# Design and Biological Evaluation of Mannich-Modified 8-Hydroxyquinoline–Phthalimide Hybrids Against Drug-Resistant Cancer Cells

## TL;DR

This study designs and tests new chemical compounds that show strong activity against drug-resistant cancer cells, particularly colorectal cancer.

## Contribution

The paper introduces Mannich-modified 8-hydroxyquinoline–phthalimide hybrids with enhanced selectivity for multidrug-resistant cancer cells.

## Key findings

- Compounds 2 and 4 showed the strongest cytotoxic activity with IC50 values as low as 4.88 µM.
- Compounds 9c, 9a, and 8a exhibited the highest selectivity for MDR cells with RR values of 0.29, 0.33, and 0.35.
- Mannich modification improved selectivity and some compounds inhibited P-glycoprotein ATPase activity.

## Abstract

Background: 8-Hydroxyquinoline and phthalimide are two significant heterocyclic scaffolds in medicinal chemistry due to their pharmacological profiles. Hybridizing these pharmacophores and further modifying them via modified Mannich reactions provides a strategy to improve their physicochemical parameters and selectivity toward multidrug-resistant (MDR) cancer cells. Objectives: To synthesize a series of 8-hydroxyquinoline–phthalimide hybrids and their Mannich base derivatives and evaluate their cytotoxic activity and resistance-selective properties against sensitive Colo205 and resistant Colo320 cancer cell lines. Methods: Four hybrid compounds were synthesized by reacting 5-amino-8-hydroxyquinoline with different phthalic anhydride derivatives. Twelve fine-tuned derivatives were prepared by using the modified Mannich reaction. Cytotoxic activity was measured using the MTT assay, and relative resistance (RR) was calculated to determine selectivity toward the resistant cell line. P-glycoprotein (Pgp) ATPase activity was evaluated for the most active compounds. Results: All derivatives displayed cytotoxic activity, with higher potency toward the resistant Colo320 cell line. Compounds 2 and 4 showed the strongest activity against both cell lines (IC50 down to 4.88 µM). Compounds 5, 8a, 9a, and 9c retained potent activity against Colo320 (IC50 = 9.89–22.79 µM). Incorporating a CH2–N group at position C7 substantially enhanced the selectivity for MDR cells. Compounds 9c, 9a, and 8a exhibited the highest selectivity, with RR values of 0.29, 0.33, and 0.35, respectively. Compounds 2, 4, 5, 8a, and 9a showed inhibitory effects on Pgp ATPase activity. Conclusions: The newly synthesized HQ–phthalimide hybrids represent promising candidates for targeting MDR in colorectal cancer, with Mannich modification enhancing the selectivity toward resistant cells.