Antibody conjugates for targeted delivery of Toll-like receptor 9 agonist to the tumor tissue

Abstract

Imiquimod, a Toll-like receptor 7 (TLR7) agonist is routinely used for topical administration in basal cell carcinoma and stage zero melanoma. Similarly, the TLR agonist Bacillus Calmette-Guérin is used for the local treatment of bladder cancer and clinical trials showed treatment efficacy of intratumoral injections with TLR9 agonists. However, when administered systemically, endosomal TLR agonists cause adverse responses due to broad immune activation. Hence, strategies for targeted delivery of TLR agonists to the tumor tissue are needed to enable the widespread use of endosomal TLR agonists in the context of tumor immunotherapy. One strategy for targeted delivery of TLR agonist is their conjugation to tumor antigen-specific therapeutic antibodies. Such antibody-TLR agonist conjugates act synergistically by inducing local TLR-mediated innate immune activation which complements the anti-tumor immune mechanisms induced by the therapeutic antibody. In this study, we explored different conjugation strategies for TLR9 agonists to immunoglobulin G (IgG). We evaluated biochemical conjugation of immunostimulatory CpG oligodesoxyribonucleotides (ODN) to the HER2-specific therapeutic antibody Trastuzumab with different cross-linkers comparing stochastic with site-specific conjugation. The physiochemical make-up and biological activities of the generated Trastuzumab-ODN conjugates were characterized in vitro and demonstrated that site-specific conjugation of CpG ODN is crucial for maintaining the antigen-binding capabilities of Trastuzumab. Furthermore, site-specific conjugate was effective in promoting anti-tumor immune responses in vivo in a pseudo-metastasis mouse model with engineered human HER2-transgenic tumor cells. In this in vivo model, co-delivery of Trastuzumab and CpG ODN in form of site-specific conjugates was superior to co-injection of unconjugated Trastuzumab, CpG ODN or stochastic conjugate in promoting T cell activation and expansion. Thereby, this study highlights that site-specific conjugation of CpG ODN to therapeutic antibodies targeting tumor markers is a feasible and more reliable approach for generation of conjugates which retain and combine the functional properties of the adjuvant and the antibody.

Targeted delivery of immune-stimulating bispecific RNA, inducing apoptosis and anti-tumor immunity in cancer cells

“…Taken together, these results have demonstrated that a dual targeting of RIG-I and PLK1 with an antibody-siRNA conjugate was achievable to induce tumoral cell death as well as immune cell activation. To date, only a few immune stimulating antibody conjugate have been described using either TLR7 40 or TLR9 41 agonists, but never targeting RIG-I using an antibody-siRNA conjugate.…”

Diverse drug delivery systems for the enhancement of cancer immunotherapy: an overview

“…Besides, some ADCs have been reported to lead to increased PD-L1 expression in tumor cells, with synergistic effects between them and immune checkpoint inhibitors ( 115 , 147 – 149 ). In addition to traditional cytotoxins, several small molecule immunomodulators have been used in the development of novel ADCs: TLR agonists and STING agonists, known as immunostimulating antibody conjugates (ISACs) ( 150 – 152 ). BDC-1001 is a novel ADC currently in clinical development (Phase I/II, NCT04278144), also known as ISACs ( 153 ).…”

Antibody–Drug Conjugates in the Treatment of Genitourinary Cancers: An Updated Review of Data

“…It consists of a monoclonal antibody, a linker, and a payload. The monoclonal antibody must be designed properly in order to exhibit its therapeutic abilities and reduce off-target toxicity [8]. The antigen on the cancer cell should be present on the cell surface to allow for the binding of the antibody and the ability for internalization of the ADC into the cell [9][10][11].…”