ABSTRACT

The extracellular ATP/adenosine axis in the tumor microenvironment (TME) has emerged as an important immune-regulatory pathway. Nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), otherwise known as CD39, is highly expressed in the TME, both on infiltrating immune cells and tumor cells across a broad set of cancer indications. CD39 processes pro-inflammatory extracellular ATP to ADP and AMP, which is then processed by Ecto-5ʹ-nucleotidase/CD73 to immunosuppressive adenosine. Directly inhibiting the enzymatic function of CD39 via an antibody has the potential to unleash an immune-mediated anti-tumor response via two mechanisms: 1) increasing the availability of immunostimulatory extracellular ATP released by damaged and/or dying cells, and 2) reducing the generation and accumulation of suppressive adenosine within the TME. Tizona Therapeutics has engineered a novel first-in-class fully human anti-CD39 antibody, TTX-030, that directly inhibits CD39 ATPase enzymatic function with sub-nanomolar potency. Further characterization of the mechanism of inhibition by TTX-030 using CD39⁺ human melanoma cell line SK-MEL-28 revealed an uncompetitive allosteric mechanism (α < 1). The uncompetitive mechanism of action enables TTX-030 to inhibit CD39 at the elevated ATP concentrations reported in the TME. Maximal inhibition of cellular CD39 ATPase velocity was 85%, which compares favorably to results reported for antibody inhibitors to other enzyme targets. The allosteric mechanism of TTX-030 was confirmed via mapping the epitope to a region of CD39 distant from its active site, which suggests possible models for how potent inhibition is achieved. In summary, TTX-030 is a potent allosteric inhibitor of CD39 ATPase activity that is currently being evaluated in clinical trials for cancer therapy.

摘要

肿瘤微环境 (TME) 中的细胞外 ATP/腺苷轴已成为重要的免疫调节途径。核苷三磷酸二磷酸水解酶-1 (NTPDase1)，也称为 CD39，在 TME 中高度表达，无论是在浸润免疫细胞还是肿瘤细胞方面，都涉及广泛的癌症适应症。CD39 将促炎性细胞外 ATP 加工成 ADP 和 AMP，然后由 Ecto-5ʹ-核苷酸酶/CD73 加工成免疫抑制性腺苷。通过抗体直接抑制 CD39 的酶促功能有可能通过两种机制释放免疫介导的抗肿瘤反应：1) 增加受损和/或垂死细胞释放的免疫刺激性细胞外 ATP 的可用性，以及 2) 减少TME 内抑制性腺苷的产生和积累。Tizona Therapeutics 设计了一种新型的一流全人抗 CD39抗体 TTX-030，它以亚纳摩尔的效力直接抑制 CD39 ATPase 酶促功能。使用 CD39 进一步表征 TTX-030 的抑制机制⁺人类黑色素瘤细胞系 SK-MEL-28 揭示了一种非竞争性变构机制 (α < 1)。非竞争性作用机制使 TTX-030 能够在 TME 中报告的升高的 ATP 浓度下抑制 CD39。细胞 CD39 ATPase 速度的最大抑制率为 85%，这与针对其他酶靶标的抗体抑制剂报告的结果相比具有优势。通过将表位映射到远离其活性位点的 CD39 区域，证实了 TTX-030 的变构机制，这暗示了如何实现有效抑制的可能模型。总之，TTX-030 是一种有效的 CD39 ATPase 活性变构抑制剂，目前正在癌症治疗的临床试验中进行评估。