study volunteers (65 years or over) received either the drug combination, one or other of the drugs or placebo tablets for six weeks and were then given a flu vaccination two weeks later. At 10-month follow-up, those receiving both drugs had the lowest rate of self-reported respiratory infection; blood tests indicated that the combination (but not single drug treatment) resulted in more complete TORC1 inhibition and that genes which control virus-fighting Type 1 interferon production were upregulated. The authors postulated that other mechanisms might also contribute to this apparent reduction in “immunosenescence”.
Time to start planning for that 100th birthday celebration? Probably not (unless centenarians run in the family), but there’s a reasonable expectation that one or more of the current development strategies in, or close to, clinical study, will eventually lead to useful medications, although perhaps in specific age-related disease states rather than universal elixirs of youth.
Photo credit: Linnaea Mallette https://www.publicdomainpictures.net
Senolytics improve physical function and increase lifespan in old age. Xu, M et al. Nature Medicine 2018. https://doi.org/10.1038/s41591-018-0092-9. Published online 9th July 2018.
TORC1 inhibition enhances immune function and reduces infections in the elderly. Mannick, JB et al. Sci. Transl. Med. 10, eaaq1564 (2018), 11th July 2018.