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Quinoxaline 1,4-dioxides: hypoxia-selective therapeutic agents
Mona Diab-Assef1, Makhluf J Haddadin, Pierre Yared
1Department of Biology, American University of Beirut, Beirut, Lebanon.
Abstract:
A problem that confronts clinicians in the treatment of cancer is the resistance of hypoxic tumors to chemotherapy and radiation therapy. Thus, the development of new drugs that are toxic to hypoxic cells found in solid tumors is an important objective for effective anticancer chemotherapy. We recently showed that the heterocyclic aromatic N-oxides, quinoxaline 1,4-dioxides (QdNOs), are cytotoxic to tumor cells cultured under hypoxia. In this study, we evaluated the hypoxia-selective toxicity of four diversely substituted QdNOs and determined their effect on the expression of hypoxia inducible factor (HIF) 1alpha in the human colon cancer cell line T-84. The various QdNOs were found to possess a 50- to 100-fold greater cytotoxicity to T-84 cells cultured under hypoxia compared with oxia. Interestingly, the hypoxia cytotoxicity ratio (HCR), the ratio of equitoxic concentrations of the drug under aerobic/anoxic conditions, was highly structure related and depended on the nature of the substituents on the QdNO heterocycle. The most cytotoxic 2-benzoyl-3-phenyl-6,7-dichloro derivative of QdNO (DCQ) was potent at a dose of 1 microM with an HCR of 100 and significantly reduced the levels of HIF-1alpha transcript and protein. The 2-benzoyl-3-phenyl derivative (BPQ) had a hypoxia potency of 20 microM and an HCR of 40. By contrast, the 2-aceto-3-methyl and the 2,3-tetramethylene (TMQ) derivatives of QdNO were much less cytotoxic under hypoxia (HCRs of 8.5 and 6.5, respectively) and reduced the expression of HIF-1alpha mRNA to a much lesser extent. Because the nonchlorinated analogue BPQ did not demonstrate behavior similar to that of DCQ, we hypothesize that the C-6, C-7-chlorine of DCQ might play a significant role in the selective hypoxic cytotoxicity of the drug.
Insights
New quinoxaline 1,4-dioxides (QdNOs) show potent and selective toxicity against hypoxic cancer cells. The most effective compound, DCQ, reduced hypoxia-inducible factor 1-alpha (HIF-1alpha) and demonstrated significant anticancer potential.
Area of Science:
- Oncology
- Medicinal Chemistry
- Molecular Biology
Background:
- Hypoxic tumors resist conventional cancer therapies.
- Developing drugs targeting hypoxic cancer cells is crucial for effective treatment.
- Quinoxaline 1,4-dioxides (QdNOs) are a promising class of compounds with potential anticancer activity.
Purpose of the Study:
- To evaluate the hypoxia-selective toxicity of various QdNO derivatives.
- To determine the effect of these compounds on hypoxia-inducible factor 1-alpha (HIF-1alpha) expression.
- To identify structural features contributing to selective cytotoxicity in hypoxic conditions.
Main Methods:
- Cytotoxicity assays on T-84 colon cancer cells under hypoxic and normoxic conditions.
- Assessment of HIF-1alpha transcript and protein levels via RT-PCR and Western blotting.
- Structure-activity relationship analysis of four substituted QdNOs.
Main Results:
- QdNOs exhibited 50- to 100-fold greater cytotoxicity in hypoxic versus normoxic conditions.
- The dichloro derivative (DCQ) showed the highest potency (1 microM) and hypoxia cytotoxicity ratio (HCR) of 100.
- DCQ significantly reduced HIF-1alpha levels, unlike less cytotoxic analogues.
- Chlorination at the C-6, C-7 positions appeared critical for DCQ's selective hypoxic toxicity.
Conclusions:
- Substituted quinoxaline 1,4-dioxides demonstrate significant hypoxia-selective cytotoxicity.
- The dichloro derivative (DCQ) is a potent candidate for targeting hypoxic tumors.
- Structure-activity relationships, particularly chlorination, influence the efficacy and selectivity of QdNOs against hypoxic cancer cells.