Influence of agents which modulate thromboxane A2 synthesis or action on R3230AC mammary carcinoma

Melatonin and carcinogenesis in mice: the 50th anniversary of relationships

The history of studies of melatonin effects on cancer in mice is outlined, the main lesson being that the systemic in vivo effects of melatonin on animals may overwhelm the in vitro effects found using tissue explants or cell cultures. In particular, the timing of melatonin administration is of crucial importance for using the drug, which is freely available over counter and thus needs no licensing for its applications in oncology.

Antidepressants, eicosanoids and the prevention and treatment of cancer. A review

Among the mechanisms of carcinogenesis are oncogene synthesis and expression, upregulation of cyclooxygenase, accelerated cell replication, failed apoptosis, viral activation, disruption of signaling pathways, autoimmunity, immunosuppression, angiogenesis and metastasis. All fall within the orbit of eicosanoids and the enzymes that synthesize them. Antidepressants may be of benefit in the prevention and treatment of cancer, as they inhibit the synthesis, antagonize the actions and accelerate the degradation of such eicosanoids as prostaglandins and thromboxanes.

Lithium and immune function

Lithium has potent antiviral and immunostimulating properties which are probably consequences of its actions on prostaglandin synthesis. Although lithium has considerable potential in the prophylaxis of some viral illnesses and other manifestations of defective immune function, it is, paradoxically, capable of activating autoimmune mechanisms in predisposed patients.

Cancer and the prostaglandins: a mini review on cancer research

This review article has explored the relationship between PGs and cancer. The experimental exploitation of PG compounds and inhibitors has disclosed many possible applications. The potential for pharmacologic manipulation of the "Arachidonic Acid Cascade" system to benefit the cancer patient is promising, and it will require close collaboration of the pathologist, the biochemist, the pharmacologist, and the clinician.

The effect of tumor promoters and antagonists on in vitro directional migration of 10T1/2 mouse embryo cells

In vitro directional migration of 10T1/2 fibroblasts is partially inhibited by TPA but not by its non-promoting analogues. Other tumor promoters, e.g., phenobarbital, saccharin, and benzoylperoxide had no measurable effect when added in concentrations known to affect in vitro two-step transformation or intercellular communication. Inhibitors of in vitro transformation do not affect migration, except for dexamethasone, which inhibited it. Hence, there is no evidence for a general correlation between tumor promoting potential and inhibition of in vitro directional migration.

The possible effect of diazepam on cancer development and growth

Diazepam has the characteristics of a tumour promoter in a number of in vitro systems. The effect is apparent at concentrations of diazepam which are clinically relevant. Diazepam also accelerated tumour growth in two different experimental animal cancers. Tranquillizer use was found to be greater in women with metastatic breast cancer at the time of diagnosis than in those without metastases. Further evaluation of the possible effects of diazepam and related drugs on human and animal cancers is urgently required.

Review: prostaglandins and cancer

This paper reviews work on the role of prostaglandins in cancer. A substantial body of evidence demonstrates elevated amounts of E series of prostaglandins in human and experimental tumors. Blockade of prostaglandin synthesis in vitro or in vivo results in inhibition of tumor growth. Involvement of prostaglandins is implicated in the actions of tumor promoters like phorbol and polycyclic aromatic hydrocarbon carcinogens. Symptoms like hypercalcemia, osteolysis and tumor metastasis are discussed where disordered synthesis and/or action of prostaglandins and related substances might have a role in the altered metabolism associated with neoplasia.

The reversibility of cancer: the relevance of cyclic AMP, calcium, essential fatty acids and prostaglandin E1

Transformed cells in culture can be normalised (made to undergo reverse transformation) by exposure to cyclic AMP, prostaglandin (PG) E1 and certain drugs. One of these drugs, thioproline, has been successfully used in treating human cancer. All cancer cells have a number of common characteristics: they exhibit aerobic glycolysis, they fail to show feedback regulation of cholesterol biosynthesis, they do not regulate cytoplasmic calcium levels normally and they produce excessive amounts of 2 series PGs. It has been known since 1975 that transformed cells cannot make PGE1 because of loss of the delta-6-desaturase enzyme which converts linoleic acid to gamma-linolenic acid. There is evidence that PGE1 acting in concert with thromboxane A2 has effects which make it able to reverse all the metabolic abnormalities common to all cancer cells. It is therefore argued that loss of the ability to make PGE1 and/or thromboxane A2 may be the critical step in malignant change in many forms of cancer. Restoration of normal PGE1 synthesis by providing gamma-linolenic or dihomogammal inolenic acids which will by-pass the blocked desaturase, whould be of value in normalising malignant cells and reversing cancer growth. Since this approach is completely non-toxic it is here seriously suggested that it might be used as a first step in treatment of those cancers where current evidence suggests that delay in the administration of orthodox treatment is unlikely to affect prognosis.

Intrarenal growth of the Walker 256 tumour and renal vein concentrations of PGE2, PGF 2 alpha, and TXB2: effects of diazepam

Walker 256 tumours grafted under the left kidney capsules in rats showed enhanced growth following daily treatment with diazepam 500 micrograms (1.7 mg/kg body weight) subcutaneously but not with 1250 micrograms. Thromboxane B2 (the metabolite of TXA2) levels in venous drainage from both the tumour bearing left kidney and from the right control kidney were reduced significantly in all the three groups of tumour bearing rats. Plasma PGE2 was higher in the venous drainage from the tumour bearing left kidney than from the right control kidney. Significantly higher levels were measured following 500 micrograms but not after 1250 micrograms of diazepam. Plasma PGF2 alpha on the other hand, was lower in the plasma from the tumour bearing kidney and was further lowered in animals receiving diazepam treatment.

The influence of diazepam administration in rats bearing the R3230AC mammary carcinoma

The growth of the R3230AC mammary carcinoma was studied in female Fisher 344 rats that were treated with diazepam. Diazepam at 250 micrograms/animal/day (2.5 mg/kg body weight) and 500 micrograms/day was administered for 4 weeks, starting 2 days before subcutaneous transplantation of uniform pieces of the tumour. Tumour size was significantly increased in the group receiving 250 micrograms but was below the levels observed in the saline treated controls in those given 500 micrograms diazepam. Plasma PGE2 and PGF2 alpha concentrations were comparable in control and diazepam treated animals.

Cellular basis of prolactin action: involvement of cyclic nucleotides, polyamines, prostaglandins, steroids, thyroid hormones, Na/K ATPases and calcium: relevance to breast cancer and the menstrual cycle

The mechanisms of prolactin action are uncertain. Prolactin effects are characterised by great variability in the prolactin concentration required to produce a response and by the frequent occurrence of "bell-shaped" dose response curves. Relationships between prolactin and thyroid hormones and steroids are difficult to understand: both steroids and thyroid hormones may potentiate or inhibit prolactin effects in different situations. At the second messenger level, claims have been made that cyclic nucleotides, polyamines, Na/K ATPases and prostaglandins are involved. There is evidence that prostaglandin E1 may be an important second messenger and it is proposed that this is the clue to understanding the complexity. At low concentrations PGE1 enhances intracellular calcium release and at high concentrations PGE1 inhibits calcium release. The other second messengers proposed are all probably dependent upon calcium. Many prolactin effects may involve both PGE1 and another second messenger: at low prolactin concentrations PGE1 will potentiate the other messenger whereas at high concentrations the PGE1 effect will be inhibitory leading to a bell-shaped response. Thryoid hormones seem to enhance while glucocorticoids inhibit PGE1 synthesis. PGE1 dependent effects will thus be enhanced by thyroid hormone and blocked by cortisol. The reverse will be true of effects dependent on other second messengers.