Monomethyl auristatin E (MMAE) is the most popular and widely used cytotoxin in the development of antibody-drug conjugates (ADCs). However, current MMAE-based ADCs are all constructed using cleavable linkers, and this design concept still has insurmountable drawbacks. Their potential instabilities and lipophilic MMAE-induced “bystander effect” inevitably increase the toxicity to normal tissues. Herein, we overturn previous negative views of MMAE-based ADCs with non-cleavable linkers and propose using ionized L-Cysteine (Cys)-linker-MMAE as a novel payload, which can ingeniously enrich and enter tumor cells through receptor-mediated endocytosis of antibodies while its lower permeability helps to avoid further off-target toxicity. We demonstrate that Cys-linker-MMAE maintains high potency similar to free MMAE at the tubulin molecular level and can also be efficiently released in target cells. As a result, the preferred ADC (mil40-15) not only exhibits ideal plasma stability and maintains potent cytotoxicity as MMAE (IC₅₀: 10⁻¹¹ M), but also shows improved safety with lower bystander toxicity (IC₅₀: 10⁻⁹ M), its maximum tolerated dose approaching the level of the naked antibody (160 mg/kg). This study indicated that Cys-linker-MMAE has the potential as a potent payload for ADCs, which is expected to provide novel strategies for the development of MMAE-based ADCs.

Methylprednisolone (MP) is often used in the treatment of various kidney diseases, but overcoming the systemic side effects caused by its nonspecific distribution in the body is a challenge. This article reports the design, synthesis, and renal targeting of methylprednisolone–lysozyme (MPS–LZM). This conjugate was obtained by covalently linking MP with the renal targeting carrier LZM through a linker containing an ester bond, which could utilize the renal targeting of LZM to deliver MP to renal proximal tubular epithelial cells and effectively release MP. The reaction conditions for the preparation of the conjugate were mild, and the quality was controllable. The number of drug payloads per LZM was 1.1. Cell-level studies have demonstrated the safety and endocytosis of the conjugate. Further pharmacokinetic experiments confirmed that, compared with that of free MP, the conjugate increased the renal exposure (AUC_0–t) of active MP from 17.59 to 242.18 h*ng/mL, and the targeting efficiency improved by approximately 14 times. Tissue and organ imaging further revealed that the conjugate could reach the kidneys quickly, and fluorescence could be detected in the kidneys for up to 12 h. This study preliminarily validates the feasibility of a renal targeting design strategy for MPS–LZM, which is expected to provide a new option for improving kidney-specific distribution of glucocorticoids.

In this article, we report the design, synthesis, photodynamic properties, and in vitro evaluation of photoactivatable prodrug for the poly (ADP-ribose) polymerase 1 (PARP-1) inhibitor Talazoparib. In order to yield a photoactivatable, inactive prodrug, photoactivatable protecting groups (PPGs) were employed to mask the key pharmacophore of Talazoparib. Our study confirmed the good stability and photolytic effect of prodrugs. A PARP-1 enzyme inhibition assay and PARylation experiment showed that the inhibitory activity of the prodrug was reduced 380 times and more than 658 times, respectively, which proved that the prodrug’s expected activity was lost after PPG protection. In BRCA1- and BRCA2-deficient cell lines, the inhibitory activity of the compound was significantly restored after ultraviolet (UV) irradiation. The results indicate that the photoactivatable prodrug strategy is an interesting approach for studying PARP inhibitors. Meanwhile, the described photoactivatable prodrug also provided a new biological tool for the mechanism research of PARP.

Immune checkpoint inhibitors (ICIs) targeting PD-L1 and CD47 are clinically limited by severe off-target toxicities. To address this issue, immunotherapeutic prodrug strategies have been developed, aimed at preventing antibodies from binding to targets in healthy tissues and thereby reducing systemic toxicity. Existing strategies include prodrug technologies that mask the active sites of antibodies via peptide or polyethylene glycol (PEG) modification—yet these approaches also cause antibodies to lose their targeting ability. Herein, we propose an antibody prodrug strategy (termed FA-PEG-S-Ab) with active targeting capability. By modifying antibodies with folate-PEG-disulfide and PEG-disulfide linkages, we developed two novel prodrugs: FA-PEG-S-Atz (PD-L1-blocking prodrug) and FA-PEG-S-Hu5 (CD47-blocking prodrug). This strategy functions through two key steps: first, folate binding to folate receptor α (FRα)-mediated tumor-specific targeting enables the prodrugs to accumulate specifically in tumor tissues; subsequently, the high concentration of glutathione (GSH) in the tumor microenvironment (TME) specifically cleaves the disulfide bonds, removing the PEG shield, releasing the antibody, and restoring the antibody’s antigen-binding activity. In vitro experiments confirmed that the modified antibody prodrug FA-PEG-S-Hu5 exhibits high affinity for FRα (K_D = 4.02 × 10⁻⁹ M) and effectively masks the antibody’s binding activity (K_D from 1.05 × 10⁻¹¹ M to 2.10 × 10⁻⁸ M). Following activation by GSH in the TME, this masking effect is reversed, and the antibody regains its binding affinity (K_D = 2.14 × 10⁻¹⁰ M). Crucially, FA-PEG-S-Hu5 completely eliminates hemolytic toxicity. This “folate targeting delivery + TME activation” prodrug strategy is expected to provide a new solution for addressing the off-target toxicities of conventional ICIs.