Avelestat, also known as AZD9668, is a novel, oral inhibitor of neutrophil elastase (NE), an enzyme implicated in the signs, symptoms, and disease progression in NE-driven respiratory diseases such as bronchiectasis, Cystic Fibrosis and chronic obstructive pulmonary disease via its role in the inflammatory process, mucus overproduction, and lung tissue damage. Its development was discontinued due to unknown reasons. Nevertheless, this drug in the phase II of clinical trial as adjunctive therapy in improving insulin sensitivity of insulin-resistant type 2 diabetic subjects. The drug's clinical profile suggests that it will be well tolerated with few, if any, side effects, and the existence of simple methods that can indirectly measure its activity in vivo.

Elbimilast or ronomilast (previously ELB 353) is a phosphodiesterase IV (PDE4) inhibitor. It has been investigated in the treatment of chronic obstructive pulmonary disease.

HDAC-IN-2 (also known as citarinostat or ACY-241) was developed as a selective histone deacetylase (HDAC) 6 inhibitor with potential antineoplastic activity. Inhibition of HDAC leads to the inhibition of tumor oncogene transcription, and the selective transcription of tumor suppressor genes, which inhibit tumor cell division and induce tumor cell apoptosis. HDAC-IN-2 participates in phase 1b clinical trial in patients with multiple myeloma to determine the maximum tolerated dose (MTD) and evaluate the safety and preliminary antitumor activity. Besides, HDAC-IN-2 in combination with paclitaxel participates in phase Ib in patients with advanced solid tumors. In addition, HDAC-IN-2 in combination with nivolumab participates in phase I in patients with unresectable non-small cell lung cancer to determine the safety, tolerability, dose-limiting toxicities (DLTs), and maximum tolerated dose (MTD) of the drug.

Icopezil (previously known as CP-118,954) was developed as a selective acetylcholinesterase inhibitor for the treatment of cognitive disorders. Phase II trials of icopezil were underway in Japan and in the USA for the treatment of patients with Alzheimer's disease. However, Pfizer has discontinued these studies.

Pepstatin is a pentapeptide of microbial origin. The peptide inhibits the acid proteases pepsin and cathepsin D and the pressor enzyme renin. Pepstatin was shown to provide long-lasting inhibition (3 to 6 days) of cathepsin D in vivo in non-tumor bearers particularly in spleen, liver, kidney, lung, and heart. Pepstatin may prove useful as "anticachexia" agent by decreasing proteolysis in muscle and other tissues. The in vivo pepstatin and IL-2 treatment decreased the T-cells and increased the natural killer-like LAK precursor cells, possibly also with an increase in its activity, which were further induced by in vitro IL-2 culture to generate an augmented LAK cell activity. This suggests the clinical potential of pepstatin in IL-2-related immunotherapy. In rats injected centrally with the specific cathepsin D inhibitor, pepstatin, the protease activity was inhibited up to 90% in most brain regions.

Sezolamide (previously known as MK-417), a potent carbonic anhydrase inhibitor capable of reducing intraocular pressure after topical application, was under investigation for the treatment of glaucoma. . Sezolamide is the more potent of the two stereo isomers of MK-927 in inhibiting human carbonic anhydrase isoenzyme II, the isoenzyme found in ciliary processes. Sezolamide, the S-enantiomer of MK-927, has demonstrated activity in vitro approximately 80 times that of the R-enantiomer of MK-927 (concentrations of 0.54 nmolll and 44 nM, respectively, inhibiting activity of human carbonic anhydrase isoenzyme II by 50%). Clinically, sezolamide has also demonstrated greater activity than MK-927 both after single-dose and after twice daily administration in patients.

GS-9190 (Tegobuvir) a novel nonnucleoside inhibitor of hepatitis C virus NS5B polymerase was investigated for treatment Hepatitis C, Chronic, but on the clinical trial II was discontinued.

Avagacestat (BMS-708163) is an oral gamma secretase inhibitor designed for selective inhibition of amyloid beta (Aβ) synthesis. Avagacestat was in development by Bristol-Myers Squibb for the treatment of Alzheimer's disease (AD). Avagacestat is a potent, selective, orally bioavailable γ-secretase inhibitor of Aβ40 and Aβ42 with IC50 of 0.3 nM and 0.27 nM, demonstrating a 193-fold selectivity against Notch. In November 2012, Bristol-Myers Squibb terminated clinical trials of the drug and announced its decision to end further development of avagacestat

Freselestat (ONO-6818) is reversible, nonpeptide high affinity and selective human neutrophil elastase inhibitor, which was under development by Ono for the potential treatment of inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease and chronic obstructive pulmonary disease (COPD). Freselestat mediated neutrophil elastase inhibition, leads to the reduction of interleukin 8 production and the reduction of the complement membrane attack complex formation. Freselestat competitively inhibits neutrophil elastase in humans, rats, and hamsters, but does not inhibit other proteases such as pancreatic elastase, trypsin, proteinase 3, cathepsin G, or matrix metalloproteinases. Freselestat inhibits acute lung injury induced by neutrophil elastase in rats, minimizing lung hemorrhage, the accumulation of neutrophils in the lung and suppresses leukocyte levels in an in vivo model of COPD. Freselestat was in phase I studies for COPD in Japan and the US. However, due to abnormal variations in liver function, the development of Freselestat was terminated.

Silmitasertib (CX-4945) is a potent and selective orally bioavailable small molecule inhibitor of Casein kinase II (CK2). The antiproliferative activity of CX-4945 against cancer cells correlated with expression levels of the CK2α catalytic subunit. CX-4945 caused cell-cycle arrest and selectively induced apoptosis in cancer cells relative to normal cells. When administered orally in murine xenograft models, CX-4945 was well tolerated and demonstrated robust antitumor activity. Senhwa Biosciences is developing silmitasertib for the treatment of cholangiocarcinoma, other solid tumours, Castleman's disease (giant lymph node hyperplasia) and multiple myeloma. The compound was originally developed by Cylene Pharmaceuticals. Phase Ib/II development is underway in the US and South Korea for the treatment of cholangiocarcinoma, and development in the remaining indications is at the phase I stage. As at July 2016, no recent reports of development had been identified for phase-I development in Giant-lymph-node-hyperplasia in USA (PO, Capsule), phase-I development in Multiple-myeloma in USA (PO, Capsule), phase-I development in Solid-tumours (Late-stage disease) in USA (PO, Capsule).