Mechanisms of selective cancer targeting exploiting distinct hallmarks of cancer cells
Creators: name: Klemt, Insa
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024
Subjects: subject: selective cancer targeting, prodrug, ROS, metal complex, clathrochelate, ER stress, hallmarks of cancer
subject: DDC Classification::5 Naturwissenschaften::54 Chemie::547 Organische Chemie
subject: DDC Classification::5 Naturwissenschaften::50 Naturwissenschaften::500 Naturwissenschaften und Mathematik
subject: DDC Classification::5 Naturwissenschaften::54 Chemie::540 Chemie und zugeordnete Wissenschaften

description: Approximately 10 million people die of cancer every year. The genetic heterogeneity exhibited by different cancers on the one hand, and the physiological similarities between cancer and normal cells on the other hand pose challenges in the development of treatment options. Most chemotherapeutics available on the market exploit the fact that cancer cells typically rely on functional mitosis to a greater extent than normal cells. In that way, however, non-cancerous fast-dividing cells such as the precursor cells of leukocytes are also affected, leading to severe, dose-limiting side effects and impairment in the chemotherapy outcome. Hence, there is a demand for more selective chemotherapeutics, that effectively kill cancer cells while sparing all normal cells. In the first part of this work, two different hallmarks of cancers are exploited as starting points for selective anti-cancer treatment. As the first hallmark, the fact that most cancer cells show a higher level of endoplasmic reticulum stress and higher amounts of un-/ misfolded proteins is leveraged. In particular, we demonstrated that a rigid, three-dimensional iron(II) clathrochelate binds unfolded proteins, causing their aggregation, increasing the endoplasmic reticulum stress levels selectively in cancer cells to the extent that apoptosis is induced. In an in vivo model, the clathrochelate not only cured a subgroup of cancer-bearing mice but in a different model also decreased the volume and number of metastases, while no side effects were detected. The work for this project is presented in Publication 1 and 2. The second project exploits increased levels of reactive oxygen species in cancerous mitochondria, which also increase the concentration of proteinogenic or small molecular thiyl radicals. Structure-guided mitochondrial accumulation combined with alkyne functionalization of small molecules thus enables radical thiol-yne coupling selectively in cancer cells. In Publication 3, the occurrence of this mechanism in cancerous mitochondria as well as the suitability of this approach for selective cancer targeting is presented for the first time. In the second part of this work, we applied the prodrug concept to develop selective anti-cancer agents. Prodrugs that are designed to increase the selectivity of a parent drug are chemically modified to yield a pharmacologically inactive prodrug, which gets activated selectively at the tumor site/in the cancer cell or upon an external trigger. Reactive oxygen species-activatable small molecular prodrugs with an aryl boronic acid as a promoiety have been reported previously. This prodrug approach was thus far, however, not transferable for oligonucleotide-based drugs such as siRNAs. We first reported on a siRNA prodrug with a 5’ aryl boronic acid promoiety that gets selectively activated in the presence of high amounts of reactive oxygen species in Publication 4. In Publication 5, another siRNA prodrug is presented, that gets activated upon red light irradiation in the presence of the photosensitizer Sn(IV)(pyropheophorbide a)dichloride. In contrast to previously published red light activatable siRNA prodrugs, the activation is mediated by electrons and not cytotoxic 1O2, with the latter inducing undesired side effects. The cholic-acid-modified N-alkyl-aminoferrocene prodrug, presented in Publication 6, undergoes activation in response to high levels of reactive oxygen species in the endoplasmic reticulum, thereby exhibiting selectivity towards cancer cells. The activation of this prodrug leads to a further increase in oxidative stress, ultimately resulting in the induction of cancer cell death. Since few normal cells such as primed neutrophils also show high levels of reactive oxygen species, a prodrug concept with a dual triggering mechanism for the activation of anticancer drugs is proposed in Publication 7. The promoiety is designed to be activated first by high levels of reactive oxygen species and secondarily by the basic pH present in mitochondria. Consequently, in (primed) neutrophils, which possess a very limited number of mitochondria, the prodrug remains incompletely activated. We implemented this prodrug concept using an exemplifying mitosis inhibitor camptothecin. Alongside the inherent cancer selectivity by targeting rapidly dividing cells, the prodrug concept enhances this selectivity by specifically targeting fast-dividing cells with elevated levels of reactive oxygen species and a high number of mitochondria. We validated the prodrug’s activation mechanism and anti-cancer activity in vitro, as well as its efficacy and selectivity in vivo. Altogether, in this thesis, several strategies for selective cancer targeting by small molecules are presented. These approaches exploit distinct hallmarks of cancer cells beyond their reliance on functional mitosis either as starting points of therapy or to selectively activate a prodrug within the cancerous environment.