IndEx-2: Deciphering the impact of antigen density on tumour targeting therapeutics

The release of our new inducible cell line development platform, IndEx-2, has been a significant achievement for all the team at RoukenBio. Our innovative inducible cell line development tool can help to transform the drug discovery process of immune-directed therapies through the determination of the precise antigen density activation thresholds of targeted candidate immunotherapies which enables the selection of candidates with improved efficacy and enhanced safety profiles at the discovery stage.

Leveraging the immune system is an effective strategy to combat cancer. However, at present there remains a need for in vitro systems to test the safety and efficacy of these modalities. Our team identified these challenges and whilst conducting our own research, we began developing the tool we know as IndEx-2 today.

In our latest whitepaper, we condense some of the key features of this new tool into a few pages, detailing the science and research behind IndEx-2. We are excited to see how this innovative tool can be practically applied to a range of pre-clinical applications, so feel free to get in touch with our team if it piqued your interest.

Challenges IndEx-2 can help to overcome

Leveraging the immune system is a powerful anti-cancer strategy but achieving acceptable clinical safety remains challenging. One of the key barriers to developing effective immune activating / targeted therapeutics, such as immune cell engagers, chimeric antigen receptor (CAR) T cell therapies and antibody drug conjugates (ADCs), is the identification of a suitable cancer associated antigen. In most cases, the antigen(s) targeted are overexpressed by neoplastic cells, but also expressed, albeit to a lower level, in healthy tissues.

A further complication is the heterogeneity of expression, particularly in solid tumours. In many cases, this renders therapies ineffective due to low expression of the targeted receptor by a subset of cancer cells. Conversely, when the targeted antigen is expressed in healthy cells, the primary consideration is the development of “on-target, off-tumour” toxicities (OTOT), that arise when non-malignant tissues are targeted.

Severe OTOT has been observed in various CAR-T clinical trials involving patients with solid tumours. These side effects constitute a significant safety hurdle for the successful development of these modalities, to the extent that there are FDA guidelines instructing the consideration of these side effects during the pre-clinical evaluation phase. These considerations also extend to other advanced therapeutics, including immune cell engagers and ADCs for which similar toxicities have been reported.

Current approaches assessing the impact of antigen density on therapeutic efficacy and safety rely on the use of cancer cell lines with varying antigen expression levels. However, establishing a large panel of such cell lines is logistically and methodologically difficult due to licensing costs, limited availability, and uncertainty around specific antigen expression levels.

Additionally, the varied backgrounds of these cell lines can confound data, as inherent genetic and epigenetic differences between these cell lines can render them susceptible, or resistant, to a potential therapeutic strategy that is independent of target antigen expression levels.

This highlights the need for improved in vitro systems to evaluate the effect of target antigen density on therapeutic efficacy and safety, earlier in the development process. With the introduction of the FDA Modernisation Act 2.0, advocating for the reduced animal model use, there is further impetus for the deployment of more cost-effective human models that can be implemented earlier in the drug discovery process. 

Agile decision-making is easier at the pre-clinical stage, and the ability to pivot is more probable, having reduced cost implications in comparison to a clinical stage therapeutic candidate.