Adozelesin (U 73975, adolezesin) is an experimental antitumor drug of the duocarmycin class. Adozelesin is a highly potent alkylating agent that undergoes binding in the minor groove of double-stranded DNA (ds-DNA) at A-T-rich sequences followed by covalent bonding with N-3 of adenine in preferred sequences. Adozelesin is therapeutically active against a broad spectrum of tumours and was in phase II clinical trials with Pharmacia Corporation (now Pfizer) in the US for breast cancer treatment. Phase I and Phase II clinical trials were conducted in 2000s, however, it was found adozelesin had marginal efficacy in the treatment of metastatic breast cancer at the dosage and schedule used.

Tasidotin (also known as ILX-651), an orally active synthetic microtubule-targeted derivative of the marine depsipeptide dolastatin-15. It was suggested, that tasidotin has a unique mechanism of action. The drug inhibits cell proliferation by suppressing spindle microtubule dynamics through a reduction of the shortening rate, reduction of the switching frequency from growth to shortening, and reduction of the time microtubules grow. Tasidotin was studied in clinical trials phase II in patients with locally advanced or metastatic non-small cell lung carcinoma, in patients with hormone-refractory prostate cancer, and in patients with inoperable locally advanced or metastatic melanoma. However, no new results were published last 5 years. It was suggested that tasidotin is no longer being used as single or even components of multiple agents today.

Sparfosate (PALA) is a stable transition state analogue for an aspartate transcarbamylase- cartalyzed reaction with antineoplastic activity. PALA is a potent inhibitor of aspartate transcarbamylase (Ki about 10(-8) M for ACTases of various origins), which in whole cells blocks the de novo synthesis of pyrimidines. Thus PALA inhibits de novo pyrimidine biosynthesis and increases the extent to which fluorouracil metabolites are incorporated into RNA. In vivo, low doses of PALA inhibit whole body pyrimidine synthesis. While this action is cytotoxic in vitro, extensive human testing demonstrates that PALA alone is devoid of selective antitumor activity. Interest in the therapeutic action of PALA derives from the demonstration that its action potentiates the cytotoxicity of several cytotoxic drugs, notably 5-fluorouracil (5-FU). Development of Sparfosate for cancer and Hepatitis B treatment is assumed to have been discontinued.

Seliciclib (CYC202, R-roscovitine) is a second-generation orally available cyclin-dependent kinases (CDKs) inhibitor that competes for ATP binding sites on these kinases. It is a direct inhibitor of cyclin CDK2/E, CDK2/A and it has inhibitory effects on cyclin H/CDK7, CDK5, and CDK9. CDKs are enzymes that are central to the process of cell division and cell cycle control and play pivotal roles in cancer cell growth and DNA damage repair. Seliciclib exerts an anti-proliferative effect via several key mechanisms: selective downregulation of proliferative and survival proteins and upregulation of p53, leading to growth arrest or apoptosis. The second one is decreasing phosphorylation of Rb and modulating E2F transcriptional activity leading to growth arrest or apoptosis. Seliciclib is currently in phase II clinical trial as a drug candidate for the treatment of Cushing's disease and as a potential therapeutic agent for the treatment of cystic fibrosis (CF). In addition, it is in Phase II trials for non-small cell lung cancer and nasopharyngeal carcinoma.

Crisnatol is a derivative of arylmethylaminopropanediol with significant antineoplastic activity in a variety of murine and human tumor models. Crisnatol functions as a DNA intercalator, with the presence of additional basic amine groups in the sidechain enhancing binding to DNA due to electrostatic interactions. Crisnatol did not show antitumor efficacy in patients with ovarian carcinoma. In another clinical study, 2 of 26 patients with glioma showed complete long-lasting responses to the drug. The dose-limiting side effect was neurotoxicity.

Emitefur or BOF-A2 is a fluorinated pyrimidine antimetabolite exerting antineoplastic properties. It is a compound composed of 5-fluorouracil (5-FU) and 3-cyano-2,6-dihydroxypyridine (CNDP), an inhibitor of 5-FU degradation by dihydrouracil dehydrogenase in order to prolong the blood 5-FU level as well as increase selective toxicity to a tumor. Emitefur demonstrated clinical activity in preliminary studies in Japan. Emitefur development for the treatment of solid tumors has been discontinued.

Enclomiphene (Androxal), in development by Repros Therapeutics Inc, is a non-steroidal estrogen receptor antagonist that promotes gonadotropin-dependent testosterone secretion by the testes. Enclomiphene constitutes the trans-stereoisomer of clomiphene citrate, a drug that has been widely prescribed for several decades for the treatment of female ovulatory dysfunction. Because of the antagonistic effects of enclomiphene, the drug has the potential to increase serum testosterone levels in men with secondary hypogonadism by restoring physiological endogenous testosterone secretion while maintaining testicular volume and, potentially, spermatogenesis. In clinical trials conducted to date, enclomiphene demonstrated significant efficacy in the physiological restoration of testosterone levels in males with secondary hypogonadism. The compound also exhibited an unanticipated favorable effect on fasting plasma glucose; this result has been accompanied by rapidly accumulating evidence from other researchers for a bidirectional relationship between low serum testosterone and obesity/metabolic syndrome (syndrome X) in men.

Taselisib (GDC-0032) is an highly selective small-molecule inhibitor of phosphatidylinositol 3-kinase (PI3K) p110-α isoform (PIK3CA). Taselisib is designed to bind to the ATP-binding pocket of PIK3CA to potentially prevent subsequent downstream signaling. Taselisib caused a strong differential growth inhibition in carcinoma cells harbored oncogenic PIK3CA mutations. In preclinical studies, taselisib induced growth inhibition in PIK3CA-mutant xenograft mouse models. Genentech (a Roche subsidiary) is developing taselib primarily for the treatment of solid tumours.

IPROPLATIN is a quadrivalent second-generation platinum complex. It binds to and forms DNA crosslinks and platinum-DNA adducts, resulting in DNA replication failure and tumor cell death. IPROPLATIN was discontinued in phase III clinical trials.

Elinafide (LU 79553) is a bisintercalating naphthalamide and a topoisomerase II inhibitor has demonstrated a higher binding affinity for DNA and significant antitumour efficacy against a panel of established tumour cell lines, including several multidrug resistant-positive sublines. Elinafide had been in phase II clinical trial for the treatment of ovarian cancer and phase I trials for the treatment of various solid tumours. The major haematological toxicities observed were anaemia and neutropenia. The major non-haematological toxicities observed in the 3-weekly schedule were neuro-muscular presenting clinically as a mixed syndrome of severe weakness (sometimes with pain in both legs), myalgia and arthralgia, asthenia/fatigue/malaise. One fatality was considered related to LU 79553, as the patient had fever and neutropenia. Clinical study of this drug candidate was discontinued due to its neuromuscular dose-limiting toxicity.