Anticancer Properties of Halogenated Pyrrolo[3,2-d]pyrimidines with Decreased Toxicity via N5 Substitution

Abstract

Halogenated pyrrolo[3,2-d]pyrimidine analogues have shown antiproliferative activity in recent studies, with cell accumulation occurring in the G₂/M stage without apoptosis. However, the mechanism of action and pharmacokinetic (PK) profile of these compounds has yet to be determined. To investigate the PK profile of these compounds, a series of halogenated pyrrolo[3,2-d]pyrimidine compounds was synthesized and first tested for activity in various cancer cell lines followed by a mouse model. EC₅₀ values ranged from 0.014 to 14.5 μm, and maximum tolerated doses (MTD) in mice were between 5 and 10 mg kg⁻¹. This indicates a wide variance in activity and toxicity that necessitates further study. To decrease toxicity, a second series of compounds was synthesized with N5-alkyl substitutions in an effort to slow the rate of metabolism, which was thought to be leading to the toxicity. The N-substituted compounds demonstrated comparable cell line activity (EC₅₀ values between 0.83–7.3 μm) with significantly decreased toxicity (MTD=40 mg kg⁻¹). Finally, the PK profile of the active N5-substituted compound shows a plasma half-life of 32.7 minutes, and rapid conversion into the parent unsubstituted analogue. Together, these data indicate that halogenated pyrrolo[3,2-d]pyrimidines present a promising lead into potent antiproliferative agents with tunable activity and toxicity, and rapid metabolism.