Proteases and Tissue Remodeling Section, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA; Program of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA, USA.
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
Toxicol Appl Pharmacol. 2014 Sep 1;279(2):220-9. doi: 10.1016/j.taap.2014.06.010. Epub 2014 Jun 24.
We have previously designed and characterized versions of anthrax lethal toxin that are selectively cytotoxic in the tumor microenvironment and which display broad and potent anti-tumor activities in vivo. Here, we have performed the first direct comparison of the safety and efficacy of three engineered anthrax lethal toxin variants requiring activation by either matrix-metalloproteinases (MMPs), urokinase plasminogen activator (uPA) or co-localized MMP/uPA activities. C57BL/6J mice were challenged with six doses of engineered toxins via intraperitoneal (I.P.) or intravenous (I.V.) dose routes to determine the maximum tolerated dose for six administrations (MTD6) and dose-limiting toxicities. Efficacy was evaluated using the B16-BL6 syngraft model of melanoma; mice bearing established tumors were treated with six I.P. doses of toxin and tumor measurements and immunohistochemistry, paired with terminal blood work, were used to elaborate upon the anti-tumor mechanism and relative efficacy of each variant. We found that MMP-, uPA- and dual MMP/uPA-activated anthrax lethal toxins exhibited the same dose-limiting toxicity; dose-dependent GI toxicity. In terms of efficacy, all three toxins significantly reduced primary B16-BL6 tumor burden, ranging from 32% to 87% reduction, and they also delayed disease progression as evidenced by dose-dependent normalization of blood work values. While target organ toxicity and effective doses were similar amongst the variants, the dual MMP/uPA-activated anthrax lethal toxin exhibited the highest I.P. MTD6 and was 1.5-3-fold better tolerated than the single MMP- and uPA-activated toxins. Overall, we demonstrate that this dual MMP/uPA-activated anthrax lethal toxin can be administered safely and is highly effective in a preclinical model of melanoma. This modified bacterial cytotoxin is thus a promising candidate for further clinical development and evaluation for use in treating human cancers.
我们之前设计并鉴定了几种炭疽致死毒素的变体，它们在肿瘤微环境中具有选择性细胞毒性，并在体内显示出广泛而强大的抗肿瘤活性。在这里，我们首次直接比较了三种需要基质金属蛋白酶（MMPs）、尿激酶纤溶酶原激活物（uPA）或共定位 MMP/uPA 活性激活的工程炭疽致死毒素变体的安全性和疗效。通过腹腔内（I.P.）或静脉内（I.V.）途径用六种工程毒素挑战 C57BL/6J 小鼠，以确定六次给药的最大耐受剂量（MTD6）和剂量限制毒性。使用 B16-BL6 黑色素瘤嵌合模型评估疗效；用六次 I.P.剂量的毒素处理患有已建立的肿瘤的小鼠，并进行肿瘤测量和免疫组织化学分析，结合终端血液检查，以详细阐述每种变体的抗肿瘤机制和相对疗效。我们发现 MMP-、uPA-和双 MMP/uPA 激活的炭疽致死毒素表现出相同的剂量限制毒性；剂量依赖性 GI 毒性。在疗效方面，所有三种毒素都显著降低了原发性 B16-BL6 肿瘤负担，减少了 32%至 87%，并且它们还通过剂量依赖性血液检查值的正常化延迟了疾病进展。虽然目标器官毒性和有效剂量在变体之间相似，但双 MMP/uPA 激活的炭疽致死毒素表现出最高的 I.P. MTD6，并且比单 MMP-和 uPA 激活的毒素耐受度高 1.5-3 倍。总体而言，我们证明这种双 MMP/uPA 激活的炭疽致死毒素可以安全给药，并且在黑色素瘤的临床前模型中非常有效。这种改良的细菌细胞毒素因此是进一步临床开发和评估用于治疗人类癌症的有前途的候选物。
