INTRODUCTION:

Low back pain is a global health problem that is directly related to intervertebral disc (IVD) degeneration. It is experienced by ~ 80% of individuals at some time in their lifespan. Despite its prevalence, little is known about the mechanisms leading to painful IVD degeneration, leaving surgical removal and vertebral fusion in end-stage disease as the most common treatment. There is growing recognition that senescent cells accumulate during tissue degeneration. In ageing and degenerating IVDs, tissue homeostasis is disrupted by the accumulation of senescent cells producing inflammatory and nociceptive factors that cause pain and inflammation, along with proteases degrading the tissue. One drawback of using a single senolytic agent is the failure to target multiple senescent anti-apoptotic pathways in the same cell type, or different cell populations within a target tissue. Concurrently targeting multiple and indirectly related anti-apoptotic pathways may result in increased selectivity for senescent cells in the absence of toxicity for normal proliferating or quiescent cells. The lower therapeutic dosages enabled by combinations also decreased side effects associated with single drugs. Combined treatment at lower doses may allow the repurposing of drugs that, were previously discarded due to undesirable side effects and increase success in clinical trials.

METHODS:

Human IVD cells: A dose response curve of o-Vanillin and RG-7112 was set up to select the most effective concentrations. Cells are treated with the 4 different combinations of o-Vanillin and RG-7112 for 6 hours. Slides are then immunohistochemically stained to measure level of senescence, level of proliferation, level of apoptosis and inflammation.

SPARC-null Mice: Animals 5-6-month-old SPARC-null mice with signs of IVD degeneration and low back pain were used. Drugs were administered by oral, once a week for 8 weeks. Grip strength, acetone-evoked behavior and mechanical sensitivity was assessed on non-treatment days during weeks 0, 2, 4, 6 and 8. The tail suspension test and distance travelled in open field was measured on weeks 4 and 8.

RESULTS SECTION:

The combination of o-Vanillin and RG-7112 significantly reduces the amount of senescence cells when compared to the senolytic drugs alone in degenerate human IVD cells. During pain behavior analysis, it was seen that cold allodynia, radicular pain and axial discomfort have been significantly reduced as of 4 weeks in the SPARC-null senolytic combination groups and single drug treated groups when compared to the SPARC-Null non-treated group. Furthermore, we observe a greater behavioral effect of the senolytic treatments when compared to the non-treated group at the 8-week time point.

DISCUSSION:

Our goal is to demonstrate the synergistic effect of combining these compounds to further reduce the expression of pain behaviours, pain mediators and improve tissue homeostasis in cells from a symptomatic patient population and from a clinically relevant mouse model of lower back pain and IVD degeneration. If proven true, these combinations therapies could revolutionize treatment of back pain for millions of patients worldwide and be one step closer to offering a preventative treatment for individuals at risk of lower back pain or avoid/prolong the need for invasive surgery.