# RK-33

Source: https://onco.cc/drugs/rk-33/  
OnCo record `rk-33` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

RK-33 is an experimental drug from NATSAR Pharmaceuticals that blocks the DDX3 protein in cancer cells. It has been studied in the laboratory and a first trial in people is planned.

## Summary

RK-33 is NATSAR Pharmaceuticals' DDX3 inhibitor. The company reports activity across 70 human cancer cell lines, with independent NCI testing, and in animal models alone and with radiation, and plans a phase 1A study of safety and maximum tolerated dose with an intravenous formulation. A National Cancer Institute SBIR award funds its development for breast cancer. No registered trial was found.

## Fields

- Kind: Treatment
- Status: preclinical
- Last checked: 2026-11-04
- Tags: pipeline
- Code: RK-33
- Modality: Small-molecule inhibitor
- Mechanism: Binds the RNA helicase DDX3 and impedes its function, which NATSAR Pharmaceuticals reports activates cell death, inhibits Wnt signalling and blocks non-homologous end-joining DNA repair, making cells more sensitive to radiation.

## Sources

- NATSAR Pharmaceuticals: https://www.natsarpharmaceuticals.com/
- NIH RePORTER: award 5R44CA295155-02: https://reporter.nih.gov/project-details/11419762

## Connected records

- targets: [DDX3X](https://onco.cc/targets/ddx3x/)
- companies: [NATSAR Pharmaceuticals](https://onco.cc/companies/natsar-pharmaceuticals/)

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JSON: https://onco.cc/api/v1/entities/rk-33.json