Imidazole-Functionalized Thieno[3,2-c]Quinoline Hybrids in Aggressive Medullary Thyroid Cancer Cell Models: Biological Evaluation and in Silico Insights

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Background/Objectives: Medullary thyroid carcinoma (MTC) is a rare and aggressive endocrine malignancy frequently associated with RET alterations and dysregulation of RET-associated signaling pathways. In previous studies, first-generation nitro-substituted thieno[3,2-c]quinolines 1 showed promising antiproliferative activity in TT(RETC634R) cells, while subsequent imidazole-based optimization generated second-generation derivatives 2 with broad-spectrum antiproliferative activity in the NCI-60 human tumor cell line panel. Since thyroid cancer models are not included in the NCI-60 platform, the present study aimed to evaluate the antiproliferative potential of these optimized derivatives in clinically relevant MTC cellular models. Methods: Imidazole-functionalized thieno[3,2-c]quinoline derivatives (2a–j) were evaluated against TT(RETC634R) and MZ-CRC-1(RETM918T) cells. The most active compounds were further characterized through induced fit docking (IFD), MM-GBSA calculations, and molecular dynamics (MD) simulations on representative molecular targets. In silico ADME/Toxicity profiling was also performed to assess their developability. Results: Several derivatives exhibited potent activity in both MTC cell models, with multiple compounds achieving submicromolar potency. Compounds 2b and 2g emerged as the most active derivatives in TT(RETC634R) cells, whereas compounds 2d and 2i displayed the most favorable profile in the aggressive MZ-CRC-1(RETM918T) model, thereby extending the biological applicability of the scaffold to an additional clinically relevant RET-mutant context. Computational studies supported RET as the most plausible molecular target for all selected lead compounds, while favorable PI3Kα interaction profiles were predicted for selected derivatives, suggesting distinct target engagement profiles within the series. The most promising derivatives also exhibited an overall favorable predicted ADME/Toxicity profile. Conclusions: The present findings support the success of imidazole-based optimization of the thieno[3,2-c]quinoline scaffold and identify thieno[3,2-c]quinolines 2 as promising lead structures for the future development of novel anti-MTC agents. Further biological and mechanistic investigations will be necessary to better clarify the molecular mechanisms underlying their antiproliferative activity and to guide future lead optimization studies.

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