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Updated: Aug 3, 2025
A GPC3-targeting Bispecific Antibody, GPC3-S-Fab, with Potent Cytotoxicity
Published on: July 12, 2018
Derivation and Preclinical Characterization of CYT-303, a Novel NKp46-NK Cell Engager Targeting GPC3
Antonio Arulanandam1, Liang Lin1, Hao-Ming Chang1
1Cytovia Therapeutics, Inc., Natick, MA 01760, USA.
Abstract:
Glypican-3 (GPC3) is an oncofetal antigen that is highly expressed in multiple solid tumors, including hepatocellular carcinoma, and is barely expressed in adult normal tissues except the placenta. NKp46 activation receptor is expressed in all-natural killer (NK) cells, including tumor-infiltrating NK cells. FLEX-NKTM is a platform for the production of tetravalent multifunctional antibody NK cell engagers (NKE). CYT-303 was designed using the FLEX-NK scaffold, incorporating a novel humanized NKp46 binder that does not induce NKp46 internalization and a humanized GPC3 binder that targets the membrane-proximal lobe to mediate NK cell-redirected killing of HCC tumors. CYT-303 shows sub-nanomolar binding affinities to both GPC3 and NKp46. CYT-303 was highly potent and effective in mediating NK cell-redirected cytotoxicity against multiple HCC tumor cell lines and tumor spheroids. More interestingly, it can reverse the dysfunction induced in NK cells following repeated rounds of serial killing of tumors. It also mediated antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity against GPC3-expressing HCC tumors. In vivo, CYT-303 showed no toxicity or cytokine release in cynomolgus monkeys up to the highest dose (60 mg/kg), administered weekly by intravenous infusion for 28 days. These results demonstrate the potential of CYT-303 to be a safe and effective therapy against HCC.
Insights
CYT-303, a novel NK cell engager, effectively targets Glypican-3 (GPC3) in hepatocellular carcinoma (HCC). This therapy shows potential for safe and potent treatment by redirecting natural killer (NK) cells against tumors.
Area of Science:
- Immunology
- Oncology
- Biotechnology
Background:
- Glypican-3 (GPC3) is a key oncofetal antigen overexpressed in hepatocellular carcinoma (HCC).
- Natural Killer (NK) cells, expressing the NKp46 receptor, are crucial for tumor surveillance.
- Existing therapies face challenges in effectively targeting HCC and overcoming NK cell dysfunction.
Purpose of the Study:
- To develop and evaluate CYT-303, a novel tetravalent antibody NK cell engager (NKE) targeting GPC3 and NKp46.
- To assess the efficacy of CYT-303 in mediating NK cell-redirected cytotoxicity against HCC.
- To investigate CYT-303's ability to reverse NK cell dysfunction and its safety profile.
Main Methods:
- CYT-303 was engineered using the FLEX-NK platform with humanized binders for GPC3 and NKp46.
- Binding affinities of CYT-303 to GPC3 and NKp46 were determined.
- In vitro assays assessed NK cell-redirected cytotoxicity, antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC) against HCC cell lines and spheroids.
- In vivo studies in cynomolgus monkeys evaluated CYT-303's toxicity and cytokine release.
Main Results:
- CYT-303 demonstrated sub-nanomolar binding affinities to both GPC3 and NKp46.
- The NKE potently induced NK cell-mediated killing of HCC cell lines and spheroids.
- CYT-303 reversed NK cell dysfunction after serial tumor killing and mediated ADCP and CDC.
- In vivo studies showed no observed toxicity or significant cytokine release in non-human primates.
Conclusions:
- CYT-303 is a potent and effective GPC3-targeted NKE with a favorable safety profile.
- This therapy has the potential to overcome NK cell dysfunction in the HCC tumor microenvironment.
- CYT-303 represents a promising therapeutic candidate for hepatocellular carcinoma treatment.
