# 858 Therapeutics

Source: https://onco.cc/companies/858-therapeutics/  
OnCo record `858-therapeutics` (Company). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

858 Therapeutics is developing a tablet that blocks PARG, a protein cancer cells use to repair damaged DNA, aiming at tumours that are already weak at DNA repair, such as some ovarian and breast cancers with BRCA changes. It is in its first human trial.

## Summary

858 Therapeutics is a San Diego biotechnology company (3115 Merryfield Row) developing small molecules against DNA damage response targets in cancer. Its lead programme ETX-19477 is an oral, selective inhibitor of poly(ADP-ribose) glycohydrolase (PARG), designed to exploit replication stress and defects in replication fork protection; it is in an open-label phase 1/2 study in advanced solid tumours (NCT06395519), with initial data presented at ASCO 2026, and received FDA Fast Track designations in January 2026 for BRCA-mutated platinum-resistant ovarian cancer and in August 2026 for BRCA-mutated HR-positive, HER2-negative metastatic breast cancer. The company exited stealth in September 2021 with a USD 60 million Series A led by Versant Ventures with NEA, Cormorant Asset Management and Logos Capital, and acquired Gotham Therapeutics at launch; in September 2024 it raised a USD 50 million Series B led by Avidity Partners with Insight Partners, Mirae Asset Capital and Alexandria Venture Investments. Its first registered cancer trial, NCT06395519, was posted on ClinicalTrials.gov in May 2024.

## Fields

- Kind: Company
- Last checked: 2026-10-29
- Also known as: 8five8 Therapeutics
- HQ: San Diego, CA
- Type: biotech
- Website: https://www.8five8tx.com/

## Notes

- Read on 29 October 2026: 8five8tx.com home, news and contact pages and the Series A and Series B releases. Founding year not stated on the company website; it exited stealth in September 2021.
- No PARG target record exists in OnCo, so targets are left empty. The ASCO 2026 data and Fast Track releases were seen as titles on the news page, not read in full.

## Sources

- Official website: https://www.8five8tx.com/
- Company news: https://www.8five8tx.com/news

## Connected records

- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Ovarian cancer](https://onco.cc/cancers/ovarian/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- fronts: [Targeted Therapy](https://onco.cc/fronts/targeted-therapy/)
- technologies: [Synthetic lethality approaches](https://onco.cc/technologies/synthetic-lethality-approaches/)
- trials: [A Study of PARG Inhibitor ETX-19477 in Patients With Advanced Solid Malignancies](https://onco.cc/trials/nct06395519/)
- companies: [Alexandria Venture Investments](https://onco.cc/companies/alexandria-venture-investments/), [Cormorant Asset Management](https://onco.cc/companies/cormorant-asset-management/), [Logos Capital](https://onco.cc/companies/logos-capital/), [Versant Ventures](https://onco.cc/companies/versant-ventures/)

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JSON: https://onco.cc/api/v1/entities/858-therapeutics.json