Science Spotlight

Steroid fused to cartilage-homing peptide alleviates systemic toxicity

From the Olson laboratory, Clinical Research Division

Rheumatoid arthritis (RA) and multi-joint inflammation affects millions of people around the United States. Many patients are treated with systemic steroids in order to reduce their painful inflammation. However, long-term use of systemic steroids can lead to many serious side effects, including vulnerability to infection, increase in insulin resistance, high blood pressure, weight gain, and psychological effects such as mood swings and depression. Alternatively, steroids can be injected directly into affected joints but their therapeutic effect is localized. While some biologics have been developed to target proteins involved in RA inflammation, they are not as broadly effective as steroids. The Olson lab in the Clinical Research Division sought to develop a new treatment modality for RA, making use of their cysteine dense peptide screening capabilities. Their results were recently published in Science Translational Medicine.

Cysteine dense peptides (CDPs) are 40-60 amino acids in length with at least three disulfide bridges, making them small, compact, and relatively resistant to degradation. The Olson lab mines CDP sequences from all branches of life and has developed a high-throughput pipeline for screening CDP therapeutic capabilities. Using this pipeline and whole-body autoradiography, they found that three radiolabeled CDPs accumulated and persisted in the cartilage of mice up to 96 hours after systemic administration. While all three CDPs varied in amino acid sequence, their crystal structures were remarkably similar, largely positively charged on their surface with only small pockets of negative charges. This 3D structure was necessary for accumulation in the knee, as CDPs mutated to eliminate disulfide bonds did not accumulate in the joint. The authors also wanted to confirm that accumulation was not rodent-specific and found that these CDPs accumulated in the extracellular matrix of human cartilage explants, indicating a general cartilage-homing specificity across species. 

Finding a cartilage-homing CDP was a huge step in the right direction for RA treatment. Dr. Olson explained: "A huge challenge with standard arthritis drugs is that cartilage is avascular, so very little of the drug gets to the joint. In order to get therapeutic amounts to the joint, higher levels go elsewhere in the body and cause toxicity - particularly for a disease like arthritis that requires decades of treatment." With a CDP that accumulated in the cartilage, the authors wanted to determine if fusing corticosteroids to the CDP would allow the drugs to act locally, instead of systemically. However, fusion of drug might eliminate its ability to act, so the authors tested multiple hydrolysable linkers that would allow the drug to be cleaved from the CDP within the body. Dexamethasone (dex) is a steroid with a long history of use in patients with arthritis and was the first fusion partner for the CDPs. However, the authors found that while the dex-CDP fusion accumulated in joints, its hydrolysis allowed too much of it to enter into bloodstream of animals, evidenced by weight decrease of spleen and thymus, two organs sensitive to systemic steroids.

Steroid-peptide fusion allows for localized activity and reduced toxicity
Modified from Hutch Communications infographic

In order to reduce systemic toxicity, the authors tried a fusion of triamcinolone acetonide (TAA) to the CDP, as TAA is cleared more rapidly from the blood and would potentially have fewer side effects. Animals treated with the TAA-CDP fusion had significant reduction of ankle diameter, a measure of inflammation, and no change in the weight of spleen or thymus, indicating that TAA-CDP was locally active with little systemic toxicity. In animals treated with the highest dose of TAA-CDP, ankle diameter was reduced to diameters prior to inflammation onset, indicating a complete reversal of disease. Dr. Olson explained how finding the right combination was key. "The major breakthrough was finding the right linker and payload combination," he said. "We tried several other steroids before focusing on TAA. Only TAA coupled with the right linker caused relief of arthritis in the joints with no evidence of circulating amounts of steroid that would cause toxicity." 

This research was supported by the National Institutes of Health, Project Violet, the Wissner-Slivka Foundation, the Kismet Foundation, the Sarah M. Hughes Foundation, Strong4Sam, Yahn Bernier and Beth McCaw, Len and Norma Klorfine, Anne Croco, Pocket Full of Hope, and Blaze Bioscience.

Fred Hutch/UW Cancer Consortium members Roland Strong, Julian Simon, and James Olson contributed to this work. 

Cook Sangar ML, Girard EJ, Hopping G, Yin C, Pakiam F, Brusniak MY, Nguyen E, Ruff R, Gewe MM, Byrnes-Blake K, Nairn NW, Miller DM, Mehlin C, Strand AD, Mhyre AJ, Correnti CE, Strong RK, Simon JA, Olson JM. 2020. A potent peptide-steroid conjugate accumulates in cartilage and reverses arthritis without evidence of systemic corticosteroid exposure. Sci Transl Med. 12(533). doi: 10.1126/scitranslmed.aay1041

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