https://www.cell.com/cell/pdf/0092-8674(92)90123-T.pdf

Induction of apoptosis in fibroblasts by c-myc protein

The most effective way to limit myocardial ischemic necrosis is reperfusion, but reperfusion itself may result in tissue injury, which has been difficult to separate from ischemic injury. This report identifies elements of apoptosis (programmed cell death) in myocytes as a response to reperfusion but not ischemia. The hallmark of apoptosis, nucleosomal ladders of DNA fragments (approximately 200 base pairs), was detected in ischemic/reperfused rabbit myocardial tissue but not in normal or ischemic-only rabbit hearts. Granulocytopenia did not prevent nucleosomal DNA cleavage. In situ nick end labeling demonstrated DNA fragmentation predominantly in myocytes. The pattern of nuclear chromatin condensation was distinctly different in reperfused than in persistently ischemic tissue by transmission electron microscopy. Apoptosis may be a specific feature of reperfusion injury in cardiac myocytes, leading to late cell death.

/pdf/reperfusion-injury-induces-apoptosis-in-rabbit-w99b92480o.pdf

Reperfusion injury induces apoptosis in rabbit cardiomyocytes.

Tumor cells expressing the herpes simplex virus thymidine kinase (HSV-TK) gene are sensitive to the drug ganciclovir (GCV). We demonstrate here that HSV-TK-positive cells exposed to GCV were lethal to HSV-TK-negative cells as a result of a "bystander effect." HSV-TK-negative cells were killed in vitro when the population of cultured cells contained only 10% HSV-TK-positive cells. The mechanism of this "bystander effect" on HSV-TK-negative cells appeared to be related to the process of apoptotic cell death when HSV-TK-positive cells were exposed to GCV. Flow cytometric and electron microscopic analyses suggested that apoptotic vesicles generated from the dying gene-modified cells were phagocytized by nearby, unmodified tumor cells. Prevention of apoptotic vesicle transfer prevented the bystander effect. The toxic effect of HSV-TK-positive cells on HSV-TK-negative cells was reproduced in an in vivo model. A mixed population of tumor cells consisting of HSV-TK-positive and HSV-TK-negative cells was inoculated s.c. into mice. Regression of the tumor mass occurred when the inoculum consisted of as few as 10% HSV-TK-expressing tumor cells. The bystander effect was also demonstrated in i.p. tumor studies. Initial experiments demonstrated that prolonged survival (> 70 days) occurred when a mixture containing 50% HSV-TK-positive and 50% HSV-TK-negative cells was injected i.p. followed by GCV treatment. Further, survival was prolonged for mice with a preexisting HSV-TK-negative i.p. tumor burden by injecting HSV-TK-positive cells and GCV. These results suggest that genetic modification of tumor cells may be useful for developing cancer therapies.

http://cancerres.aacrjournals.org/content/canres/53/21/5274.full.pdf

The "bystander effect": tumor regression when a fraction of the tumor mass is genetically modified.

Most of the cytotoxic anticancer drugs in current use have been shown to induce apoptosis in susceptible cells. The fact that disparate agents, which interact with different targets, induce cell death with some common features (endonucleolytic cleavage of DNA, changes in chromatin condensation) suggests that cytotoxicity is determined by the ability of the cell to engage this so-called 'programmed' cell death. The mechanism of the coupling of a stimulus (drug-target interaction) to a response (cell death) is not known, but modulation of this coupling may affect the outcome of drug treatment. This review surveys the recent evidence which supports the idea that the drug-target interaction per se is not the sole determinant of cellular sensitivity of cytotoxic drugs. Studies of the signals which might engage apoptosis, the genes which modulate it and the biochemical process of drug-induced apoptosis itself are described, where possible, for glucocorticoids, topoisomerase inhibitors, alkylating agents, antimetabolites and antihormones. It is suggested that identification of the gene products which couple the stimulus to the response, and so determine intrinsic cellular sensitivity (and resistance), will be important targets for new types of drugs. These might then allow responses to occur in the major cancers of man, which are chemoresistant.

Apoptosis induced by anticancer drugs.

Intracellular K+ Suppresses the Activation of Apoptosis in Lymphocytes

Cell death can occur by two possible mechanisms, necrosis or apoptosis. Necrosis is the classically recognised form of cell death and is characterised by high amplitude swelling of the mitochondria, nuclear flocculation and uncontrolled cell lysis. Tissue necrosis is normally seen following severe trauma to cells. The alternative form of cell death is via a programmed sequence of events and is termed apoptosis. Apoptosis occurs under a variety of physiological conditions and cells dying by this process undergo cytoplasmic and nuclear condensation, coupled with cleavage of the cell's DNA into nucleosome size fragments. DNA cleavage is due to the activation of a specific endogenous endonuclease. The cell finally fragments into apoptotic bodies which are engulfed by neighbouring cells and degraded. Apoptosis is an energy requiring process requiring intact energy generating systems, unlike that of necrosis. In relation to malignant disease, apoptosis is the mechanism by which cytotoxic T cells kill tumour target cells; it may also be the mechanism which accounts for the high loss of cells in growing tumour masses. Extensive apoptosis is seen in regressing tumours and also in those treated with chemotherapeutic agents. This form of death may require the activation of specific death genes, although in view of work carried out in this and other laboratories, demonstrating that inhibitors of both protein and RNA synthesis will readily induce apoptosis, this may not be universal. Finally, apoptosis has far reaching implications for the treatment of malignant disease, since only by understanding how cells die will be able to develop more effective means of killing them.

J G Glynn

Papers

Cell death via apoptosis and its relationship to growth, development and differentiation of both tumour and normal cells.