Novel Therapeutic Agents Targeting B7-H3 (CD276)
Multiple novel therapeutic platforms targeting B7-H3 (CD276) are in active development, including antibody-drug conjugates (ADCs), CAR-T cells, Fc-optimized monoclonal antibodies, and targeted alpha therapy agents, with the most advanced being enoblituzumab-based conjugates and dual-payload ADCs.
Antibody-Drug Conjugates (ADCs)
The most promising approach involves dual-payload ADCs that simultaneously deliver chemotherapy and immunotherapy. A humanized anti-CD276 antibody conjugated with deruxtecan (chemotherapeutic) and imidazoquinoline (Toll-like receptor agonist) demonstrated superior antitumor efficacy in triple-negative breast cancer models, with favorable biodistribution, high tumor burden reduction, and low systemic toxicity 1. This two-site co-conjugation technology (cysteine and lysine sites) represents a significant advancement over single-payload ADCs.
Targeted Alpha Therapy
Enoblituzumab, conjugated with Actinium-225 via Macropa-PEG2 chelation, shows exceptional promise for solid tumors. The [225Ac]Ac-Macropa-PEG2-Enoblituzumab conjugate demonstrated:
- High-affinity binding (KD = 0.18 nM)
- Sustained tumor accumulation (15.7%ID/g at 72 hours)
- Significant tumor growth inhibition with good tolerability
- Excellent stability (>90% intact up to 7 days) 2
This addresses previous limitations of chelate stability and conjugation reproducibility in alpha therapy.
Fc-Optimized Monoclonal Antibodies
The 8H8_SDIE antibody represents an Fc-engineered approach that enhances natural killer (NK) cell activity through improved CD16 binding. This agent has shown efficacy in:
- Colorectal cancer: Particularly relevant for microsatellite-stable disease unresponsive to PD-1/PD-L1 inhibitors 3
- Non-small cell lung cancer: Offers alternative for patients failing conventional checkpoint inhibitors 4
The mechanism involves enhanced antibody-dependent cellular cytotoxicity (ADCC) with increased NK cell activation markers (CD69, CD107a) and cytotoxic mediator secretion (IFNγ, perforin, granzyme B).
CAR-T Cell Therapies
Adapter CAR-T (AdCAR-T) platforms targeting CD276 address a critical limitation: CD276 expression is induced on activated T-cells, causing fratricide that limits conventional anti-CD276 CAR-T expansion. The AdCAR-T platform uses Fab-based adapter molecules that allow:
- CAR-T expansion in absence of CD276 targeting
- Intermittent dosing to prevent fratricide
- IL-18 armoring for enhanced in vivo persistence
- Demonstrated efficacy in small cell lung cancer 5
Clinical Context and Target Rationale
B7-H3 (CD276) is broadly overexpressed across multiple solid tumors (colorectal, lung, breast, prostate) while showing minimal expression in normal tissues, making it an ideal therapeutic target. Beyond direct tumor cell expression, B7-H3 is enriched in tumor-derived exosomes where it promotes immune evasion, metastasis, and therapy resistance through STAT3, PI3K, and lipid metabolism pathway activation 6.
Key Clinical Considerations
Common pitfall: Conventional anti-CD276 CAR-T approaches fail due to activation-induced CD276 expression on the CAR-T cells themselves, leading to self-destruction. The AdCAR-T platform with intermittent adapter molecule dosing circumvents this issue 5.
Toxicity management: While specific B7-H3-targeted agents are not yet FDA-approved, emerging bispecific antibodies and cell engagers will likely require monitoring for cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), similar to other lymphocyte engager therapies 7.
Patient selection: Fc-optimized antibodies offer particular value for patients with PD-1/PD-L1-resistant disease, as they engage NK cells rather than T-cells, providing an orthogonal mechanism of action 3, 4.