Arbaclofen (STX209, R-baclofen), a selective agonist of GABA-B receptors, has been investigated in clinical trials for the treatment of autism spectrum disorder ASD, phase II and for the treatment of patients with fragile X syndrome in phase III. As a result, the drug did not meet the primary outcome of improved social avoidance in FXS in either study. In spite of positive results in some children with ASD, further study will be needed to replicate and extend these initial findings. Arbaclofen has also been investigated in phase III clinical trials as a treatment for spasticity due to multiple sclerosis.

Velusetrag (TD-5108) is a potent, selective high intrinsic activity serotonin 5-HT(4) receptor agonist. Velusetrag has achieved proof-of-concept in patients with chronic idiopathic constipation and was on phase II of clinical trial for the treatment of Alzheimer's disease and constipation, when studies were discontinued. In addition, velusetrag is on the phase II of clinical trial for the treatment of gastroparesis.

2-Cyano-3,12-dioxooleana-1,9-diene-28-oic acid (CDDO, also known as Bardoxolone) is a synthetic triterpenoid that displays potent anti-inflammatory and antitumorigenic activities. CDDO was in the clinical trial phase I for the treatment patients with Solid tumors and leukemia, but that studies were discontinued. It is known, that CDDO blocks the cellular synthesis of inducible nitric oxide synthase and inducible COX-2. In addition, was discovered, that CDDO disrupted intracellular redox balance and thereby induce apoptosis. Moreover, CDDO is a ligand for peroxisome proliferator-activated receptor that it induces genes regulated by Nrf2, including heme oxygenase-1 and eotaxin-1, which play a role in antioxidant response element signaling activity.

Talotrexin (also known as PT-523) was developed as a nonpolyglutamatable antifolate drug for the treatment of various types of tumors. It is known that antifolates are a class of cytotoxic or antineoplastic agents, which inhibit or prevent the maturation and proliferation of malignant cells. Talotrexin was studied in clinical trials for the treatment of brain and central nervous system tumors, leukemia, lymphoma, unspecified childhood solid tumor. However, this study was withdrawn because of toxicity. In addition, was studied in phase I/II multicenter clinical trial in patients with non-small-cell Lung carcinoma, this study was also withdrawn. The withdrawal was related to incidences of dose-limiting mucositis and myelosuppression. However, on May 22, 2006, was announced that the U.S. Food and Drug Administration has granted orphan drug designation for talotrexin in patients with acute lymphoblastic leukemia (ALL).

Liarozole is an imidazole-containing compound that inhibits the cytochrome P-450-dependent metabolism of all-trans-retinoic acid (RA). Liarozole, a retinoic acid (RA) metabolism-blocking agent (RAMBA) in clinical development, has been granted orphan drug designation for congenital ichthyosis by the European Commission and the U.S. Food and Drug Administration. Later, based on the mixed results from a phase II/III trial of liarozole for the treatment of ichthyosis, Barrier decided to discontinue the development of liarozole. Liarozole displays antitumor activity against androgen-dependent and independent rat prostate carcinomas.A large phase III international study was completed comparing liarozole 300 mg twice daily with cyproterone acetate (CPA) 100 mg twice daily in a total of 321 patients with metastatic prostate cancer in relapse after first-line endocrine therapy. The results indicate that liarozole might be a possible treatment option for prostate cancer (PCA) following failure of first-line endocrine therapy.

Fosbretabulin (Combretastatin A4 phosphate, CA4P) is the lead compound of a relatively new class of agents termed vascular disrupting agents that target existing tumor blood vessels. Rapid tumor blood flow shutdown has been demonstrated in preclinical models and patients by various techniques such as dynamic contrast-enhanced MRI, perfusion computed tomography and PET scans following CA4P infusion. CA4P typically induces rapid tumor necrosis in the center of the tumor and leaves a rim of viable cells in the periphery. In oncology, CA4P does not appear to be that active by itself, but may be more efficacious when combined with chemotherapy, antiangiogenic therapy and radiation therapy. Combretastatin was initially isolated from the root bark of the South African Bush willow Combretum caffrum in 1982 by Pettit and colleagues at the Arizona State University (AZ, USA). Combretastatin A4 phosphate binds avidly to tubulin at the colchicine-binding site to inhibit microtubule assembly and destabilize the cytoskeleton. CA4P is a tubulin-binding agent that binds at or near the colchicine binding site of β-tubulin (Kd = 0.40 uM), inhibits tubulin assembly with IC50 of 2.4 uM. Fosbretabulin has orphan drug status in the EU and the US for the treatment of ATC (Anaplastic Thyroid Cancer). Later the development of this drug was discontinued.

Ditiocarb, the sodium salt of diethyldithiocarbamate, is a drug with strong antioxidant capacity and chelating activities. It improves the depressed immune responses of newborn and aged mice and mice that are treated with chemotherapy or irradiation. Ditiocarb prevents cisplatin nephrotoxicity in animals without reducing the drug's antitumor activity. Ditiocarb has therapeutic activity in the LP-BM5 murine retrovirus-induced immunodeficiency disease. In that AIDS model, it reduces lymphadenopathy and hypergammaglobulinemia, restores immunocompetence, and prolongs survival. Ditiocarb was safe and reduced the incidence of opportunistic infections in patients with symptomatic HIV infection but ditiocarb had no positive effect on HIV patients. The administration of ditiocarb did not induce any major adverse clinical or biological reactions. Sixty-four patients with nonmetastatic high-risk breast cancer were randomized in a double-blind trial of adjuvant immunotherapy with sodium ditiocarb (DDC) versus placebo. At 6 years, overall survival was 81% in DDC group versus 55%.

Perifosine is an orally active alkyl-phosphocholine compound with potential antineoplastic activity. Perifosine is an Akt inhibitor, which targets the pleckstrin homology domain of Akt, thereby preventing its translocation to the plasma membrane. Perifosine exerts Akt-dependent and Akt-independent effects, and although many preclinical studies have documented Akt inhibition by perifosine, clinical validation of these findings is lacking. Perifosine is in phase II and III clinical trials for the treatment of neuroblastoma, glioblastoma multiforme and other solid tumors.

Talabostat is a prolineboronate ester derivative patented by Boehringer Ingelheim Pharmaceuticals, Inc. as an antineoplastic agent. Talabostat inhibits dipeptidyl peptidases, such as fibroblast activation protein (FAP), resulting in the stimulation of cytokine and chemokine production and specific T-cell immunity and T-cell dependent activity. Talabostat has been shown to cause caspase-1 activation and IL-1β induction in macrophages, which in turn causes upregulation of the cytokines and chemokines that characterize the responses to talabostat, both in vitro and in tumor-bearing mice. Talabostat may also stimulate the production of colony stimulating factors, such as granulocyte colony stimulating factor (G-CSF), resulting in the stimulation of hematopoiesis. In clinical trials, the combination of talabostat and cisplatin was well tolerated compared to historical data using cisplatin alone. The most frequent adverse events were nausea, vomiting, fatigue, anemia, edema, and constipation. Unfortunately was no evidence that Talabostat enhanced the clinical activity of other anticancer drugs and further development was discontinued.

Sarizotan (also known as EMD-128,130), a chromane derivative that was developed as a selective 5-HT1A receptor agonist and D2 receptor antagonist. Experiments on animal models have shown that the drug effectively suppressed levodopa-induced dyskinesia in primate and rodent models of Parkinson's disease, and tardive dyskinesia in a rodent model. Sarizotan participated in phase II/III clinical trials in the treatment of dyskinesia associated with the dopaminergic treatment of Parkinson's disease. However, further development for this disease was discontinued by Merk, because phase III did not confirm earlier Phase II findings. On July 14, 2015, Newron Pharmaceuticals, research, and development company focused on the novel central nervous system (CNS) and pain therapies, announced that the U.S. Food and Drug Administration (FDA) has granted Orphan Drug Designation to sarizotan for treatment of Rett syndrome. Besides, the drug now is an ongoing clinical trial phase II/III to investigate its the tolerability and efficacy in reducing respiratory abnormalities in Rett Syndrome.