# Ras Isoforms from Lab Benches to Lives--What Are We Missing and How Far Are We?
## 6 Future Recommendations for Devising Isoform-Specific Targeting
A better understanding of such characteristics of codon-specific mutants, co-occurring mutations, genetic heterogeneity, and functionally distinct allelic forms is a prerequisite to generating efficient inhibitors  
Bacterial protein toxins and effector proteins can specifically target heterotrimeric G Proteins or small GTPases of the Rho and Ras family to modify host cell signaling [193]. While the vast majority of toxins modify Rho GTPases, there are also examples of Ras being the target. To date, however, there is no known bacterial toxin that specifically modifies only Ras. Toxins that act on Ras include Tcsl and Tcsl from _Clostridium sordelli_ (UDP glycosylation), TpeL from _Clostridium perfringens_ (\(N\)-acetylglucosamine), ExoS from _Pseudomonas aeruginosa_ (ADP ribosylation), and DUF5 Vv (endopeptidase) from _Vibrio vulnificans_. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**S. No.** & **Category** & **Condition** & **Intervention/Treatment** & **Clinical Trial Status** \\ \hline
3 & N-Ras mutation & Solid Tumor & Drug: ARQ 736 & Phase 1 \\ \hline
4 & N-Ras mutation & Cancer & & \\  & N-Ras mutation & Lung Cancer Metastatic & Drug: PDR001 & Phase 2 \\  & Immunotherapy & & & \\ \hline
5 & N-Ras mutation & Metastatic or Unresectable Cutaneous & Drug: MEK162 & Phase 3 \\  & & Melanoma & Drug: Dacarbazine & Phase 3 \\ \hline
6 & N-Ras mutation & BRAF or NRAS Mutant Metastatic & & \\  & Melanoma & Drug: MEK162 & Phase 2 \\ \hline  & & Advanced Lymphoma & & \\  & & Advanced Malignant Solid Neoplasm & & \\  & & Hematopoietic and lymphoid Cell & & \\
7 & N-Ras mutation & Neoplasm & Drug: Binimetinib & Phase 2 \\  & & Refractory Lymphoma & & \\  & & Refractory Malignant Solid Neoplasm & & \\  & & Refractory Plasma Cell Myeloma & & \\ \hline
8 & N-Ras mutation & Solid Tumor & Drug: HM95573 & Phase 1 \\ \hline
9 & N-Ras mutation & Lung Cancer, Non-Small Cell & & \\  & & & Drug: GSK1120212 & \\  & & & Drug: docetaxel & \\ \hline
10 & N-Ras mutation & Metastatic Malignant Solid Neoplasm & & \\  & & Refractory Malignant Solid Neoplasm & & \\  & & Unresectable Malignant Solid Neoplasm & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Cont. The lethal toxin of _C. sordelli_, TcsL, modifies H, K, and N-Ras at Thr35 in the switch I region by catalyzing the transfer of glucose from UDP-Glucose to the threonine residue [194]. This keeps the protein in an inactive, GDP-bound state which eventually causes cell death through cell cycle arrest and induction of apoptosis [195; 196]. Large cytotoxin TpeL from _C. perfringens_ catalyzes \(N\)-acetylglucosamination of the same Thr35 residue in all main types of oncogenic Ras. Again, the toxin modification resulted in a loss of MapK activity and cell death [197]. _Pseudomonas_ ExoS is an effector protein that is transferred into host cells via a type III secretion system. Among many other cellular targets, ExoS inhibits Ras through ADP ribosylation of the residues Arg41 and Arg128, both outside the switch I region. Still, this modification attenuates loading with GTP and blocks interaction with downstream effectors [198]. Last but not least, a new family of \"Ras/Rap specific proteases\" (RRSP) was recently defined that comprises toxins from _Vibrio vulnificus_, _Aeromonas hydrophilia_, and the insect-specific pathogen _Photorhabbus asymbiotica_[199]. DUF5 Vc belongs to the class of multifunctional-autoprocessing repeats-in-toxin (MARTX) toxins. The prototypic DUF5 Vc of _Vibrio vulnificus_ targets Ras and Rap located at the plasma membrane with its endopeptidase activity which cleaves the GTPase between Y32 and D33 and prepares it for subsequent protein degradation [196]. MARTX toxins translocate across the plasma membrane to deliver their effector proteins from the holotoxin through autoprocessing [200]. DUF5 Vc targets all isoforms of Ras as well as the most important oncogenic mutants which results in cell death by inhibition of cell division. Thus, this toxin might be employed to specifically delete Ras and kill tumor cells.