Technological advances have reemerged ADCs as a viable treatment strategy for advanced solid tumors. ADCs targeting several tumor targets have shown great potential in treating refractory NSCLC, including HER2, HER3, TROP2, CEACAM5, and MET. On August 11, 2022, the FDA accelerated the approval of the HER2 ADC drug Enhertu (trastuzumab deruxtecan, T-DXd) jointly developed by AstraZeneca and Daiichi Sankyo for the treatment of patients with unresectable or metastatic Non-Small Cell Lung Cancer (NSCLC) with HER2 mutations. It is the first drug approved by the FDA for the treatment of HER2-mutated NSCLC, confirming that ADC drugs have great potential for NSCLC. In this paper, five potential ADC targets for NSCLC and representative drugs are briefly introduced.
HER2 gene amplification, gene mutation and protein overexpression are all found in NSCLC. HER2 is overexpressed in nearly 20% of NSCLC, and HER2 mutations are found in 2-4% of NSCLC. Activating mutations in the HER2 gene promote internalization of the HER2 receptor, providing mechanistic feasibility for exploring ADC therapy in this subtype of NSCLC.
Ado-Trastuzumab Emtansine (T-DM1)
T-DM1 is an ADC targeting HER2 with a DAR of 3.5, consisting of the HER2 mAb trastuzumab linked to the microtubule inhibitor Emtansine (DM1) via a non-cleavable linker. T-DM1 has been approved by the FDA for the treatment of advanced HER2-positive breast cancer. Early trials have also shown efficacy in HER2-mutated and amplified NSCLC. In a single-center Phase II NSCLC cohort, 49 NSCLC patients q3w with HER2 mutation or amplification were treated with T-DM1 at 3.6 mg/kg, resulting in an ORR of 31% and mPFS of 5 months. Treatment was well tolerated with only one grade 3 (G3) treatment-related adverse event. Based on these data, T-DM1 was classified as Class 2A by the NCCN for the treatment of patients with HER2 mutant advanced NSCLC. The efficacy of T-DM1 in NSCLC patients with HER2 protein overexpression is not satisfactory. In several clinical trials, trials were stopped early because of limited efficacy.
Trastuzumab Deruxtecan (T-DXd)
T-DXd is an ADC drug that combines HER2 monoclonal antibody trastuzumab with topoisomerase inhibitor DXd via an enzyme-cleavable polypeptide linker with a DAR of 8. It has a significant bystander effect on neighboring cells, providing a mechanistic feasibility for use in NSCLC tumors with heterogeneously expressed HER2.
T-DXd was evaluated in patients with refractory advanced solid tumors with HER2 expression or HER2 mutation in single-arm Phase I dose escalation and dose expansion trials. The trial included 18 patients with NSCLC. Results showed that 10 patients had partial response (ORR 55.6%), mPFS 11.3 was months, and median response time (mDOR) was 10.7 months. In NSCLC patients with HER2 mutations, ORR was 72.7%(8/11), mPFS was 11.3 months, and mDOR was 9.9 months. On this basis, the Destination-Long01 phase II trial evaluated the efficacy of T-DXd 6.4 mg/kg q3w in advanced, refractory HER2-mutated NSCLC. The study included patients with HER2 overexpression (cohort 1, HER2 IHC 3+ or 2+) or patients with HER2 activating mutations (cohort 2). The efficacy of T-DXd in patients with HER2-mutant NSCLC (cohort 2) was impressive. In 91 patients, ORR was 55%, mDOR, mPFS, and OS were 9.3, 8.2, and 17.8 months, respectively. 46% of patients had ≥G3 TRAE, of which neutropenia (19%), anemia (10%), nausea (9%), and fatigue (7%) were the most common. Another 24 patients (26%) had drug-related interstitial lung disease (ILD) : 4 (17%) were G3, and 2 (8%) died (G5). T-DXd activity was also seen in HER2-overexpressing NSCLC patients (cohort 1), but with limited efficacy. Among the 49 patients, the ORR was only 24.5%, the mDOR was 6.0 months, the mPFS was 5.4 months, and the mOS was 11.3 months. Toxicities were similar to cohort 2, with ≥G3 TRAEs observed in 55% of patients, with neutropenia (20%) being the most common. The incidence of drug-related ILD was 16.3%, including 3 deaths.
The accelerated FDA approval of T-DXd is based on superior data from the DESTINY-Lung02 Phase II trial. ORR was as high as 58% in 52 patients with HER2+, unresectable and/or metastatic NSCLC.
HER3 is an important molecule for HER2 heterodimerization and activation of PI3K/AKT signaling pathway. HER3 is expressed in a variety of solid tumors, including 83% of NSCLC. Given its high expression in NSCLC and its potential role in mediating EGFR tyrosine kinase inhibitor (TKI) resistance, HER3 is an attractive ADC target in NSCLC.
Patritumab Deruxtecan (HER3-DXd) is an antibody–drug conjugate consisting of a HER3 antibody attached to a topoisomerase I inhibitor payload via a tetrapeptide-based cleavable linker, with a DAR of 8.
HER3-DXd was evaluated in a Phase I study of patients with advanced NSCLC who activated EGFR mutations after TKI and chemotherapy progression (cohort 1) and patients who did not activate EGFR after anti-PD (L)1 immune checkpoint blocking (cohort 2). In Cohort 1, 81 patients were enrolled, regardless of HER3 expression, and the dose of HER3-DXD was increased from 3.2 mg/kg to 6.4 mg/kg q3w. In this population, 47% of patients experienced ≥G3 TRAE, with thrombocytopenia (26%), neutropenia (15%), and fatigue (10%) being the most common. ILD occurred in 4 patients (5%) due to treatment, of which only 1 patient was G3. 5.6 mg/kg was selected as the recommended dilated dose (RDE). The results were significant in 57 patients treated with RDE. The ORR was 39%, the mDOR was 6.9 months, and the mPFS was 8.2 months. Antitumor efficacy was observed in patients with a range of EGFR-resistant mechanisms, including EGFR C797S mutation, MET amplification, HER2 mutation, BRAF fusion, and PIK3CA mutation. All evaluable patients had HER3 expression, and the median HER3 expression score was higher in patients who responded than in patients with disease progression. Based on these findings, HER3-DXd was granted Breakthrough Therapy Designation by the FDA in December 2021.
TROP2, a glycoprotein transmembrane calcium signaling protein, is expressed in various epithelial tumors, including lung cancer. In NSCLC, the expression of TROP2 in lung adenocarcinoma and lung squamous cell carcinoma was 100% and 92%, respectively, and the high expression of TROP2 protein was 64% and 75%, respectively. Several ADCs targeting trop-2 are currently undergoing clinical trials.
Sacituzumab govitecan (SG) is an ADC drug consisting of a humanized anti-TROP2 monoclonal antibody Sacituzumab that linked to the topoisomerase-I inhibitor SN-38 via an acid-cleavable linker with a DAR of 7.6.
The first clinical trial to explore the safety and efficacy of SG is the phase I/II dose escalation and expansion IMMU-132-01 basket trial. The study included 495 patients who were not selected for TROP2 expression and were treated at doses ranging from 8 to 18 mg/kg on days 1 and 8 of a 21-day cycle. In this cohort, 59.6% of patients experienced ≥G3 TRAEs, characterized by neutropenia (42.4%), anemia (10.3%), diarrhea (7.9%), fatigue (6.3%), and febrile neutropenia (5.2%) were the most common. Based on these data, a dose of 10 mg/kg was selected for dose extension.
In the SCLC cohort (n=62), patients were treated with 8, 10, 12, or 18 mg/kg SG on day 1 and day 8 of the 21-day cycle. ORR was 17.7%, mPFS was 3.7 months, mDOR was 5.7 months, and OS was 7.1 months. In the NSCLC cohort, 54 patients were treated with SG at 8, 10 or 12 mg/kg on day 1 and day 8 of the 21-day cycle. ORR is 16.7%, mPFS is 4.4 months, mDOR is 6.0 months, and OS is 7.3 months. Squamous cell carcinoma and adenocarcinoma were both reactive. 92% of patients had moderate or high expression of TROP2 on IHC staining, which precludes its usefulness as a predictive biomarker. Based on these data, the Phase III EVOKE-01 trial is evaluating the efficacy of SG 10 mg/kg versus Docetaxel 75 mg/m2 in patients with advanced EGFR/ALK wild-type NSCLC following anti-PD (L)-1 immunotherapy and platinum-based chemotherapy.
Datopotamab Deruxtecan (Dato‑DXd)
Datopotamab Deruxtecan (Dato-DXd) is an ADC consisting of TROP2 monoclonal antibody Datopotamab conjugated to DXd with a DAR of 4.
Preliminary results from 138 patients in the Phase I TROPION PanTumor01 trial of Dato-DXd showed an acceptable safety, with 45% presenting ≥G3 TEAE, with dyspnea (4%), fatigue (3%), stomatitis (3%), and anemia (3%) being the most common. ORR was 27% in 85 patients with evaluable efficacy. The expression of TROP2 was not correlated with the efficacy of TROP2.
In the NSCLC expansion cohort of this study, 180 patients with advanced NSCLC received 4, 6, or 8 mg/kg of Dato-DXd every 3 weeks. The ORR was 24%, and the ORR was similar across doses. The mPFS of the three doses were 4.3, 8.2 and 5.4 months, respectively. Drug-related ≥G3 TEAEs occurred in 35% of patients treated at the 8 mg/kg dose, compared with 14% and 16% of patients treated at the 4 mg/kg and 6 mg/kg doses, respectively. The most common ≥G3 TEAEs at different dose levels included stomatitis, nausea, fatigue, mucosal inflammation, and anemia. The incidence of drug-related ILD was 10.6%(19/180), of which the most occurred at 8 mg/kg (12/19) (G1/2(14/19), but 3 patients died of drug-related ILD. Dato-DXd also shows therapeutic potential in patients with mutated NSCLC. In 34 patients with a drive mutation in TROPION-PanTumor01, an ORR of 35% and a mDOR of 9.5 months were observed. Dato-DXd is being evaluated in the TROPION-Lung01 trial in patients with advanced NSCLC. Patients were randomized to treatment with 6 mg/kg Dato-DXd or 75 mg/m2 Docetaxel. In the Phase III TROPION-Lung08 trial, Dato-DXd was also evaluated in the first-line setting of highly expressed PD-L1 (TPS≥50%)NSCLC and was randomized to either Dato-DXd plus pembrolizumab or pembrolizumab alone.
Carcioembryonic antigen-related cell adhesion molecules (CEACAMs) are members of the glycosylphosphatidylinositol (GPI)-linked immunoglobulin (Ig) superfamily. CEACAM5 is selectively expressed in several tumor types, including lung cancer.
Tusamitamab ravtansine (TUSA) is a CEACAM5 antibody conjugated to DM4 via a cleavable SPDB linker, with a DAR of 3.8.
Phase I clinical evaluation of TUSA in the treatment of patients with solid tumors that express or may express CEACAM5 at doses ranging from 5 to 150 mg/m2 every two weeks. The maximum tolerated dose of 100 mg/m2 was selected for two NSCLC expansion cohorts: (1)
The Phase I study evaluated TUSA in patients with solid tumors that expressed or were likely to express CEACAM5 at doses ranging from 5 to 150 mg/m2 every two weeks. The maximum tolerance selected for the two extended NSCLC cohorates was 100 mg/m2: (1) 64 patients with advanced non-squamous NSCLC, IHC ≥ 2+ and ≥ 50% cells highly expressed CEACAM5; (2) 28 patients with non-squamous NSCLC, IHC ≥ 2+ and 1-49% cells expressed moderately CEACAM5. ORR values were higher in the "high expression" group, at 20.3%, compared to 7.1% in the "medium expression" group and 5.6 months of mDOR in the high expression group. The rate of ≥G3 TEAE in 92 patients was 51.1%, among which reversible keratopathy/keratitis (10.9%), dyspnea (10.9%) and fatigue (4.3%) were the most common. Based on excellent data, the Phase III trial of CARMEN-LC03 enrolled patients with refractory advanced non-squamous NSCLC whose IHC≥2+ and ≥50% cells had high CEACAM5 expression, They were randomized to receive TUSA 100 mg/m2 once every 2 weeks or docetaxel 75 mg/m2 once every 3 weeks.
In NSCLC, a series of changes in mesenchymal-epithelial transition (MET) genes have been observed, including activating mutations (METex 14), gene amplification, and protein overexpression.
Telistuzumab Vedotin (Teliso-V)
Teliso-V is an ADC drug conjugated by cMET monoclonal antibody ABT-700 and MMAE through a cleavable vc linker, with a DAR of 3.1. Preclinical evidence shows that the threshold level of c-Met expression molecule on tumor cell surface >100,000 is a necessary condition to induce tumor cell killing. The expression level of c-Met was low in normal tissues.
The first human clinical study of Teliso-V was conducted in NSCLC patients overexpressing c-MET (IHC H-score ≥ 150). Treatment was well tolerated, with recommended phase II doses of 1.9 mg/kg q2w and 2.7 mg/kg q3w. Based on these excellent data, the dose-expansion cohort of NSCLC continues to enroll patients with c-MET+ (H-Score ≥150) or those with MET amplification/exon 14 skipping mutations. Of the 113 patients evaluated, ≥G3 TEAEs occurred in 44% of patients, with pneumonia (5.3%) and hyponatremia (4.4%) being the most common. G≥3 anemia, dyspnea, fatigue, elevated GGT, peripheral neuropathy and pneumonia each accounted for 2.7%. In terms of efficacy, non-squamous NSCLC patients had the most effective results, with an ORR of 35.1% (13/37) and an mDOR of 6.9 months. In patients with non-squamous NSCLC and c-Met high expression of c-MET (3 + IHC ≥ 50% cells), the ORR value was 53.8% (7/13). Based on these excellent data, Teliso-V was approved by the FDA in 2022 for the breakthrough treatment of advanced EGFR wild-type NSCLC patients with high expression of c-MET.
In the EGFR mutation-positive and squamous NSCLC cohorts, the efficacy was moderate, with ORRs of 13.3% (4/30) and 14.3% (3/21), respectively, and the study was terminated early. Teliso-V was also evaluated with erlotinib in NSCLC patients with EGFR mutations. In a single phase Ib study, 29 patients with treatment-refractory EGFR-mutated NSCLC and c-Met+ (IHC H-Score ≥150), METex 14 skipping or MET amplification received TelisV 2.7 mg/kg q3w plus erlotinib 150 mg/day. The ORR was 34.5%, and the response was mainly in patients with high expression of c-MET. In 16 patients with a cMET H-Score of ≥225, an ORR of 50% was observed. A phase III trial is evaluating Teliso-V in 698 patients with advanced, refractory, EGFR wild-type, c-MET overexpressing NSCLC. The ORR was 34.5%, and the response was mainly in patients with high c-MET expression. In 16 patients with a cMET H-Score of ≥225, an ORR of 50% was observed. A phase III trial is evaluating Teliso-V in 698 patients with advanced, refractory, EGFR wild-type, c-MET overexpressing NSCLC.
Technological advances have led to the rebirth of ADCs as effective anti-cancer agents for a class of solid tumors, including lung cancer. Although multiple ADC drugs are promising to be approved for the treatment of NSCLC patients, many challenges remain, such as optimal sequencing of drugs, new combination strategies, and management of unique toxicities such as ILD. But in any case, the future of ADC drugs is bright. More breakthroughs in ADC will further improve the treatment of NSCLC and greatly improve the survival benefits of NSCLC patients.
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