Regadenoson (Lexiscan), a low affinity agonist of the A2A adenosine receptor, increases coronary blood flow (CBF) and mimics the increase in CBF caused by exercise. Myocardial uptake of the radiopharmaceutical is proportional to CBF creating the contrast required to identify stenotic coronary arteries. It is a pharmacologic stress agent indicated for radionuclide myocardial perfusion imaging (MPI) in patients unable to undergo adequate exercise stress. The most common adverse reactions to Lexiscan are dyspnea, headache, flushing, chest discomfort, dizziness, angina pectoris, chest pain, and nausea. Methylxanthines, e.g., caffeine and theophylline, may interfere with the activity of Lexiscan. Aminophylline may be used to attenuate severe and/or persistent adverse reactions to Lexiscan.

Adenosine is a nucleoside that is composed of adenine and d-ribose, occurring in all cells of the body and play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter. Adenocard (adenosine injection) is used as an initial treatment for the termination of paroxysmal supraventricular tachycardia (PVST), including that associated with accessory bypass tracts (Wolff-Parkinson-White Syndrome). When clinically advisable, appropriate vagal maneuvers. Adenocard does not convert atrial flutter, atrial fibrillation, or ventricular tachycardia to normal sinus rhythm. In the presence of atrial flutter or atrial fibrillation, a transient modest slowing of ventricular response may occur immediately following Adenocard administration. Adenosine slows conduction time through the A-V node, can interrupt the reentry pathways through the A-V node, and can restore normal sinus rhythm. This effect may be mediated through the drug's activation of cell-surface A1 and A2 adenosine receptors. Adenocard is antagonized competitively by methylxanthines such as caffeine and theophylline, and potentiated by blockers of nucleoside transport such as dipyridamole. Adenocard is not blocked by atropine. Adenosine also inhibits the slow inward calcium current and activation of adenylate cyclase in smooth muscle cells, thereby causing relaxation of vascular smooth muscle. By increasing blood flow in normal coronary arteries with little or no increase in stenotic arteries, adenosine produces a relative difference in thallous (thallium) chloride TI 201 uptake in myocardium supplied by normal verus stenotic coronary arteries.

8-Chloroadenosine-3',5'-cyclic-monophosphate (8-Cl-cAMP), an analog of c-AMP, is a novel antineoplastic agent. It has been shown to be effective against different human cancer cell lines modulating the cellular signal transduction pathway, thereby causing growth inhibition, cell differentiation, and apoptosis. 8-Cl-cAMP preferentially binds to the R2 subunit of protein kinase A (PKA) and induces rapid R2 up-regulation and eventual R1 subunit down-regulation. It has potent inhibitory effects on a wide variety of human cancer cell lines, with an IC50 ranging from 0.1 to 20 uM. The IC50 falls with the length of drug exposure. It can suppress c-myc and c-ras proto-oncogenes in vitro and in vivo. It was shown that 8-Cl-cAMP induces cell growth inhibition through AMP-activated protein kinase (AMPK) activation with p38 MAPK acting downstream of AMPK in this signaling pathway. 8-Cl-cAMP induced apoptosis, apparently through activation of the p38 MAPK pathway by inducing progressive phosphorylation of the p38 mitogen-activated protein kinase (MAPK), via activation of AMPK by its metabolite 8-Cl-adenosine. 8-Cl-cAMP does not significantly inhibit the growth of NIH 3T3 cells, rat kidney fibroblasts, mammary epithelial cells, or peripheral blood lymphocytes, nor does it inhibit the growth of parental cells whose progeny have been transformed. Such selectivity makes it an attractive candidate for cancer therapy suggesting that it should not cause the toxicity of conventional cytotoxic agents but should inhibit tumor growth. 8-Cl-cAMP has been evaluated in phase I/II clinical trials.

Pinometostat, also known as EPZ-5676, is a small molecule inhibitor of histone methyltransferase with potential antineoplastic activity. Upon intravenous administration, EPZ-5676 specifically blocks the activity of the histone lysine-methyltransferase DOT1L, thereby inhibiting the methylation of nucleosomal histone H3 on lysine 79 (H3K79) that is bound to the mixed lineage leukemia (MLL) fusion protein which targets genes and blocks the expression of leukemogenic genes. Epizyme is developing pinometostat, a small molecule inhibitor of DOT1L, for the treatment of patients with MLL-r, a genetically defined acute leukemia. Epizyme is conducting a phase 1 clinical trial in pediatric patients. Epizyme is evaluating preclinical combinations of pinometostat with other anti-cancer agents in MLL-r leukemia. Pinometostat is being developed in collaboration with Celgene. Epizyme retains all U.S. rights to pinometostat and has granted Celgene an exclusive license to pinometostat outside of the U.S.

Puromycin dihydrochloride belongs to the aminonucleoside family of antibiotics and is isolated from Streptomyces alboniger. Since the partial structure of this antibiotic showed it to be a purine derivative, puromycin was assigned as its generic name. Puromycin is a broad spectrum antibiotic and antibacterial agent. It is active against Gram-positive microorganisms, less active against acid-fast bacilli, and weakly active against Gram-negative microorganisms. It acts very quickly and can kill 99% of the cells within 2 days. It also exhibits antitumor activity in studies on brain tumor cells. Puromycin is a protein synthesis inhibitor that causes premature chain termination by acting as an analog of the 3’-terminal end of aminoacyl-tRNA. It has been used to study transcriptional regulatory mechanisms that control the sequential and coordinate expression of genes during cell differentiation.