Tailored biological retention and efficient clearance of pegylated ultra-small MnO nanoparticles as positive MRI contrast agents for molecular imaging.

A majority of MRI procedures requiring intravascular injections of contrast agents are performed with paramagnetic chelates. Such products induce vascular signal enhancement and they are rapidly excreted by the kidneys. Unfortunately, each chelate is made of only one paramagnetic ion, which, taken individually, has a limited impact on the MRI signal. In fact, the detection of molecular events in the nanomolar range using T1-weighted MRI sequences requires the design of ultra-small particles containing hundreds of paramagnetic ions per contrast agent unit. Ultra-small nanoparticles of manganese oxide (MnO, 6-8 nm diameter) have been developed and proposed as an efficient and at least 1000× more sensitive "positive" MRI contrast agent. However no evidence has been found until now that an adequate surface treatment of these particles could maintain their strong blood signal enhancement, while allowing their rapid and efficient excretion by the kidneys or by the hepatobiliairy pathway. Indeed, the sequestration of MnO particles by the reticuloendothelial system followed by strong uptake in the liver and in the spleen could potentially lead to Mn2+-induced toxicity effects. For ultra-small MnO particles to be applied in the clinics, it is necessary to develop coatings that also enable their efficient excretion within hours. This study demonstrates for the first time the possibility to use MnO particles as T1 vascular contrast agents, while enabling the excretion of >70% of all the Mn injected doses after 48 h. For this, small, biocompatible and highly hydrophilic pegylated bis-phosphonate dendrons (PDns) were grafted on MnO particles to confer colloidal stability, relaxometric performance, and fast excretion capacity. The chemical and colloidal stability of MnO@PDn particles were confirmed by XPS, FTIR and DLS. The relaxometric performance of MnO@PDns as "positive" MRI contrast agents was assessed (r1 = 4.4 mM-1 s-1, r2/r1 = 8.6; 1.41 T and 37 °C). Mice were injected with 1.21 µg Mn per kg (22 µmol Mn per kg), and scanned in MRI up to 48 h. The concentration of Mn in key organs was precisely measured by neutron activation analysis and confirmed, with MRI, the possibility to avoid RES nanoparticle sequestration through the use of phosphonate dendrons. Due to the fast kidney and hepatobiliairy clearance of MnO particles conferred by PDns, MnO nanoparticles can now be considered for promising applications in T1-weighted MRI applications requiring less toxic although highly sensitive "positive" molecular contrast agents.

[Biochemical changes in the connective tissue components of malignant tumors and lungs in mice during metastatic spreading and chemotherapy]. / Biokhimicheskie izmeneniia soedinitel'notkannykh komponentov zlokachestvennykh novoobrazovanii i legkikh u myshei pri metastazirovanii i primenenii khimiopreparatov.

The highest content of hydroxyproline, hexuronic acids and hexoses was found in nonmetastatic tumor tissue Ca 755 of mice as compared with metastatic neoplasms carcinoma 3LL and melanoma B-16. Development of melanoma B-16 metastases involved the active lung stromal reaction, while carcinoma 3LL metastatic spreading did not cause any distinct connective tissue reactions in lungs. Non-toxic doses of drugs, operating via dissimilar mechanisms (cyclophosphane, trielin, parmidine), resulted in similar alterations of the connective tissue components studied in primary tumors of both carcinoma 3LL and melanoma B-16. Content of hydroxyproline, hexuronic acids and hexoses was increased in lung tissue of mice with carcinoma 3LL, simultaneously with distinct inhibition of metastases development after administration of these drugs. The chemotherapeutic treatment did not increase the stromal reaction of lungs with metastases of melanoma B-16 and its antimetastatic effect was less distinct as compared with carcinoma 3LL.

[The components of the blood plasma fibrinolytic system in mice with Lewis lung carcinoma]. / Izuchenie komponentov fibrinoliticheskoi sistemy plazmy krovi u myshei s kartsinomoi legkikh L'iuis.

The fibrinolysis system components of the circulating blood plasma have been studied in experiments on C57Bl/6 mice in the dynamics of growth and metastasis of the Lewis lung carcinoma. It has been shown that a growth and metastasis of malignant tumours are accompanied by the fibrinolysis activity inhibition. Changes in the fibrinolysis processes are observed already on the 3rd day after tumour inoculation. These changes increased in the course of the tumour growth progress.

[Plasminogen activators in malignant tissues and lungs of mice during metastatic spreading and administration of various pharmacological agents]. / Aktivatory plazminogena v tkaniakh zlokachestvennykh novoobrazovanii i legkikh myshei pri metastazirovanii i nekotorykh farmakologicheskikh vozdeistviiakh.

The method of fibrin plates and electrophoresis in PAAG was used to study the activity and forms of plasminogen activators (PA) in extracts of normal tissues (muscle, lungs) as well as of the malignant tumours and the lungs of mice during metastatic spreading and under certain drugs (trielin and cyclophosphane). It was stated that determination of the specific activity level of plasminogen activator in a target organ (lungs) may be used as one of the indices during evaluation of the antimetastatic effect.

[Growth and metastasis of Lewis' lung carcinoma in mice under the pharmacological action on metabolism and the effects of kinins]. / Rost i metastazirovanie kartsinomy legkikh L'iuis u myshei pri farmakologicheskikh vozdeistviiakh na metabolizm i éffekty kininov.

In experiments on C57 Bl mice the effects of growth and metastatic proliferation of Lewis lung carcinoma inoculated intramuscularly on metabolism and kinin activity have been studied during the application of pharmacologic agents (parmidin, cellulose sulphate, unithiol). Causing a weak inhibition of the primary tumour growth, parmidin if administered repeatedly in given doses, inhibits partially metastatic process, which is manifested in an essential decrease of the quantity, size and weight of lung metastases. Parmidin also inhibits an adverse effect of cellulose sulphate and unithiol on metastatic process. It is believed that the action of parmidin is of an indirect character and is mainly associated with the elimination of the kinin component of microcirculatory disorders in the lungs.

[Changes in the total proteolytic activity and inhibitory potential of tumor and lung tissue in mice during growth and metastatic spread of malignant neoplasms]. / Izmeneniia obshchei proteoliticheskoi aktivnosti i ingibitornogo potentsiala tkani opukholei i legkikh u myshei v protsesse rosta i metastazirovaniia zlokachestvennykh novoobrazovanii.

In tumour tissue and in lungs of mice with carcinoma 3LL, melanoma B-16, adenocarcinoma 755 different changes of proteolytic and antitryptic activities have been revealed. An excessive level of the protease activity and/or a decrease of the inhibitory potential activity are the factors of decompensation of the body's protease-inhibitory system and stimulate development of metastatic process.

[Changes in the proteolytic activity and components of the blood kallikrein-kinin system during the growth and metastasis of experimental neoplasms]. / Izmeneniia proteoliticheskoi aktivnosti i nekotorykh komponentov kallikrein-kininovoi sistemy krovi pri roste i metastazirovanii éksperimental'nykh novoobrazovanii.

Changes in the total blood proteolytic activity, prekallikrein level, serum kallikrein inhibitors and other proteinases were studied during the growth and metastatic spreading of different experimental tumours. It has been established that the dissemination and metastatic spreading of Guérin carcinoma inoculated intratesticularly to rats is accompanied by a decrease in the content of prekallikrein and serum kallikrein inhibitors, which shows the activation of blood kinins. Changes in the total proteolysis and in prekallikrein content in mice with carcinoma 3LL and melanoma B-16 are of two-phase character: at the first stage after tumour inoculation there occurs an increase in the proteolytic activity and in prekallikrein content. At the second stage (14 to 28 days) characterized by the appearance of lung metastases, quite a pronounced and stable inhibition of the total proteolysis and of prekallikrein level was observed together with an increased level of proteinase inhibitors. The data obtained show that disturbances in the reactions of limited proteolysis, in particular shifts of the blood kallikrein-kinin system, play a definite role in the development of the metastatic process.

[Effect of polysaccharides on the cyclic nucleotide content and phosphodiesterase activity in the organs of mice with Lewis lung carcinoma]. / Vliianie nekotorykh polisakharidov na soderzhanie tsiklicheskikh nukleotidov i aktivnost' fosfodiésterazy v organakh myshei s kartsinomoi legkikh L'iuis.

Prodigiozan and zymosan were shown to have different effects both on the intracellular content of cyclic nucleotides and pulmonary metastases formation in mice with Lewis' carcinoma. The authors believe that determination of cyclic nucleotide ratio in immunocompetent organs (thymus and spleen) may be used as an additional criterion for identification of new antitumour immunomodulators.

[The role of cyclic nucleotides in the development of resistance to metastases after treatment with immunomodulators]. / Uchastie tsiklicheskikh nukleotidov v formirovanii soprotivliaemosti organizma razvitiiu metastazov pod vliianiem immunomoduliatorov.

It is shown that zymosan, prodigiosan, tiloron and levamisol have a different effect on the level of cyclic nucleotides and the cAMP/cGMP correlation in the lungs, thymus and spleen of mice during metastatic spreading of the Lewis carcinoma. A more pronounced antimetastatic effect after administration of immunomodulators is accompanied by a more considerable increase in the cAMP/cAMP coefficient in immunocompetent organs. There exists a close negative correlation between the increase in the cAMP/cGMP coefficient in the thymus and spleen, on the one hand, and inhibition of the metastatic spreading in the lungs under the effect of levamisol and zymosan, on the other.

[Changes in the metastasis of experimental tumors and in the antimetastatic effect of cytostatics in their pharmacological action on adrenergic processes]. / Izmenenie metastazirovaniia éksperimental'nykh opukholei i antimetastaticheskogo éffekta tsitostatikov pri farmakologicheskikh vozdeistviiakh na adrenergicheskie protsessy.

Different pharmacologic drugs (isadrin, obsidan, phentolamine) changing adrenergic processes are shown to have different effect on the growth and development of lung metastases. An increase in the antimetastatic effect of some cytostatics is also observed in mice with Lewis carcinoma and melanoma B-16 under the influence of isadrin, a stimulator of beta-adrenoreceptors. In authors' opinion, isadrin changes microcirculation in lungs and prevents inhibition of the immune reactivity in animals with metastatic tumours, thus contributing to inhibition of the development and growth of metastases.

[Effect of new antihistaminic preparations on the body's immunologic reactivity]. / Vliianie novykh protivogistaminovykh preparatov na immunologicheskuiu reaktivnost' organizma.

The effect of new antihistaminic drugs, phencarol and bicarphen, on immunologic reactivity of experimental animals was studied in comparison with diphenhydramine. Phencarol and bicarphen inhibited the delayed type allergic reactions to a greater degree than diphenydramine. Unlike diphenhydramine, phencarol and bicarphen injected simultaneously with test-antigen markedly decreased the number of rosette-forming lymphocytes in the immunocompetent organs (spleen, thymus, lymph nodes). Phencarol, bicarphen and diphenhydramine produced the same inhibitory effect on the content of antibody-producing cells in the spleen of mice.

[Comparative study of the effect of certain nonspecific stimulators on the body's immune response]. / Sravnitel'noe izuchenie vliianiia nekotorykh nespetsificheskikh stimuliatorov na immunnyi otvet organizma.

The effect of nonspecific stimulants of different nature on the quantitative and qualitative composition of immune rosette-forming cells (RFC) and intensity of hypersensitivity of delayed type was studied and compared in BALB/c mice. The data obtained show that the living BCG vaccine, zymosan and levamisol largely affect T-cell immunity, while prodigiozan, dextran sulfate and tiloron the humoral immune response. Unlike the living vaccine, BCG exerts less stimulant effect on the immune response and increases mainly the level of B-RFC in the spleen of normal mice.

[Immunostimulating and antitumor action of psychotropic preparations of the sydnonimine series]. / Ob immunostiomuliruiushchem i protivoopukholevom deistvii nekotorykh psikhotropnykh preparatov sidnoniminovogo riada.

In healthy animals and in those with different experimental tumours, the psychostimulant drug sydnophen activates the immune reactions: increases the number of RFC, the intensity of delayed hypersensitivity, blast transformation of lymphocytes, and the QD coefficient. This activation is attended by a slight inhibition of transplanted tumours. The psychostimulant sydnocarb exerts no immunostimulant action or any effect on the growth of experimental tumours.

[Effect of hypothalamic electrostimulation on the 11-hydroxy-corticosteroid content in the blood and on the immunological indices in rabbits with Brown-Pearce carcinoma]. / Vliianie élektrostimuliatsii gipotalamusa na soderzhanie 11-oksikortikosteroidov v krovi i immunologicheskie pokazateli u krolikov s kartsinomoi Brauna-Pirs.

In animals with Brown--Pearce carcinoma electric stimulation of the hypothalamus makes it possible to model an increased corticosterone level in blood at early stages of the tumor growth, which conditions more active development of antitumor reactions and consequently an enhanced tumor resorption. The increased level of free corticosterone seems to be essential for "triggering" and an active mode of proceeding of antitumor immune reactions.

[Tilorone, a synthetic immunostimulator possessing antitumor activity]. / Tiloron--sinteticheskii immunostimuliator, obladaiushchii protivoopukholevoi aktivnost'iu.

The authors report the results of studies on antitumor, immunostimulating and interieron-inducing properties of diethylamine fluorene derivative--tiloron, synthesized at Odessa laboratories of IGIC of the Ukrainian SSR Academy of Sciences by the originally elaborated method. It was found that tiloron does not suppress leucopoiesis, stimulates a number of protective reactions of the organism, including the factors of humoral and cell immunity, especially manifested under immunosuppression. Tiloron is shown to possess the definite antitumor activity being retained in peroral administration of the drug. Tiloron used together with cytostatic agents results in enhanced suppression of experimental tumors growth. Antitumor and immunostimulating action of tiloron on the experimental patterns under study is believed by the authors to be somewhat related with its interieron-inducing ability.