SunnyBay Biotech
Developing therapies that stop tumor growth and metastasis by targeting HERV‑K, expressed across 70–80% of solid tumors
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MCF-7 human breast cancer cells strongly express pro-metastatic CK-19

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
SunnyBay Biotech CEO Feng Wang-Johanning pictured in the lab

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, SN-38, 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
Colorectal Cancer
Melanoma

In xenograft studies, SBB001 produced significant tumor growth inhibition compared with both vehicle and antibody-only controls — confirming that payload delivery adds meaningfully to antibody-mediated activity alone. A clear dose-response was observed, and anti-tumor activity correlated with tumor HERV-K expression, supporting on-target activity. SBB001 also reduced metastatic spread and extended survival in aggressive models, including hard-to-treat KRAS- and p53-mutant tumors (NCI-H23) associated with poor prognosis and limited therapeutic options.

A differentiated target

Most ADC programs in clinical development converge on a narrow set of established targets — HER2, TROP2, and B7-H3 — creating substantial target overlap and limiting reach to antigen-positive patient subsets. HERV-K combines broad tumor prevalence with tumor-restricted expression in an open, first-in-class field, addressing patient populations underserved by current targeted therapies.
Feature HER2 ADCs TROP2 ADCs B7-H3 ADCs SBB001 (HERV-K)
Tumor prevalence ~15–20% ~40–60% 50–90% ~70–80%
Normal tissue expression Moderate High Low Low / None
Approved ADCs 5+ 2 0 (in trials) 0 (open field)
Competitive intensity Very crowded Crowded Extremely high Open / first-in-class

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.

Path to the clinic

SBB001 has completed lead optimization. The next stage of work takes the program through IND-enabling studies and into a focused, biomarker-driven first-in-human trial.
1
IND-enabling studies
GLP toxicology in rodent and non-rodent species, alongside GMP antibody and ADC manufacturing.
2
IND submission
Filing to open the clinical program, with IND allowance as the first value inflection point.
3
Phase 1 dose escalation
Standard dose-escalation design in solid tumors selected for high HERV-K expression by IHC-based screening.
4
Expansion cohorts
Focused cohorts in selected indications, with safety, pharmacokinetics, and early efficacy signals as endpoints.

Beyond the lead program

SunnyBay's HERV-K platform extends well beyond its lead ADC. The same target biology enables multiple therapeutic approaches, each representing future optionality rather than a near-term capital requirement:
Antibody-Drug Conjugates

Targeted delivery of anti-cancer drugs directly to tumor cells.

CAR-T, TCR & Cell Therapies

Engineering immune cells to recognize and attack HERV-K-expressing tumors.

BiTEs

Bridging immune cells directly to tumor cells for enhanced killing.

Cancer Vaccines & Prevention

Training the immune system to prevent or fight HERV-K-driven cancers.

Companion Diagnostics

Biomarker-driven patient selection to identify HERV-K-expressing tumors.

Single-Cell Immune Profiling

Characterizing immune responses at single-cell resolution to identify T and B cells that kill HERV-K-expressing tumor cells.


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 four international PCT filings covering antibodies and ADCs, cellular therapies, and vaccines, alongside US applications extending to diagnostics, with international filings in Canada, Japan, Europe, and China.

SunnyBay Biotech Chief Scientific Officer Gary Johanning pictured standing next to a liquid nitrogen tank

Board & collaborators

SunnyBay's founders are supported by a board and advisory group spanning academic oncology, translational immunology, clinical development, regulatory strategy, and life sciences finance.
Dr. Dean Tang
Chair, Pharmacology & Therapeutics, Roswell Park Comprehensive Cancer Center
Dr. Laszlo Radvanyi
Ottawa Hospital Research Institute and University of Ottawa
Dr. Victoria Manax
Pharmaceutical executive; clinical development and strategy
Dr. Toufigh Gordi
Executive Director, Clinical Pharmacology, Rigel Pharmaceuticals Inc.
Dr. Greta Wodarcyk
President and Founder, CatalystBio
Dr. Michael Boyne
Co-Founder and Principal, CatalystBio
Franklin Rice, MBA
25+ years as a life sciences finance leader and strategy consultant
Lawrence Florin, MBA
Clinical operations, project management, and risk-based project management
Dr. Sue Cheung
Strategic advisor to tech, biotech, and VC/PE; AI, data, and financial strategy
Dr. Edward Njoo
Stanford University; Director of Research and Chair of Chemistry and Biochemistry, ASDRP

Want to learn more?

SunnyBay Biotech is advancing a first-in-class approach to cancer treatment — a novel, biologically validated tumor target with broad relevance across solid tumors, backed by decades of research, more than $15M in non-dilutive NIH and DoD funding, and an international patent estate.

Get in touch to discuss the program, our data, or partnership opportunities.
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