Precision targeting of T cell cytotoxicity with PET

最近针对免疫检查点蛋白（例如CTLA-4、PD-L1）的抑制剂的临床成功， 被认为刺激T细胞对肿瘤的反应，已经彻底改变了癌症治疗。然而，即使在 肿瘤突变负荷高的患者，只有约20-30%的患者达到深度缓解， 用常规成像来区分应答者与非应答者是具有挑战性的。在此基础上， 迫切需要开发区分反应性和治疗抗性患者的生物标志物， 以识别处于不期望的免疫相关不良事件风险中的患者。我们假设成像 能够选择性地测量T细胞用于赋予细胞毒性的生物学的生物标志物可能解决 这些未满足的需求。由于抗肿瘤T细胞的细胞毒性主要由促凋亡丝氨酸蛋白酶赋予， 颗粒酶B，我们已经开发了一种基于肽的化学传感器，我们称之为“限制性相互作用肽”， 能够时空测量颗粒酶B蛋白水解活性，因为酶穿过 T细胞和靶细胞之间免疫突触。在蛋白水解切割全长后， 通过颗粒酶B释放限制性相互作用肽（称为GB 1），放射性标记的抗微生物肽 并经历导致稳定（和无毒）膜结合的自发构象转变。 我们已经证明，放射性标记的GB 1检测肿瘤和正常组织中的T细胞活化， 免疫检查点抑制剂。根据这些令人鼓舞的临床前数据，我们现在已经收集了一个 多学科团队进行翻译研究，以评估颗粒酶B生物化学作为 生物标记物。在三个具体目标上，我们将（1）对64 Cu-GB 1进行IND使能研究，（2）进行一个阶段 0首次在人体研究中确定示踪剂安全性、药代动力学和剂量学，以及（3）执行I期 一项研究，以确定检测尿路上皮癌和肾癌的准确性， 由于用标准护理免疫检查点抑制剂治疗引起的反应。如果成功，该项目将 建立了一个新的范例，用于测量体内T细胞的细胞毒性，这可能对免疫学产生影响。 临床管理其他有问题的人类疾病，如细菌或病毒（HIV，SARS-CoV）感染。 此外，成像方法是全新的，从这个项目中出现的有利数据可以激励 进一步研究开发限制性相互作用肽，以测量其他疾病相关的酶学 蛋白酶在体内与PET。

The recent clinical success of inhibitors against immune checkpoint proteins (e.g. CTLA-4, PD-L1), which are thought to stimulate T cell responses against tumors, has revolutionized cancer therapy. Yet even among patients with high tumor mutational burden, only approximately 20-30% of patients achieve deep response, and discerning responders from non-responders is challenging with conventional imaging. On this basis, there is an urgent unmet need to develop biomarkers that distinguish responsive and treatment resistant patients, as well as identify patients at risk for undesired immune related adverse events. We hypothesized that an imaging biomarker capable of selectively measuring the biology that T cells use to impart cytotoxicity might address these unmet needs. Since antitumor T cell cytotoxicity is conferred primarily by the pro-apoptotic serine protease granzyme B, we have developed a peptide-based chemosensor we term “restricted interaction peptide” that enables spatiotemporal measurements of granzyme B proteolytic activity as the enzyme traverses the immunological synapse between T cell and target cell. Upon proteolytic cleavage of the full length, pro-form of the restricted interaction peptide (termed GB1) by granzyme B, a radiolabeled antimicrobial peptide is liberated and undergoes a spontaneous conformational shift that results in stable (and non-toxic) membrane association. We have shown that radiolabeled GB1 detects T cell activation in tumors and normal tissues elicited by systemic immune checkpoint inhibitors. Following on these encouraging preclinical data, we have now assembled a multidisciplinary team to conduct translational studies to evaluate the utility of granzyme B biochemistry as a biomarker. Over three specific aims, we will (1) perform IND enabling studies for 64Cu-GB1, (2) conduct a phase 0 first in human study to determine tracer safety, pharmacokinetics, and dosimetry, and (3) execute a phase I study to determine the accuracy for detection of urothelial and renal cancers undergoing a productive immune response due to treatment with standard of care immune checkpoint inhibitors. If successful, this project will establish a new paradigm for the measurement of T cell cytotoxicity in vivo that could have implications for the clinical management of other problematic human disorders like bacterial or viral (HIV, SARS-CoV) infections. Moreover, the imaging approach is entirely new, and favorable data emerging from this project could motivate further studies to develop restricted interaction peptides to measure the enzymology of other disease associated proteases in vivo with PET.