Expanding the Functionality and Target Spectrum of Kinase Inhibitors using PROTACs

• Applicants: Professor Dr. Stefan Knapp; Professor Dr. Elmar Wolf
• Subject Area: Hematology, Oncology ; Biochemistry ; Cell Biology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496561415

Kinase inhibitors are widely used drugs that have significantly improved the prognosis of cancer patients. However, many kinases or kinase-related proteins remain to be targeted, as inhibitors did not meet the expectations raised by genetic experiments or they have been associated with intolerable toxicity. An example where conventional inhibition of a kinase by ATP competitive inhibitors has not led to clinical success so far is the Aurora-A kinase. Aurora-A plays a central role in tumorigenesis and genetic data have demonstrated that many tumours critically depend on Aurora-A for growth, making this a compelling case for therapeutic targeting of Aurora-A in cancer. Unfortunately, all clinical trials with Aurora-A kinase inhibitors showed no significant therapeutic effect, but dose-limiting toxicity, and many trials have been terminated prematurely. Therefore, no Aurora-A-targeting drugs are currently available.As many reports indicate also a non-catalytic function of Aurora-A in tumour cells, we explored the inhibition of Aurora-A by a new class of small molecules called proteolysis targeting chimeras (PROTACs). Instead of inhibiting the catalytic activity, PROTACs recruit targets to cellular E3 ubiquitin ligases and thereby induce proteasomal degradation, thus also addressing non-catalytic protein functions. We recently developed a PROTAC that induced rapid and specific degradation of Aurora-A in leukaemia cells. Strikingly, this tool compound caused S phase arrest and rampant apoptosis, which is markedly different from the cellular effects of Aurora-A kinase inhibitors. While these results open a new avenue to target Aurora-A scaffolding function in cancer therapy, the developed PROTACs also provide a versatile tool to study Aurora-A function and its mediated interaction with signalling partners. Based on our preliminary data, we will now develop the Aurora-A PROTAC for in vivo use in mouse models to explore the potential of Aurora-A degradation in cancer therapy. We will improve the pharmacokinetics of the compound based on our model of the ternary Aurora-PROTAC-CEREBLON complex. We will use this optimized PROTAC to explore the efficacy and safety Aurora-A PROTACs in pre-clinical leukaemia models. At the same time, we will use our compounds to obtain a better understanding of the scaffolding role of Aurora-A regulating the cell cycle.In a second line of experiments, we will develop PROTACs for the promising cancer targets RUVBL1 and RUVB2. As Aurora-A, RUVBL proteins directly bind the onco-protein MYC and are indispensable for MYC´s oncogenic function. Moreover, and again similar to Aurora-A, both proteins bind and hydrolyse ATP, but have additional important oncogenic functions that are independent from their catalytic activity. Building on our experience with Aurora-A PROTACs, we will design, synthesize and characterize RUVBL1/2 PROTACs and test their anti-cancer properties in leukaemia models.

• DFG Programme: Research Grants