Trichostatin A (TSA) was originally isolated as an antifungal antibiotic along with its fermentation congeners trichostatin B ((TSA)3-Fe) and the D-glucopyranosides trichostatin C and D. TSA inhibits HDAC in the low nanomolar range and is an inducer of histone hyperacetylation, both in vitro and in vivo. It inhibits all class I and II deacetylases to a similar extent in both tumor and non-tumor cells, although HDAC4 is slightly resistant when compared with HDAC1 and HDAC6. Class III HDAC is not affected by TSA. It has been shown that TSA dosedependently inhibits growth and induces apoptosis in a plethora of carcinoma cell lines in vitro. Recently, it was also found that TSA inhibits angiogenesis, which is important for the growth and metastasis of solid tumors, both in vivo and in vitro. In HT-29 colon carcinoma cells, a single dose of TSA induced transient hyperacetylation of histone H4 resulting in the induction of p21WAF1/Cip1 and inhibition of cellular proliferation at both the G1 and G2 phases of the cell cycle. Growth inhibition was associated with decreased cyclin D1 mRNA and cdk6 protein levels and increased cyclin D3 protein and p21WAF1/Cip1 mRNA levels. Cyclin D1 protein, cyclin D3 mRNA, cdk2 and cdk4 remained unaffected. In addition, TSA induced apoptosis by upregulating the expression of the pro-apoptotic genes ID1, ID2 and ID3, whereas the expression of the anti-apoptotic genes BclxL and Hsp27 was decreased In vivo, TSA induces differentiation and shows chemotherapeutic activity against N-methylnitrosureainduced rat mammary cancer without toxic side effects. TSA may also have therapeutic potential for the treatment of a variety of genetic and infectious diseases since silenced, transduced genes are reactivated probably due to structural changes of the chromatin on integrated viral sequences.

Droloxifene, a derivative of the triphenylethylene drug tamoxifen, is a novel selective estrogen receptor modulator (SERM). Droloxifene also exhibits more rapid pharmacokinetics, reaching peak concentrations and being eliminated much more rapidly than tamoxifen. Its higher affinity to the estrogen receptor, higher anti-estrogenic to estrogenic ratio, more effective inhibition of cell growth and division in estrogen receptor-positive cell lines, and lower toxicity give it theoretical advantages over tamoxifen in the treatment of human breast cancer. Short-term toxicity was generally mild, and similar to that seen with other antiestrogens. Droloxifene appears active and tolerable. It may have a particular role in situations in which rapid pharmacokinetics, or an increased antiestrogenic to estrogenic ratio, are required. Droloxifene may also be a potentially useful agent for the treatment of postmenopausal osteoporosis because it can prevent estrogen deficiency-induced bone loss without causing uterine hypertrophy. Droloxifene may have an effect on bone and breast tissue because it induces apoptosis. Droloxifene has an anti-implantation effect in rats, and the effect appears to be not completely due to its anti-estrogenic activity.

Abarelix is a synthetic decapeptide antagonist to gonadotropin releasing hormone (GnRH). It is marketed by Praecis Pharmaceuticals as Plenaxis. Used in the palliative treatment of advanced prostate cancer. Abarelix is a luteinizing hormone agonist that results in suppression of testicular or follicular steroidogenesis. Abarelix binds to the gonadotropin releasing hormone receptor and acts as a a potent inhibitor of gonadotropin secretion. Praecis announced in June 2006 that it was voluntarily withdrawing the drug from the market.

Rofecoxib is a nonsteroidal anti-inflammatory drug which selectively inhibits COX-2 and subsequent prostaglandin synthesis. The drug was developed by Merk and approved by FDA in 1999 for relief of signs and symptoms of arthritis, acute pain in adults, and painful menstrual cycles under the name Vioxx. Later on Merck voluntarily withdrawn Vioxx from the market due to safety concerns (high risk of heart attack and stroke).

Streptozotocin (Streptozocin, STZ, Zanosar) is a naturally occurring chemical that is particularly toxic to the insulin-producing beta cells of the pancreas in mammals. It is used in medicine for treating certain cancers of the Islets of Langerhans and used in medical research to produce an animal model for hyperglycemia in a large dose as well as Type 1 diabetes with multiple low doses. Streptozocin inhibits DNA synthesis in bacterial and mammalian cells. In bacterial cells, a specific interaction with cytosine moieties leads to degradation of DNA. The biochemical mechanism leading to mammalian cell death has not been definitely established; streptozocin inhibits cell proliferation at a considerably lower level than that needed to inhibit precursor incorporation into DNA or to inhibit several of the enzymes involved in DNA synthesis. Although streptozocin inhibits the progression of cells into mitosis, no specific phase of the cell cycle is particularly sensitive to its lethal effects. Streptozocin is active in the L1210 leukemic mouse over a fairly wide range of parenteral dosage schedules. In experiments in many animal species, streptozocin induced a diabetes that resembles human hyperglycemic nonketotic diabetes mellitus. This phenomenon, which has been extensively studied, appears to be mediated through a lowering of beta cell nicotinamide adenine dinucleotide (NAD) and consequent histopathologic alteration of pancreatic islet beta cells. The metabolism and the chemical dissociation of streptozocin that occurs under physiologic conditions has not been extensively studied. When administered intravenously to a variety of experimental animals, streptozocin disappears from the blood very rapidly. In all species tested, it was found to concentrate in the liver and kidney. As much as 20% of the drug (or metabolites containing an N-nitrosourea group) is metabolized and/or excreted by the kidney. Metabolic products have not yet been identified.

Testolactone (Teslac brand name) is an anti-cancer agent, which was used as adjunctive therapy in the palliative treatment of advanced or disseminated breast cancer. The mechanism of testolactone action is reported to be related to the inhibition of aromatase enzymatic activity. Testolactone is no longer available in the USA.

Pipobroman (trade names Vercite, Vercyte) is an anti-cancer drug that probably acts as an alkylating agent. It is marketed by Abbott Laboratories. Pipobroman (PB) has well documented clinical activity in polycythemia vera (PV) and essential thrombocythemia (ET). The mechanism of action is uncertain but pipobroman is thought to alkylate DNA leading to disruption of DNA synthesis and eventual cell death

Aminoglutethimide, marketing as Cytadren has been used in the treatment of advanced breast and prostate cancer. It was formerly used for its weak anticonvulsant properties. Cytadren is indicated for the suppression of adrenal function in selected patients with Cushing’s syndrome. Morning levels of plasma cortisol in patients with adrenal carcinoma and ectopic ACTH producing tumors were reduced on the average to about one half of the pretreatment levels, and in patients with adrenal hyperplasia to about two thirds of the pretreatment levels, during 1-3 months of therapy with Cytadren. Data available from the few patients with adrenal adenoma suggest similar reductions in plasma cortisol levels. Measurements of plasma cortisol showed reductions to at least 50% of baseline or to normal levels in one third or more of the patients studied, depending on diagnostic groups and time of measurement. Because Cytadren does not affect the underlying disease process, it is used primarily as an interim measure until more definitive therapy such as surgery can be undertaken or in cases where such therapy is not appropriate. Only small numbers of patients have been treated for longer than 3 months. A decreased effect or “escape phenomenon” seems to occur more frequently in patients with pituitary dependent Cushing’s syndrome, probably because of increasing ACTH levels in response to decreasing glucocorticoid levels. Cytadren blocks several other steps in steroid synthesis, including the C-11, C-18, and C-21 hydroxylations and the hydroxylations required for the aromatization of androgens to estrogens, mediated through the binding of Cytadren to cytochrome P-450 complexes. A decrease in adrenal secretion of cortisol is followed by an increased secretion of pituitary adrenocorticotropic hormone (ACTH), which will overcome the blockade of adrenocortical steroid synthesis by Cytadren. The compensatory increase in ACTH secretion can be suppressed by the simultaneous administration of hydrocortisone. Since Cytadren increases the rate of metabolism of dexamethasone but not that of hydrocortisone, the latter is preferred as the adrenal glucocorticoid replacement. Although Cytadren inhibits the synthesis of thyroxine by the thyroid gland, the compensatory increase in thyroid-stimulating hormone (TSH) is frequently of sufficient magnitude to overcome the inhibition of thyroid synthesis due to Cytadren. In spite of an increase in TSH, Cytadren has not been associated with increased prolactin secretion. At low doses, aminogluthethimide is only an effective inhibitor of aromatase (Cytochrome P450 11A1), but at higher doses, it effectively blocks Cytochrome P450 11A1 (P450scc) as well. Citadel was marketed previously as an anticonvulsant but was withdrawn from marketing for that indication in 1966 because of the effects on the adrenal gland.

Lornoxicam (Xefo®) is a nonsteroidal anti-inflammatory drug of the oxicam class with analgesic, anti-inflammatory and antipyretic properties. It differs from other oxicam compounds in its potent inhibition of prostaglandin biosynthesis, a property that explains the particularly pronounced efficacy of the drug. The inhibition of the cyclooxygenase enzymes (COX-1 and COX-2) by lornoxicam (Xefo®) leads to desensitisation of peripheral nociceptors and consequently inhibition of inflammation. A central effect on nociception which seems to be independent of anti-inflammatory effects has also been suggested.