Cytotoxic effects of neuroleptic drugs.

Agranulocytosis and the release of transaminase enzymes from liver cells are known consequences of neuroleptic drug use. These effects are most common with low potency neuroleptic drugs. It has been hypothesized that these effects are due to the direct toxic action of these drugs on blood and liver cells. The purpose of this study is to compare the cytotoxic effects of eight neuroleptic drugs in five different biological test systems. In all of the test systems, thioridazine, chlorpromazine, trifluoperazine, fluphenazine and thiothixene (group one drugs) were the most toxic drugs and molindone was the least toxic. Thioridazine was between 25 and 84 times more toxic than molindone. Loxapine was significantly more toxic than molindone, but less toxic than the group one drugs. Haloperidol was intermediate in toxicity between the group one drugs and loxapine. We conclude that the difference in cytotoxicity of the neuroleptic drugs observed in these experiments accounts in part for the increase in agranulocytosis and hepatotoxicity with thioridazine and chlorpromazine and for the lower incidence of these side effects with less toxic drugs. The possibility that tardive dyskinesia may be due to the cytotoxic effects of neuroleptic drugs is discussed and an experiment to test this hypothesis is suggested.

Thymidine kinaseless revertants of Ltk- cells transformed by herpes simplex virus type 1 are resistant to retransformation by homologous virus.

Mouse L cells lacking thymidine kinase (Ltk-) that had been transformed to the thymidine kinase-positive (tk+) phenotype by herpes simplex virus type 1 (HSV-1) were cultured in medium containing tritiated thymidine. Six clonal lines of cells surviving this treatment were found to have the following properties: (i) the cells were tk- and had spontaneous back-reversion frequencies to the tk+ phenotype of 10(-5) or less, (ii) the cells contained HSV antigens, although in lesser amounts than in the parental transformed cells, and (iii) the cells were retransformable to the tk+ phenotype by HSV-1 at frequencies of about 1 to 13% of the frequency of the primary transformation of LtK- cells. HSV-1 plaqued as efficiently on monolayers of these cells and replicated in them to the same extent as it did in Ltk- cells. These results indicate that HSV-1-transformed L cells surviving selection with tritiated thymidine are unlike the parental Ltk- cells in that they are damaged in such a way that the cells are resistant to retransformation by homologous virus, although they remain fully permissive for virus replication.

Mutant of herpes simplex virus type 1 conditionally able to transform thymidine kinaseless L cells to a tk+ phenotype.

After nitrous acid mutagenesis of herpes simplex virus type 1 (HSV-1), a mutant, 1093, was isolated which, during productive infection, induced very low levels of thymidine kinase (tk). The mutant virus was found, after UV irradiation, to be unable to transform L cells lacking tk (Ltk-) to a tk+ phenotype as chararcterized by growth of the cells in a modified HAT-selective medium containing 1.6 X 10(-5) M thymidine. Cells transformed by wild-type virus grew vigorously under the same conditions. The mutant was able to transform Ltk- cells if the medium contained 10(-3) M thymidine. These transformed cells maintained their conditional character and would not grow in low concentrations of thymidine in selective medium. Therefore, this mutant is conditional on the thymidine concentration in the selection medium in its ability to transform Ltk- cells to a tk+ phenotype. The conditionally transformed cells could be supertransformed with wild-type UV-irradiated HSV-1 to a phenotype which would grow in low-thymidine selective medium. The frequency of supertransformation closely approximated the frequency of transformation of Ltk- cells by wild-type virus. Supertransformation at high frequency could not be effected by mutant 1093 or the tk- mutant B2006. These results indicate that the presence of HSV-1 genetic information in HSV-1-transformed cells does not preclude the acquisition by these cells of at least one additional HSV-1 gene, that for tk.

Temperature-sensitive mutants of herpes simplex virus type 1 defective in lysis but not in transformation.

Twelve temperature-sensitive (ts) mutants of herpes simplex virus type 1 (HSV-1), representing seven complementation groups, were isolated subsequent to 5-bromodeoxyuridine mutagenesis. These mutants were identified by their inability to replicate in a line of monkey (CV-1) cells at 39 C. Seven of these mutants, representing six complementation groups, induced thymidine kinase (tk) and transformed Ltk- cells, a line of mouse L cells lacking tk, to a tk+ phenotype at both the permissive (34 C) and nonpermissive (39 C) temperatures. Thus, the defective cistrons in these six complementation groups, although necessary for lysis, have no essential function in this transformation system. Transformation by these 12 mutants was dependent on prior UV irradiation. Infection of cells with unirradiated virus under conditions which did not permit virus replication was not sufficient to allow cell transformation. Five mutants, representing two complementation groups, were tk- and were incapable of causing the tk--to-tk+ transformation at either 34 C of 39 C. The tk defects in these mutants are probably unrelated to the ts defects, since one of these complementation groups contains a tk+ member. Therefore, transformation of Ltk- cells to a tk+ phenotype by HSV-1 requires an active viral tk gene. One complementation group was represented by a single tk- member. The role of this cistron in transformation remains undetermined since the primary block to transformation is presumed to be the tk- phenotype. Mutants representing the seven complementation groups were unable to replicate at 39 C in two lines of HSV-1-transformed cells, indicating that the activities of resident wild-type copies of the defective cistrons, if present, could not be detected by complementation.