The challenge
Most cancer treatments today work by targeting specific markers on tumor cells. But the markers currently used are only found in a small fraction of patients, and they also appear on healthy cells, which can cause serious side effects. Many patients with solid tumors still have few effective options.
The field needs a new kind of target: one that is present on tumors but largely absent from normal tissue.
70-80%
of solid tumors express HERV-K
Low / None
expression in normal adult tissues
6,000+
tumor & normal biopsies analyzed
Our approach
Buried in our DNA are ancient viral sequences called human endogenous retroviruses (HERVs), making up about 8% of the human genome. They are normally silent in healthy adults.
HERV‑K, one family of these sequences, gets reactivated in cancer cells. It appears on their surface, acts as an upstream driver of tumor growth, and its expression increases as the disease progresses and spreads.
SunnyBay has developed therapies that specifically recognize HERV‑K on cancer cells, delivering treatment directly to tumors while leaving healthy tissue unharmed.
How it works
SunnyBay's lead therapy, SBB001, is an antibody-drug conjugate (ADC) built on a fully humanized monoclonal antibody with high specificity for HERV-K, paired with clinically validated payloads including MMAE, SN38, and DXd. Think of it as a guided missile: an antibody that finds cancer cells, combined with a powerful drug that destroys them from the inside.
1
Find
The antibody recognizes HERV-K on the surface of tumor cells and binds to it selectively.
2
Enter
The cancer cell absorbs the antibody-drug complex, pulling it inside.
3
Release
Once inside, the drug payload is released directly within the cancer cell.
4
Destroy
The cancer cell is killed while healthy cells remain unaffected.
Cancers we target
HERV-K is expressed in approximately 70-80% of multiple solid tumor types. SunnyBay's approach has shown activity across a broad range of cancers, including:
Breast Cancer
Lung Cancer
Ovarian Cancer
Pancreatic Cancer
Colon Cancer
Melanoma
In preclinical studies, SBB001 has demonstrated tumor growth inhibition, reduced metastatic spread, and extended survival, including in hard-to-treat tumors with KRAS and p53 mutations.
Safety profile
Preclinical data support a favorable therapeutic window for SBB001. No significant body-weight loss has been observed at efficacious doses, activity in non-malignant cell lines is minimal, and repeat dosing has produced no overt toxicity signals. The biology of HERV-K — restricted to tumor tissue — suggests limited on-target risk to normal tissue.
Next milestone: formal GLP toxicology studies in rodent and non-rodent species, in support of IND submission.
The team
SunnyBay's founders, Dr. Feng Wang-Johanning (CEO) and Dr. Gary Johanning (CSO), have spent over 25 years as pioneers in HERV biology, with affiliations including MD Anderson Cancer Center, Stanford Cancer Institute, SRI International, and UAB Comprehensive Cancer Center.
Their work spans over 6,000 tumor and normal biopsies and more than $15M in non-dilutive NIH and DoD research funding. SunnyBay's IP estate includes multiple PCT filings — covering antibodies and ADCs, cellular therapies, vaccines, and diagnostics — with international filings in Canada, Japan, Europe, and China.
