Target Protein Degradation of the cAMP dependent protein kinase A catalytic subunit to overcome immune therapy failure in melanoma

• Applicant: Dr. Johannes Köckenberger
• Subject Area: Pharmacy ; Biological and Biomimetic Chemistry ; Organic Molecular Chemistry - Synthesis and Characterisation ; Pharmacology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553027799

Immune checkpoint blockade (ICB) therapies which block the inactivation of T-Cells by cancer cells via binding immune checkpoint receptors was a breakthrough in cancer treatment. Unfortunately, many cancer types show immune dysfunction including T-Cell exhaustion leading to primary and acquired drug resistance to immune checkpoint blockade. For example, the non-response in melanoma is 42 – 56%. In 2023, the Gutkind laboratory at UC San Diego Cancer Center discovered that the activation of the Gαs-PKA-signaling cascade is central to CD8+ T-cell dysfunction and exhaustion mechanisms in cancer. However, many different Gαs-receptors are enriched on exhausted CD8+ T-cells. Therefore, targeting PKA, the central downstream node for dysregulated Gαs-receptor mediated signaling, is a promising approach to find a combinatorial therapy to enhance the responsiveness to immune checkpoint blockade therapy. In a variety of studies, it was shown that target protein degradation can be superior to simple inhibition by enhancing selectivity, overcoming drug resistances, and diminishing scaffolding roles of proteins. PKA is organized in large protein complexes (signalosomes) in close proximity to its substrates. Therefore, ATP-binding site inhibition is likely to be insufficient for durable inactivation and disruption of functional PKA complexes. Furthermore, occupancy-dependent inhibitors are particularly vulnerable to the development of resistance in cancer. A more specific targeting of the enzymatic and scaffolding roles of PKA via targeted protein degradation is an attractive therapeutic strategy for anti-cancer immune system activation. Based on the recently published PKA inhibitor BLU0588, we performed docking studies and designed a pilot library of targeted protein degraders. Synthesis and testing in live cancer cells identified active PKACA degraders. With this initial set of compounds, we set up a biological testing pipeline featuring a comprehensive set of assays to identify early hits and guide chemical optimization. We want to study pharmacological PKACA depletion in immunotherapy response and T-cell exhaustion in cancer. We also want to study the possibility of the addition of PKACA-degrading drugs to immune checkpoint blockade as a combinatorial therapy to overcome immune therapy failure. To accomplish these goals, I will collaborate with world class experts in targeted protein degrader development (Fleur Ferguson, mentor), immune-oncology (Silvio Gutkind, co-mentor), and PKA structural biology (Susan Taylor, collaborator). Our specific aims are: Aim 1: Optimization of PKACA degraders using our established assay workflow for biological characterization, to develop potent and selective degrader molecules with good pharmacokinetic properties. Aim 2: Apply PKACA degraders to in vitro and in vivo models of T-cell exhaustion, to validate PKA as a therapeutic target in immune-oncology and measure the therapeutic index by comparison with healthy cells.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professorin Fleur M. Ferguson, Ph.D.