(99m)Tc-ixolaris targets glioblastoma-associated tissue factor: in vitro and pre-clinical applications

A Kunitz-type inhibitor from tick salivary glands: A promising novel antitumor drug candidate

Salivary glands are vital structures responsible for successful tick feeding. The saliva of ticks contains numerous active molecules that participate in several physiological processes. A Kunitz-type factor Xa (FXa) inhibitor, similar to the tissue factor pathway inhibitor (TFPI) precursor, was identified in the salivary gland transcriptome of Amblyomma sculptum ticks. The recombinant mature form of this Kunitz-type inhibitor, named Amblyomin-X, displayed anticoagulant, antiangiogenic, and antitumor properties. Amblyomin-X is a protein that inhibits FXa in the blood coagulation cascade and acts via non-hemostatic mechanisms, such as proteasome inhibition. Amblyomin-X selectively induces apoptosis in cancer cells and promotes tumor regression through these mechanisms. Notably, the cytotoxicity of Amblyomin-X seems to be restricted to tumor cells and does not affect non-tumorigenic cells, tissues, and organs, making this recombinant protein an attractive molecule for anticancer therapy. The cytotoxic activity of Amblyomin-X on tumor cells has led to vast exploration into this protein. Here, we summarize the function, action mechanisms, structural features, pharmacokinetics, and biodistribution of this tick Kunitz-type inhibitor recombinant protein as a promising novel antitumor drug candidate.

The tick and I: Parasite-host interactions between ticks and humans

Ticks, particularly hard ticks (Ixodidae), which are among the most important vectors of dangerous infectious agents, feed on their hosts for extended periods of time. With this lifestyle, numerous adaptations have evolved in ticks and their hosts, the pharmacological importance of which is increasingly being recognized. Many bioactive substances in tick saliva are being considered as the basis of new drugs. For example, components of tick cement can be developed into tissue adhesives or wound closures. Analgesic and antipruritic salivary components inhibit histamine or bradykinin, while other tick-derived molecules bind opioid or cannabinoid receptors. Tick saliva inhibits the extrinsic, intrinsic, or common pathway of blood coagulation with implications for the treatment of thromboembolic diseases. It contains vasodilating substances and affects wound healing. The broad spectrum of immunomodulatory and immunosuppressive effects of tick saliva, such as inhibition of chemokines or cellular immune responses, allows development of drugs against inflammation in autoimmune diseases and/or infections. Finally, modern vaccines against ticks can curb the spread of serious infections. The medical importance of the complex tick-host interactions is increasingly being recognized and translated into first clinical applications. Using selected examples, an overview of the mutual adaptations of ticks and hosts is given here, focusing on their significance to medical advance.

The sialotranscriptome of the gopher-tortoise tick, Amblyomma tuberculatum

The gopher tortoise tick, Amblyomma tuberculatum, is known to parasitize keystone ectotherm reptile species. The biological success of ticks requires precise mechanisms to evade host hemostatic and immune responses. Acquisition of a full blood meal requires attachment, establishment of the blood pool, and engorgement of the tick. Tick saliva contains molecules which counter the host responses to allow uninterrupted feeding on the host. RNASeq of the salivary glands of Amblyomma tuberculatum ticks were sequenced resulting in 138,030 pyrosequencing reads which were assembled into 29,991 contigs. A total of 1875 coding sequences were deduced from the transcriptome assembly, including 602 putative secretory and 982 putative housekeeping proteins. The annotated data sets are available as a hyperlinked spreadsheet. The sialotranscriptome assembled for this tick species made available a valuable resource for mining novel pharmacological activities and comparative analysis.

Development of 131I-ixolaris as a theranostic agent: metastatic melanoma preclinical studies

Tissue factor (TF), a blood coagulation protein, plays an important role in tumor growth, invasion, and metastasis. Ixolaris, a tick-derived non-immunogenic molecule that binds to TF, has demonstrated in vivo inhibitory effect on murine models of melanoma, including primary growth and metastasis. This work aimed to: I) develop an efficient and stable labeling technique of ixolaris with Iodine-131(¹³¹I); II) compare the biodistribution of ¹³¹I and ¹³¹I-ixolaris in tumor-free and melanoma-bearing mice; III) evaluate whether ¹³¹I-ixolaris could serve as an antimetastatic agent. Ixolaris radioiodination was performed using iodogen, followed by liquid paper chromatography. Labeling stability and anticoagulant activity were measured. Imaging studies were performed after intravenous administration of free ¹³¹I or ¹³¹I-ixolaris in a murine melanoma model employing the B16-F10 cell line. Animals were divided in three experimental groups: the first experimental group, D0, received a single-dose of 9.25 MBq of ¹³¹I-ixolaris at the same day the animals were inoculated with melanoma cells. In the second group, D15, a single-dose of 9.25 MBq of ¹³¹I-ixolaris or free ¹³¹I was applied into mice on the fifteenth day after the tumor induction. The third group, D1-D15, received two therapeutic doses of 9.25 MBq of ¹³¹I-ixolaris or ¹³¹I. In vitro studies demonstrated that ¹³¹I-ixolaris is stable for up to 24 h and retains its inhibitory activity on blood coagulation. Biodistribution analysis and metastasis assays showed that all treatment regimens with ¹³¹I-ixolaris were effective, being the double-treatment (D1/D15) the most effective one. Remarkably, treatment with free ¹³¹I showed no anti-metastatic effect. ¹³¹I-ixolaris is a promising theranostic agent for metastatic melanoma.

The Use of Tick Salivary Proteins as Novel Therapeutics

The last three decades of research into tick salivary components have revealed several proteins with important pharmacological and immunological activities. Two primary interests have driven research into tick salivary secretions: the search for suitable pathogen transmission blocking or “anti-tick” vaccine candidates and the search for novel therapeutics derived from tick salivary components. Intensive basic research in the field of tick salivary gland transcriptomics and proteomics has identified several major protein families that play important roles in tick feeding and overcoming vertebrate anti-tick responses. Moreover, these families contain members with unrealized therapeutic potential. Here we review the major tick salivary protein families exploitable in medical applications such as immunomodulation, inhibition of hemostasis and inflammation. Moreover, we discuss the potential, opportunities, and challenges in searching for novel tick-derived drugs.