Antibody drug conjugates (ADCs) – the role of in vitro models in safety assessment

One the fastest growing approaches to treat cancer is the use of antibody drug conjugates (ADCs). Since the approval of the first antibody drug conjugate  in 2000, 14 more have been approved by the FDA and there are over 100 antibody drug conjugates in development[1]. Antibody drug conjugates thus represent an effective and promising approach in the fight against cancer.

Cancer is a leading cause of death worldwide. The World Health Organisation (WHO) estimates that in 2019 cancer was the first or second leading cause of death in 61% of countries it surveyed[2]. The search for effective treatments for a range of cancers has seen the medical profession and  pharmaceutical industry innovate new therapeutic interventions over a period of 140 years[3].  For many years chemotherapy was the mainstay of cancer treatment and more recently monoclonal antibodies. New innovations have arisen as researchers look to target hard to treat cancers or improve the therapeutic index, antibody drug conjugates represent on of the most promising approaches. .

Antibody drug conjugates (ADCs)  are typically composed of a monoclonal antibody covalently attached to a cytotoxic drug (warhead or payload) via a chemical linker. They combine both the advantages of highly specific targeting ability and highly potent killing effect to achieve accurate and efficient elimination of cancer cells.

Despite the promises of ADCs (antibody drug conjugates), their clinical use can be associated with dose-limiting toxicities which has caused them to fail in clinic.[4] The complexity of antibody drug conjugates means there can be multiple determinants of toxicity associated with the antibody, payload and the linker. This complexity has meant the route to Investigational New Drug (IND) application through the completion of non-clinical studies requires a case-by-case approach and the use of multiple in vitro and in vivo assays[5].

It is estimated that only 0.1% of the injected dose of an ADC (antibody drug conjugate) is delivered to the targeted diseased cell and analysis of clinical data has concluded that toxicity is primarily associated with impacts on healthy tissue. ADCs with similar payload/linker combinations exhibit similar toxicity profiles regardless of the antigen targeted or the expression level in healthy tissues[6]. While the safety profile of modern antibody drug conjugates  are more favourable, dose-limiting toxicities can still be wide ranging including hepatic, neurological and ophthalmic affects. In the field of breast cancer, the use of ERBB2-directed ADCs has improved the treatments options, however recent clinical data has raised the issue of lung toxicity[7], and in other classes of antibody drug conjugates’ nephrotoxicity has been a concern.

Given the trend of increasing emphasis on adopting in vitro models to reduce the reliance on and improve the execution of in vivo pre-clinical studies it is surprising that limited literature exists examining the use of such models for assessing ADC safety. Although as discussed above the mechanism of antibody drug conjugate toxicity can be complex, common chemical classes of drug warheads do have known propensities to negatively affect specific organs or tissues.  For example, MMAF and DM4 are associated with ocular toxicity and using in vitro models such as human derived retinal organoids or retinal pigmented epithelia (RPE) could give important data on the safety profile of ADCs in early discovery. Using such microphysiological system (MPS) models can give insights into the toxicity profiles and potential strategies to minimise negative effects and improve the therapeutic index.

Toxicity associated with antibody drug conjugates can be the result of premature release of the drug into the plasma followed by uptake into healthy cells or uptake of the intact ADC by non-antigen endocytosis followed by intracellular metabolism. It is important that any in vitro model expresses both large and small molecule transport mechanisms to ensure these effects can by assessed. At Newcells we have adapted our aProximate^TM human proximal tubule model to measure the toxicity of antibody drug conjugates and the variation with linker chemistry. The model expresses all the major transporter classes for small and large molecules including the megalin/cubilin systems. As well as closely modelling in vivo physiology, the system can be used to look at co-drug strategies where transport uptake inhibitors reduce the renal toxicity of plasma released warhead. Another advantage of this MPS model is that it is available in rat and non-human primate formats. The latter is particularly important because NHP is one of the favoured species for pre-clinical studies of antibody drug conjugates.

The promising class of ERBB2-directed ADCs have come under scrutiny due to adverse reactions including drug related interstitial lung disease (ILD). In a pooled study of patients treated for breast, gastric, lung and colorectal cancer the overall incidence of drug related ILD/pneumonitis was 15.4%[8]. It is still unclear as to the mechanisms associated with these adverse effects. Even though lung epithelial cells express HER2, the involvement of this antigen in the pathophysiology is unknown and ILD has been observed in antibody drug conjugates that target different proteins[9]. The use of in vitro lung models that can mimic the in vivo interaction with ADCs and can recapitulate the fibrotic processes would be a valuable addition to the tools for early development of this class of antibody drug conjugates.

Antibody drug conjugates represent a rapidly growing innovative class of therapeutics targeting cancer.  They have already shown efficacy in improving the prognosis of patients suffering from a range of cancers.  As with other therapeutics they do exhibit toxicity which needs to be assessed on a case-by-case basis as no comprehensive guidance has yet been developed on pre-clinical safety assessment.  The use of MPS in vitro models of the retina, lung and kidney, along with other types of tissue models has the potential to contribute to the understanding of the mechanisms of toxicity as well as providing screening platforms as part of the discovery cascade.

[1] Fu, Z., Li, S., Han, S. et al. Antibody drug conjugate: the “biological missile” for targeted cancer therapy. Sig Transduct Target Ther 7, 93 (2022). https://doi.org/10.1038/s41392-022-00947-7

[2] World Health Organization (WHO). Global Health Estimates 2020: Deaths by Cause, Age, Sex, by Country and by Region, 2000-2019. WHO; 2020.

[3] https://static.scientificamerican.com/sciam/assets/media/multimedia/msktimeline/index.html

[4] Nguyen TD, Bordeau BM, Balthasar JP. Mechanisms of ADC Toxicity and Strategies to Increase ADC Tolerability. Cancers (Basel). 2023 Jan 24;15(3):713. doi: 10.3390/cancers15030713. PMID: 36765668; PMCID: PMC9913659.

[5] Roberts, Stanley A.; Andrews, Paul A.; Blanset, Diann; Flagella, Kelly M.; Gorovits, Boris; Lynch, Carmel M.; Martin, Pauline L.; Kramer-Stickland, Kimberly; Thibault, Stephane; Warner, Garvin (2013). Considerations for the nonclinical safety evaluation of antibody drug conjugates for oncology. Regulatory Toxicology and Pharmacology, 67(3), 382–391. doi:10.1016/j.yrtph.2013.08.017

[6] Nguyen, T.D.; Bordeau, B.M.; Balthasar, J.P. Mechanisms of ADC Toxicity and Strategies to Increase ADC Tolerability. Cancers 2023, 15, 713. https://doi.org/10.3390/cancers15030713

[7] Tarantino P, Modi S, Tolaney SM, et al. Interstitial Lung Disease Induced by Anti-ERBB2 Antibody-Drug Conjugates: A Review. JAMA Oncol. 2021;7(12):1873–1881. doi:10.1001/jamaoncol.2021.3595

[8] https://doi.org/10.1016/j.esmoop.2022.100554

[9] Sandra M. Swain, Mizuki Nishino, Lisa H. Lancaster, Bob T. Li, Andrew G. Nicholson, Brian J. Bartholmai, Jarushka Naidoo, Eva Schumacher-Wulf, Kohei Shitara, Junji Tsurutani, Pierfranco Conte, Terufumi Kato, Fabrice Andre, Charles A. Powell, Multidisciplinary clinical guidance on trastuzumab deruxtecan (T-DXd)–related interstitial lung disease/pneumonitis—Focus on proactive monitoring, diagnosis, and management, Cancer Treatment Reviews, Volume 106, 2022