25 patients were treated. All patients suffered from solid tumors with colorectal (n = 4) and non-small cell lung cancer (n = 4) being the most frequent diagnoses. Patients were heavily pretreated with half of the patients having received ≥ 4 prior systemic treatment lines. 80% of patients were refractory to the last systemic treatment. Details on patient enrollment, disposition, and demographics are shown in supplementary Fig. 1 and Supplementary Table 2.
ATX-101 has a favorable safety profile
DLT were not observed, and the maximum tolerated dose was not reached. With exception of one grade 3 adverse event (elevated cholesterol in a patient with hepatocellular carcinoma) only mild and moderate treatment-related adverse events were observed (Table 1). Vital signs, ECG, and laboratory values didn’t show a trend of changes during the treatment with ATX-101. Details on all treatment-emergent adverse events are shown in Supplementary Table 3.
Table 1 Incidence of treatment-related TEAE that occurred in more than 1 patient. Full size table
Infusion-related reactions (IRR) were identified as the only specific adverse event of ATX-101. Two measures were implemented to prevent the occurrence of IRR: (i) a premedication comprising glucocorticoids, H1 and H2 blockers, diphenhydramine and montelukast, (ii) a stepwise increase of the infusion rate. Despite these measures, IRR were observed in 64% of the patients (Table 2), and in 83% of these patients this was seen on the first infusion day. There was no evidence of dose dependency. IRR were allergic reactions primarily characterized by itching, urticaria and rash. They resolved quickly after treatment interruption or slowing the infusion rate with or without appropriate symptomatic treatment. ATX-101 treatment could be safely restarted in all patients. Notably, the intra-individual recurrence rate of IRR was higher in the 60 mg/m2 cohort compared to the other cohorts. This resulted in longer infusion times at the highest dose, i.e., in average 246 min [143-346] (infusion times are shown in Supplementary Table 4). Eventually, the Safety Monitoring Committee recommended to stop the dose escalation after completion of the 60 mg/m2 cohort despite lack of safety concerns. The reason is that infusion times of more than 4–5 h can hardly be managed in an outpatient clinic. Consequently, the recommended phase 2 dose (RP2D) for ATX-101 monotherapy was defined as 60 mg/m2.
Table 2 Incidence and CTCAE grading of infusion-related reactions (IRR). Full size table
The reason for IRR has not been completely clarified. In vitro data from mast cells and data generated in dogs suggest a correlation of IRR with a transient increase in histamine levels induced by ATX-101 (unpublished data). Such increases of histamine could not be reproduced in this study because data from only 3 patients experiencing an IRR were available. Further investigations are ongoing in current clinical studies. The development of anti-drug antibodies is deemed to be unlikely because of the above-mentioned preclinical data and clinical data showing that IRR occurred in most patients during the first infusion and did not exacerbate during the treatment. In addition, peptide with cell penetrating, cationic parts are known to cause histamine release [22].
ATX-101 is rapidly cleared from plasma indicating quick cell penetration
ATX-101 was rapidly cleared from blood with a half-life shorter than 30 min in all dosing groups. PK parameters (Table 3) showed that maximum plasma concentrations (C max ) and area under the curve (AUC) were dose dependent. C max were reached at mid or directly at the end of infusion. However, C max values were very different for the individual patients. For instance, in the highest dosing group C max values varied between 527 and 3056 ng/mL (mean 1,150). One contributor to this variation is probably the infusion time in the context of the short half-life of ATX-101 in plasma; as longer the infusion time is, as more ATX-101 is cleared already during the infusion and this results in smaller C max values. Therefore, despite a dose dependence, the C max appear to be comparable for the 45 and 60 mg/m2 cohorts due to the different average infusion times: 142 and 246 min, respectively (Supplementary Table 4). Figure 1 shows the individual plasma concentration-time curves for the highest dosing cohort. The quick clearance of ATX-101 from plasma is in accordance with preclinical data showing rapid cell penetration and degradation in serum, but still good tissue distribution [10, 15]. In cell cultures, activity, characterized by inhibition of growth and increased apoptosis, was observed for up to five days after addition of the peptide [10]. Of note, no full-length peptide was found in the culture media 1–2 h after the peptide addition (unpublished data). Based on these data, it is concluded that the plasma concentration doesn’t reflect the biological availability of ATX-101 in patients.
Table 3 Summary of PK parameters (primary PK population). Full size table
Fig. 1: Individual plasma concentration–time curves for patients treated with 60 mg/m2 (recommended phase 2 dose). Infusion times were in the range of 115–346 min. For the sake of simplicity, the infusion time has been arbitrarily shortened and presented uniformly for all patients. Full size image
ATX-101 showed antitumor activity
Fourteen (70%) of 20 patients belonging to the Efficacy Population had stable disease at the end of the dose escalation study. Twelve patients (60%) continued treatment in the long-term follow-up study. At treatment discontinuation, after a median time of 18 weeks [7–74], 5 of 12 patients (41.7%) had stable disease, and 7 patients (58.3%) had progressive disease (treatment duration is shown in Supplementary Fig. 2). No partial or complete responses were observed. Overall, in 8 patients (40% of Efficacy Population) disease stabilization was observed over a period of at least 4.1 months. The longest disease stabilization was observed in a patient with uterine leiomyosarcoma. She was treated over 17 months and remained stable after 29 months when she was lost to follow-up. Disease stabilization can probably be attributed to ATX-101, considering that 96% of the patients had progressive disease at study entry, 80% were refractory to the most recent systemic treatment, and most patients were heavily pretreated.
Of note, the above-mentioned disease stabilization was independent of the dose and was observed in 50%, 33.3%, 50% and 33.3% of patients belonging to the Efficacy Population in Cohorts 1–4, respectively.
Due to the heterogenous patient population with different tumor entities characterized by differences in prognoses, prior treatment lines and life expectancies, no meaningful efficacy or efficacy-dose relationship evaluations were possible. So far, no clinical pharmacodynamic (PD) markers have been identified that help to describe the mode of action in patients and to support the clinical dose finding. Biopsies collected in an ongoing study will be analyzed in order to identify potential biomarkers. Blood samples have also been collected at all visits for all patients in this Phase 1 study for use in future analysis.