Transferrin dependence of Ga (NO3)3 inhibition of growth in human-derived small cell lung cancer cells

Using a Chemical Genetic Screen to Enhance Our Understanding of the Antimicrobial Properties of Gallium against Escherichia coli

The diagnostic and therapeutic agent gallium offers multiple clinical and commercial uses including the treatment of cancer and the localization of tumors, among others. Further, this metal has been proven to be an effective antimicrobial agent against a number of microbes. Despite the latter, the fundamental mechanisms of gallium action have yet to be fully identified and understood. To further the development of this antimicrobial, it is imperative that we understand the mechanisms by which gallium interacts with cells. As a result, we screened the Escherichia coli Keio mutant collection as a means of identifying the genes that are implicated in prolonged gallium toxicity or resistance and mapped their biological processes to their respective cellular system. We discovered that the deletion of genes functioning in response to oxidative stress, DNA or iron–sulfur cluster repair, and nucleotide biosynthesis were sensitive to gallium, while Ga resistance comprised of genes involved in iron/siderophore import, amino acid biosynthesis and cell envelope maintenance. Altogether, our explanations of these findings offer further insight into the mechanisms of gallium toxicity and resistance in E. coli.

Re-assessing gallium-67 as a therapeutic radionuclide

INTRODUCTION

Despite its desirable half-life and low energy Auger electrons that travel further than for other radionuclides, 67Ga has been neglected as a therapeutic radionuclide. Here, 67Ga is compared with Auger electron emitter 111In as a potential therapeutic radionuclide.

METHODS

Plasmid pBR322 studies allowed direct comparison between 67Ga and 111In (1MBq) in causing DNA damage, including the effect of chelators (EDTA and DTPA) and the effects of a free radical scavenger (DMSO). The cytotoxicity of internalized (by means of delivery in the form of oxine complexes) and non-internalized 67Ga and 111In was measured in DU145 prostate cancer cells after a one-hour incubation using cell viability (trypan blue) and clonogenic studies. MDA-MB-231 and HCC1954 cells were also used.

RESULTS

Plasmid DNA damage was caused by 67Ga and was comparable to that caused by 111In; it was reduced in the presence of EDTA, DTPA and DMSO. The A50 values (internalized activity of oxine complexes per cell required to kill 50% of cells) as determined by trypan blue staining was 1.0Bq/cell for both 67Ga and 111In; the A50 values determined by clonogenic assay were 0.7Bq/cell and 0.3Bq/cell for 111In and 67Ga respectively. At the concentrations required to achieve these uptake levels, non-internalized 67Ga and 111In caused no cellular toxicity. Qualitatively similar results were found for MDA-MB-231 and HCC1954 cells.

CONCLUSION

67Ga causes as much damage as 111In to plasmid DNA in solution and shows similar toxicity as 111In at equivalent internalized activity per cell. 67Ga therefore deserves further evaluation for radionuclide therapy.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

The data presented here is at the basic level of science. If future in vivo and clinical studies are successful, 67Ga could become a useful radionuclide with little healthy tissue toxicity in the arsenal of weapons for treating cancer.

Influence of novel gallium complexes on the homeostasis of some biochemical and hematological parameters in rats

The aim of this study was to detect possible homeostasis changes in some biochemical and hematological parameters after the administration of gallium (Ga) complexes C (24) and C (85) on an experimental animal model (Wistar strain rats). In order to observe chronobiological aspects, a morning (m) and an evening (e) animal series were constituted. Further on, each series were divided into three groups: control (C), experimental I (EI), and experimental II (EII). Both Ga complexes were solubilized in a carrier solution containing polyethylene glycol (PEG) 400, water, and ethanol. Animals of the C groups received the carrier solution by intraperitoneal injection, those from the EI groups received the solubilized C(24) gallium complex, and those of the EII groups received the solubilized C(85) gallium complex. At the end of the experiment, blood and tissue samples were taken and the following parameters were determined: serum concentration of the nonprotein nitrogenous compounds (uric acid, creatinine, and blood urea nitrogen), hematological parameters (erythrocytes, hemoglobin, leukocytes, and platelets), and the kidney tissue concentration of three essential trace elements (Fe, Cu, and Zn). With the exception of uric acid, the results revealed increased concentrations of the nonprotein nitrogenous compounds both in the morning and in the evening experimental groups. Hematological data showed increased levels of erythrocytes, hemoglobin, and leukocytes and decreased platelet levels in the experimental group given the C(24) gallium complex in the morning (EI-m) group; increased levels of leukocytes and decreased levels of the other parameters in the experimental group given the C(24) gallium complex in the evening (EI-e) group; and increased levels of all hematological parameters in the experimental groups receiving the C(85) gallium complex in the morning (EII-m) group and in the evening (EII-e) group. Decreased kidney tissue concentrations of metals were found in all the experimental groups. Fe levels were significantly decreased in the EI-m receiving the C(24) gallium complex and EII-m which received the C(85) gallium complex and in the EII-e group which received the C(85) gallium complex. In the EI-e group which received the C(24) gallium complex, a significant decrease of Cu concentration was reported.

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.

Iron deprivation induces apoptosis via mitochondrial changes related to Bax translocation

In order to elucidate the mechanisms involved in apoptosis induction by iron deprivation, we compared cells sensitive (38C13) and resistant (EL4) to apoptosis induced by iron deprivation. Iron deprivation was achieved by incubation in a defined iron-free medium. We detected the activation of caspase-3 as well as the activation of caspase-9 in sensitive cells but not in resistant cells under iron deprivation. Iron deprivation led to the release of cytochrome c from mitochondria into the cytosol only in sensitive cells but it did not affect the cytosolic localization of Apaf-1 in both sensitive and resistant cells. The mitochondrial membrane potential (Deltapsi(m)) was dissipated within 24 h in sensitive cells due to iron deprivation. The antiapoptotic Bcl-2 protein was found to be associated with mitochondria in both sensitive and resistant cells and the association did not change under iron deprivation. On the other hand, under iron deprivation we detected translocation of the proapoptotic Bax protein from the cytosol to mitochondria in sensitive cells but not in resistant cells. Taken together, we suggest that iron deprivation induces apoptosis via mitochondrial changes concerning proapoptotic Bax translocation to mitochondria, collapse of the mitochondrial membrane potential, release of cytochrome c from mitochondria, and activation of caspase-9 and caspase-3.

Transferrin/transferrin receptor-mediated drug delivery

Since transferrin was discovered more than half a century ago, a considerable effort has been made towards understanding tranferrin-mediated iron uptake. However, it was not until recently with the identification and characterization of several new genes related to iron homeostasis, such as the hemochromatosis protein HFE and the iron transporter DMT1, that our knowledge has been advanced dramatically. A major pathway for cellular iron uptake is through internalization of the complex of iron-bound transferrin and the transferrin receptor, which is negatively modulated by HFE, a protein related to hereditary hemochromatosis. Iron is released from transferrin as the result of the acidic pH in endosome and then is transported to the cytosol by DMT1. The iron is then utilized as a cofactor by heme and ribonucleotide reductase or stored in ferritin. Apart from iron, many other metal ions of therapeutic and diagnostic interests can also bind to transferrin at the iron sites and their transferrin complexes can be recognized by many cells. Therefore, transferrin has been thought as a "delivery system" for many beneficial and harmful metal ions into the cells. Transferrin has also be widely applied as a targeting ligand in the active targeting of anticancer agents, proteins, and genes to primary proliferating malignant cells that overexpress transferrin receptors. This is achieved by conjugation of transferrin with drugs, proteins, hybride systems with marcomolecules and as liposomal-coated systems. Conjugates of anticancer drugs with transferrin can significantly improve the selectivity and toxicity and overcome drug resistance, thereby leading to a better treatment. The coupling of DNA to transferrin via a polycation such as polylysine or via cationic liposomes can target and transfer of the extrogenous DNA particularly into proliferating cells through receptor-mediated endocytosis. These kinds of non-viral vectors are potential alternatives to viral vectors for gene therapy, if the transfection efficiency can be improved. Moreover, transferrin receptors have shown potentials in delivery of therapeutic drugs or genes into the brain across blood-brain barrier.

Differing sensitivity of tumor cells to apoptosis induced by iron deprivation in vitro

We studied the sensitivity of tumor cells to the induction of apoptosis by iron deprivation. Iron deprivation was achieved by the employment of a defined iron-deficient culture medium. Mouse 38C13 cells and human Raji cells die within 48 and 96 h of incubation in iron-deficient medium, respectively. On the contrary, mouse EL4 cells and human HeLa cells are completely resistant to the induction of death under the same experimental arrangement. Deoxyribonucleic acid fragmentation analysis by agarose gel electrophoresis as well as flow cytometric analysis after propidium iodide staining detected in 38C13 and Raji cells, but not in EL4 and HeLa cells, changes characteristic to apoptosis. The 38C13 cells, sensitive to iron deprivation, also displayed a similar degree of sensitivity to apoptosis induction by thiol deprivation (achieved by 2-mercaptoethanol withdrawal from the culture medium) as well as by rotenone (50 nM), hydroxyurea (50 microM), methotrexate (20 nM), and doxorubicin (100 nM). Raji cells shared with 38C13 cells a sensitivity to rotenone, methotrexate, doxorubicin, and, to a certain degree, to hydroxyurea. However, Raji cells were completely resistant to thiol deprivation. EI4 and HeLa cells, resistant to iron deprivation, also displayed a greater degree of resistance to most of the other apoptotic stimuli than did their sensitive counterparts. We conclude that some tumor cells in vitro are sensitive to apoptosis induction by iron deprivation, while other tumor cells are resistant. All the tumors found to be sensitive to iron deprivation in this study (four cell lines) are of hematopoietic origin. The mechanism of resistance to apoptosis induction by iron deprivation differs from the mechanism of resistance to thiol deprivation.