Receptor-Mediated Conjugates: Key Design Factors and Clinically Validated Targets

The authors of Receptor-Mediated Drug Delivery: Redefining Targeted Drug Conjugates in Oncology describe receptor-mediated targeted drug conjugates as a delivery strategy built around two coupled choices: which cell-surface receptor is targeted to increase conjugate delivery and local concentration in tumor tissue, and how the conjugate is engineered to translate receptor binding into intratumoral drug exposure. In their framing, tumor accumulation and local payload levels reflect both target biology (including receptor abundance and trafficking) and construct-level “dials” such as ligand format and release chemistry. The review uses receptors with approved conjugates as anchor examples, then contrasts them with emerging targets highlighted in this design space.

Four receptors are presented as clinically validated in the context of approved conjugates, with examples spanning antibody-, peptide-, and radionuclide-based platforms. For HER2, the authors discuss trastuzumab emtansine and trastuzumab deruxtecan as HER2-directed antibody–drug conjugates (ADCs). For Trop-2, they describe sacituzumab govitecan and datopotamab deruxtecan as Trop-2–directed ADCs. For Nectin-4, enfortumab vedotin is described as an ADC targeting that adhesion molecule. For SSTR2, the review highlights 177Lu-DOTA-TATE as a somatostatin receptor–targeted peptide–radionuclide (radioligand) conjugate. These mappings are used to illustrate how receptor selection and conjugate class are paired in pursuit of receptor-driven tumor uptake.

Across these case studies, the authors link selectivity and delivery to several receptor-level features: on-tumor versus off-tumor expression patterns, surface density, and endocytosis/trafficking behavior after ligand engagement. They note, for example, that HER2 overexpression can reach roughly 2 million receptors per cell in breast cancer models discussed, while Trop-2 densities are reported across breast cancer lines from tens of thousands to several hundred thousand copies per cell; Nectin-4 density is described as variable across urothelial carcinoma lines up to the tens of thousands per cell, and SSTR2 density is reported as high in some medulloblastoma lines (on the order of 10⁵–10⁶ receptors per cell). Internalization is described as receptor-specific: HER2 is portrayed as relatively stable at the surface with recycling behavior, Trop-2 as undergoing constitutive internalization with lysosomal routing emphasized after ADC binding, Nectin-4 as having more limited evidence with macropinocytosis suggested, and SSTR2 as agonist-dependent (with one cited example noting that antibody binding alone showed no significant internalization in the absence of an agonist), with recycling behavior varying by ligand type. In the authors’ framework, these differences contribute to variability in cellular uptake and, downstream, intratumoral payload exposure.

The review also emphasizes conjugate engineering parameters that modulate tumor accumulation and intratumoral distribution, including ligand format and size (full antibodies versus peptides and intermediate-size constructs), diffusion/penetration considerations, linker chemistry, payload properties, and drug-to-antibody ratio (DAR) trade-offs. Linkers are described as balancing systemic stability with efficient release after uptake, and the authors use approved ADCs to exemplify different release logics, including enzyme-cleavable and acid-sensitive designs as well as the bystander effect concept tied to membrane-permeable payloads. In discussing these design trade-offs, they contrast DAR choices across Trop-2 ADCs (reporting sacituzumab govitecan at DAR 8 versus datopotamab deruxtecan at approximately DAR ~4) as one illustration of how payload potency and exposure considerations interact with construct loading. Overall, the authors present linker stability, size, and payload physicochemistry as interdependent levers rather than isolated variables.

Beyond the clinically validated receptors, the authors highlight EGFR, DLL3, and keratin 1 as emerging targets with conjugates described at clinical or preclinical stages in the review. For EGFR, they discuss multiple EGFR-directed conjugate formats under development, including ADC and peptide–drug conjugate approaches, in the context of leveraging receptor overexpression without relying on downstream signaling inhibition. For DLL3, the review recounts rovalpituzumab tesirine (Rova-T) as an early DLL3-targeted ADC effort and describes a subsequent shift toward next-generation designs that adjust payload choice and release strategy in response to translational observations from that program. For keratin 1, the authors describe cell-surface localization in certain breast cancer subtypes and present peptide–drug conjugates as a development direction. Taken together, these examples are used to depict an active pipeline in which receptor choice and conjugate architecture are iteratively refined within the constraints of delivery, distribution, and tolerability described by the authors.

Key Takeaways:

• The review describes four clinically validated receptors with approved conjugate examples: HER2 (trastuzumab emtansine; trastuzumab deruxtecan), Trop-2 (sacituzumab govitecan; datopotamab deruxtecan), Nectin-4 (enfortumab vedotin), and SSTR2 (177Lu-DOTA-TATE).
• Receptor attributes the authors associate with uptake/selectivity include tumor versus normal-tissue distribution, surface density, and receptor-specific internalization and trafficking behavior (including recycling versus lysosomal routing and agonist-regulated endocytosis for SSTR2).
• Conjugate parameters linked to tumor accumulation and intratumoral concentration include ligand size/format and penetration, linker chemistry and release behavior, payload potency/permeability, and DAR; EGFR, DLL3, and keratin 1 are positioned as development-stage targets where these design considerations are being applied.