Precision targeting of T cell cytotoxicity with PET

最近针对免疫检查点蛋白(如CTLA-4、PD-L1)的抑制剂的临床成功，这些蛋白是 被认为可以刺激T细胞对肿瘤的反应，已经彻底改变了癌症的治疗方法。然而，即使是在 肿瘤突变负荷高的患者，只有大约20%-30%的患者达到深度应答，并且 用传统的成像方法来区分应答者和非应答者是一项挑战。在此基础上，有一个 迫切需要开发生物标记物来区分敏感患者和耐药患者 识别有不良免疫相关不良事件风险的患者。我们假设一种成像 一种生物标记物，能够选择性地测量T细胞用于传递细胞毒作用的生物学特性 这些未得到满足的需求。由于抗肿瘤T细胞的细胞毒作用主要是由促凋亡的丝氨酸蛋白酶产生的 Granzyme B，我们已经开发了一种基于多肽的化学传感器，我们称之为“限制相互作用肽” 能够在颗粒酶B穿过 T细胞与靶细胞之间的免疫突触。在全长蛋白水解性切割的基础上， 释放放射性标记抗菌肽颗粒酶B的限制性相互作用肽(GB1) 并经历自发的构象变化，导致稳定的(无毒的)膜结合。 我们已经证明，放射性标记的GB1可以检测到全身性T细胞在肿瘤和正常组织中的激活。 免疫检查点抑制剂。根据这些令人鼓舞的临床前数据，我们现在已经组装了一个 多学科团队将进行翻译研究，以评估颗粒酶B生物化学作为一种 生物标志物。在三个具体目标上，我们将(1)对64Cu-GB1进行IND使能研究，(2)进行一个阶段 首次在人体研究中确定示踪剂的安全性、药代动力学和剂量学，以及(3)执行I阶段 产生性免疫检测尿路上皮癌和肾癌准确性的研究 因使用标准护理免疫检查点抑制剂治疗而产生的反应。如果成功，这个项目将 建立一种测量体内T细胞杀伤活性的新范式，这可能对 其他有问题的人类疾病的临床管理，如细菌或病毒(艾滋病毒、SARS-CoV)感染。 此外，成像方法是全新的，从这个项目中产生的有利数据可能会激励 进一步研究开发限制性相互作用多肽以测量其他相关疾病的酶学 体内的蛋白水解酶与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.