Drugs with less than 50 atoms

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Bicalutamide

 Bicalutamide is an antineoplastic hormonal agent primarily used in the treatment of prostate cancer. Bicalutamide is a pure, nonsteroidal anti-androgen with affinity for androgen receptors (but not for progestogen, estrogen, or glucocorticoid receptors). Consequently, Bicalutamide blocks the action of androgens of adrenal and testicular origin which stimulate the growth of normal and malignant prostatic tissue. Prostate cancer is mostly androgen-dependent and can be treated with surgical or chemical castration. To date, antiandrogen monotherapy has not consistently been shown to be equivalent to castration.

Pemetrexed

indication	Used in combination with cisplatin for the treatment of malignant pleural mesothelioma in adults whose disease is unresectable or who otherwise are not candidates for potentially curative surgery. Also used as a monotherapy for the treatment of locally advanced or metastatic non-small cell lung cancer (NSCLC) after prior chemotherapy
Pharmacodynamics	Preclinical studies have shown that pemetrexed inhibits the in vitro growth of mesothelioma cell lines (MSTO-211H, NCI-H2052). Studies with the MSTO-211H mesothelioma cell line showed synergistic effects when pemetrexed was combined concurrently with cisplatin.
Mechanism of action	Pemetrexed is an antifolate containing the pyrrolopyrimidine-based nucleus that exerts its antineoplastic activity by disrupting folate-dependent metabolic processes essential for cell replication. In vitro studies have shown that pemetrexed inhibits thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT), all folate-dependent enzymes involved in the de novo biosynthesis of thymidine and purine nucleotides. Pemetrexed is transported into cells by both the reduced folate carrier and membrane folate binding protein transport systems. Once in the cell, pemetrexed is converted to polyglutamate forms by the enzyme folylpolyglutamate synthetase. The polyglutamate forms are retained in cells and are inhibitors of TS and GARFT. Polyglutamation is a time- and concentration-dependent process that occurs in tumor cells and, to a lesser extent, in normal tissues. Polyglutamated metabolites have an increased intracellular half-life resulting in prolonged drug action in malignant cells.

Oxaliplatin:

Oxaliplatin is a platinum-based chemotherapy drug in the same family as cisplatin and carboplatin. It is typically administered in combination with fluorouracil and leucovorin in a combination known as Folfox for the treatment of colorectal cancer. Compared to cisplatin the two amine groups are replaced by cyclohexyldiamine for improved antitumour activity. The chlorine ligands are replaced by the oxalato bidentate derived from oxalic acid in order to improve water solubility. Oxaliplatin is marketed by Sanofi-Aventis under the trademark Eloxatin®.

Trimetrexate

Indication	For use, with concurrent leucovorin administration (leucovorin protection), as an alternative therapy for the treatment of moderate-to-severe Pneumocystis carinii pneumonia (PCP) in immunocompromised patients, including patients with the acquired immunodeficiency syndrome (AIDS). Also used to treat several types of cancer including colon cancer.
Pharmacodynamics	Trimetrexate, a non-classical folate antagonist, is a synthetic inhibitor of the enzyme dihydrofolate reductase (DHFR). During DNA synthesis and cellular reproduction, folic acid is reduced to tetrahydrofolic acid by the enzyme folic acid reductase. By interfering with the reduction of folic acid, trimetrexate interferes with tissue cell reproduction. Generally, the most sensitive cells to the antimetabolite effect of trimetrexate are those cells which are most actively proliferating such as malignant cells, dermal epithelium, buccal and intestinal mucosa, bone marrow, fetal cells, and cells of the urinary bladder. Because the proliferation of cells in malignant tissues is greater than in most normal tissues, trimetrexate may impair the growth of the malignant tissues without causing irreversible damage to normal tissues. Due to very serious and potentially life-threatening side-effects of this drug, leucovorin must be co-administered for at least 72 hours after the last dose.
Mechanism of action	In vitro studies have shown that trimetrexate is a competitive inhibitor of dihydrofolate reductase (DHFR) from bacterial, protozoan, and mammalian sources. DHFR catalyzes the reduction of intracellular dihydrofolate to the active coenzyme tetrahydrofolate. Inhibition of DHFR results in the depletion of this coenzyme, leading directly to interference with thymidylate biosynthesis, as well as inhibition of folate-dependent formyltransferases, and indirectly to inhibition of p.r.n. biosynthesis. The end result is disruption of DNA, RNA, and protein synthesis, with consequent cell death.

Thalidomide 

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Indication	For the acute treatment of the cutaneous manifestations of moderate to severe erythema nodosum leprosum (ENL). Also for use as maintenance therapy for prevention and suppression of the cutaneous manifestations of ENL recurrence.
Pharmacodynamics	Thalidomide is an immunomodulatory agent with a spectrum of activity that is not fully characterized. Thalidomide is racemic — it contains both left and right handed isomers in equal amounts: one enantiomer is effective against morning sickness, and the other is teratogenic. The enantiomers are converted to each other in vivo. That is, if a human is given D-thalidomide or L-thalidomide, both isomers can be found in the serum. Hence, administering only one enantiomer will not prevent the teratogenic effect in humans.
Mechanism of action	In patients with erythema nodosum leprosum (ENL) the mechanism of action is not fully understood. Available data from in vitro studies and preliminary clinical trials suggest that the immunologic effects of this compound can vary substantially under different conditions, but may be related to suppression of excessive tumor necrosis factor-alpha (TNF-a) production and down-modulation of selected cell surface adhesion molecules involved in leukocyte migration. For example, administration of thalidomide has been reported to decrease circulating levels of TNF-a in patients with ENL, however, it has also been shown to increase plasma TNF-a levels in HIV-seropositive patients. As a cancer treatment, the drug may act as a VEGF inhibitor.

Norelgestromin 

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Indication	Norelgestromin is used for contraception and menopausal hormonal therapy. Norelgestromin may potentially be used in breast cancer treatment due to its inhibitory effect on estrone sulfatase . They convert sulfated steroid precursors to estrogen during pregnancy.
Pharmacodynamics	Norelgestromin is used for contraception and menopausal hormonal therapy transdermally or in combination with ethinyl estradiol as a vaginal ring. Norelgestromin, in combination with ethinyl estradiol inhibits ovulation by suppressing gonadotropins.
Mechanism of action	Norelgestromin inhibits estrone sulfatase, which converts sulfated steroid precursors to estrogen during pregnancy. Norgelgestromin/ethinylestradiol suppresses follicular development, induces changes to the endometrium, which decreases chances of implantation and thickens the cervical mucus, impeding sperm swimming into the uterus. It also has similar agonisting binding affinities as its parent compound, Norgestimate, for progesterone and estrogen receptors.

Megestrol 

17-Hydroxy-6-methylpregna-3,6-diene-3,20-dione. A progestational hormone used most commonly as the acetate ester. As the acetate, it is more potent than progesterone both as a progestagen and as an ovulation inhibitor. It has also been used in the palliative treatment of breast cancer. [PubChem]

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Indication	For the treatment of anorexia, cachexia, or an unexplained, significant weight loss in patients with a diagnosis of acquired immunodeficiency syndrome (AIDS). Also used for the palliative management of recurrent, inoperable, or metastatic breast cancer, endometrial cancer, and prostate cancer in Canada and some other countries.
Pharmacodynamics	Megestrol is a synthetic progestin and has the same physiologic effects as natural progesterone. These effects include induction of secretory changes in the endometrium, increase in basal body temperature, pituitary inhibition, and production of withdrawal bleeding in the presence of estrogen. Mestrogel has slight glucocorticoid activity and very slight mineralocorticoid activity. This drug has no estrogenic, androgenic, or anabolic activity. The precise mechanism of megestrol’s antianorexic and anticachetic effects is unknown. Initially developed as a contraceptive, it was first evaluated in breast cancer treatment in 1967.
Mechanism of action	The precise mechanism by which megestrol acetate produces effects in anorexia and cachexia is unknown at the present time, but its progestin antitumour activity may involve suppression of luteinizing hormone by inhibition of pituitary function. Studies also suggest that the megestrol's weight gain effect is related to its appetite-stimulant or metabolic effects rather than its glucocorticoid-like effects or the production of edema. It has also been suggested that megestrol may alter metabolic pathyways via interferences with the production or action of mediators such as cachectin, a hormone that inhibits adipocyte lipogenic enzymes.