FGF2-Derived PeptibodyF2-MMAE Conjugate for Targeted Delivery of Cytotoxic Drugs into Cancer Cells Overexpressing FGFR1

The FGF/FGFR signalling mediated anti-cancer drug resistance and therapeutic intervention

ABSTRACT Fibroblast Growth Factor (FGF) ligands and their receptors are crucial factors driving chemoresistance in several malignancies, challenging the efficacy of currently available anti-cancer drugs. The Fibroblast growth factor/receptor (FGF/FGFR) signalling malfunctions in tumor cells, resulting in a range of molecular pathways that may impact its drug effectiveness. Deregulation of cell signalling is critical since it can enhance tumor growth and metastasis. Overexpression and mutation of FGF/FGFR induce regulatory changes in the signalling pathways. Chromosomal translocation facilitating FGFR fusion production aggravates drug resistance. Apoptosis is inhibited by FGFR-activated signalling pathways, reducing multiple anti-cancer medications' destructive impacts. Angiogenesis and epithelial-mesenchymal transition (EMT) are facilitated by FGFRs-dependent signalling, which correlates with drug resistance and enhances metastasis. Further, lysosome-mediated drug sequestration is another prominent method of resistance. Inhibition of FGF/FGFR by following a plethora of therapeutic approaches such as covalent and multitarget inhibitors, ligand traps, monoclonal antibodies, recombinant FGFs, combination therapy, and targeting lysosomes and micro RNAs would be helpful. As a result, FGF/FGFR suppression treatment options are evolving nowadays. To increase positive impacts, the processes underpinning the FGF/FGFR axis' role in developing drug resistance need to be clarified, emphasizing the need for more studies to develop novel therapeutic options to address this significant problem. Communicated by Ramaswamy H. Sarma.

Drug Conjugation via Maleimide-Thiol Chemistry Does Not Affect Targeting Properties of Cysteine-Containing Anti-FGFR1 Peptibodies

With a wide range of available cytotoxic therapeutics, the main focus of current cancer research is to deliver them specifically to the cancer cells, minimizing toxicity against healthy tissues. Targeted therapy utilizes different carriers for cytotoxic drugs, combining a targeting molecule, typically an antibody, and a highly toxic payload. For the effective delivery of such cytotoxic conjugates, a molecular target on the cancer cell is required. Various proteins are exclusively or abundantly expressed in cancer cells, making them a possible target for drug carriers. Fibroblast growth factor receptor 1 (FGFR1) overexpression has been reported in different types of cancer, but no FGFR1-targeting cytotoxic conjugate has been approved for therapy so far. In this study, the FGFR1-targeting peptide previously described in the literature was reformatted into a peptibody-peptide fusion with the fragment crystallizable (Fc) domain of IgG1. PeptibodyC19 can be effectively internalized into FGFR1-overexpressing cells and does not induce cells' proliferation. The main challenge for its use as a cytotoxic conjugate is a cysteine residue located within the targeting peptide. A standard drug-conjugation strategy based on the maleimide-thiol reaction involves modification of cysteines within the Fc domain hinge region. Applied here, however, may easily result in the modification of the targeting peptide with the drug, limiting its affinity to the target and therefore the potential for specific drug delivery. To investigate if this is the case, we have performed conjugation reactions with different auristatin derivatives (PEGylated and unmodified) under various conditions. By controlling the reduction conditions and the type of cytotoxic payload, different numbers of cysteines were substituted, allowing us to avoid conjugating the drug to the targeting peptide, which could affect its binding to FGFR1. The optimized protocol with PEGylated auristatin yielded doubly substituted peptibodyC19, showing specific cytotoxicity toward the FGFR1-expressing lung cancer cells, with no effect on cells with low FGFR1 levels. Indeed, additional cysteine poses a risk of unwanted modification, but changes in the type of cytotoxic payload and reaction conditions allow the use of standard thiol-maleimide-based conjugation to achieve standard Fc hinge region cysteine modification, analogously to antibody-drug conjugates.

Peptibody Based on FGFR1-Binding Peptides From the FGF4 Sequence as a Cancer-Targeting Agent

Targeted therapies are a promising alternative to conventional chemotherapy, with an increasing number of therapeutics targeting specific molecular aberrancies in cancer cells. One of the emerging targets for directed cancer treatments is fibroblast growth factor receptors (FGFRs), which are known to be involved in the pathogenesis and progression of multiple cancer types, specially in lung, bladder, and breast cancers. Here, we are demonstrating the development of the FGFR1-targeting agent based on the interactome screening approach, based on the isolation of binding regions from ligands interacting with the receptor. The parallel analysis by FGFR1 pull-down of chymotryptic peptides coupled with MS analysis, and PepSpot analysis yielded equivalent peptide sequences from FGF4, one of the FGFR1 ligands. Three sequences served as a basis for peptibody (Fc-fusion) generation, to overcome clinical limitations of peptidic agents, and two of them showed favorable FGFR1-binding in vitro and FGFR1-dependent internalization into cells. To validate if developed FGFR1-targeting peptibodies can be used for drug delivery, similar to the well-established concept of antibody-drug conjugates (ADCs), peptibodyF4_1 was successfully conjugated with monomethylauristatin E (MMAE), and has shown significant and specific toxicity toward FGFR1-expressing lung cancer cell lines, with nanomolar EC50 values. Essentially, the development of new effective FGFR1 binders that comprise the naturally occurring FGFR-recognition peptides and Fc region ensuring high plasma stability, and long bloodstream circulation is an interesting strategy expanding targeted anticancer agents' portfolio. Furthermore, identifying peptides effectively binding the receptor from sequences of its ligands is not limited to FGFRs and is an approach versatile enough to be a basis for a new peptide/peptibodies development strategy.