Newly designed pentacyclic benzimidazole derivatives, featuring amino or amido side chains, were synthesized to assess their in vitro antiproliferative activity. Additionally, we conducted investigations into their direct interaction with nucleic acids, aiming to uncover potential mechanisms of biological action. These compounds were synthesized using conventional organic synthesis methodologies, alongside photochemical and microwave-assisted reactions. Upon synthesis, the newly derived compounds underwent in vitro testing for their antiproliferative effects on various human cancer cell lines. Notably, derivatives 6 and 9 exhibited significant antiproliferative activity within the submicromolar concentration range. Our biological assessment highlighted that the biological activity was strongly influenced by both the position of the N atom on the quinoline moiety and the position and nature of the side chain on the pentacyclic skeleton. Findings from fluorescence, circular dichroism spectroscopy, and thermal melting assays indicated a mixed binding mode—comprising intercalation and the binding of aggregated compounds along the polynucleotide backbone—of these pentacyclic benzimidazoles with DNA and RNA.