Peptide-Drug Conjugate

Peptide-drug conjugates, like ADCs, are an emerging class of prodrugs. Antibody-drug conjugate is a class of biopharmaceutical drugs for treating cancer. ADCs are complex bioconjugates and immunoconjugates used as targeted therapy. Antibody-drug conjugates are composed of a monoclonal antibody connected to a cytotoxic payload. The monoclonal antibody acts as a carrier to target and penetrate a specific tumor cell and delivers a cytotoxic drug inside the cell. So, ADCs combine targeting, penetration and cytotoxic properties as well as tolerability and PK properties of mAbs making them a valuable therapeutic strategy.

Antidoby-drug conjugate

Peptide-drug conjugates (PDCs) only differ from ADCs by their homing device. Indeed, PDCs are composed of a homing peptide (addressing and/or cell penetrating peptide) conjugated to a cytotoxic payload. A chemical linker is also present between the peptide/antibody and the cytotoxic payload. The choice of the chemical linker is a critical step to the success of an ADC or PDC. The chemical linker can be “non-cleavable” or “cleavable”. Cleavable linkers are mostly used to control and release the cytotoxic drug inside cells after bond cleavage. Several cleavage strategies exist :

Hydrazone linker (pH-sensitive) is used to release a cytotoxic payload through acidic hydrolysis of the cleavable linker once ADCs or PDCs get into endosomes or lysosomes. The antibody BR96-DOX to treat metastatic breast cancer was designed with hydrazone linker between BR96 antibody and doxorubicin.

Cathepsin B-responsive linkers (protease-sensitive) are the most employed linkers, for instance to construct the chimeric anti-CD30 antibody MMAE conjugate. Cathepsin B recognizes specific sequences such as phenylalanine-lysine (Phe-Lys) and valine-citrulline (Val-Cit) and cleave them.

Disulfide linker is a glutathione-sensitive linker such as SPDB, the disulfide-containing linker releases cytotoxins after reduction by glutathione.

Pyrophosphate diester linker is used to release payloads through the endosomal-lysosomal pathway.

Peptide-drug conjugates

Cytotoxic payloads

Cytotoxic payloads can be grouped in two categories depending on their action and their specificity: DNA damaging agents and tubulin inhibitors.

Microtubule inhibitors’ action result in apoptosis. In fact, microtubule dynamic is suppressed by stabilization or destabilization of microtubule induced by inhibitors. Microtubule dynamic is important for the mitotic step. So, tubulin inhibitors block cell cycle progression and lead to cell apoptosis.

DNA damaging agents are composed of DNA cleavers, DNA intercalators, DNA transcription inhibitors, DNA cross-linker, Akt inhibitors and Dihydrofolate Reductase (DHFR) inhibitor. Their mechanisms of action are the introduction of DNA strand breaks, the introduction of intercalators between nucleic acid base pairs blocking DNA replication and binding transcription initiator to inhibit DNA transcription…

Cytotoxic payload list

DNA damaging agents Tubulin inhibitors
Doxorubicin MMAE
Aldoxorubicin MMAF
Daunorubicin Mertansine DM1
Camptothecin CPT Paclitaxel PTX
SN-38 Tubulysin IM-2/IM-3
Dxd Taltobulin
Calicheamicin Ansamitocin

Drug conjugation technics

Conjugation of chemical cytotoxic payloads to biological compound (peptides or antibodies) can be quite complex. To avoid reducing the performance of antibodies or peptides, the cytotoxin must be placed at specific positions in a defined stoichiometry. Various conjugation linkages can be created such as amide bonds, thioether bonds or click-chemistry.

Site-specific conjugation of a cytotoxic payload to antibodies is challenging and requires long developments. Peptide-drug conjugates are very attractive thanks to the possibility to synthesize chemically peptides. Peptide chemistry is highly versatile and allows to easily integrate conjugation moieties at specific positions.


ADC and PDC services at SB-PEPTIDE:

SB-PEPTIDE offers a wide range of services in the field of biologic drug conjugates.

– Peptide synthesis and cytotoxin conjugation

SB-PEPTIDE is expert in complex peptide synthesis and conjugations. The company is able to synthesize on-demand peptide-drug conjugates. The company successfully produced various peptide-drug conjugates including MMAE cytotoxic payload or Doxoribucin cytotoxic payload.

Peptide-Drug Conjugates

Illustration of the various structure possibilities

– Antibody-drug conjugate services

SB-PEPTIDE is offering analytical services to characterize ADCs including MALDI, analytical SEC-HPLC, preparative SEC-HPLC and MS/MS.

Peptide analytical method development / Peptide-Drug Conjugates



1- Wang Y. et al. Adv Drug Deliv Rev. 110-111:112-126 (2017)
Peptide-Drug Conjugates Peptide-drug conjugates as effective prodrug strategies for targeted delivery


Peptide-drug conjugates (PDCs) represent an important class of therapeutic agents that combine one or more drug molecules with a short peptide through a biodegradable linker. This prodrug strategy uniquely and specifically exploits the biological activities and self-assembling potential of small-molecule peptides to improve the treatment efficacy of medicinal compounds. We review here the recent progress in the design and synthesis of peptide-drug conjugates in the context of targeted drug delivery and cancer chemotherapy. We analyze carefully the key design features in choosing the peptide sequence and linker chemistry for the drug of interest, as well as the strategies to optimize the conjugate design. We highlight the recent progress in the design and synthesis of self-assembling peptide-drug amphiphiles to construct supramolecular nanomedicine and nanofiber hydrogels for both systemic and topical delivery of active pharmaceutical ingredients.

2- Hamblett K. J. et al. Clin Cancer Res. 10(20):7063-70 (2004)
Peptide-Drug Conjugates Effects of drug loading on the antitumor activity of a monoclonal antibody drug conjugate


Purpose: An antibody-drug conjugate consisting of monomethyl auristatin E (MMAE) conjugated to the anti-CD30 monoclonal antibody (mAb) cAC10, with eight drug moieties per mAb, was previously shown to have potent cytotoxic activity against CD30(+) malignant cells. To determine the effect of drug loading on antibody-drug conjugate therapeutic potential, we assessed cAC10 antibody-drug conjugates containing different drug-mAb ratios in vitro and in vivo.

Experimental design: Coupling MMAE to the cysteines that comprise the interchain disulfides of cAC10 created an antibody-drug conjugate population, which was purified using hydrophobic interaction chromatography to yield antibody-drug conjugates with two, four, and eight drugs per antibody (E2, E4, and E8, respectively). Antibody-drug conjugate potency was tested in vitro against CD30(+) lines followed by in vivo xenograft models. The maximum-tolerated dose and pharmacokinetic profiles of the antibody-drug conjugates were investigated in mice.

Results: Although antibody-drug conjugate potency in vitro was directly dependent on drug loading (IC(50) values E8

Conclusions: By decreasing drug loading per antibody, the therapeutic index was increased demonstrating that drug loading is a key design parameter for antibody-drug conjugates.

3- Hafeez U., Parakh S., Gan H. K. and Scott A. M. Molecules. 25(20):4764 (2020)
Peptide-Drug Conjugates Antibody-Drug Conjugates for Cancer Therapy


Antibody-drug conjugates (ADCs) are novel drugs that exploit the specificity of a monoclonal antibody (mAb) to reach target antigens expressed on cancer cells for the delivery of a potent cytotoxic payload. ADCs provide a unique opportunity to deliver drugs to tumor cells while minimizing toxicity to normal tissue, achieving wider therapeutic windows and enhanced pharmacokinetic/pharmacodynamic properties. To date, nine ADCs have been approved by the FDA and more than 80 ADCs are under clinical development worldwide. In this paper, we provide an overview of the biology and chemistry of each component of ADC design. We briefly discuss the clinical experience with approved ADCs and the various pathways involved in ADC resistance. We conclude with perspectives about the future development of the next generations of ADCs, including the role of molecular imaging in drug development.

4- Vrettos E. I., Mezo G. and Tzakos A. G. Beilstein J Org Chem. 14:930-954 (2018)
Peptide-Drug Conjugates On the design principles of peptide-drug conjugates for targeted drug delivery to the malignant tumor site


Cancer is the second leading cause of death affecting nearly one in two people, and the appearance of new cases is projected to rise by >70% by 2030. To effectively combat the menace of cancer, a variety of strategies have been exploited. Among them, the development of peptide-drug conjugates (PDCs) is considered as an inextricable part of this armamentarium and is continuously explored as a viable approach to target malignant tumors. The general architecture of PDCs consists of three building blocks: the tumor-homing peptide, the cytotoxic agent and the biodegradable connecting linker. The aim of the current review is to provide a spherical perspective on the basic principles governing PDCs, as also the methodology to construct them. We aim to offer basic and integral knowledge on the rational design towards the construction of PDCs through analyzing each building block, as also to highlight the overall progress of this rapidly growing field. Therefore, we focus on several intriguing examples from the recent literature, including important PDCs that have progressed to phase III clinical trials. Last, we address possible difficulties that may emerge during the synthesis of PDCs, as also report ways to overcome them.

5- Mazel M. et al. Anticancer Drugs. 12(2):107-16 (2001)
Peptide-Drug Conjugates Doxorubicin-peptide conjugates overcome multidrug resistance


A well-known mechanism leading to the emergence of multidrug-resistant tumor cells is the overexpression of P-glycoprotein (P-gp), which is capable of lowering intracellular drug concentrations. To overcome this problem, we tested the capability of two peptide vectors that are able to cross cellular membranes to deliver doxorubicin in P-gp-expressing cells. The antitumor effect of peptide-conjugated doxorubicin was tested in human erythroleukemic (K562/ ADR) resistant cells. The conjugate showed potent dose-dependent inhibition of cell growth against K562/ADR cells as compared with doxorubicin alone. Doxorubicin exhibited IC50 concentrations of 65 microM in the resistant cells, whereas vectorized doxorubicin was more effective with IC50 concentrations of 3 microM. After treatment of the resistant cells with verapamil, the intracellular levels of doxorubicin were markedly increased and consequent cytotoxicity was improved. In contrast, treatment of resistant cells with verapamil did not cause any further enhancement in the cell uptake nor in the cytotoxic effect of the conjugated doxorubicin, indicating that the conjugate bypasses the P-gp. Finally, we show by the in situ brain perfusion method in P-gp-deficient and competent mice that vectorized doxorubicin bypasses the P-gp present at the luminal site of the blood-brain barrier. These results indicate that vectorization of doxorubicin with peptide vectors is effective in overcoming multidrug resistance.