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Novel treatment options for metastatic colorectal cancer (CRC) are urgently needed to improve patient outcome. Here, we screen a library of non-characterized small molecules against a heterogeneous collection of patient-derived CRC spheroids. By prioritizing compounds with inhibitory activity in a subset of-but not all-spheroid cultures, NCT02 is identified as a candidate with minimal risk of non-specific toxicity. Mechanistically, we show that NCT02 acts as molecular glue that induces ubiquitination of cyclin K (CCNK) and proteasomal degradation of CCNK and its complex partner CDK12. Knockout of CCNK or CDK12 decreases proliferation of CRC cells in vitro and tumor growth in vivo. Interestingly, sensitivity to pharmacological CCNK/CDK12 degradation is associated with TP53 deficiency and consensus molecular subtype 4 in vitro and in patient-derived xenografts. We thus demonstrate the efficacy of targeted CCNK/CDK12 degradation for a CRC subset, highlighting the potential of drug-induced proteolysis for difficult-to-treat types of cancer., Competing Interests: Declaration of interests C.S. is an employee of Merck KGaA. P.L.C. is an employee of CureVac AG. A.N. is an employee of Spark Therapeutics Inc. A.H., D.M., S.J.H., U.S., J.W., L.-M.T., G.S., S.J., and M.L. are or were employees of Bayer AG and are shareholders or may have additional stock options. U.S., J.W., L.M.T., G. Stoehr, S.J.H., G. Siemeister, and M.L. are employees of Nuvisan ICB GmbH. G. Stoehr and H.H. are employees of OmicScouts GmbH. B.K. and H.H. are shareholders of OmicScouts GmbH. All other authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Obligate intracellular bacteria depend entirely on nutrients from the host cell for their reproduction. Here, we show that obligate intracellular Chlamydia downregulate the central tumor suppressor p53 in human cells. This reduction of p53 levels is mediated by the PI3K-Akt signaling pathway, activation of HDM2, and subsequent proteasomal degradation of p53. The stabilization of p53 in human cells severely impaired chlamydial development and caused the loss of infectious particle formation. DNA-damage-induced p53 interfered with chlamydial development through downregulation of the pentose phosphate pathway (PPP). Increased expression of the PPP key enzyme glucose-6-phosphate dehydrogenase rescued the inhibition of chlamydial growth induced by DNA damage or stabilized p53. Thus, downregulation of p53 is a key event in the chlamydial life cycle that reprograms the host cell to create a metabolic environment supportive of chlamydial growth.