Several attempts to attack tumours in experimental systems have been made using conjugates of chemotherapeutic agents or potent toxins with antibodies (immunotoxins). In vitro studies have been highly successful, showing target specificity of a high order in some cases. However, so far, such conjugates have been inadequate in vivo, probably for two main reasons. First, conventional heteroclonal antibodies are perhaps inappropriate, because purification by biochemical methods leaves a large amount of non-antibody gamma-globulins. The use of monoclonal antibodies may overcome this problem. Second, when whole toxins have been conjugated to antibodies there has been a strong residual nonspecific cytotoxicity due to the binding capacity of a subunit, the B-piece of the toxin. (Diphtheria toxin or ricin consist of two polypeptide subunits. The A-piece is responsible for inhibition of protein synthesis on ribosomes, and the B-piece binds to galactose residues on the cell membrane and facilitates the transmembrane passage of the A-piece.) In the present work the problem of nonspecific binding by the B-piece has been circumvented by using the A-piece only as the toxin component of immunotoxins; these immunotoxins are active both in vitro and in vivo.

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In recent years, antibody -ricin-A-chain immunotoxins have been investigated as anti-neoplastic agents. To achieve in vivo therapy it is necessary that the immunotoxin remains in circulation at a sufficiently high level for a sufficiently long time to allow binding to tumor cells to occur. Therefore, examination of the pharmacology of immunotoxins may elucidate the reasons for the poor in vivo tumoricidal effect of immunotoxin described before. In this study the plasma clearance of antibody -ricin-A-chain immunotoxins, after intravenous injection in animals of different species, has been examined. Sensitive and reproducible techniques were developed to monitor the level of immunotoxin and its constituents in the blood. It is shown that immunotoxins are rapidly eliminated from the bloodstream. Neither the properties of the antibody moiety nor the nature of the linkage binding rich A-chain to antibody account for the disappearance of immunotoxin from the plasma. On the other hand, we found that the rapid clearance of immunotoxin is due to the mannose residues on the rich A-chain moiety which are specifically recognized by liver cells. When immunotoxin is administrated together with yeast mannan, which enhances the level of active immunotoxin in circulation by inhibition of liver uptake, the anti-cancer efficacy of immunotoxin in vivo is drastically improved.Progress has been made in rendering monoclonal antibodies highly cytotoxic by coupling them to the A-chain subunit of the phytotoxin ricin (RTA). Such hybrid molecules, termed immunotoxins (ITS), are now currently prepared according to standardized methods and their biological properties have been studied in detail [l -41. Although these conjugates showed specific cytotoxicity, their efficiency varies greatly from one IT to another. Obviously, the most attractive use of the IT is its in vivo application as a therapeutic agent for cancer. However, the results of initial trials in which ITS have been used therapeutically in animals showed, with one exception [3], that, even when the tumor load was small, the anti-cancer effects were relatively unimpressive [lo, 111. To improve the cancerocidal action of these conjugates, a detailed examination of potential agonists of the action of IT in vivo is needed. Site-specific toxin delivery requires the fulfillment of two sequential steps. First, IT should localize on the desired target site and subsequently bind to the relevant cell surface antigen; secondly, the toxin subunit should be translocated into the cytoplasm to inhibit protein synthesis and thus induce cell death.It has been shown from in vitro studies that to achieve high efficiency of this latter step it is necessary to administer most ITS together with IT enhancers. It has recently been demonstrated that IT enhancers that promote RTA delivery into the cytosol could also be effective in vivo (unpublished work). In order to achieve efficient binding, the IT must remain in the systemic circulation, in its active form, a sufficiently long time and at a sufficie...

Conjugates (immunotoxins) comprising ricin A-chain and monoclonal antibody 96.5, which is specific for human melanoma-associated antigen p97, inhibited protein synthesis and colony formation of cultured human melanoma cells that expressed more than 80,000 molecules of p97 per cell. Cells expressing fewer than 5,000 molecules of p97 were not killed. The presence of 10 mM ammonium chloride significantly increased the efficiency of the immunotoxin, tumor cells expressing high levels of p97 being killed at immunotoxin concentrations as low as 10(-10) M.

Superposition of physical states in the wave function of quantum mechanics is difficult to transpose to the macrocosm, as illustrated by "Schrödinger's cat" thought experiment. Nevertheless, in this example, consciousness does not seem to be shown in its complete reality, when evaluated from a biological view-point. Although consciousness functions with reality systems, it also uses potentiality systems, which essentially consist in superposition of several probable situations. Some examples of superposition in consciousness are described, to illustrate the requirement of potentiality systems in order to predict situations in the future or to complement events in the past. Incomplete observations, such as lacking time or space coordinates, automatically induce potentiality systems in the consciousness, in order to complete the lacking coordinates b y only potential but most probable coordinates. In contrast, reality systems are only present, when complete observations with exact time and space coordinates can be obtained. Potentiality systems in human consciousness also show the characteristics of Heisenberg's uncertainty principle, as well as non-locality and entanglement and are compatible with interfering conditions. Superposition in potentiality systems is an essential function of consciousness and is the only way to allow a perception of future and past events. The basic concept of superposition without corresponding mathematical formalism, seems demonstrate partial isomorphism in the larger sense of Douglas Hofstadter, between consciousness and quantum mechanics.