Genetic and Chemical Capsid Modifications of Adenovirus Vectors to Modulate Vector-Host Interactions

Adenovirus-based vectors are playing an important role as efficacious genetic vaccines to fight the current COVID-19 pandemic. Furthermore, they have an enormous potential as oncolytic vectors for virotherapy and as vectors for classic gene therapy. However, numerous vector-host interactions on a cellular and noncellular level, including specific components of the immune system, must be modulated in order to generate safe and efficacious vectors for virotherapy or classic gene therapy. Importantly, the current widespread use of Ad vectors as vaccines against COVID-19 will induce antivector immunity in many humans. This requires the development of strategies and techniques to enable Ad-based vectors to evade pre-existing immunity. In this review article, we discuss the current status of genetic and chemical capsid modifications as means to modulate the vector-host interactions of Ad-based vectors.

Polymer-ritonavir derivate nanomedicine with pH-sensitive activation possesses potent anti-tumor activity in vivo via inhibition of proteasome and STAT3 signaling

Drug repurposing is a promising strategy for identifying new applications for approved drugs. Here, we describe a polymer biomaterial composed of the antiretroviral drug ritonavir derivative (5-methyl-4-oxohexanoic acid ritonavir ester; RD), covalently bound to HPMA copolymer carrier via a pH-sensitive hydrazone bond (P-RD). Apart from being more potent inhibitor of P-glycoprotein in comparison to ritonavir, we found RD to have considerable cytostatic activity in six mice (IC₅₀ ~ 2.3-17.4 μM) and six human (IC₅₀ ~ 4.3-8.7 μM) cancer cell lines, and that RD inhibits the migration and invasiveness of cancer cells in vitro. Importantly, RD inhibits STAT3 phosphorylation in CT26 cells in vitro and in vivo, and expression of the NF-κB p65 subunit, Bcl-2 and Mcl-1 in vitro. RD also dampens chymotrypsin-like and trypsin-like proteasome activity and induces ER stress as documented by induction of PERK phosphorylation and expression of ATF4 and CHOP. P-RD nanomedicine showed powerful antitumor activity in CT26 and B16F10 tumor-bearing mice, which, moreover, synergized with IL-2-based immunotherapy. P-RD proved very promising therapeutic activity also in human FaDu xenografts and negligible toxicity predetermining these nanomedicines as side-effect free nanosystem. The therapeutic potential could be highly increased using the fine-tuned combination with other drugs, i.e. doxorubicin, attached to the same polymer system. Finally, we summarize that described polymer nanomedicines fulfilled all the requirements as potential candidates for deep preclinical investigation.

The dawning era of polymer therapeutics

As we enter the twenty-first century, research at the interface of polymer chemistry and the biomedical sciences has given rise to the first nano-sized (5-100 nm) polymer-based pharmaceuticals, the 'polymer therapeutics'. Polymer therapeutics include rationally designed macromolecular drugs, polymer-drug and polymer-protein conjugates, polymeric micelles containing covalently bound drug, and polyplexes for DNA delivery. The successful clinical application of polymer-protein conjugates, and promising clinical results arising from trials with polymer-anticancer-drug conjugates, bode well for the future design and development of the ever more sophisticated bio-nanotechnologies that are needed to realize the full potential of the post-genomic age.

Targeting of human and mouse T-lymphocytes by monoclonal antibody-HPMA copolymer-doxorubicin conjugates directed against different T-cell surface antigens

Binding of HPMA copolymer-conjugated doxorubicin targeted with monoclonal antibodies directed against various T-cell surface receptors, i.e. Thy1.2 (CDw90), I-A (MHC class II. glycoprotein), L3T4 (CD4), IL-2R (CD25) and CD3, is considerably increased in Con A stimulated T-lymphocytes. FACS analysis showed that the binding is most intensive with anti-Thy1.2 and anti-L3T4 targeted derivatives and it is proportional to the antiproliferative effect of the antibody-targeted drug. No binding and no antiproliferative capacity was observed after in vitro incubation of mouse T-cells with a nonspecific mouse IgG-HPMA-DOX conjugate. [3H]-TdR incorporation was inhibited considerably more in Con A stimulated T-cell culture and in EL4 mouse T-cell lymphoma as compared with the culture of nonactivated T-lymphocytes. This proves that intensively proliferating cells are more susceptible to the inhibitory action of an antibody-targeted drug. The cytotoxic efficacy of HPMA copolymer with GlyPheLeuGly or GlyLeuPheGly side-chains to which the drug is conjugated was superior to HPMA copolymer with GlyPheGly or GlyLeuGly side-chains. However, there is no direct correlation between the rate of in vitro drug release and the in vitro cytotoxicity of the respective conjugates. This suggests that the rate of drug release from the conjugate is only one factor responsible for the pharmacological efficacy of the preparation. Furthermore, we detected substantial and prolonged inhibition of proliferation of Con A activated T-cells only if doxorubicin was injected in vivo in the form of an anti-Thy1.2-targeted conjugate.

HPMA-based biodegradable hydrogels containing different forms of doxorubicin. Antitumor effects and biocompatibility

Novel hydrogels based on N-(2-hydroxypropyl)methacrylamide (HPMA) and N,O-dimethacryloylhydroxylamine containing either doxorubicin (DOX) or water-soluble HPMA carrier-bound doxorubicin (P-GlyPheLeuGly-DOX; HPMA-DOX) were synthesized. The cross-linkages are susceptible to hydrolytic cleavage at physiological pH 7.4. Hydrogels in the form of rods or discs loaded with DOX or P-GlyLeuGly-DOX were implanted subcutaneously on the back of C57BL/10 mice on day 1 or on day 9 after inoculation with EL4 mouse T-cell lymphoma. The implanted hydrogels varied in the total load of DOX and rate of hydrolysis, which is dependent on the crosslinking density of the gels. The effect of HPMA based hydrogels containing DOX or HPMA carrier-bound DOX on tumor growth, animal life span, leukocyte populations in peripheral blood and bone marrow function evaluated by reticulocyte count was investigated. It was shown that: a) DOX and HPMA carrier-bound DOX administered in the form of HPMA-based hydrogels has better antitumor activity against experimental EL4 mouse T-cell lymphoma than soluble forms of the drug, b) hydrogels with shorter degradation rate (16-17 h) show better antitumor activity than hydrogels with longer duration time (48-52 h), c) the therapeutic effect of hydrogels with rate 16-17 h is directly related to the doxorubicin content; the higher the doxorubicin content, the better antitumor activity, d) the gel containing free doxorubicin showed significant antitumor activity even when implanted on day 9, i.e., in the time when tumor growth is already established, e) the hydrogel matrix without drug does not induce release of IL-1 or IL-6 into peripheral blood, does not induce formation of antibodies, and it is not mitogenic. Use of doxorubicin in the form of HPMA-based hydrogels allows a several-fold increase in the administered dose compared to soluble forms without detectable serious toxic side-effects.

Morphology of rat kidney and thymus after native and antibody-coupled cyclosporin A application (reduced toxicity of targeted drug)

This study compares the toxic effects of native cyclosporia A (CyA) with those of targeted CyA that is conjugated with the anti-rat-thymocyte antibody of rabbit origin via the N-(2-hydroxypropyl)methacrylamide (HPMA) carrier bearing digestible, reactive oligopeptide side chains. Ten toxic doses of native CyA (50 mg/kg i.p.) given to young adult rats in the course of 14 d produced a severe renal lesion-diffuse microvacuolization of the proximal tubules in the deep cortex, and hypergranulation of juxtaglomerular regions. Severe atrophy of the thymic medulla was documented by morphometry. In the cortex the epithelial reticular (but not deep interdigitating) cells showed ultrastructural signs of severe degeneration and lysis. The immature CD4+8+ double-positive cortical lymphocytes were preserved whereas the single-positive medullary thymocytes were greatly depleted; there was also a restriction of MHC class II antigen expression in the medulla. The number of medullary B cells was increased. The cytokeratin net was focally shrunken in the cortex and almost negative in the medulla, with loss of Hassall's corpuscles. After ten corresponding doses of antibody-targeted conjugated CyA no damage to the renal tubules and arterioles appeared and the antiGBM or immune-complex deposition was absent. The thymus had a normal medulla with numerous mature thymocytes and the cortical epithelial reticulum remained well preserved. Thus, the main toxic effects of CyA could be eliminated by targeting. The T-cell-targeted drug was tested for preserved immunosuppressive properties and non-toxic character of HPMA copolymer carrier.

Targeting of drugs to cell surface receptors

The new approach to the treatment of cancer or to immunomodulation is drug targeting. The effort to achieve either an absolute or a relative amplification of the tumoricidal effect of anticancer drugs through increased generation or acquisition of reactive molecules at the tumor site or a reduction of the toxic molecules available to the periphery has led to a number of strategies. Among them are (1) targeting using antibodies to their fragments, hormones, carbohydrates, and growth factors; (2) retargeting using bispecific antibodies; (3) construction of chimeric genes; (4) streptavidin-biotin based immunotherapy; (5) prodrug activation strategies (ADEPT); (6) antibody-targeted superantigens; and (7) gene delivery for the purpose of gene therapy.

Antibody-targeted polymer-bound drugs

Drug targeting is an attractive new approach to killing cancer cells while leaving normal tissue unharmed. Recently we have developed a new generation of antibody-targeted immunosuppressive (cyclosporin A) and cytostatic (daunomycin, doxorubicin) drugs and photosensitizers (chlorin e6) effective in vitro and in vivo. The drugs and the targeting antibody (polyclonal and monoclonal) are conjugated to the oligopeptidic side chains of a water-soluble synthetic carrier, copolymer of N-(2-hydroxypropyl)methacrylamide. The composition of the side chains ensures the stability of the linkage between the drug and the polymeric carrier in the bloodstream and its intralysosomal degradability which is a prerequisite for the pharmacological activity of the preparation. Antibody-targeted polymer bound drugs show considerably decreased hepatotoxicity, cardiotoxicity, myelotoxicity and nephrotoxicity. Two adriamycin-HPMA copolymers are in Phase I/II clinical trials in United Kingdom.