Hypoxia as a factor for 67Ga accumulation in tumour cells

Lanthanum, Gallium and their Impact on Oxidative Stress

The role metals play in living organisms is well established and subject to extensive research. Some of them participate in electron-exchange reactions. Such reactions cause generation of free radicals that can adversely impact biological systems, as a result of oxidative stress. The impact of 'non-biological' metals on oxidative stress is also a worthy pursuit due to the crucial role they play in modern civilization. Lanthanides (Ln) are widely used in modern technology. As a result, human exposure to them is increasing. They have a number of established medical applications and are being extensively researched for their potential antiviral, anticancer and anti-inflammatory properties. The present review focuses on lanthanum (La) and its impact on oxidative stress. Another metal, widely used in modern high-tech is gallium (Ga). In some respects, it shows certain similarities to La, therefore it is a subject of the present review as well. Both metals exhibit ionic mimicry which allows them to specifically target malignant cells, initiating apoptosis that makes their simple salts and coordination complexes promising candidates for future anticancer agents.

Anticancer activity of dinuclear gallium(III) carboxylate complexes

The reaction of 3-methoxyphenylacetic acid, 4-methoxyphenylacetic acid, mesitylthioacetic acid, 2,5-dimethyl-3-furoic acid and 1,4-benzodioxane-6-carboxylic acid with trimethylgallium (1:1) yielded the dimeric complexes [Me(2)Ga(micro-O(2)CCH(2)C(6)H(4)-3-OMe)](2) (1), [Me(2)Ga(micro-O(2)CCH(2)C(6)H(4)-4-OMe)](2) (2), [Me(2)Ga(micro-O(2)CCH(2)SMes)](2) (3) (Mes=2,4,6-Me(3)C(6)H(2)), [Me(2)Ga{micro-O(2)C(Fur)}](2) (4) (Fur=2,5-dimethylfuran) and [Me(2)Ga{micro-O(2)C(Bdo)}](2) (5) (Bdo=1,4-benzodioxane) respectively. The molecular structure of 5 was determined by X-ray diffraction studies. The cytotoxic activity of the gallium(III) complexes (1-5) was tested against human tumor cell lines 8505C anaplastic thyroid cancer, A253 head and neck tumor, A549 lung carcinoma, A2780 ovarian cancer, DLD-1 colon carcinoma and compared with that of cisplatin. Taking into account the standard deviation, there is no significant difference in the activity for any of the compounds in any cell line. However, complex 5 presents the best IC(50) value against A253 head and neck tumor (6.6+/-0.2 microM), while complex 3 seems to be the most active against A2780 ovarian cancer (12.0+/-0.4 microM) and marginally on DLD-1 colon carcinoma (12.4+/-0.1 microM).

Antitumour metal compounds: more than theme and variations

Triggered by the resounding success of cisplatin, the past decades have seen tremendous efforts to produce clinically beneficial analogues. The recent achievement of oxaliplatin for the treatment of colon cancer should, however, not belie the imbalance between a plethora of investigated complexes and a very small number of clinically approved platinum drugs. Strategies opening up new avenues are increasingly being sought using complexes of metals other than platinum such as ruthenium or gallium. Based on the chemical differences between these metals, the spectrum of molecular mechanisms of action and potential indications can be broadened substantially. Other approaches focus on complexes with tumour-targeting properties, thereby maximizing the impact on cancer cells and minimizing the problem of adverse side effects, and complexes with biologically active ligands.

Characterization of transferrin receptor-dependent GaC–Tf–FeN transport in human leukemic HL60 cells

BACKGROUND

Understanding the uptake of GaC-Tf-FeN by cells will provide key insights into studies on transferrin-mediated drug delivery.

METHODS

The mechanism of GaC-Tf-FeN transporting into and out of HL60 cells has been investigated by comparing transports between GaC-Tf-FeN and apoTf by means of 125I-labeled transferrin.

RESULTS

An association constant for GaC-Tf-FeN was 2 times that for apoTf. GaC-Tf-FeN and apoTf of cell surface-bound displayed similar kinetics during the uptake, but the release rates of internalized GaC-Tf-FeN and apoTf from cells were different which showed characteristic disparate. The release continued to occur during the incubation of GaC-Tf-FeN in the presence of nonradioactive apoTf. Neither NaN3 nor NH4Cl could completely block internalization of GaC-Tf-FeN, but they prevented the release of GaC-Tf-FeN from the cells. Excess cold unlabeled apoTf could overcome the block in the release due to NH4Cl but not NaN3. The binding and internalization of GaC-Tf-FeN could be competitively inhibited by nonradioactive apoTf. It implies that both bind to the same receptor on the membrane and the localization of GaC-Tf-FeN resembles that of apoTf inside cells. Pretreated cells with pronase abolished the binding of GaC-Tf-FeN significantly.

CONCLUSION

On the basis of these findings, we proposed the "transferrin receptor" for the mechanism of GaC-Tf-FeN transport by HL60 cells.