# Moving towards Personalized Medicine--The Broad Use of Aptamers for Targeted Theranostic
## 2 Cancer Therapeutics  
Aptamers can be applied as therapeutic agents acting mostly as antagonists, binding to the target, and blocking its function, but they can also be applied as agonists, stimulating the targets' function [8; 9; 10]. As therapeutic agents, the features of aptamers potentiate their utilization on drug delivery systems for human disease treatment [9; 11], as they are capable of transporting a variety of therapeutic agents as small molecules, peptides, or toxins [11]. However, in vivo applications of aptamers actually possess some issues. As an example, the conformation of the target during in vitro selection could be different to the conformation under in vivo conditions, affecting its ability in binding. Also, they have short half-life in vivo due to nuclease sensitivity and fast renal filtration [9; 10; 12; 13]. Nowadays, cancer remains one of the deadliest diseases, with a limited number of reliable biomarkers, as well as reduced specificity, affecting healthy tissues. Examples such as chemotherapy or antagonism, like DNA damage repair drugs, can induce modification in the microenvironment, which can lead to an opposite effect, triggering invasion and/or tumor metastases [6]. In view with this, more efficient, specific, and refined therapies are being studied, targeting different hallmarks of the cancer. One of the most promising is the use of oligonucleotide aptamers, which can bind to specific membrane receptors to start the intended action, having already shown solid results against tumor growth and metastatic capacity, as well as modulating the tumor microenvironment to become more susceptible and easier to treat. This methodology also allows combination with other molecules, such as antibodies, which can enhance and potentiate the response. In fact, studies have shown higher biocompatibility and more refined targeting toward the tumor site, also reducing the possibility of developing resistance to treatment [6]. There are several aptamers being tested in different cancer types, as presented in Table 1, as well as the target and their application (diagnostic, therapy, or both). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Cancer Site**} & \multirow{2}{*}{**APtamer**} & \multirow{2}{*}{**Target**} & \multicolumn{3}{c}{**Application**} & \multirow{2}{*}{**References**} \\ \cline{3-4} \cline{6-6}  & & & **Diagnostic** & & **Therap** & **Therap** \\ \hline \multirow{4}{*}{Breast} & HeA2-3 & HER2 & \(\times\) & [14] \\  & PNDA-3 & Periostin & \(\times\) & [15] \\  & apMNK2F & MNK1 & \(\times\) & [16] \\  & apMNK3R & \(\times\) & [17] \\  & ex-50.T & Exosomes & \(\times\) & [18] \\  & \(2^{\prime}\)-Fluoropyrimidines-RNA & Photothermal therapy in & \(\times\) & [19] \\  & AS1411 & Nucleolin & \(\times\) & [20] \\ \hline \multirow{4}{*}{Colorectal} & YJ-1 & CEA & \(\times\) & [21] \\  & & Death receptor 5 & \(\times\) & [21] \\  & apPDG-BB & PDGF-BB & \(\times\) & [22] \\  & apPD-1 & PD-1 & \(\times\) & [23] \\  & NOX-A12 & CXCL12 & \(\times\) & [24] \\ \hline \multirow{4}{*}{Lung} & aptPD-L1 & Tumor microenvironment (induce & \(\times\) & [25] \\  & AP-74 M-545 & \(\times\) & Galechin-1 & \(\times\) & [26] \\  & TBA353 & TBA & \(\times\) & [27] \\  & TBA535 & \(\times\) & \(\times\) & [28] \\  & RA16 & NSCLC cells & \(\times\) & [28] \\ \hline \multirow{2}{*}{Liver} & AS1411 & Nucleolin & \(\times\) & [29] \\  & AS1411 modified & Galectin-14 & \(\times\) & [30] \\  & CL-4 RNV616 & EGFR & \(\times\) & [31] \\ \hline \multirow{2}{*}{Renal} & SW-4 & Caveole-mediated endocytosis & \(\times\) & [32] \\  & SW-4b & process & \(\times\) & [32] \\ \cline{1-1}  & AS1411 & Nucleolin & \(\times\) (PCS II) & [33] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main aptamers used in different cancer sites, their targets and applications.