A phase 1 clinical trial has demonstrated that lorlatinib, a third-generation ALK inhibitor, shows promising efficacy and manageable safety in children, adolescents, and adults with ALK-driven refractory or relapsed neuroblastoma. The study, conducted by the New Approaches to Neuroblastoma Therapy (NANT) Consortium, represents a significant advance in precision medicine for this challenging pediatric cancer.
Trial Design and Patient Characteristics
Between September 2017 and February 2022, 49 patients with ALK-mutated or ALK-amplified neuroblastoma were enrolled across three cohorts: patients under 18 years (cohort A1, n=25), patients 18 years and older (cohort A2, n=15), and patients under 18 years receiving lorlatinib in combination with topotecan/cyclophosphamide chemotherapy (cohort B2, n=9).
Patients were heavily pre-treated, with a median time from diagnosis to study enrollment of 23.5 months. Most had relapsed disease (82%), while 18% had refractory neuroblastoma. Many had previously received myeloablative chemotherapy with autologous stem cell transplant (59%) and/or GD2-directed immunotherapy (71%). Notably, 41% had received a prior ALK inhibitor.
All common neuroblastoma ALK hotspot mutations were represented, including F1174C/L (51%), R1275Q (33%), and F1245Y/L (12%), along with one ALK amplification and one pathologic D1276_R1279 ALK-activating mutation.
Safety Profile and Recommended Dosing
The study established a recommended phase 2 dose (RP2D) of 115 mg/m²/day for patients under 18 years, approximately twice the adult RP2D used in non-small cell lung cancer (NSCLC). For patients 18 years and older, the RP2D was determined to be 150 mg daily.
The most common treatment-related adverse events across all ages included hypertriglyceridemia (90%), weight gain (87%), and elevated cholesterol (79%). These metabolic effects were generally manageable with supportive care, dietary management, and statins.
Central nervous system (CNS) effects were more common in adults (27% developed grade 2-4 CNS effects) compared to pediatric patients (only 6% developed grade 2 CNS effects). Real-time neurobehavioral screening helped identify patients at risk for CNS toxicity before clinical manifestation.
Clinical Efficacy
Lorlatinib demonstrated activity across all three neuroblastoma-specific ALK hotspot mutations, including in patients previously treated with other ALK inhibitors. Response rates varied by age group:
- In cohort A1 (patients <18 years), the objective response rate (complete or partial response) was 13%, with a modified response rate (including minor responses) of 30%.
- In cohort A2 (patients ≥18 years), the objective response rate was significantly higher at 47%, with a modified response rate of 67%.
- In cohort B2 (combination therapy), the objective response rate was 25%, with a modified response rate of 62%.
Notably, adolescents and adults with ALK-driven neuroblastoma had particularly strong and sustained responses, an important finding for a patient population that often has an indolent clinical course with de novo chemotherapy resistance and poor outcomes.
Patients with MYCN-amplified tumors and ALK mutations had fewer responses to lorlatinib monotherapy, but showed better responses when lorlatinib was combined with chemotherapy, suggesting that MYCN amplification may require combination approaches.
Functional Imaging Responses
A key finding was the significant improvement in functional imaging that often exceeded the best overall response determined by conventional criteria. Across all cohorts, 45% of patients with a best overall response of stable disease, minor response, or partial response had complete resolution of metabolic activity in soft tissue lesions by MIBG/FDG-PET imaging.
This suggests that ALK inhibition may induce tumor differentiation rather than immediate shrinkage, highlighting the need for novel response criteria to fully capture the anti-tumor activity of molecularly targeted agents.
Mechanisms of Resistance Identified Through ctDNA Analysis
A companion correlative study analyzed circulating tumor DNA (ctDNA) from patients enrolled in the trial to identify mechanisms of resistance to lorlatinib. Serial blood samples were collected at predefined timepoints including pretreatment, after courses 2, 4, 6, and then after every 4th course and at disease progression.
The analysis revealed three distinct patient groups based on ALK variant allele frequency (VAF) patterns:
- "ALK Dependent" (51%): ALK VAF correlated with clinical response
- "ALK Independent" (27%): No correlation between ALK VAF and clinical response
- "ALK Undetectable" (20%): ALK mutations not detected in ctDNA samples
Two key mechanisms of resistance were identified:
1. Compound ALK Mutations
Six patients developed secondary mutations in the ALK tyrosine kinase domain at the time of disease progression. These compound mutations included F1174L/G1202R, F1174L/D1203N, F1174C/G1202R, and F1174L/L1196M.
Laboratory studies confirmed that these compound mutations directly cause resistance to lorlatinib. For example, the F1174L/L1196M mutation increased the IC50 for lorlatinib by approximately 50-fold in cell line models.
Molecular dynamics simulations revealed that the G1202R mutation in particular can adopt a "gate-closed" conformation that fully occludes the lorlatinib binding site while still allowing ATP binding, explaining the mechanism of resistance.
Importantly, none of the patients treated at the RP2D of 115 mg/m² developed compound ALK mutations, suggesting that higher drug exposure may prevent the emergence of these resistance mechanisms.
2. RAS-MAPK Pathway Mutations
Mutations in the RAS-MAPK pathway represented the most common mechanism of off-target genetic resistance to lorlatinib. Patients with concurrent ALK and RAS-MAPK pathway mutations at enrollment did not respond to lorlatinib, and acquisition of new mutations in this pathway during treatment heralded disease progression.
These findings suggest that combination strategies targeting both ALK and the RAS-MAPK pathway might be necessary for certain patients, particularly those with dual mutations or those who develop RAS-MAPK alterations during treatment.
Clinical Implications
The results of this phase 1 study have already led to a major amendment in the Children's Oncology Group phase 3 trial (NCT03126916), replacing crizotinib with lorlatinib in newly diagnosed patients with ALK-driven, high-risk neuroblastoma. A similar change is planned for the European phase 3 trial in collaboration with the International Society of Paediatric Oncology European Neuroblastoma (SIOPEN).
The higher recommended dose for pediatric patients (approximately twice the adult dose) may be crucial for preventing the emergence of compound ALK mutations that cause resistance. The ongoing phase 3 trials will collect prospective serial ctDNA samples to further investigate clinical response and resistance mechanisms in therapy-naïve patients.
Conclusion
This landmark study demonstrates that lorlatinib is safe and effective in patients with ALK-driven neuroblastoma across all age groups and common ALK mutations. The identification of specific resistance mechanisms through serial ctDNA analysis provides valuable insights for developing future treatment strategies, including potential combination approaches targeting both ALK and the RAS-MAPK pathway.
The integration of lorlatinib into frontline therapy for newly diagnosed patients with ALK-aberrant, high-risk neuroblastoma holds substantial promise for improving outcomes in this challenging pediatric cancer.
