Folitixorin, a thymidylate synthase inhibitor is a substrate used by the enzyme methylenetetrahydrofolate reductase (MTHFR) to generate 5-methyltetrahydrofolate. Folitixorin was studied in clinical trials for the treatment of breast cancer, metastatic colorectal cancer and for the treatment of advanced pancreatic cancer. Folitixorin had been granted orphan drug status for the treatment of pancreatic cancer in both the U.S. and EU. However, further development of this drug was discontinued.

Litronesib is a specific, ATP-uncompetitive, allosteric, and potent small-molecule inhibitor of Eg5 with potential antineoplastic activity. Litronesib selectively inhibits the activity of Eg5, which may result in mitotic disruption, apoptosis and consequently cell death in tumor cells that are actively dividing. Histone-H3 phosphorylation of tumor and proliferating skin cells is a promising pharmacodynamic biomarker for in vivo anticancer activity of litronesib. Litronesib had been in phase I clinical trial for the treatment of solid tumors. The most frequent-related adverse events were hematologic such as neutropenia.

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 However, this study was withdrawn because of toxicity.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studied in phase I/II multicenter clinical trial in patients with non-small-cell Lung carcinoma, this study was also withdrawn.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.

Ditiomustine is a nitrosourea compound with alkylating activity. Ditiomustine crosslinks DNA, resulting in the inhibition of DNA replication and eventually cellular proliferation. It was developed as antineoplastic agent.

Ditercalinium is the antineoplastic agent. Ditercalinium itself is not a natural product, however, it is derived from the natural product 5,11-dimethyl-6H-pyrido-[4,3- b]carbazole (ellipticine) that was isolated in 1959. It is a rare example of a noncovalent DNA-binding ligand that forms bisintercalation complexes via the major groove of the double helix. Ditercalinium selectively recognizes certain GC-rich sequences in DNA. It preferentialy binds with antiparallel quadruplex sequence d(AG(3)[T(2)AG(3)](3)). Ditercalinium chloride can deplete mitochondrial DNA in both mouse and human cells. Ditercalinium chloride inhibits human DNA polymerase gamma activity as efficiently as does ethidium bromide. Ethidium bromide distributes diffusely in the mitochondria of HeLa cells, while ditercalinium chloride distributes granularly and hence may be strongly associated with mitochondrial DNA.

Amustaline (S-303) is a quinacrine mustard compound with potential antineoplastic activity. Amustaline binds to, intercalates and crosslinks DNA and RNA. This agent is mainly used for ex vivo purposes, specifically for the inactivation of pathogens such as viruses, protozoa and bacteria in red blood cells (RBCs). When S-303 is added to red blood cells, the compound rapidly passes through membranes, including those of cells and viral envelopes, due to its amphipathic character, and intercalates into helical regions of the nucleic acids of pathogens and white blood cells. TERCEPTTMBlood System usingamustaline (S-303) and glutathione (GSH) was able to inactivate high levels of DENV and ZIKV in RBCs. S-303 system has been shown to effectively inactivate a broad spectrum of pathogens, while maintaining RBC quality.

Amotosalen (S-59, psoralen derivative), a chemical capable of binding to nucleic acids is added to platelets. UVA illumination (320 – 400 nm wavelengths) of amotosalen-treated platelet components induces covalent cross-linking of any nucleic acids to which amotosalen is bound; thereby, preventing further replication. Amotosalen is used in the INTERCEPT process to cross-link DNA and RNA. Amotosalen has protective activity against pathogens such as bacteria, viruses, protozoa, and leukocytes. Prior to administration amotosalen is added to plasma and platelets, then in vivo this agent penetrates pathogens and targets DNA and RNA. Upon activation by ultraviolet A light, amotosalen forms interstrand DNA and RNA crosslinks and prevents replication. Thus, the pathogen-inactivation system using amotosalen/ultraviolet A offers the potential to mitigate the risk of ZIKV transmission by plasma and platelet transfusion. Inactivation of leukocytes can prevent graft versus host disease upon transfusion.

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.

Piroxantrone is one of a series of compounds commonly known as anthrapyrazoles developed in an effort to combine the broad antitumor activity of the anthracyclines with decreased myocardial toxicity. The mechanism of action of piroxantrone and other anthrapyrazoles is incompletely understood but likely involves DNA binding with induction of DNA strand breaks, DNA-protein cross-linking, and inhibition of DNA, RNA, and protein synthesis. Collectively, these findings suggested an interaction with topoisomerase II. Piroxantrone demonstrated antitumor activity in a wide spectrum of experimental systems against breast carcinoma, colon carcinoma, sarcoma, melanoma and leukemia. Piroxantrone is inactive in patients with persistent, progressive, or recurrent ovarian cancer who recently had received a platinum-based regimen. Piroxantrone has detectable but minimal activity against disseminated malignant melanoma. A phase II clinical trial of the piroxantrone administration for the treatment of advanced metastatic or recurrent endometrial cancer was prematurely terminated due to lack of patient accrual.