In a search for novel therapeutic options for head and neck squamous cell carcinomas (HNSCCs) generally treated with limited therapeutic success, we synthesized a series of novel erlotinib–chalcone molecular hybrids with 1,2,3-triazole and alkyne linkers and evaluated them for their anticancer activity on Fadu, Detroit 562 and SCC-25 HNSCC cell lines. Time- and dose-dependent cell viability measurements disclosed a significantly increased efficiency of the hybrids compared to the 1:1 combination of erlotinib and a reference chalcone. The clonogenic assay demonstrated that hybrids eradicate HNSCC cells in low micromolar concentrations. Experiments focusing on potential molecular targets indicate that the hybrids trigger the anticancer effect by a complementary mechanism of action that is independent of the canonical targets of their molecular fragments. Confocal microscopic imaging and real-time apoptosis/necrosis detection assay pointed to slightly different cell death mechanisms induced by the most prominent triazole- and alkyne-tethered hybrids (6a and 13, respectively). While 6a featured the lowest IC₅₀ values on each of the three HNSCC cell lines, in Detroit 562 cells, this hybrid induced necrosis more markedly compared to 13. The therapeutic potential indicated by the observed anticancer efficacy of our selected hybrid molecules validates the concept of development and justifies further investigation to reveal the underlying mechanism of action.

Imipridones, including ONC201, ONC206 and ONC212 (which are emblematic members of this class of compounds developed by Oncoceutics) constitute a novel class of anticancer agents, with promising results in clinical trials. With the aim of increasing the ROS (reactive oxygen species) responsivity of the synthesized molecules, a set of novel ferrocene–imipridone hybrids were designed and synthesized. Our strategy was motivated by the documented interplay between the imipridone-triggered activation of TRAIL (the tumor necrosis factor-related apoptosis-inducing ligand) and mitochondrial ClpP (Caseinolytic protease P) and the ROS-mediated effect of ferrocene-containing compounds. In order to obtain novel hybrids with multitarget characters, the ferrocene moiety was tethered to the imipridone scaffold through ethynylene and 1,2,3-triazolyl linkers by using Sonogashira coupling of Cu(I)- and Ru(II)-catalyzed azide–alkyne cycloadditions. The biological activities of the new hybrids were examined by using in vitro cell viability assays on four malignant cell lines (PANC-1, A2058, EBC-1 and Fadu), along with colony formation assays on the most resistant PANC-1 cell line. Several hybrids caused a significantly greater drop in the cell viability compared to ONC201, and two of them completely overcame the resistance, with IC₅₀ values comparable to those produced by ONC201. The two most potent hybrids, but not ONC201, induced apoptosis/necrosis in PANC-1 and A2058 cells after 24 h of treatment.

Our ongoing research focuses on developing imipridone derivatives capable of complete and selective eradication of cancer cells after relatively short treatment. We have synthetized systematically designed novel hybrids and evaluated their antiproliferative activity on PANC-1 and Fadu cell lines. We have also conducted preliminary studies on the mechanism including colony formation as well as dose-response tests in HEK293T wild-type (WT) and HEK293T CLPP-/- cells. Following gradual structural fine-tuning based on high throughput screening we identified two imipridone hybrids as the most potent derivatives. Their unique substitution pattern includes N-methylated propargylamine and ferrocenyl/phenyltriazole moieties on the benzyl groups attached to opposite sides of the imipridone core. The compounds with IC50 values similar to those of ONC201 were found capable of complete eradication of cancer cells at ca. 4 M, while ONC201 treatment at even higher concentrations left 30-50% of viable cells behind. Both compounds were found to exert equal activity in WT and CLPP-/- HEK293T cells, indicating a ClpP-independent mechanism. Further development is needed to improve the tumor selectivity of the two potent imipridone derivatives in order to develop novel drug candidates that evade resistance and can be applied in a sufficiently broad therapeutic window.

Our ongoing research focuses on the development of new imipridone derivatives. We aim to design compounds that can completely and selectively eradicate cancer cells after relatively short treatment. We have synthetized systematically designed novel hybrids and evaluated their antiproliferative activity against PANC-1 and Fadu cell lines. We have also conducted preliminary studies on the mechanism, including colony formation as well as dose–response tests in HEK293T wild-type (WT) and HEK293T CLPP^−/− cells. Following gradual structural fine-tuning based on high throughput screening, we identified two imipridone hybrids as the most potent derivatives. Their unique substitution pattern includes N-methylated propargylamine and ferrocenyl/phenyltriazole moieties on the benzyl groups attached to opposite sides of the imipridone core. We found that the compounds with IC₅₀ values similar to those of ONC201 completely eradicated cancer cells at about 4 μM, while ONC201 treatment at even higher concentrations left 30–50% of viable cells behind. Both compounds exerted equal activity in WT and CLPP^−/− HEK293T cells, indicating a ClpP-independent mechanism. Further development is needed to improve the tumor selectivity of the two potent imipridone derivatives. By preserving tumor cytotoxicity, we aim to generate new drug candidates that evade resistance and can be applied in a sufficiently broad therapeutic window.