A clinical trial of synkavit in the treatment of carcinoma of the bronchus

Menadione-resistant Chinese hamster ovary cells have an increased capacity for glutathione synthesis

A cell line (MRc40) resistant to the model quinone compound, menadione, has been isolated from a parental Chinese hamster ovary cell line (CHO-K1). The known relationship between menadione toxicity and glutathione (GSH) depletion led us to investigate whether the mechanism of resistance of MRc40 was related to alteration in GSH homeostasis. Intracellular concentrations of GSH and cysteine (CySH) were twofold and 3.2-fold greater in MRc40 than in CHO-K1. Following exposure to menadione, GSH and CySH were depleted, but subsequent recovery of thiols was more rapid and of greater magnitude in MRc40 than in CHO-K1. Twelve hours after exposure to menadione, the concentrations of GSH and CySH were 9.7- and 4.2-fold greater in MRc40 than in CHO-K1. Using nuclear magnetic resonance (NMR) spectroscopy, we observed the in situ removal of menadione from cell suspensions of CHO-K1 and MRc40. However, only in CHO-K1 did we observe concomitant depletion of NMR-visible GSH. We conclude that the perturbation of GSH metabolism contributes to the resistant phenotype and is an important characteristic of menadione-resistant CHO cells.

Synkavit and its direct labelling with iodine-125, as a potential anti-cancer drug

The compound known as "synkavit" is a diphosphate derivative of vitamin K3 (menadion), which is capable of being selectively accumulated in certain tumour cells, and covalently bonded to DNA producing considerable DNA damage. On the other hand, iodine-125 nuclide incorporated into the nucleus of living cells causes extreme radiotoxic effects. Consequently, synkavit can be used as a specific carrier of iodine-125 into the nucleus of tumour cells. Thus, its iodo-derivatives have become interesting agents on the potential application of iodine-125 in cancer therapy. 6-Iodo-synkavit is a unique iodo-derivative described in the literature. In addition, its synthesis and radioiodination is still problematic, and consequently the results obtained using 6-iodo-synkavit labelled with iodine-125 remains in question. For this reason, the synthesis of 6-iodo-synkavit was examined in this study. It is finally determined that a mixture of different iodo-isomers of synkavit has been produced rather than its specific 6-iodo-isomer, when the synthetic sequence was begun with the direct sulfonation of 2-methyl-naphthalene. On the other hand, it is also determined that synkavit can directly be radioiodinated using different iodination techniques, and iodogen especially can be successfully used as an oxidative agent.

Molecular mechanisms of quinone cytotoxicity

Quinones are probably found in all respiring animal and plant cells. They are widely used as anticancer, antibacterial or antimalarial drugs and as fungicides. Toxicity can arise as a result of their use as well as by the metabolism of other drugs and various environmental toxins or dietary constituents. In rapidly dividing cells such as tumor cells, cytotoxicity has been attributed to DNA modification. However the molecular basis for the initiation of quinone cytotoxicity in resting or non-dividing cells has been attributed to the alkylation of essential protein thiol or amine groups and/or the oxidation of essential protein thiols by activated oxygen species and/or GSSG. Oxidative stress arises when the quinone is reduced by reductases to a semiquinone radical which reduces oxygen to superoxide radicals and reforms the quinone. This futile redox cycling and oxygen activation forms cytotoxic levels of hydrogen peroxide and GSSG is retained by the cell and causes cytotoxic mixed protein disulfide formation. Most quinones form GSH conjugates which also undergo futile redox cycling and oxygen activation. Prior depletion of cell GSH markedly increases the cell's susceptibility to alkylating quinones but can protect the cell against certain redox cycling quinones. Cytotoxicity induced by hydroquinones in isolated hepatocytes can be attributed to quinones formed by autoxidation. The higher redox potential benzoquinones and naphthoquinones are the most cytotoxic presumably because of their higher electrophilicty and thiol reactivity and/or because the quinones or GSH conjugates are more readily reduced to semiquinones which activate oxygen.

Single and combination treatment with vitamin K3 and adriamycin: in vitro effects on cell survival and DNA damage in human chronic myeloid leukemia cells

Utility of drug response modulators to increase therapeutic:toxic ratio of anticancer drugs in the treatment of refractory malignancies is becoming desirable. In this study, we have attempted to potentiate the tumor cell killing ability of Adriamycin (ADR) against chronic myeloid leukemia cells (CML), in the presence of vitamin K3. Cell growth was evaluated by the MTT assay and the 3H-thymidine incorporation inhibition assay. A highly significant (p less than 0.001) inhibition of cell survival and 3H-thymidine incorporation was effected in CML cells exposed to the combination of ADR and vitamin K3. When the CML cells were treated with ADR and vitamin K3 simultaneously, a greater fragmentation of the intact DNA was revealed as observed by the enhanced formation of DNA single strand breaks. Results demonstrate the therapeutic significance of employing vitamin K3 as an adjuvant in CML chemotherapy with ADR.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.

The treatment of carcinoma of the lung by radiotherapy

Where the diagnosis of cancer of the lung is made by bronchoscopy the preferred treatment is surgery for squamous lesions and radiotherapy for anaplastic and oat-cell lesions. In inoperable tumours 8% of patients survive for more than 3 years after a radical course of radiotherapy; some clinical trials aimed at improving this survival rate are described. This lecture deals with the established disease, earlier diagnosis, before spread, would make radical treatment with a possibility of cure possible in more patients but this disease can be prevented to a large degree and this is the obvious method of attack.