Ca2+ and calmodulin are involved in the processes conferring stability to DNA in proliferating neoplastic cells

The validity of melatonin as an oncostatic agent

The validity of melatonin as a prominent, naturally occurring oncostatic agent is examined in terms of its putative oncostatic mechanism of action, the correlation between melatonin levels and neoplastic activity, and the outcome of therapeutically administered melatonin in clinical trials. Melatonin's mechanism of action is summarized in a brief analysis of its actions at the cellular level, its antioxidative functions, and its indirect immunostimulatory effects. The difficulties of interpreting melatonin levels as a diagnostic or prognostic aid in cancer is illustrated by referral to breast cancer, the most frequently studied neoplasm in trials regarding melatonin. Trials in which melatonin was used therapeutically are reviewed, i.e., early studies using melatonin alone, trials of melatonin in combination with interleukin-2, and controlled studies comparing routine therapy to therapy in combination with melatonin. A table compiling the studies in which melatonin was used in the treatment of cancer in humans is presented according to the type of neoplasm. Melatonin's suitability in combination chemotherapy, where it augments the anticancer effect of other chemotherapeutic drugs while decreasing some of the toxic side effects, is described. Based on the evidence derived from melatonin's antiproliferative, antioxidative, and immunostimulatory mechanisms of action, from its abnormal levels in cancer patients and from clinical trials in which melatonin was administered, it is concluded that melatonin could indeed be considered a physiological anticancer substance. Further well-controlled trials should, however, be performed in order to find the link between its observed effects and the underlying mechanisms of action and to define its significance as a therapeutic oncostatic agent.

Chlorpromazine in combination with nitrosourea inhibits experimental glioma growth

Modern cancer therapy has improved the prognosis for several tumour types. This, however, does not apply to the largest group of brain tumours, the malignant astrocytomas grades III-IV. Hence, there is need for new ideas to improve treatment. Ca2+ and the Ca(2+)-binding protein calmodulin have been shown to be involved in the processes conferring stability to DNA in proliferating neoplastic cells. We have combined the calmodulin-inhibiting neuroleptic drug chlorpromazine (CPZ), with the anti-neoplastic drug 1,3-bis(2-chloroethyl-1)-nitrosourea (BCNU) in a treatment regime for rats with glioma cells implanted in the brain. A highly significant inhibiting effect upon the tumour growth was noticed, not by CPZ or BCNU as single drugs, but with their combination.

W-7, a calmodulin inhibitor, potentiates dacarbazine cytotoxicity in human neoplastic cells

Dacarbazine induces damage in replicative DNA, with a maximum level at 24 hr after treatment. Repair of these lesions does not occur when cells are post-treated with the calmodulin inhibitor W-7. In parallel cell cytotoxicity increases. The augmentation effect of W-7 is prevented by simultaneous incubation of cells with high levels of calmodulin and does not occur in cells pre-treated with aphidicolin (to stop DNA synthesis). Furthermore, W-5, an analogue of W-7 with a less inhibitory effect on calmodulin, does not interfere with DNA repair. The results show that calmodulin and/or calmodulin-regulated proteins are involved in the repair process of dacarbazine-induced DNA lesions.