Cytoplasmic-delivery of polyinosine-polycytidylic acid inhibits pancreatic cancer progression increasing survival by activating Stat1-CCL2-mediated immunity

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer without effective therapies and with poor prognosis, causing 7% of all cancer-related fatalities in the USA. Considering the lack of effective therapies for this aggressive cancer, there is an urgent need to define newer and more effective therapeutic strategies. Polyinosine-polycytidylic acid (pIC) is a synthetic double-stranded RNA (dsRNA) which directly activates dendritic cells and natural killer cells inhibiting tumor growth. When pIC is delivered into the cytoplasm using polyethyleneimine (PEI), pIC-PEI, programmed-cell death is induced in PDAC. Transfection of [pIC]PEI into PDAC cells inhibits growth, promotes toxic autophagy and also induces apoptosis in vitro and in vivo in animal models.

METHODS

The KPC transgenic mouse model that recapitulates PDAC development in patients was used to interrogate the role of an intact immune system in vivo in PDAC in response to [pIC]PEI. Antitumor efficacy and survival were monitored endpoints. Comprehensive analysis of the tumor microenvironment (TME) and immune cells, cytokines and chemokines in the spleen, and macrophage polarization were analyzed.

RESULTS

Cytosolic delivery of [pIC]PEI induces apoptosis and provokes strong antitumor immunity in vivo in immune competent mice with PDAC. The mechanism underlying the immune stimulatory properties of [pIC]PEI involves Stat1 activation resulting in CCL2 and MMP13 stimulation thereby provoking macrophage polarization. [pIC]PEI induces apoptosis via the AKT-XIAP pathway, as well as macrophage differentiation and T-cell activation via the IFNγ-Stat1-CCL2 signaling pathways in PDAC. In transgenic tumor mouse models, [pIC]PEI promotes robust and profound antitumor activity implying that stimulating the immune system contributes to biological activity. The [pIC]PEI anti-PDAC effects are enhanced when used in combination with a standard of care (SOC) treatment, that is, gemcitabine.

CONCLUSIONS

In summary, [pIC]PEI treatment is non-toxic toward normal pancreatic cells while displaying strong cytotoxic and potent immune activating activities in PDAC, making it an attractive therapeutic when used alone or in conjunction with SOC therapeutic agents, potentially providing a safe and effective treatment protocol with translational potential for the effective therapy of PDAC.

Tricking melanoma to self-digest: a deal of a meal!

Melanoma cells acquire multiple genetic and epigenetic alterations that promote their metastasis and resistance to available therapies. In this issue of Cancer Cell, Soengas and colleagues reveal that the induction of endosome-mediated autophagy results in efficient melanoma cell death, thereby offering new potential means for treatment of this devastating cancer.

Interferon inducer, polyriboguanylic.polyribocytidylic acid, inhibits experimental hepatic metastases in mice

The antitumour activity of an interferon inducer, the double-stranded complex of polyriboguanylic.polyribocytidylic acid was studied on murine lymphosarcoma LS/BL. The antitumour effect was determined with the aid of an experimental liver-colony model and compared to that exhibited by another synthetic RNA, polyriboinosinic.polyribocytidylic acid. We found that both polynucleotide complexes decreased the number of liver colonies and prolonged the survival of the tumour-bearing mice. This effect was only observed if the complexes were applied in an appropriate dose schedule which included the administration of the drug prior to tumour cell inoculation and subsequent continuous treatment. We have also verified that the polynucleotide complexes did not exert their antitumour effect by a direct action on tumour cells.

[Dependence of the antiviral activity of the poly(G).poly(C) complex on the size of the continuous poly(C)segments]

Modification of poly(C) by various frequency treatment with adenosine non-complementary to guanosine has produced poly(G) X poly (C.A) complexes with continuous double-stranded areas the length of which is determined by C/A ratio. Studies of the antiviral activity of poly(G).poly(C,A) complexes with C/A from 10:1 to 90:1 and poly(G).poly(C) in vesicular stomatitis virus-infected chick embryo cell cultures and in experimental tick-borne encephalitis of mice demonstrated that the maximum activity is achieved at an average lengths of double-stranded areas of 90 nucleotide pairs. At the same time, a low but statistically significant antiviral activity is observed at a length of double-stranded areas of 10-30 nucleotide pairs.

[Evaluation of the size of the continuous poly(G) site necessary for the biological activity of the poly(G).poly(C) complex]

On the basis of synthesis of a series of poly(G, A).poly(C) copolymers with changing G:A ratio from 15:1 to 90:1 and trials of their biological activity in comparison with poly(G).poly(C), the size of poly(G) in it was evaluated within the range of a continuous double-stranded area necessary for the activity. The antiviral activity close to that of poly(G).poly(C) in experimental tick-borne encephalitis of mice and vesicular stomatitis virus infection of chick embryo cells was found only in poly(G,A).poly(C) complexes with a G:A ratio equal to or higher than 90:1. Consequently, the high activity of poly(G).poly(C) is present at an average length of poly(G) equal to 90-100 nucleotides within the limits of the continuous double-stranded area.

[Effect of virazole on the antiviral activity of poly(G) X poly(C) and other polyribonucleotide interferonogens]

The effect of virazole on the antiviral activity of poly (G) X poly (C), poly (G, A) X X poly (C) and poly(G, I) X poly (C) was studied in cell cultures and on mice. It was shown that virazole in concentrations not sufficient for significant inhibition of the development of vesicular stomatitis virus or Sindbis virus in chick embryo cell cultures markedly increased the antiviral effect and allowed decreasing the minimum effective doses of the synthetic polyribonucleotide complexes with respect to the above viruses. Combined administration of poly (G) X poly (C) and virazole to mice 1-2 or 24 hours after infection with tick-borne encephalitis virus provided a much more pronounced decrease in the death rate of the animals than the use of the interferonogen alone. Virazole per se was little active and had no significant effect on the intensity of interferonogenesis promoted by the use of poly (G) X poly (C). A possibility of successful therapy of viral infections with polyribonucleotide interferonogens in combination with virazole or other chemotherapeutic drugs with broad antiviral spectrum is discussed.

[Combined antiviral effect of synthetic polyribonucleotide interferonogens and specific antiviral antibodies in arbovirus infections]

A model of tick-borne encephalitis in BALB/c mice was used to investigate the protective anti-viral effect of an interferon inducer, poly(G).poly(C), and specific gamma-globulin administered to the animals together or separately in small doses 24 hours before or after virus inoculation. Administration to the animals of poly(G).poly(C) alone or gamma-globulin alone was shown to produce a poor protective effect. Simultaneous administration of both preparations resulted in a significant decrease of mouse mortality after infection. As a result of the pretreatment of chick embryo cell cultures with poly(G).poly(C) before inoculation and the addition of specific immune serum to the agar overlay after the Sindbis virus inoculation, its multiplication was inhibited much more than after treatment of the cells with interferon inducer alone or antibody alone. Possible mechanisms of the observed additive antiviral effects of the interferon inducer and antibody, including those associated with the influence on the virus-induced interferon production, as well as the possibility of their combined use for the prevention and treatment of viral infections are discussed.

[Protective action of double-stranded complexes--interferon inducers in encephalomyocarditis in mice]

Interferon inducers, dsRNA and poly (G) X poly (C) ( polyguacyl ), injected into mice intraperitoneally induced interferon formation, the maximal activity being equal to 640-1280 U/ml. Antiviral effect of the inducers was studied upon intraperitoneal and intracerebral injections. Both polyguacyl and dsRNA exerted a marked antiviral action against infection induced by murine encephalomyocarditis virus. The most powerful effect was attained when the inducers were injected 24 or 4 h before challenge. The protective action was produced by polyguacyl and dsRNA even after intracerebral infection. There is a good agreement between the interferon-inducing and antiviral activity of interferon inducers. The data obtained demonstrate the fitness of experimental encephalomyocarditis of mice for testing interferon inducers.

[Immunostimulating effect of interferon inducers]

The effect of interferon inducers on the immune response to vaccination was determined. The prophylactic effect of interferon inducers in combination with vaccines was determined with regard to experimental influenza, the therapeutic effect with regard to rabies and tick-borne encephalitis. Despite the differences in the experimental design (administration of the inducers before, after, or together with vaccines), the additive or synergistic effect was regularly observed with a 2-6-fold increase in the level of protection of the animals infected with the appropriate viruses as compared with the use of vaccines or interferon inducers separately. The protective effect depends a lot on the concentration, site and time of inoculation of the preparations, multiplicity of infection, and some other conditions.

[Thermoactivation of poly(G).poly(C): a description of the effect and its hypothetical mechanism]

Heating of poly(G).poly(C) complex solutions at a temperature about 100 degrees C was shown to overcome a decrease in the antiviral and interferon-inducing activity of the preparations which were obtained at relatively high concentrations of polynucleotides from poly(G) stored in solution, or were stored frozen themselves. These unfavourable conditions contributed to stabilization of the poly(g) secondary structure and decrease in the degree of regularity of the complex molecules. The results suggest that thermal activation of such poly (G). poly(C) preparations occurred in 2 stages by melting residual free regions of poly(G) and their subsequent interaction with poly(C) with formation of a more regular complex.

Antiviral effects of single-stranded polynucleotide inhibitors of the influenza virion-associated transcriptase against influenza virus infection of hamsters and ferrets

Administration of a single-stranded polynucleotide copolymer containing 9% cytidine residues and 91% 4-thiouridine residues [poly(C,S4U10)], a known potent inhibitor of the virion transcriptase of influenza viruses, suppressed the amount of virus recoverable from the nasal washes of influenza virus-infected hamsters and ferrets. The incidence of sneezing and nasal discharge in infected ferrets was also reduced. In hamsters, poly(C,S4U10) was more effective than amantadine-HCl or Virazole. Polyinosinic acid in combination with poly-5-hydroxy cytidylic acid also had anti-influenza effects. Poly(C,S4U10) annealed to polyadenylic acid was not effective, nor was the double-stranded polymer (polyinosinic acid) . (polycytidylic acid) even when complexed with carboxymethylcellulose and polylysine. No toxic effects of poly(C,S4U10) were apparent in the treated hamsters and ferrets, and high doses (greater than or equal to 2.86 g/kg) administered intraperitoneally to mice produced no adverse effects.

Studies on the mode of action of single-stranded polynucleotides which are antiviral against encephalomyocarditis virus infection of mice

Poly(dI) and poly(dC) administered separately or sequentially show no antiviral effects against EMC virus infection of mice, whereas poly(rI) and poly(rC) are antiviral in such treatment regimens without evidence of interferon induction. The antiviral effects of poly(rI) and poly(rC) appear to depend on single-strandedness because their antiviral effects are decreased by annealing to poly(dC) and poly(dI) respectively. This decrease in antiviral effect would not seem to be due to an adverse effect of polydeoxyribonucleotides on EMC virus infection because the polydeoxyribonucleotides have no effect on the antiviral activity of another single-stranded RNA, E. coli tRNA.

[Interferon-inducing and protective action of polyguacyl in an experimental influenza infection]

A comparative study of the interferon-inducing and anti-influenza activity of polyguacyl, an interferon inducer, given to human volunteers intranasally and as an aerosol, was carried out. The induction of endogenous interferon in the blood to 100-127 units/ml was observed only after intranasal administration of 5 mg polyguacyl. By both routes of administration the inducer did not diminish the implantation of the virus and development of postvaccination reactions in volunteers to intranasal administration of live influenza A (H1N1) vaccine.

[Trial of polyguacyl safety and tolerance]

The results of studies of the antiviral and interferon-inducing activity of the synthetic interferon inducer polyguacyl in white mice as well as the results of the study of safety and tolerance of this drug given to human subjects as aerosol and intranasally are presented. Both modes of administration to mice induced production of endogenous interferon, although after intranasal inoculation high interferon titres in the blood serum of the animals were observed for longer periods of time, whereas after aerosol administration interferon disappeared more rapidly. Significant antiviral protection was achieved only by the intranasal administration of the inducer resulting in 84.0% survival of the animals challenged with the mouse-adapted influenza A/Aichi virus. Clinical trials of polyguacyl in human volunteers demonstrated the safety and good tolerance of this drug given both as aerosol and intranasally.

[Clinical trials with mercapto polycytidylic acid in the treatment of acute childhood leukemia (author's transl)]

Mercapto Polycytidylic acid (MPC) is a potent inhibitor of oncornaviral reverse transcriptase. The fact that this enzyme has been found in human leukemic cells, has let to the clinical trials of MPC in the treatment of childhood acute leukemia. This report discribes the first pilot clinical trial on 23 patients. The results are encouraging, and have let to a second pilot study including other clinical centers on the clinical efficacy of MPC in the treatment of leukemia.

The direct anti-viral activity of single stranded polyribonucleotides. I. Potentiation of activity by mixtures of polymers which do not anneal

Mixtures containing equal masses of polyinosinic acid (poly (I)) and copoly­mers containing poly(5-hydroxycytidylic acid), (poly(ho 5 C) copolymers), protect mice against encephalomyocarditis (e. m. c.) virus infection and the protective effect is greatest 6 h before infection. The batches of poly(ho 5 C) copolymer used in these studies were obtained by bromine water treat­ ment of polycytidylic acid (poly(C)) and contained cytidine, bromocytidine and hydroxycytidine residues with the latter component comprising between 50% and 81% of the total residues in different preparations. These copolymers were used in solution or in a gelled form obtained by freezing in the absence of salt. Evidence is presented which shows that double stranded complexes do not form when the poly(ho 5 C) copolymers are mixed with poly(I). Protection of mice with mixtures of poly(I) and poly(ho 5 C) copolymer was slightly greater than had previously been observed with sequential administration of poly(I) followed by poly(C) or the homopolymer form of poly(ho 5 C). The gelled form of poly(ho 5 C) copolymer conferred slightly greater protection than poly(ho 5 C) copolymer used in the soluble state. The percentage of hydroxycytidine residues in the copolymers did not affect the degree of protection conferred by mixtures of the copolymers with poly (I). Administration of mixtures of poly(I) and soluble poly (ho 5 C) copoly­mer by the intraperitoneal route was more effective than the intravenous route when high doses were used at 6 h before infection. At this time, 200 μg/mouse of a mixture of poly (I) and poly(ho 5 C) copolymer was as protec­tive as 60μg/mouse poly(I:C) but the toxicity of mixtures of poly(I) and poly(ho 5 C) was less than one tenth that of poly(I:C). The mechanism of the protective effect with single stranded polynucleo­ tides cannot yet be stated with confidence. However, the protection by mixtures of poly(I) and poly(ho6C) copolymer does not seem to be through interferon production. Serum from mice treated with the nurture of polynucleotides cannot confer protection on other mice subsequently exposed to infection. Further, the mixtures do not hypo-reactivate the protective effect of poly (I : C) treatment which would have been expected had both effects had a common basis in the interferon phenomenon. Moreover, treatment with the mixture does not result in a stimulation of immune response produced by e. m. c. virus infection.

The direct anti-viral activity of single stranded polyribonucleotides. II. The effect of molecular size and the involvement of cellular receptors

We have examined the dependence on molecular size of various singlestranded polynucleotides that protect mice against encephalomyocarditis (e. m. c.) virus infection in the absence of circulating interferon. Sequential treatment of mice with various sizes of poly(I) at 8 h before infection followed by poly(C) at 4 h before infection conferred highly significant protection against e. m. c. virus infection. At 100 μg/mouse of both the polynucleotides significant protection occurred with all the sizes of poly(I) examined but the degree of protection decreased with poly(I) smaller than S 20, w of 6.13. In this case a decrease in the size of the poly(C) component lowered the degree of protection. On lowering the polynucleotide doses to 20 μg/mouse, significant protection was achieved only when the poly(I) had an S 20, w value equal to or greater than 4.39 and again the degree of protection conferred was related to the size of poly( C). Mixtures of poly(I) and a copolymer containing 5-hydroxycytidylic acid, here designated poly(ho 5 C) copolymer, also conferred significant protection against infection at 8 h before infection providing that the two components were sufficiently large. We only examined the anti-viral activity of mixtures containing equal masses of poly (I) and the poly(ho 5 C) copolymer at a dose of 20 μg/mouse of each polynucleotide. With poly(l) of all sizes examined ( S 20,W between 2.50 and 12.5) significant protection occurred when the poly(ho 5 C) copolymer had an S 20,W value of 8.29 or greater. With poly(ho 5 C) copolymer preparations of progressively smaller sizes significant protection only occurred with progressively larger sizes of poly(I). These results are considered in relation to other phenomena, including interferon induction by the double stranded complex, poly(I:C), showing dependence on the size of poly(i).

Anti-viral activity of single-stranded homopolynucleotides against encephalomyocarditis virus and Semliki Forest virus in adult mice without interferon induction

Single administrations of poly C or poly I are anti-viral against infections of encephalomyocarditis (EMC) and Semliki Forest virus (SFV) in mice but poly U and poly A are not. The degree of protection is dose-dependent and mice which die do so at a later time when untreated controls even in a strain of mouse in which the time of death is not dependent on the dose of virus given. No circulating interferon is found after treating mice with poly C or poly I even at polynucleotide doses which give the same degree of protection as the interferon inducer, poly I:C. Several additional features distinguish the protection by poly C and poly I from interferon induction: the effect is low 24h before infection and maximal 6 h before infection, the effect is short-lived and mice do not show hypo-reactivation to repeated treatment. Limited treatment of mice with poly I:C, interferon or poly C before infection itself results in additional protection when poly C is also administered after infection, indicating that poly C has an effect after onset of virus replication. After infection poly C and poly I are both more effective by the intravenous route but before infection they are most effective when administered by the same route as the virus. Quantitative comparisons of the protective effects of poly C, poly I and the interferon inducer, poly I:C, are possible from dose response curves of the polynucleotides at different times relative to infection and by different routes of administration. The results are considered in relation to the presence of homopolyribonucleotide tracts in the viral genomes and effects on the reticulo-endothelial system of the mice.