Diazoacetyl choline bromide

Evaluation of drug efficacy in vitro using human small cell carcinoma of the lung spheroids

Five human small cell carcinoma of the lung (SCCL) cell lines selected from 25 established cultures were grown as three-dimensional spheroid tumor models in either spinner culture or in static, agar-coated multiwells. Volume doubling times for the cell lines were approximately 4.5 days. Decreases in spheroid volumes after exposure to a variety of chemotherapeutic agents were used as indicators of drug activity. To further quantify cell killing in SCCL spheroids by chemotherapeutic agents 24 hours after exposure to drugs, a technique was employed that measured maximum levels of incorporation of 125IUdR after continuous labeling for 48 hours. The results of the use of this assay report for SCCL spheroid responses to various concentrations of doxorubicin hydrochloride, cytosine arabinoside, mechlorethamine hydrochloride, cisplatin, or etoposide. Some evidence for an intertumor heterogeneous response to chemotherapy is presented for some of the drugs tested. This assay was also used to characterize a potentiated cell kill when etoposide is combined with cisplatin and to identify activity by a new compound, diazoacetylcholine iodide (DACI), which was synthesized as an agent targeted for SCCL cells.

Photoreactivity of lysergic acid diethylamide and its possible utility as a photoaffinity labeling reagent

Aqueous solutions of lysergic acid diethylamide (LSD) are extremely sensitive to light in the near-ultraviolet region of the spectrum. This rather efficient photoreaction yields a variety of products which have very low affinity for LSD-binding sites on plasma membranes from Fasciola hepatica. Since this photoreaction may be elicited by normal white fluorescent lighting in the laboratory, it represents a potential source of error in determining the binding affinity of LSD. Utilizing this photoreactivity advantageously, [3H]LSD was used to photolabel membrane proteins. Covalent binding of [3H]LSD was shown to be a function of the duration of illumination and was inhibited by 5-hydroxytryptamine and nonradioactive LSD. Sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis of [3H]LSD labeled membranes from F. hepatica showed two proteins which were selectively labeled by the photoreactive [3H]LSD. This method of direct photolabeling with non-derivatized [3H]LSD may allow identification of LSD-binding proteins in a variety of systems.

Preparation and application of a photoreactive thrombin analogue: binding to human platelets

alpha-Thrombin has previously been shown to bind to specific, saturable glycoproteins on the platelet surface. Modification of the thrombin active site with tosyllysyl chloromethyl ketone (TosLysCH2Cl) does not alter thrombin's binding characteristics. Interaction of alpha-thrombin with high-affinity binding sites (KD = 10(-9) M) initiates the platelet response which involves proteolytic hydrolysis of this glycoprotein. Although TosLysCH2Cl--thrombin binds to and competes for the same sites as alpha-thrombin, it cannot induce platelet stimulation because it is enzymatically inactive. In this study, we describe the preparation and application of photoreactive tritium-labeled thrombin analogues. The alpha-thrombin derivative retains its platelet-stimulating and enzymatic activities and, upon photoactivation, covalently binds to specific platelet membrane components. When freshly washed human platelets are exposed to less than saturation doses (less than or equal to 2 nM) of the thrombin derivatives in the dark and photoactivated, a single labeled complex is detected. The same experiment with greater than saturating doses (greater than or equal to 20 nM) of the thrombin derivative yields a similar complex as well as two additional ones. Molecular weight estimates of these thrombin-bound complexes were obtained by gel filtration and NaDodSO4--polyacrylamide gel electrophoresis. The low dose (high affinity) complex with TosLysCH2Cl--thrombin has an approximate molecular weight of 200 000, while that with active alpha-thrombin is smaller, approximately 120 000, due to enzymatic cleavage. The additional complexes detected with the high thrombin dose had estimated molecular weights of 400 000 and 46 000, respectively, and appeared to be the same for TosLysCH2Cl--thrombin and for the alpha-thrombin coupled platelets. These isolated complexes appear to correspond to the two previously detected populations of thrombin binding sites on the platelet.

Affinity-labelling of the muscarinic receptor of the guinea-pig illeum

1. The activities of some cholinergic compounds were investigated on the terminal ileum of the guinea-pig and their muscarinic potencies were found to be in the following order: acetylcholine (ACh) greater than diazoacetylcholine (DACh) greater than iodoacetylcholine (IACh) greater than azidoacetylcholine (AACh). 2. Protection experiments with atropine showed a decreased affinity of the four cholinergic compounds for the muscarinic receptor, demonstrating a direct interaction of the drugs and the receptor. 3. The maximal contractions (intrinsic activity) caused by DACh were greater than those casued by ACh, IACh and AACh. 4. Incubation of the ileum with ACh was followed by a reversible loss of its ability to contract (desensitization). The time course of recovery was similiar to that after incubation with AACh. 5. IACh caused a partial (50%), irreversible paralysis of the muscle. 6. The furaziridines seem to react partially irreversibly (30%), whereas paranitrophenyldiazonium fluoborate (p-NDP) caused a complete, irreversible blockade of the muscarinic receptor.