Therapeutic Target Database (TTD) is a pharmaceutical and medical repository[1] constructed by the Innovative Drug Research and Bioinformatics Group (IDRB) at Zhejiang University, China and the Bioinformatics and Drug Design Group at the National University of Singapore. It provides information about known and explored therapeutic protein and nucleic acid targets,[2] the targeted disease,[3] pathway information[4] and the corresponding drugs directed at each of these targets.[1] Detailed knowledge about target function, sequence, 3D structure, ligand binding properties, enzyme nomenclature and drug structure, therapeutic class, and clinical development status.[1] TTD is freely accessible without any login requirement at https://idrblab.org/ttd/.
Statistics
This database contains 3,730 therapeutic targets (532 successful, 1,442 clinical trial, 239 preclincial/patented and 1,517 research targets) and 39,862 drugs (2,895 approved, 11,796 clinical trial, 5,041 preclincial/patented and 20,130 experimental drugs). The targets and drugs in TTD cover 583 protein biochemical classes and 958 drug therapeutic classes, respectively.[1] The latest version of the International Classification of Diseases (ICD-11) codes released by WHO are incorporated in TTD to facilitate the clear definition of disease/disease class.[5]
Validation of Primary Therapeutic Target
Target validation normally requires the determination that the target is expressed in the disease-relevant cells/tissues,[6] it can be directly modulated by a drug or drug-like molecule with adequate potency in biochemical assay,[7] and that target modulation in cell and/or animal models ameliorates the relevant disease phenotype.[8] Therefore, TTD collects three types of target validation data:[9]
Experimentally determined potency of drugs against their primary target or targets.[6]
Evident potency or effects of drugs against disease models (cell-lines, ex-vivo, in-vivo models) linked to their primary target or targets.[8]
Observed effects of target knockout, knockdown, RNA interference, transgenetic, antibody or antisense treated in-vivo models.[7]
Categorization of Therapeutic Targets based on Clinical Status
The therapeutic targets in TTD are categorized into successful target, clinical trial target, preclinical target, patented target, and literature-reported target, which are defined by the highest status of their corresponding drugs.
Successful target: targeted by at least one approved drug;
Clinical trial target: not targeted by any approved drug, but targeted by at least one clinical trial drug;
Preclinical target: not targeted by any approved/clinical trial drug, but targeted by at least one preclinical drug;
Patented target: not targeted by any approved/clinical trial/preclinical drug, but targeted by at least one patented drug;
Literature-reported target: targeted by investigative drugs only.
Classification of Therapeutic Targets based on Molecular Types
The molecular types of therapeutic targets in TTD include protein, nucleic acid, and other molecule.
Protein: the most common type of target in drug development
Nucleic acid: include DNA, mRNA, miRNA, lncRNA targets
Other molecule: such as uric acid, iron, and reactive oxygen species
Different Types of Drugs Collected in TTD
The main drug types in TTD include small molecule, antibody, nucleic acid drug, cell therapy, gene therapy and vaccine.
Small molecule: the most common medications in the pharmaceutical market
Antibody: includes monoclonal antibodies and several alternatives such as antibody-drug conjugates, bispecific antibodies, IgG mixtures, and antibody fusion proteins
Nucleic acid drug: mainly include antisense oligonucleotides, small interfering RNAs, small activating RNA, microRNAs, mRNAs and so on
Cell therapy: inject, graft or implant viable cells into a patient in to effectuate a medicinal effect
Gene therapy: manipulate gene expression or alter the biological properties of living cells to produce the therapeutic effect
Vaccine: provide active acquired immunity to a particular infectious or malignant disease
^Overington JP, Al-Lazikani B, Hopkins AL (2006). "How many drug targets are there?". Nature Reviews Drug Discovery. 5 (12): 993–6. doi:10.1038/nrd2199. PMID17139284. S2CID11979420.
^Zheng CJ, Han LY, Yap CW, Ji ZL, Cao ZW, Chen YZ (2006). "Therapeutic targets: progress of their exploration and investigation of their characteristics". Pharmacol. Rev. 58 (2): 259–79. doi:10.1124/pr.58.2.4. PMID16714488. S2CID3082221.
^ abVidalin, Olivier; Muslmani, Machadiya; Estienne, Clément; Echchakir, Hamid; Abina, Amine M. (1 October 2009). "In vivo target validation using gene invalidation, RNA interference and protein functional knockout models: it is the time to combine". Current Opinion in Pharmacology. 9 (5): 669–676. doi:10.1016/j.coph.2009.06.017. ISSN1471-4973. PMID19646923.
^ abOverall, Christopher M.; Kleifeld, Oded (15 March 2006). "Tumour microenvironment - opinion: validating matrix metalloproteinases as drug targets and anti-targets for cancer therapy". Nature Reviews. Cancer. 6 (3): 227–239. doi:10.1038/nrc1821. ISSN1474-175X. PMID16498445. S2CID21114447.