An inhibitor of CD28-CD80 interactions impairs CD28-mediated costimulation of human CD4 T cells

Toward Small-Molecule Inhibition of Protein-Protein Interactions: General Aspects and Recent Progress in Targeting Costimulatory and Coinhibitory (Immune Checkpoint) Interactions

Protein-Protein Interactions (PPIs) that are part of the costimulatory and coinhibitory (immune checkpoint) signaling are critical for adequate T cell response and are important therapeutic targets for immunomodulation. Biologics targeting them have already achieved considerable clinical success in the treatment of autoimmune diseases or transplant recipients (e.g., abatacept, belatacept, and belimumab) as well as cancer (e.g., ipilimumab, nivolumab, pembrolizumab, atezolizumab, durvalumab, and avelumab). In view of such progress, there have been only relatively limited efforts toward developing small-molecule PPI inhibitors (SMPPIIs) targeting these cosignaling interactions, possibly because they, as all other PPIs, are difficult to target by small molecules and were not considered druggable. Nevertheless, substantial progress has been achieved during the last decade. SMPPIIs proving the feasibility of such approaches have been identified through various strategies for a number of cosignaling interactions including CD40-CD40L, OX40-OX40L, BAFFR-BAFF, CD80-CD28, and PD-1-PD-L1s. Here, after an overview of the general aspects and challenges of SMPPII-focused drug discovery, we review them briefly together with relevant structural, immune-signaling, physicochemical, and medicinal chemistry aspects. While so far only a few of these SMPPIIs have shown activity in animal models (DRI-C21045 for CD40-D40L, KR33426 for BAFFR-BAFF) or reached clinical development (RhuDex for CD80-CD28, CA-170 for PD-1-PD-L1), there is proof-of-principle evidence for the feasibility of such approaches in immunomodulation. They can result in products that are easier to develop/ manufacture and are less likely to be immunogenic or encounter postmarket safety events than corresponding biologics, and, contrary to them, can even become orally bioavailable.

High-affinity small molecule inhibitors of T cell costimulation: compounds for immunotherapy

Costimulatory molecules are important regulators of T cell activation and thus favored targets for therapeutic manipulation of immune responses. One of the key costimulatory receptors is CD80, which binds the T cell ligands, CD28, and CTLA-4. We describe a set of small compounds that bind with high specificity and low nanomolar affinity to CD80. The compounds have relatively slow off-rates and block both CD28 and CTLA-4 binding, implying that they occlude the shared ligand binding site. The compounds inhibit proinflammatory cytokine release in T cell assays with submicromolar potency, and as such, they represent promising leads for the development of novel therapeutics for immune-mediated inflammatory disease. Our results also suggest that other predominantly beta proteins, such as those that dominate the cell surface, may also be accessible as potentially therapeutic targets.

Increased costimulatory responses in African-American kidney allograft recipients

BACKGROUND

The issue of racial differences in immune responses has been seldom investigated, despite the increased incidence of transplant rejection and inferior allograft outcomes in African-Americans (AA). We previously reported significantly increased expression of costimulatory molecules on peripheral blood cells from healthy adult AA compared with Caucasian (CS) volunteers. This report extends the study to pediatric kidney allograft recipients.

METHODS

Surface antigen expression by peripheral blood mononuclear cells (MNC) from AA and CS transplant patients was determined by flow cytometry, after staining with specific antibodies. In vitro proliferation, in a one-way mixed lymphocyte response (MLR), was measured after stimulation with allogeneic irradiated mononuclear cells. The concentration of cyclosporine (CsA) achieving 50% inhibition (IC50) of in vitro proliferative responses to PHA and OKT3 was calculated.

RESULTS

MNC from AA patients were shown to have significantly higher expression of CD80 (CS 5.2% +/- 0.6, AA 9.6% +/- 1.2, P < 0.0001) than cells from CS patients. Additionally, the cells from AA transplant recipients proliferated significantly more in an MLR (stimulation index: CS 8 +/- S2, AA 25 +/- 8, P < 0.05), and the CsA IC50 values, during proliferation to PHA and OKT3, were significantly higher in AA compared to CS patients.

CONCLUSIONS

Although socioeconomic factors and therapeutic compliance are undoubtedly important issues in long-term allograft survival, our data suggest that AA patients mount more vigorous immune responses to antigens. The increased requirement for immunosuppression may be linked to racial variations in costimulatory molecule expression on antigen-presenting cells.