A phase I study of enfortumab vedotin (ASG-22CE; ASG-22ME): Updated analysis of patients with metastatic urothelial cancer

106 Background: Enfortumab vedotin, an antibody–drug conjugate, delivers monomethyl auristatin E to tumors expressing Nectin-4, which is overexpressed in metastatic urothelial cancer (mUC). Methods: This Phase I study (NCT02091999) enrolled patients (pts) with solid tumors, including pts with mUC, treated with ≥1 prior chemotherapy regimen. All pts received different dose levels of IV enfortumab vedotin (0.5, 0.75, 1, 1.25 mg/kg) once weekly for 3 out of 4 wks. Nectin-4 expression was determined by IHC on archival tumor specimens and quantified by histochemical scoring (H-score). Primary endpoint was tolerability; secondary endpoint was antitumor activity assessed every 8 wks per RECIST v1.1. Results: As of 3 Jan 2017, 68 pts with mUC (46 M/22 F; median age, 67 yr [range: 41–84]) had been treated. Of these, 62% received ≥2 prior therapies in the metastatic setting and 40% had prior immune checkpoint inhibitor (CPI) therapy. In these pts, Nectin-4 expression was high and prevalent (median H-score, 280 [range: 32–300]). Treatment-related adverse events (TRAEs) were reported in 58 pts (85%); diarrhea, fatigue, nausea, and pruritus were TRAEs reported in ≥25% of pts. Most TRAEs were grade ≤2 in severity; 19 pts (28%) experienced a TRAE of grade ≥3. The most common grade ≥3 AEs (occurring in ≥5 pts), regardless of attribution to treatment, were urinary tract infection (10%) and hypophosphatemia (9%). No treatment-related deaths have occurred. Sixty pts had ≥1 post-baseline assessment. Antitumor activity was observed across the dose range; overall response rate (ORR) was 40% (95% CI: 27.6–53.5) for all evaluable pts (n = 60), 46% (95% CI: 25.6–67.2) in pts with prior CPI exposure (n = 24), and 44% (95% CI: 19.8–70.1) in pts with metastasis to the liver (n = 16). Complete responses were noted in 3 pts at doses ≥1 mg/kg. Median treatment duration was 26 wks (range: 5.1–64.6), median duration of response was 18 wks (95% CI: 8.4–40.1), and median progression-free survival was 17 wks (95% CI: 15.1–23.3). Study enrollment is ongoing. Conclusions: Enfortumab vedotin demonstrated a favorable tolerability profile with encouraging antitumor activity in heavily pretreated mUC, including pts for whom CPIs have failed. Clinical trial information: NCT02091999

In vitro and in vivo evaluation of cysteine and site specific conjugated herceptin antibody-drug conjugates.

Antibody drug conjugates (ADCs) are monoclonal antibodies designed to deliver a cytotoxic drug selectively to antigen expressing cells. Several components of an ADC including the selection of the antibody, the linker, the cytotoxic drug payload and the site of attachment used to attach the drug to the antibody are critical to the activity and development of the ADC. The cytotoxic drugs or payloads used to make ADCs are typically conjugated to the antibody through cysteine or lysine residues. This results in ADCs that have a heterogeneous number of drugs per antibody. The number of drugs per antibody commonly referred to as the drug to antibody ratio (DAR), can vary between 0 and 8 drugs for a IgG1 antibody. Antibodies with 0 drugs are ineffective and compete with the ADC for binding to the antigen expressing cells. Antibodies with 8 drugs per antibody have reduced in vivo stability, which may contribute to non target related toxicities. In these studies we incorporated a non-natural amino acid, para acetyl phenylalanine, at two unique sites within an antibody against Her2/neu. We covalently attached a cytotoxic drug to these sites to form an ADC which contains two drugs per antibody. We report the results from the first direct preclinical comparison of a site specific non-natural amino acid anti-Her2 ADC and a cysteine conjugated anti-Her2 ADC. We report that the site specific non-natural amino acid anti-Her2 ADCs have superior in vitro serum stability and preclinical toxicology profile in rats as compared to the cysteine conjugated anti-Her2 ADCs. We also demonstrate that the site specific non-natural amino acid anti-Her2 ADCs maintain their in vitro potency and in vivo efficacy against Her2 expressing human tumor cell lines. Our data suggests that site specific non-natural amino acid ADCs may have a superior therapeutic window than cysteine conjugated ADCs