Targeting of CDK9 with indirubin 3’-monoxime safely and durably reduces HIV viremia in chronically infected humanized mice

Successful propagation of HIV in the human host requires entry into a permissive cell, reverse transcription of viral RNA, integration into the human genome, transcription of the integrated provirus, and assembly/release of new virus particles. Currently, there are antiretrovirals against each of these viral steps, except for provirus transcription. An inhibitor of HIV transcription could both increase potency of treatment and suppress drug-resistant strains. Cellular cyclin-dependent kinase 9 (CDK9) serves as a cofactor for the HIV Tat protein and is required for effective transcription of the provirus. Previous studies have shown that the CDK9 inhibitor Indirubin 3’-monoxime (IM) inhibits HIV transcription in vitro and in short-term in vivo studies of HIV acute infection in humanized mice (PBMC-NSG model), suggesting a therapeutic potential. The objective of this study is to evaluate the toxicity, pharmacokinetics and long-term antiviral activity of IM during chronic HIV infection in humanized mice (HSC-NSG model). We show that IM concentrations above EC50 values are rapidly achieved and sustained for > 3 h in plasma, and that non-toxic concentrations durably reduce HIV RNA levels. In addition, IM enhanced the antiviral activity of antiretrovirals from the reverse transcriptase, protease and integrase inhibitor classes in in vitro infectivity assays. In summary, IM may enhance current antiretroviral treatments and could help achieve a “functional cure” in HIV patients by preventing expression of proviruses.

人类免疫缺陷病毒（HIV）在人体宿主中的成功增殖，需依次完成以下关键步骤：进入允许性细胞、病毒RNA逆转录、整合至人类基因组、整合前病毒转录，以及新病毒颗粒的组装与释放。目前，除整合前病毒转录环节外，其余各病毒复制步骤均已有对应的抗逆转录病毒治疗药物。HIV转录抑制剂既可提升治疗效力，亦可抑制耐药毒株的增殖。细胞周期蛋白依赖性激酶9（CDK9）作为HIV Tat蛋白的辅助因子，是整合前病毒有效转录的必需因子。既往研究表明，CDK9抑制剂靛玉红3'-单肟（Indirubin 3’-monoxime, IM）可在体外及人源化小鼠（PBMC-NSG模型）的HIV急性感染短期体内实验中抑制HIV转录，提示其具备治疗应用潜力。本研究旨在评估IM在人源化小鼠（HSC-NSG模型）慢性HIV感染模型中的毒性、药代动力学特征及长期抗病毒活性。研究结果显示，IM可在血浆中快速达到并维持高于半数效应浓度（EC50）的药物水平，且该持续时长超过3小时；同时，无毒浓度的IM可持续降低HIV RNA水平。此外，在体外感染性实验中，IM可增强逆转录酶抑制剂、蛋白酶抑制剂及整合酶抑制剂类抗逆转录病毒药物的抗病毒活性。综上，IM可优化现有抗逆转录病毒治疗方案，或可通过阻断前病毒表达，帮助HIV患者实现“功能性治愈”。