Drug repositioning

Drug repositioning (also called drug repurposing) involves the investigation of existing drugs for new therapeutic purposes.[1][2]

A number of successes have been achieved, the foremost including sildenafil (Viagra) for erectile dysfunction and pulmonary hypertension and thalidomide for leprosy and multiple myeloma.[2][3] Clinical trials have been performed on posaconazole and ravuconazole for Chagas disease. Other antifungal agents clotrimazole and ketoconazole have been investigated for anti-trypanosome therapy.[4] Successful repositioning of antimicrobials has led to the discovery of broad-spectrum therapeutics, which are effective against multiple infection types.[5]

Drug repositioning is a "universal strategy" for neglected diseases due to 1) reduced number of required clinical trial steps could reduce the time and costs for the medicine to reach market, 2) existing pharmaceutical supply chains could facilitate "formulation and distribution" of the drug, 3) known possibility of combining with other drugs could allow more effective treatment, 4) the repositioning could facilitate the discovery of "new mechanisms of action for old drugs and new classes of medicines",[6] 5) the removal of “activation barriers” of early research stages can enable the project to advance rapidly into disease-oriented research.[7] Often considered as a serendipitous approach, where repurposable drugs are discovered by chance, drug repurposing has heavily benefited from advances in human genomics and network biology. It is now possible to identify serious repurposing candidates by finding genes involved in a specific disease and checking if they interact, in the cell, with other genes which are targets of known drugs.[8] It was shown that drugs against targets supported by human genetics are twice as likely to succeed than overall drugs in the pharmaceutical pipeline.[9] Drug repurposing can be a time and cost effective strategy for treating dreadful diseases such as cancer.[10][11]

However, there are also a number of downsides to drug repositioning. Firstly, the dosage required for the treatment of a novel disease usually differs from that of its original target disease, and if this happens, the discovery team will have to begin from Phase I clinical trials, which effectively strips drug repositioning of its advantages of over de novo drug discovery.[7] Secondly, the finding of new formulation and distribution mechanisms of existing drugs to the novel-disease-affected areas rarely includes the efforts of "pharmaceutical and toxicological" scientists.[7] Thirdly, patent right issues can be very complicated for drug repurposing due to the lack of experts in the legal area of drug repositioning, the disclosure of repositioning online or via publications, and the extent of the novelty of the new drug purpose.[7]

Drug repositioning evidence level (DREL) assessment of repositioning studies[5]
Drug repositioning evidence level Quality of scientific evidence
0 No evidence; includes in silico predictions without confirmation
1 In vitro studies with limited value for predicting in vivo/human situation
2 Animal studies with hypothetical relevance in humans
3 Incomplete studies in humans at the appropriate dose e.g. proof of concept; few cases from medical records; some clinical effects observed
4 Well-documented clinical end points observed for repositioned drug at doses within safety limits

References
  1. Sleigh SH, Barton CL (23 August 2012). "Repurposing Strategies for Therapeutics". Pharmaceutical Medicine. 24 (3): 151–159. doi:10.1007/BF03256811. S2CID 25267555.
  2. Ashburn TT, Thor KB (August 2004). "Drug repositioning: identifying and developing new uses for existing drugs". Nature Reviews. Drug Discovery. 3 (8): 673–83. doi:10.1038/nrd1468. PMID 15286734. S2CID 205475073.
  3. Institute of Medicine (2014). Drug Repurposing and Repositioning: Workshop Summary. National Academies Press. ISBN 978-0-309-30204-3.
  4. Gambino D, Otero L (2019). "Chapter 13. Metal Compounds in the Development of Antiparasitic Agents: Rational Design from Basic Chemistry to the Clinic". In Sigel A, Freisinger E, Sigel RK, Carver PL (eds.). Essential Metals in Medicine:Therapeutic Use and Toxicity of Metal Ions in the Clinic. Metal Ions in Life Sciences. 19. Berlin: de Gruyter GmbH. pp. 331–357. doi:10.1515/9783110527872-019. ISBN 978-3-11-052691-2. PMID 30855114.Section 2.2.2. "Repositioning of Drugs"
  5. Firth A, Prathapan P (1 January 2021). "Broad-spectrum therapeutics: A new antimicrobial class". Current Research in Pharmacology and Drug Discovery. 2: 100011. doi:10.1016/j.crphar.2020.100011. ISSN 2590-2571.
  6. Rosa SG, Santos WC (2020). "Clinical trials on drug repositioning for COVID-19 treatment". Revista Panamericana de Salud Pública. 44: e40. doi:10.26633/RPSP.2020.40. PMC 7105280. PMID 32256547.
  7. Oprea TI, Bauman JE, Bologa CG, Buranda T, Chigaev A, Edwards BS, et al. (2011). "Drug Repurposing from an Academic Perspective". Drug Discovery Today. Therapeutic Strategies. 8 (3–4): 61–69. doi:10.1016/j.ddstr.2011.10.002. PMC 3285382. PMID 22368688.
  8. Nabirotchkin, Serguei; Peluffo, Alex E; Rinaudo, Philippe; Yu, Jinchao; Hajj, Rodolphe; Cohen, Daniel (January 2020). "Next-generation drug repurposing using human genetics and network biology". Current Opinion in Pharmacology. doi:10.1016/j.coph.2019.12.004.
  9. King, Emily A.; Davis, J. Wade; Degner, Jacob F.; Marchini, Jonathan (12 December 2019). "Are drug targets with genetic support twice as likely to be approved? Revised estimates of the impact of genetic support for drug mechanisms on the probability of drug approval". PLOS Genetics. 15 (12): e1008489. doi:10.1371/journal.pgen.1008489.
  10. "Targeting ion channels for cancer therapy by repurposing the approved drugs". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1848 (10): 2747–2755. 2015-10-01. doi:10.1016/j.bbamem.2015.03.034. ISSN 0005-2736.
  11. Kale, Vijay P.; Habib, Hasan; Chitren, Robert; Patel, Milan; Pramanik, Kartick C.; Jonnalagadda, Subash C.; Challagundla, Kishore; Pandey, Manoj K. (March 2020). "Old drugs, new uses: Drug repurposing in hematological malignancies". Seminars in Cancer Biology. doi:10.1016/j.semcancer.2020.03.005. ISSN 1044-579X.

Further reading
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