Poly-l-glutamic acid modification modulates the bio-nano interface of a therapeutic anti-IGF-1R antibody in prostate cancer.

Modifying biological agents with polymers such as polyethylene glycol (PEG) has demonstrated clinical benefits; however, post-market surveillance of PEGylated derivatives has revealed PEG-associated toxicity issues, prompting the search for alternatives. We explore how conjugating a poly-l-glutamic acid (PGA) to an anti-insulin growth factor 1 receptor antibody (AVE1642) modulates the bio-nano interface and anti-tumor activity in preclinical prostate cancer models. Native and PGA-modified AVE1642 display similar anti-tumor activity in vitro; however, AVE1642 prompts IGF-1R internalization while PGA conjugation prompts higher affinity IGF-1R binding, thereby inhibiting IGF-1R internalization and altering cell trafficking. AVE1642 attenuates phosphoinositide 3-kinase signaling, while PGA-AVE1642 inhibits phosphoinositide 3-kinase and mitogen-activated protein kinase signaling. PGA conjugation also enhances AVE1642's anti-tumor activity in an orthotopic prostate cancer mouse model, while PGA-AVE1642 induces more significant suppression of cancer cell proliferation/angiogenesis than AVE1642. These findings demonstrate that PGA conjugation modulates an antibody's bio-nano interface, mechanism of action, and therapeutic activity.

Poly(L-glutamic acid)-co-poly(ethylene glycol) block copolymers for protein conjugation.

Poly(L-glutamic acid)-co-poly(ethylene glycol) block copolymers (PLE-PEG) are here investigated as polymers for conjugation to therapeutic proteins such as granulocyte colony stimulating factor (G-CSF) and human growth hormone (hGH). PLE-PEG block copolymers are able to stabilize and protect proteins from degradation and to prolong their residence time in the blood stream, features that are made possible thanks to PEG's intrinsic properties and the simultaneous presence of the biodegradable anionic PLE moiety. When PLE-PEG copolymers are selectively tethered to the N-terminus of G-CSF and hGH, they yield homogeneous monoconjugates that preserve the protein's secondary structure. During the current study the pharmacokinetics of PLE10-PEG20k-G-CSF and PLE20-PEG20k-G-CSF derivatives and their ability to induce granulopoiesis were, respectively, assessed in Sprague-Dawley rats and in C57BL6 mice. Our results show that the bioavailability and bioactivity of the derivatives are comparable to or better than those of PEG20k-Nter-G-CSF (commercially known as Pegfilgrastim). The therapeutic effects of PLE10-PEG20k-hGH and PLE20-PEG20k-hGH derivatives tested in hypophysectomized rats demonstrate that the presence of a negatively charged PLE block enhances the biological properties of the conjugates additionally with respect to PEG20k-Nter-hGH.

A non-covalent antibody complex for the delivery of anti-cancer drugs.

Antibody drug conjugates (ADCs), which are obtained by coupling a potent cytotoxic agent to a monoclonal antibody (mAb), are traditionally bound in a random way to lysine or cysteine residues, with the final product's heterogeneity having an important impact on their activity, characterization, and manufacturing. A new antibody drug delivery system (ADS) based on a non-covalent linkage between a Fc-binding protein, in this case Protein A or Protein G, and a mAb was investigated in the effort to achieve greater homogeneity and to create a versatile and adaptable drug delivery system. Recombinant staphylococcal Protein A and streptococcal Protein G were chemically PEGylated at the N-terminus with a 5 kDa and a 20 kDa PEG, respectively, yielding two monoconjugates with a mass of ≈50 and ≈45 kDa. Circular dichroism studies showed that both conjugates preserved secondary structures of the protein, and isothermal titration calorimetry experiments demonstrated that their affinity for mAb was approximately 107 M-1. Upon complexation with a mAb (Trastuzumab or Rituximab), in vitro flow-cytometry analysis of the new ADSs showed high selectivity for the specific antigen expressing cells. In addition, the ADS complex based on Trastuzumab and Protein G, conjugated with a heterobifunctional 20 kDa PEG carrying the toxin Tubulysin A, had a marked cytotoxic effect on the cancer cell line overexpressing the HER2/neu receptor, thus supporting its application in cancer therapy.

Molecular platforms for targeted drug delivery.

The targeted delivery of bioactive molecules to the appropriate site of action, one of the critical focuses of pharmaceutical research, improves therapeutic outcomes and increases safety at the same time; a concept envisaged by Ehrlich over 100 years ago when he described the "magic bullet" model. In the following decades, a considerable amount of research effort combined with enormous investment has carried selective drug targeting into clinical practice via the advent of monoclonal antibodies (mAbs) and antibody-drug conjugates derivatives. Additionally, a deeper understanding of physiopathological conditions of disease has permitted the tailored design of targeted drug delivery platforms that carry drugs, many copies of the same drug, and different drugs in combination to the appropriate site of action least selectively or preferentially. The acquired know-how has provided the field with the design rationale to develop a successful delivery system that will provide new and improved means to treat many intractable diseases and disorders. In this review, we discuss a wide range of molecular platforms for drug delivery, and focus on those with more success in the clinic, given their potential for targeted therapies.

Transglutaminase and Sialyltransferase Enzymatic Approaches for Polymer Conjugation to Proteins.

Proteins hold a central role in medicine and biology, also confirmed by the several therapeutic applications based on biologic drugs. Such therapies are of great relevance thanks to high potency and safety of proteins. Nevertheless, many proteins as therapeutics might present issues like fast kidney clearance, rapid enzymatic degradation, or immunogenicity. Such defects implicate frequent administrations or administrations at high doses of the therapeutics, thus yielding or exacerbating potential side effects. A successful technology for improving the clinical profiles of proteins is the conjugation of polymers to the protein surface. The design of a protein-polymer conjugate presents critical aspects that determine the efficacy and safety of the final product. The control over stoichiometry and conjugation site is a strict criterion on which researchers have been intensively focused during the years, in order to obtain homogeneous and batch-to-batch reproducible products. An innovative site-specific conjugation strategy relies on the use of enzymes as tools to mediate polymer conjugation. Enzymatic approaches are attractive because they allow site-selective polymer conjugation at specific protein amino acids. In these reactions, the polymer is a substrate analog that replaces the native substrate. Furthermore, enzymes can count other advantages such as high yields of conversion and physiological conditions of reaction. This chapter provides a meaningful description of protein-polymer conjugation through transglutaminase-mediated and sialyltransferase-mediated enzymatic strategies, reporting the mechanism of action and some relevant examples.

Transgultaminase-Mediated Nanoarmoring of Enzymes by PEGylation.

PEGylation, the covalent attachment of polyethylene glycol to bioactive molecules, is one of the leading approaches used to prolong pharmacokinetics, to improve the stability, and to reduce the immunogenicity of therapeutic proteins. PEG-conjugated products are associated with better therapy outcomes and improved patient compliance. Widely applied in clinical practice, the technology is mainly used to modify proteins, peptides, and oligonucleotides but also other drug delivery systems such as the liposomal one. Undergoing continuous attempts to optimize therapeutic efficacy and to tune the formation of conjugates, a number of different PEGylation processes are now available to researchers for protein conjugation. Although the possibility of obtaining highly homogeneous conjugate mixtures, preferably formed by a single monoconjugate, from a chemical conjugation reaction continues to be limited, several enzymatic conjugation approaches have recently been investigated to address this need. PEGylation mediated by microbial transglutaminase and its many advantages and modifications are outlined in detail in the current work permitting interested readers to perform site-specific protein derivatization to glutamines or lysines.