New insights into the possible role of bacteriophages in host defense and disease

Hoc protein regulates the biological effects of T4 phage in mammals

We previously investigated the biological, non-antibacterial effects of bacteriophage T4 in mammals (binding to cancer cells in vitro and attenuating tumour growth and metastases in vivo); we selected the phage mutant HAP1 that was significantly more effective than T4. In this study we describe a non-sense mutation in the hoc gene that differentiates bacteriophage HAP1 and its parental strain T4. We found no substantial effects of the mutation on the mutant morphology, and its effects on electrophoretic mobility and hydrodynamic size were moderate. Only the high ionic strength of the environment resulted in a size difference of about 10 nm between T4 and HAP1. We compared the antimetastatic activity of the T2 phage, which does not express protein Hoc, with those of T4 and HAP1 (B16 melanoma lung colonies). We found that HAP1 and T2 decreased metastases with equal effect, more strongly than did T4. We also investigated concentrations of T4 and HAP1 in the murine blood, tumour (B16), spleen, liver, or muscle. We found that HAP1 was rapidly cleared from the organism, most probably by the liver. Although HAP1 was previously defined to bind cancer cells more effectively (than T4), its rapid elimination precluded its higher concentration in tumours.

Effects of bacteriophages on free radical production and phagocytic functions

Reactive oxygen species (ROS) play a major role in mediating antibacterial functions of phagocytic cells. However, excessive ROS production may cause oxidative stress and tissue damage. Uncompensated ROS release has been implicated in a variety of disorders. Novel means of controlling elevated ROS production are urgently needed. We showed that homologous but not the heterologous phages inhibited, in a dose dependent manner, the degree of chemiluminescence in phagocytes induced by Escherichia coli. Treatment of the cells with the phages alone resulted in a small increase in ROS production. Homologous phages also facilitated phagocytosis when preincubated with bacteria. On the other hand, both homologous and heterologous phages inhibited phagocytosis following preincubation with phagocytic cells. The treatment of infected and uninfected mice with phages did not significantly alter the rate of phagocytosis by blood granulocytes and monocytes. In conclusion, we showed that bacteriophages can decrease ROS production by phagocytes. Although in some in vitro experimental models the phages tended to diminish phagocytosis, this phenomenon may be of little significance in clinical situations, since the process of eliminating bacteria in phage-treated patients is predominantly accomplished by both phages and phagocytes.

Bacterial viruses against viruses pathogenic for man?

In this review, we discuss possible models of bacteriophage-virus interactions. The first is based on the mechanism by which phages may interact indirectly with viruses. Its essence is that bacteriophage-derived nucleic acid may inhibit pathogenic virus infection. It seems that this phenomenon can be partly explained on the basis of interferon induction. We also discuss a study by Borecky's group (conducted over two decades ago) which provided some clinical data on the effectiveness of the application of native bacteriophage RNA in the treatment of viral infections. The second interaction model is based on the direct competition of bacteriophages and viruses for cellular receptors for viral cell-entry. The use of bacteriophages as inducers or displayers of antibodies with antiviral action is considered as the third model. In this part of the article, we also discuss other data and hypotheses on conceivable interactions between bacterial and animal viruses. As our current supply of antiviral drugs is quite limited, using natural agents such as bacteriophages as a weapon against pathogenic viruses could be an attractive and cost-efficient alternative, and further studies are urgently needed to test this possibility.

Possible association between phages, Hoc protein, and the immune system

Mammals have become "an environment" for enterobacterial phage life cycles. Therefore it could be expected that bacteriophages adapt to them. This adaptation must comprise bacteriophage proteins. Gp Hoc seems to have significance neither for phage particle structure nor for phage antibacterial activity. It is evidently not necessary for the "typical" antibacterial actions of bacteriophages. But the rules of evolution make it improbable that gp Hoc really has no function, and non-essential genes of T4-type phages are probably important for phages' adaptation to their particular lifestyle. More interesting is the eukaryotic origin of gp Hoc: a resemblance to immunoglobulin-like proteins that reflects their evolutionary relation. Substantial differences in biological activity between T4 and a mutant that lacks gp Hoc were observed in a mammalian system. Hoc protein seems to be one of the molecules predicted to interact with mammalian organisms and/or modulate these interactions.

New insights into the possible role of bacteriophages in transplantation

Due to the increasing prevalence of drug-resistant bacterial infections in the "post-antibiotic era," bacteriophages (bacterial viruses, BP) may be useful to administer to transplant recipients without exposing them to an increased risk of rejection, which occurs consequent to some viral infections. Herein we present evidence that at least some coliphages (T4) do not pose such risk. Interestingly, they may produce immunosuppressive effects extending transplant survival. Our data suggest that BP may be used in clinical transplantation to treat drug-resistant bacterial infections and perhaps as an adjunct to immunosuppressive therapy.

Selective targeting of cancer cells using synthetic peptides

To establish efficient and reliable therapeutic delivery into cancer cells, a number of delivery agents and concepts have been investigated in the recent years. Among many improvements in targeted and controlled delivery of therapeutics, cell-targeting peptides have emerged as the most valuable non-immunogenic approach to target cancer cells. Peptides can be incorporated into multicomponent gene-delivery complexes for cell-specific targeting. In contrast to larger molecules such as monoclonal antibodies, peptides have an excellent tumor penetration, which make them ideal carriers of therapeutics to the site of primary tumor and the distant metastatic sites. Here we give an update on the progress made during the last two years on the identification and potential of specific synthetic tumor targeting peptides.