Mitochondria as oncotarget: a comparison between the tetracycline analogs doxycycline and COL-3

Tetracyclines have anticancer properties in addition to their well-known antibacterial properties. It has been proposed that tetracyclines slow metastasis and angiogenesis through inhibition of matrix metalloproteinases. However, we believe that the anticancer effect of tetracyclines is due to their inhibition of mitochondrial protein synthesis, resulting in a decrease of the mitochondrial energy generating capacity. Several groups have developed analogs that are void of antibacterial action. An example is COL-3, which is currently tested for its anticancer effects in clinical trials. We have undertaken a comparative study of the tetracycline analogs COL-3 and doxycycline, which has an antibacterial function, to further investigate the role of the mitochondrial energy generating capacity in the anticancer mechanism and, thereby, evaluate the usefulness of mitochondria as an oncotarget. Our experiments with cultures of the human A549, COLO357 and HT29 cancer cells and fibroblasts indicated that COL-3 is significantly more cytotoxic than doxycycline. Mitochondrial translation assays demonstrated that COL-3 has retained its inhibitory effect on mitochondrial protein synthesis. Both drugs caused a severe decrease in the levels of mitochondrially encoded cytochrome-c oxidase subunits and cytochrome-c oxidase activity. In addition, COL-3 produced a marked drop in the level of nuclear-encoded succinate dehydrogenase subunit A and citrate synthase activity, indicating that COL-3 has multiple inhibitory effects. Contrary to COL-3, the anticancer action of doxycycline appears to be based specifically on inhibition of mitochondrial protein synthesis, which is thought to affect rapidly proliferating cancer cells more than healthy tissue. Doxycycline is likely to cause less side effects that COL-3.

Clonal expansion of T cells in abdominal aortic aneurysm: a role for doxycycline as drug of choice?

Most reported studies with animal models of abdominal aortic aneurysm (AAA) and several studies with patients have suggested that doxycycline favourably modifies AAA; however, a recent large long-term clinical trial found that doxycycline did not limit aneurysm growth. Thus, there is currently no convincing evidence that doxycycline reduces AAA expansion. Here, we critically review the available experimental and clinical information about the effects of doxycycline when used as a pharmacological treatment for AAA. The view that AAA can be considered an autoimmune disease and the observation that AAA tissue shows clonal expansion of T cells is placed in the light of the well-known inhibition of mitochondrial protein synthesis by doxycycline. In T cell leukaemia animal models, this inhibitory effect of the antibiotic has been shown to impede T cell proliferation, resulting in complete tumour eradication. We suggest that the available evidence of doxycycline action on AAA is erroneously ascribed to its inhibition of matrix metalloproteinases (MMPs) by competitive binding of the zinc ion co-factor. Although competitive binding may explain the inhibition of proteolytic activity, it does not explain the observed decreases of MMP mRNA levels. We propose that the observed effects of doxycycline are secondary to inhibition of mitochondrial protein synthesis. Provided that serum doxycycline levels are kept at adequate levels, the inhibition will result in a proliferation arrest, especially of clonally expanding T cells. This, in turn, leads to the decrease of proinflammatory cytokines that are normally generated by these cells. The drastic change in cell type composition may explain the changes in MMP mRNA and protein levels in the tissue samples.

The CREATE project: development of certified reference materials for allergenic products and validation of methods for their quantification

Allergen extracts have been used for diagnosis and treatment of allergy for around 100 years. During the second half of 20th century, the notion increasingly gained foothold that accurate standardization of such extracts is of great importance for improvement of their quality. As a consequence, manufacturers have implemented extensive protocols for standardization and quality control. These protocols have overall IgE-binding potencies as their focus. Unfortunately, each company is using their own in-house reference materials and their own unique units to express potencies. This does not facilitate comparison of different products. During the last decades, most major allergens of relevant allergen sources have been identified and it has been established that effective immunotherapy requires certain minimum quantities of these allergens to be present in the administered maintenance dose. Therefore, the idea developed to introduce major allergens measurements into standardization protocols. Such protocols based on mass units of major allergen, quantify the active ingredients of the treatment and will at the same time allow comparison of competitor products. In 2001, an EU funded project, the CREATE project, was started to support introduction of major allergen based standardization. The aim of the project was to evaluate the use of recombinant allergens as reference materials and of ELISA assays for major allergen measurements. This paper gives an overview of the achievements of the CREATE project.

Regulatory aspects of allergen products for immunotherapy--considerations from the viewpoint of manufacturers

The present publication describes the actual situation anno 2005 with respect to registration of allergen products for specific immunotherapy (SIT) in Europe. It is concluded that the lack of the implementation of regulations and directives in force, is due to underestimation of the specific demands and aspects of the pathogenicity of allergic diseases at the one hand and of allergen products as a unique set of biological medicinal products at the other. The issues of regulatory nature that need careful attention and consideration in the opinion of the manufacturers are given in a number of statements. The main conclusion is that an EU-guideline for allergen products is urgently needed. A dialogue between regulatory authorities and representatives of the manufacturers, prior to the formulation of a new guideline seems of the utmost importance, as to prevent a similar stalemate as after the introduction of the foreseen regulatory measures of the past. The new guideline should include: An allergen product monograph. Recommendations for clinical development of allergen products like: Number of patients for efficacy and safety Acceptability of different efficacy parameters. Recommendations for toxicology.

The EAMG position on the regulation of existing products for treatment with special reference to named patient products (NPPs)

Allergen products have a long history in both diagnosis and management of allergic disease. It is emphasized that the availability of named patient products presents a valuable and indispensable option for the effective and safe treatment of patients suffering from IgE-mediated allergic diseases. A regulatory climate should be achieved in which these products can survive until a safe and effective alternative is borne out. Within the context of the paper the following definition is used: A named patient product or NPP is an allergen product, prepared with a specific reference number in accordance with a prescription for an individual patient, identified by the name of this patient and the reference number, and delivered after control of consistency with previous treatments. It is stressed that the standards of quality that hold for registered products are also applicable for named patient preparations which, for various reasons, can not be filed for registration. The paper frequently refers to a Position Paper that has recently been adopted by the European Allergen Manufacturers Group, the EAMG. The presentation breaks a lance for a concerted approach of the NPP-concept by striving at harmonization of legal, regulatory, manufacturing, and distribution conditions.

Long-term treatment with allergoid immunotherapy with Parietaria. Clinical and immunologic effects in a randomized, controlled trial

BACKGROUND

Specific immunotherapy (SIT) is a valuable treatment for respiratory allergy, and the use of chemically modified allergens (allergoids) has improved its safety, as testified by several studies. We evaluated the effects of a SIT course with an allergoid extract of Parietaria pollen in a double-blind, placebo-controlled trial.

METHODS

The study was double-blind in the first year; then it was prolonged up to 3 years with all patients on active treatment. Clinical effectiveness, safety, skin reactivity, systemic immunologic parameters, and subjective assessment were evaluated. We also had available a self-evaluation recorded in a follow-up visit 4 years after the discontinuation of SIT.

RESULTS

A significant reduction of the symptoms plus drug intake scores during the pollen seasons was observed in the patients receiving active SIT. The placebo patients, after switching to active SIT, also showed significant clinical improvement. The clinical efficacy persisted during years 2 and 3 of treatment. After year 1, the actively treated patients reported a significant subjective improvement (frequency of symptoms, P = 0.001; duration of symptoms, P = 0.024; physical performance, P = 0.043) compared with the placebo group. The self-evaluation by visual analog scale showed that all patients maintained a significant clinical improvement up to 4 years after discontinuing SIT (year 1: active=+31.6%, placebo=-15.7%; year 7: active=+35.8%, placebo=+31.3%). The systemic immunologic changes after active SIT paralleled those described elsewhere (IgE decreased from 22 to 9 and from 21 to 8 IU/ml; IgG4 increased from 43 to 87 and from 18 to 60 IU/ml). A significant decrease in skin reactivity to three different allergen concentrations was observed at year 3 compared with pretreatment values (P<0.05).

CONCLUSIONS

The investigational SIT with Parietaria appeared to be effective and safe; a 3-year course of treatment achieved a long-lasting efficacy.

Measurement of IgE antibodies against purified grass pollen allergens (Lol p 1, 2, 3 and 5) during immunotherapy

BACKGROUND

IgE titres tend to rise early after the start of immunotherapy, followed by a decline to pre-immunotherapy levels or lower.

OBJECTIVES

We were interested to know whether the early increase in IgE antibodies includes new specificities of IgE, and whether these responses persist.

METHODS

Sera of 64 patients undergoing grass pollen immunotherapy were tested for IgE against four purified grass pollen allergens: Lol p 1, 2, 3, and 5. At least two serum samples were taken, one before the start of therapy and one between 5 and 18 months after the first immunization (mean: 10 months).

RESULTS

The mean IgE responses to Lol p 1, 2 and 3 showed a moderate but not significant increase. In contrast, the mean IgE response to Lol p 5 showed a significant decrease of > 30%. IgE against total Lohum perenne pollen extract moderately increased (> 20%), showing that a RAST for total pollen is not always indicative for the development of IgE against its major allergens. For > 40% of the patients it was found that IgE against one or more of the four allergens increased, while IgE against the remaining allergen(s) decreased. For 10 sera the ratio of IgE titres against at least two allergens changed by at least a factor of 5. The changes in specific IgE also included conversions from negative (< 0.1 RU) to positive (0.6 to 5.0 RU) for five patients. For two patients, the induction of these 'new' IgE antibodies against major allergens was shown to result in a response that was persistent over several years.

CONCLUSION

Although active induction of new IgE specificities by immunotherapy was not really proven, the observations in this study indicate that monitoring of IgE against purified (major) allergens is necessary to evaluate changes in specific IgE in a reliable way.

Grass pollen immunotherapy induces highly cross-reactive IgG antibodies to group V allergen from different grass species

Sera from two groups of patients receiving grass pollen immunotherapy were tested on IgG reactivity with group V allergen from six different grass species. One group of patients was treated with a mixture of 10 grass species, and the other with a mixture of five. Only Lolium perenne, Dactylis glomerata, and Phleum pratense were present in both mixtures. Although Anthoxanthum odoratum and Secale cereale were absent from the mixture of five, IgG responses to Ant o V and Sec c V were comparable in both patient groups. This reactivity was inhibited for 92-99% with L. perenne extract, illustrating the cross-reactive nature of the IgG antibodies. The presence of A. odoratum and S. cereale in the mixture resulted in only minor amounts of species-specific anti-group V IgG. These results indicate that application of just one grass species in immunotherapy might be sufficient to induce an IgG response that covers other relevant Gramineae species as well.

[Therapy of hayfever and pollen asthma in children with a new, modified allergen extract]

During a period of 3 years a controlled and prospective study was performed, in which 20 children with pollinosis and pollen asthma (grass pollen) were treated either with a new modified allergenic extract (preparation I: Purethal) or with a standard semi-depot extract (preparation II: Depot-HAL) from the same producer. During the pollen season symptoms, side effects, additional medication, and pollen counts were registered. 20 patients were treated perennially: 5 with preparation II and with reduction of the doses during the pollen season (group A: treatment during 3 successive years), 15 without reduction of the doses during te season with preparation I (group B, 8 patients: treatment during 3 successive years; group C, 7 patients: treatment during 2 successive years). Patients in all groups showed more symptoms in May and June. In the groups B and C less symptoms were recorded. Especially, the score of asthma symptoms decreased. However, the need for additional medication was somewhat higher in these groups as compared to group A. The differences were not statistically significant. In 50% of the children no local side reactions were observed after the subcutaneous injections. In the groups B and C the number of late local reactions after 6 to 8 hours was somewhat higher. The patients treated with preparation I did not show an increase of allergen-specific IgG during the pollen season. The relative contribution of allergen-specific IgG1 and IgG4 to total specific IgG was lower in the blood samples of these patients as compared to those of group A. The efficacy and the therapeutic safety of the two preparations are comparable. Preparation I has a number of practical advantages, especially in the treatment of children.

Changes in nuclear protein pattern by glucocorticoid treatment of lymphoid cells

Glucocorticoids initiate a cytolytic process in lymphoid cells. The ultimate response is preceded by several phenomena. It is generally accepted that these are mediated through messenger proteins. The induction of these proteins is considered the primary effect of glucocorticoids. However, as yet specific gene products have not been identified. In electrophoretic assays, we observed an increased concentration of 6 nuclear proteins within a few hours of exposure of lymphoid cells to glucocorticoids. These proteins displayed prominent DNase activity. However, further studies showed: (1) that the proteins concerned are histones, (2) that histones are more easily extracted after glucocorticoid-induced alterations of lymphoid cells, and (3) that basic proteins in general express nuclease activity under certain experimental conditions. This nuclease activity is, however, artifactual. Therefore, though the changes observed are certainly related to glucocorticoid-induced effects, these do not reflect the induction of specific proteins. The results of the study indicate that glucocorticoid-induced changes in the concentration of cellular proteins should be interpreted with caution.

Mitochondrial biogenesis during the activation of lymphocytes by mitogens: the immunosuppressive action of tetracyclines

The role of mitochondrial biogenesis and function during mitogenic stimulation of rat thymocytes was investigated. The results show that mitochondrial biogenesis is required to provide the ATP for the energy-requiring processes occurring during blastogenesis. Impairment of mitochondrial biogenesis by inhibition of mitochondrial protein synthesis inhibits blast transformation. Since the tetracyclines impair mitochondrial protein synthesis, the results offer an explanation for the well-known immunosuppressive effects of these antibiotics.

Inhibition of mitochondrial protein synthesis influences the glucocorticoid sensitivity of lymphoid cells

Inhibition of mitochondrial protein synthesis impairs the formation of the 13 polypeptides encoded on the mitochondrial genome. These polypeptides are part of enzyme complexes involved in oxidative phosphorylation. Prolonged inhibition of mitochondrial protein synthesis thus reduces the oxidative phosphorylation capacity which ultimately results in impairment of energy-requiring processes. Via a different mechanism glucocorticoid hormones also decrease the oxidative phosphorylation capacity of, e.g., lymphoid cells. The present study shows that inhibition of mitochondrial protein synthesis influences glucocorticoid-induced responses of lymphoid cells in two opposing manners. (a) It is enhanced after induction in cells with a reduced oxidative phosphorylation capacity resulting from preceding inhibition of mitochondrial protein synthesis. This can be explained by the synergistic effects of glucocorticoids and prolonged inhibition of mitochondrial protein synthesis on energy-producing processes. (b) It is counteracted when mitochondrial protein synthesis is impaired during induction of the response. The latter observation suggests that mitochondrial protein synthesis is involved in the generation of glucocorticoid-induced effects on lymphoid cells.

Doxycycline in combination chemotherapy of a rat leukemia

Inhibition of mitochondrial protein synthesis by doxycycline (DC), a tetracycline analogue, has significant antitumor effects in several tumor systems. In the present study, the effects of continuous DC treatment combined with intermittent administration of Adriamycin or 1-beta-D-arabinofuranosyl cytosine on the growth of a rat leukemia were investigated. The presence of DC retards tumor relapse after 1-beta-D-arabinofuranosyl cytosine or Adriamycin treatment significantly. DC may therefore be of value in several modalities of antitumor treatment.

Mitochondrial biogenesis and mitochondrial activity during the progression of the cell cycle of human leukemic cells

Mitochondrial (mt) biogenesis and mt function were investigated during the cell cycle of leukemic cells. The study shows that the activity of enzymes involved in oxidative phosphorylation increases in the early G1 phase. This increase in activity precedes that of other mt enzymes such as citrate synthase and adenylate kinase. Therefore, the synthesis of mt enzymes, needed for the reduplication of the mt mass in the course of the cell cycle, occurs in a sequential order. The enzymes of the system for oxidative phosphorylation are composed of several subunits. Some of these subunits are encoded on mtDNA and synthesized by mt-specific RNA and protein synthesis. This explains why inhibition of mt protein synthesis during the progression of the cell cycle of G1-enriched cells results in an increasing shortage of ATP. This lack of ATP results first in progression delay and, subsequently, in a cell cycle block in early G1. Furthermore, shortage of ATP impairs the increase in activity of at least one mt matrix enzyme. This study offers new information about a number of aspects of mt biogenesis and mt function during cell cycle progression and elucidates the cytostatic mechanism resulting from prolonged inhibition of mt protein synthesis.

Different effects of oxytetracycline and doxycycline on mitochondrial protein synthesis in rat liver after long-term treatment

The tetracyclines inhibit specifically mitochondrial (mt) and bacterial protein synthesis when they are present in low concentrations (2-10 micrograms/ml). There is no difference between the various members of this group of antibiotics in this respect. In the present study, however, it is shown that the inhibitory effect of doxycycline on mt-protein synthesis in rat liver is partially lost after continuous treatment for more than 1 week, whereas oxytetracycline continues to inhibit mt-protein synthesis effectively after 1 week of treatment. To find an explanation for this difference between doxycycline and oxytetracycline, a detailed study was made of the distribution and the effects on mt-protein synthesis of both tetracyclines under various conditions in rat liver. The results of the studies lead to the hypothesis that doxycycline treatment induces the formation of a doxycycline complex, and thus to a reduced amount of free doxycycline. This may explain the loss of effective inhibition of mt-protein synthesis.

Biogenesis of mitochondria and genetics of mitochondrial defects

Mitochondria are formed by the concerted action of two genetic systems: the nucleocytoplasmic system and the intrinsic mitochondrial system. The genetic contribution of the mitochondria is modest because the genetic potential of mtDNA of mammals is restricted to the equivalent of about 16,000 base pairs. For various animals and man the complete base sequence of mtDNA is known and all possible polypeptide genes have now been assigned to subunits of the respiratory enzymes. The mtDNA sequences are not present on the nuclear genome. From a genetic point of view it is important that the inheritance of mtDNA is strictly maternal. Mutations of mtDNA primarily lead to impairments of energy metabolism. In view of the indispensability of oxidative phosphorylation for obligatory aerobic organisms, such mutations should be lethal. However, there are various inborn errors of metabolism with tissue-specific manifestations, which are maternally inherited. The question discussed is whether these diseases can be explained on the basis of mutations of mitochondrial gene products. Tissue specificity poses a special problem, since it is not very attractive to assume that there is a heterogenous population of mtDNA molecules in the fertilized egg. Therefore, one should rather think in terms of a double mutational event, one tissue-specific cytoplasmic and the other general mitochondrial. These mutations only give rise to metabolic disturbances if they are expressed together in the same cell.

The effect of inhibition of mitochondrial protein synthesis on the proliferation and phenotypic properties of a rat leukemia in different stages of in-vivo tumor development

It has been shown before that prolonged treatment with doxycycline (DC), an inhibitor of mitochondrial protein synthesis, leads to proliferation arrest of a leukemia in the rat and, moreover, to eradication of this tumor. It has also been demonstrated that the period of treatment required to achieve this is shorter when DC administration is started in later stages of tumor progression. Therefore, the leukemic cells may have properties with regard to DC sensitivity which change with time during tumor progression. In the present study this hypothesis was tested by studying the permeability for DC, the presence of cell-surface molecules, and the mitochondrial content of the leukemic cells in various stages of tumor development in control and in DC-treated rats. Changes in DC permeability or antigenic phenotype were not observed, but the content of mitochondria decreases during tumor progression. DC treatment leads to an additional reduction of the content of functional mitochondria which results in proliferation arrest. The higher mitochondrial content of the leukemic cells during the earlier stages of tumor development explains thus why a longer period of DC treatment is needed to achieve growth arrest when treatment is started in these stages.

The effect of doxycycline on polyvinylpyrrolidone-induced granuloma formation in the rat liver

The tetracyclines specifically inhibit mitochondrial protein synthesis when present at the same low concentrations as used for their antibacterial action. Inhibition of mitochondrial protein synthesis leads to decrease in the oxidative energy-generating capacity of cells. Therefore, the presence of tetracyclines may result in proliferation arrest. In the present study we show that continuous intravenous administration of polyvinylpyrrolidone (PVP) induces the formation of granulomas in the normal rat liver; the rats usually die within 2 weeks of continuous PVP treatment. Athymic (nude) rats appear to be more resistent to the deleterious effects of PVP as they survive the treatment for at least 5 weeks. Although the livers of the PVP-treated nude rats are heavily infiltrated with phagocytic cells, they seldom show granulomas. Reconstitution of nude rats with syngenic thymocytes leads, on the other hand, to extensive granuloma formation. Normal rats treated continuously with PVP plus doxycycline, however, all survive, their livers showing only a few very small granulomas and the normal low number of phagocytic cells. We conclude that the formation of granulomas induced by PVP is a process which is mediated by T-lymphocytes. Because doxycycline prevents this kind of granuloma formation it seems likely that doxycycline not only impairs the proliferation and differentiation of T-lymphocytes but also of monocytes and macrophages.

Arrest of the proliferation of renal and prostate carcinomas of human origin by inhibition of mitochondrial protein synthesis

The results described in this paper demonstrate that proliferation arrest by low concentrations of tetracyclines, which has previously been shown in experiments with animal tumor systems, can also be achieved in tumor systems of human origin. Tetracyclines specifically inhibit mitochondrial protein synthesis. Prolonged and continuous impairment of protein synthesis inside the mitochondria leads to reduction of the cellular concentration of the polypeptide products which are coded and synthesized within mitochondria. These products are part of the oxidative phosphorylative system of the cell. Long-term tetracycline treatment leads to a decrease of oxidative ATP-generating capacity as monitored by cytochrome c oxidase activity. This may cause severe energetic or metabolic disturbances which explain the proliferation arrest observed. Proliferation arrest, provided that mitochondrial protein synthesis is blocked effectively, is found in vitro as well as in vivo. It is shown that the effect of doxycycline is not limited to cytostasis; prolonged doxycycline treatment is clearly cytotoxic for the tumor cells.

Inhibition of mitochondrial protein synthesis leads to proliferation arrest in the G1-phase of the cell cycle

Mitochondrial protein synthesis is specifically inhibited by low concentrations of tetracyclines. Prolonged inhibition of mitochondrial protein synthesis leads to a lack of oxidative ATP generating capacity, which results in proliferation arrest of normal and malignant cells of epithelial origin, as has been shown previously. The present study indicates that this holds true also for fibroblasts and sarcoma cells. It is shown that this proliferation arrest leads to accumulation of the growth-arrested cells in the G1-phase of the cell cycle. This offers several interesting possibilities to use tetracyclines in anticancer combination therapies.

Specific inhibition of mitochondrial protein synthesis influences the amount of complex I in mitochondria of rat liver and Neurospora crassa directly

Specific inhibition of mitochondrial protein synthesis reduces the oxidation rate of NADH-linked substrates in rat liver as well as in Neurospora crassa mitochondria. The present study shows that this is due to the fact that inhibition of mitochondrial protein synthesis leads to a decrease of the concentration of active complex I. Therefore, these results demonstrate that at least one of the genes for the subunits of complex I is localized on mitochondrial DNA.

The effect of long-term inhibition of mitochondrial protein synthesis on the oxidation capacity of mitochondria for NADH-linked substrates

Experiments are presented showing that specific inhibition of mitochondrial protein synthesis by tetracyclines decreases the activity of the NADH-dehydrogenase complex in liver mitochondria, if rats are treated for long periods with these antibiotics. The corresponding inhibition of this complex in tumor cells (Zajdela hepatoma) and tumor mitochondria (Leydig cell tumor) is even more pronounced. It is concluded that the mitochondrial genetic system is involved in the assembly of the NADH-dehydrogenase complex, most likely by coding for one or more subunits. It is argued that this information, contrary to the situation for cytochrome c oxidase, the cytochrome bc1 complex and ATPsynthase, has been missed in previous experiments employing differential inhibition of mitochondrial protein synthesis, because of the circumstance that the inhibition did not reach the level at which it became rate-limiting.

The antitumour effect of doxycycline on a T-cell leukaemia in the rat

Previous studies showed that T-lymphoid cells are permeable to the tetracyclines, whereas B-lymphoid and erythroid cells are not. The tetracyclines impair mitochondrial protein synthesis if they have access to cells. Inhibition of mitochondrial protein synthesis during a number of cell cycles results, as a consequence, in proliferation arrest. The tetracyclines can therefore be considered as cytostatics. In the present study the effect of prolonged treatment with doxycycline on the growth of a T-cell type leukaemia of the rat was investigated. It is shown that doxycycline treatment inhibits not only tumour cell proliferation, but leads moreover to complete tumour eradication. The way by which the latter is achieved depends on the doxycycline concentration and, surprisingly, on the stage of tumour progression at which doxycycline administration is started. As, because of the permeability barrier, the proliferation of erythroid and B-lymphoid cells is not affected by the tetracyclines, the tetracyclines may provide a tool without serious side-effects in the therapy of T-type tumours.

The mitochondrial genetic system as a target for chemotherapy: tetracyclines as cytostatics

The mitochondrial genetic system is indispensable for the biosynthesis of the enzyme complexes involved in aerobic energy generation. Tetracyclines inhibit the expression of only the mitochondrial genes because they specifically block mitochondrial protein synthesis. A salient feature is that this inhibition occurs at the low concentration required for anti-bacterial treatment, provided that this concentration is maintained continuously. Evidence is presented that the growth of carcinogen-induced tumors can be inhibited by tetracyclines. It is further shown that the development in the cheek pouch of the Syrian hamster of a transplantable hypernephroma from human origin can be strongly retarded by tetracyclines as well. Therefore, the mitochondrial genetic system has to be reckoned as a target for chemotherapy and tetracyclines as cytostatic agents.

Antibacterial drugs and their interference with the biogenesis of mitochondria in animal and human cells

Mitochondrial RNA and protein synthesis in mammalian cells is sensitive to inhibition by a variety of antibiotics which are used in medical practice. In spite of the intrinsic sensitivity of the synthetic processes to these drugs it appears that inhibition in intact cells and living organisms is not observed in all cases because the cellular membranes may act as barriers which prevent the antibiotics from reaching their intramitochondrial targets. This holds for the rifamycins, the lincomycins and a number of macrolides, but not for chloramphenicol and its analogues. Some of the toxic side-effects of the latter antibiotics can be related to their antimitochondrial action. For the tetracyclines selectivity in permeability exists in the sense that some cell types are permeable and other are not. The hypothesis is developed that the deliberate inhibition of mitochondrial protein synthesis in vivo may lead to cell proliferation arrest and offer a device in combined modality treatments of malignant growths. This hypothesis is supported by the results of two studies with experimental tumour models in rats and by retrospective and prospective clinical data.

Arrest of in vivo growth of a solid Leydig cell tumor by prolonged inhibition of mitochondrial protein synthesis

Oxytetracycline was given by means of chronic i.v. infusion, in amounts which impair specifically mitochondrial protein synthesis, to Wistar rats carrying a solid Leydig cell tumor. The prolonged inhibition of mitochondrial protein synthesis finally results in proliferation arrest of the s.c. growing tumor. As long as the tumor is growing, the energy-generating capacity of the mitochondrial becomes diluted, until it is reduced to a critical level, which results in growth arrest. This cytostatic effect is found after treatment for 8 to 12 days. During this period, the tumor volume increases to an extent comparable to 2 to 3 tumor cell divisions. The proliferation arrest found is, at least after treatment for 3 weeks, reversible. Withdrawal of oxytetracycline results in continuation of tumor growth after a latent period of about 5 days. The data confirm previous observations made in experimental systems about the usefulness of mitochondrial protein synthesis as target for cancer chemotherapy. They support, moreover, the explanation given for the marked prolongation of survival time found in tetracycline-treated patients with a squamous cell carcinoma of the larynx-pharynx. If antineoplastic therapy, based on inhibition of mitochondrial protein synthesis, is considered, the tetracyclines should be the drugs of choice, because their toxic side effects are minimal at dosages which cause tumor proliferation arrest.

Non-random patterns of nucleotide substitutions and codon strategy in the mammalian mitochondrial genes coding for identified and unidentified reading frames

The base sequence of large part of the mitochondrial DNA of Wistar rats is presented. The sequence is compared with those of other mammalian mitochondrial DNAs. The nucleotide and amino acid homologies, codon strategy, nature and patterns of substitutions are reported. It results a very high amount of silent substitutions and, in short divergence time, a predominance of transitions on transversions. In both types of substitutions a strong bias in avoiding the use of the G in the third codon position is observed.

Impairment of liver regeneration during inhibition of mitochondrial protein synthesis by oxytetracycline

Under standard conditions, liver regeneration is impaired if mitochondrial protein synthesis is completely blocked. By treating rats with oxytetracycline for various periods of time directly prior to partial hepatectomy, livers were led to a condition of relative deficiency in cytochrome c oxidase and ATP synthetase. To this end, oxytetracycline was administered by means of continuous intravenous infusion up to concentrations of 20 micrograms/ml serum, giving a gradual decrease in cytochrome c oxidase activity. This activity was used as a marker for functionally capable mitochondria and as a tool to monitor the efficiency of inhibition of mitochondrial protein synthesis. It is shown that liver regeneration is strongly impaired after a period of pretreatment of 22 days or more and continuation of oxytetracycline treatment during regeneration. The mitochondrial respiratory capacity is reduced to 14% of the control value under these conditions. To obtain inhibitory levels within the regenerating liver, it was necessary to raise the serum levels slightly above 20 micrograms/ml. This measure is most likely required because of the poor vascularization of the regenerating liver. The serum levels were kept, however, far below those known to inhibit cytoplasmic protein synthesis. The results show that in normal liver the respiratory capacity must be reduced drastically before energy-requiring processes become affected. In Zajdela hepatoma cells, similar effects are found after reduction of the cytochrome c oxidase activity to 38%. This difference in sensitivity is probably based on the different mitochondrial content of liver cells and the liver-derived Zajdela cells.

Characterization of a 45-kDa polypeptide as the precursor of subunit 1 of cytochrome c oxidase in Neurospora crassa

In a previous paper (Van 't Sant, P., Mak, J.F.C. and Kroon, A.M. (1981) Eur. J. Biochem. 121, 21-26) we showed the existence of three elongated precursor proteins (45, 36 and 25 kDa) of mitochondrial translation products in Neurospora crassa. We presented some indications that the largest precursor could be related to subunit 1 of cytochrome c oxidase. Here we present conclusive evidence that the 45-kDa polypeptide is indeed this precursor by demonstrating that an immunodetectable 45-kDa polypeptide displays the same behaviour as the labeled 45-kDa precursor; both accumulate after long incubation with cycloheximide or by decreasing the temperature and both are not tightly membrane bound. Moreover the antibody against subunit 1 of cytochrome c oxidase also recognizes, in immunoadsorption experiments, besides subunit 1, the 45-kDa polypeptide accumulated by cycloheximide incubation. Furthermore, we developed a small scale purification of antibodies against subunit 1 of cytochrome c oxidase. By means of these purified antibodies it is demonstrated that the 45-kDa polypeptide and subunit 1 have corresponding antigenic determinants. Under the various conditions tested, all three precursors are less firmly membrane-bound than the mature subunits. Finally, it is observed that in short incubations in vivo, chloramphenicol inhibits the processing of the mitochondrially synthesized precursors, under conditions where mitochondrial translation is only partially inhibited.

Effects of oxytetracycline on in vivo proliferation and differentiation of erythroid and lymphoid cells in the rat

Previous studies revealed that inhibition of mitochondrial protein synthesis by tetracyclines during a number of cell divisions results in proliferation arrest, in vitro as well as in in vivo. The tetracyclines may, therefore, be considered as cytostatics. In this context it is of interest to know the effect of the tetracyclines on rapidly dividing normal cell types, such as erythroid and lymphoid cells. To investigate the influence of the tetracyclines on the proliferation of these cells, we studied immunological responses to sheep red blood cells and recovery from severe anaemia in rats in the presence or absence of oxytetracycline (OTC). Under the experimental conditions used, effects of OTC on the immune responses were only found for events directly or indirectly related to T cell proliferation. The results presented thus strongly suggest that OTC inhibits the division of T lymphoid cells only. The proliferation of other haemopoietic cells is not influenced, most likely because these cells are not permeable to OTC.

The nucleotide sequences of several tRNA genes from rat mitochondria: common features and relatedness to homologous species

We have determined the nucleotide sequences of thirteen rat mt tRNA genes. The features of the primary and secondary structures of these tRNAs show that those for Gln, Ser, and f-Met resemble, while those for Lys, Cys, and Trp depart strikingly from the universal type. The remainder are slightly abnormal. Among many mammalian mt DNA sequences, those of mt tRNA genes are highly conserved, thus suggesting for those genes an additional, perhaps regulatory, function. A simple evolutionary relationship between the tRNAs of animal mitochondria and those of eukaryotic cytoplasm, of lower eukaryotic mitochondria or of prokaryotes, is not evident owing to the extreme divergence of the tRNA sequences in the two groups. However, a slightly higher homology does exist between a few animal mt tRNAs and those from prokaryotes or from lower eukaryotic mitochondria.

Larger precursors of mitochondrial translation products in Neurospora crassa. Indications for a precursor of subunit 1 of cytochrome c oxidase

Specific labeling in vivo of the formylated N termini of mitochondrial translation products revealed that some mitochondrially synthesized proteins were not labeled this way. As a consequence, it was worthwhile considering that larger precursor proteins of mitochondrial translation products exist. Although we used a rapid isolation procedure, only after 2-h of labeling in the presence of cycloheximide, could three additional mitochondrial translation products (molecular mass 45, 36, and 25 kilodaltons) be detected. Preincubation with cycloheximide indicated that these proteins might be larger precursors which were no longer processed due to the prolonged presence of cycloheximide. To prevent processing of the precursors during isolation, cells of the slime mutant were directly lysed in boiling sodium dodecyl sulphate solution. In this way, the same three additional mitochondrial translation products were detected after a pulse-labeling of 1 min. These proteins behave in a precursor-like fashion. Labeling at 9 degrees C resulted in a partial accumulation of the three additional proteins. Finally protein blots treated with antibodies and 125I-labeled protein A, support the idea that the 45-kDa protein is a precursor of subunit 1 of cytochrome c oxidase; 50-80% of this precursor could be detected in the post-mitochondrial supernatant, indicating that this polypeptide is not tightly bound to the membrane.

The nucleotide sequence of the large ribosomal RNA gene and the adjacent tRNA genes from rat mitochondria

We have sequenced the Eco R(1) fragment D from rat mitochondrial DNA. It contains one third of the tRNA (Val) gene (the remaining part has been sequenced from the 3' end of the Eco R(1) fragment A) the complete gene for the large mt 16S rRNA, the tRNA (Leu) gene and the 5' end of an unidentified reading frame. The mt gene for the large rRNA from rat has been aligned with the homologous genes from mouse and human using graphic computer programs. Hypervariable regions at the center of the molecule and highly conserved regions toward the 3' end have been detected. The mt gene for tRNA Leu is of the conventional type and its primary structure is highly conserved among mammals. The mt gene for tRNA(Val) shows characteristics similar to those of other mt tRNA genes but the degree of homology is lower. Comparative studies confirm that AGA and AGG are read as stop codons in mammalian mitochondria.

The characterization of the area of rat mitochondrial DNA containing the large ribosomal RNA gene

The base sequence of the Eco-RI D fragment from rat liver mtDNA, cloned in recombinant plasmid, has been analyzed, This fragment contains the genes for the 16SRNA of the large ribosomal subunit and the tRNA(Leu). Comparisons between these genes and corresponding regions either in other mitochondrial genomes or in E. coli DNA are presented, that allow some interesting evolutionary and phylogenetic considerations.

Arrest of in vivo proliferation of Zajdela tumor cells by inhibition of mitochondrial protein synthesis

The proliferation of Zajdela tumor cells, grown in vivo in Wistar rats, is arrested by low amounts of oxytetracycline. Oxytetracycline is administered by means of continuous infusion in such a way that the oxytetracycline concentration in serum and ascitic fluid is maintained at a level at which only mitochondrial protein synthesis is blocked. Under these conditions, Zajdela mitochondrial tumor cells cease dividing after a few cell generations, an event which is preceded by reduction of cytochrome c oxidase activity of the tumor cells. Toxicity to host tissues is limited to the immune system which is apparently suppressed by the drug. Even so, oxytetracycline might have therapeutic potential in human cancer therapy, especially because it does not influence the hemopoietic system.

Fluorometric determination of tetracyclines in small blood and tissue samples

A reported fluorometric method to determine tetracycline in biological material was modified to determine low levels of the antibiotics when using only small amounts of starting material. The method is applicable to tissue distribution studies in small experimental animals and also can be used for serial determinations in blood samples of these animals and for biopsy material. The tetracyclines are extracted in the presence of ethylenediaminetetraacetic acid, and the phosphate precipitation steps are omitted. This omission makes the procedures considerably less time consuming. The recoveries of the tetracyclines, oxytetracycline and doxycycline, are approximately 80-100%. The values obtained by this method were consistent with those from microbiological assays, and its reliability was shown further in a comparison with the fate of radioactive tetracycline.

The biogenesis of rat mitochondrial ATPase. Two subunits are synthesized inside the mitochondria

Isolated mitochondria from regenerating rat liver synthesize at least five different polypeptides with molecular weights ranging from 19 000 to 43 000. Among these, two polypeptides with molecular weights of 22 000 and 25 ooo could be identified as ATPase subunits. It has previously been shown that these subunits, designated 6 and 7, are lacking in the ATPase complex that is formed in vivo when mitochondrial protein synthesis is blocked by thiamphenicol treatment. The 22 000 Mr protein is enriched in the fraction containing the fully assembled ATPase complex, whereas the 25 000 Mr protein is not.

Further analysis of the type differences of rat-liver mitochondrial DNA

1. The sequence of the small Hind III fragment F of rat-liver mitochondrial DNA (mtDNA) type A and type B was determined in order to investigate the nature of the differences between the two types of mtDNA and to determine its position in the Hind III fragment map. 2. The three differences found were point mutations. No deletion or insertion and no modification was observed. Two of the three differences affect the sequences which are recognition sites for Eco RI, Alu I and Taq I in type A, but not in type B, mtDNA. 3. The presence of an Eco RI restriction site only within the Hind III fragment F of type A shows that the fragment is situated in between the Hind III fragments A and E. 4. In one of the six reading frames, the Hind III fragment F contains the code for a carboxyl-terminal end of a polypeptide in which the three mutations do not lead to alterations in the possible aminoacid sequence. 5. The restriction sites for Taq I and a number of the sites for Alu I and Hae III were mapped. 6. The positions of the Hap II fragment J, and of a Hind III fragment G on the mtDNA were determined.

The biogenesis of rat-liver mitochondrial ATPase. Evidence that the N, N'-dicyclohexyl carbodiimide-binding protein is synthesized outside the mitochondria

1. Radioactive N,N'-dicyclohexyl carbodiimide (DCCD) is bound as effectively to the N, N'-dicyclohexyl carbodiimide- and oligomycin-sensitive ATPase complex in submitochondrial particles of normal rat liver as to the similar but partially N,N'-dicyclohexyl carbodiimide- and oligomycin-insensitive complex of thiamphenicol-treated rats. The latter complex is deficient in 3 subunits (subunit 6, 7 and 10). 2. Radioactive N,N'-dicyclohexyl carbodiimide is exclusively bound to the subunits present in the bands 8 and 11 of SDS-PAA gels of the purified ATPase complex. These subunits, most likely the dimer and monomer of the N,N'-dicyclohexyl carbodiimide-binding protein, are products of the cytoplasmic protein synthesis. 3. The results together indicate that the N,N'-dicyclohexyl carbodiimide-insensitivity of the ATPase complex formed during in vitro inhibition of mitochondrial protein synthesis, is not caused by a lack of inhibitor binding protein. The same holds for the oligomycin-insensitivity.

The biogenesis of rat liver mitochondrial ATPase. Subunit composition of the normal ATPase complex and of the deficient complex formed when mitochondrial protein synthesis is blocked

1. An ATPase complex containing 12 subunits was isoalted from rat liver mitochondria. 2. In vivo inhibition of mitochondrial protein synthesis by the chloramphenicol analogue thiamphenicol leads to the formation of an oligomycin-insensitive membrane-bound ATPase complex in mitochondria of regenerating rat liver. 3. This oligomycin-insensitive, membrane-bound ATPase was isolated by the same procedure as the ATPase complex from regenerating livers of untreated animals. 4. SDS-polyacrylamide gel electrophoresis of in vivo labelled ATPase complexes from control and from thiamphenicol-treated rats reveals that three subunits out of the 12 are not synthesized or assembled when the mitochondrial translation activity is blocked. 5. From the subunits synthesized and assembled when mitochondrial pror (Fo) of the ATPase complex (subunit 5). 6. The oligomycin sensitivity-conferring protein seems absent in the ATPase complex formed in the presence of thiamphenicol.

Mitochondrial DNA from various organisms does not contain internally methylated cytosine in -CCGG- sequences

Mitochondrial DNAs from yeast, Neurospora, rat and calf do not contain internally methylated cytosine in -CCGG- sequences.

The heterogeneity of rat-liver mitochondrial DNA

Two types of mitochondrial DNA (mtDNA) can be distinquished in an inbred strain of rats of the Wistar type. The population of DNA molecules of the liver of one single rat is homogeneous. This was shown for a number of 100 animals and confirms the data of other investigators. The two types of mitochondrial DNA, designated A and B, differ in their number of cleavage sites for the restriction endonucleases Eco RI (2sites), Hind II (1 site) and Hha I (1 site). No differences were found for the restriction enzymes Bam HI, Hap II, Hind III and Hpa I. The degree of sequence divergence of the two types of DNA is calculated to be roughly 5% on the basis of these observations. From 20 rats part of the liver was taken and the mtDNA was characterized. Heterologous and homologous crosses between type A and type B rats were made. Analysis of the offspring revealed strictly maternal inheritance of the A and B mtDNA traits. For purposes of base-sequence analysis and RNA.DNA hybridization the strain could easily be "purified" genetically.