Anecdotal evidence of anti-GD2 therapy exists in OS from prior Phase 1 trials that included patients with OS. In a Phase 1/1B trial of the murine antibody (14.2G2a) plus IL2, 2/33 patients had OS. One patient had multiple bone metastases and received 1 cycle of therapy. Two months later, repeat scans showed a complete response. This patient remained disease free for 8 months but subsequently relapsed.

The Children's oncology group recently investigated the use of dinutuximab monotherapy in patients with recurrent pulmonary OS in complete surgical remission in a single-arm phase II study (AOST1421). Patients received 5 cycles of dinutuximab 70mg/m2/cycle with GM-CSF in 2 different dinutuximab infusion schedules: 35mg/m2/day over 20 hours (2-day) and 17.5mg/m2/day over 10 hours (4-day) schedule. The primary end point was Disease Control Rate (DCR), defined as the proportion of patients' event-free at 12 months from enrollment and success was defined as ≥16/ 39 patients (\> 40%) event-free at 12 months from enrollment. The preliminary results of this study were showed at ASCO 2020. Thirty-nine patients were eligible and evaluable (median age 15 yr). One of 136 administered therapy cycles met the criteria for unacceptable toxicity when 1 patient receiving the 2-day schedule died after cycle 2 due to an unknown cause and 1 patient experienced grade 4 neurotoxicity (depressed level of consciousness and respiratory depression) attributed as probably related to the protocol therapy. The protocol was revised to allow only the 4-day schedule. Other ≥ Grade 3 toxicities occurring in \> 10 % of participants were predictable dinutuximab toxicities such as pain, diarrhea, hypoxia and hypotension. A DCR of 30.7% (95% CI 17- 47%) was found, as 27/39 patients experienced an event. The final official results have not been published yet, and analyses are ongoing. A humanized version of the anti-GD2 antibody, Naxitamab (hu3F8), developed at Memorial Sloan Kettering Cancer Center, is currently being tested for efficacy against recurrent OS (NCT02502786).

Rationale dose and schedule of Dinutuximab beta in MaQ trial.

The recommended dosage of Dinutuximab (Unituxin, United Therapeutics) is 17.5 mg/m2/day administered IV over 10-20 hours for 4 consecutive days for a maximum of 5 cycles. In AOST1421, patients with recurrent pulmonary OS received 5 cycles of dinutuximab 70mg/m2/cycle with GM-CSF in 2 different infusion schedules: 35mg/m2/day over 20 hours (2-day) (experimental infusion) and 17.5mg/m2/day over 10 hours (4-day) schedule. However, during this trial, 2 serious adverse events (n=1 death, n=1 grade 4 neurotoxicity), possibly related to the experimental infusion schedule of dinutuximab were reported. In light of these events, the protocol was modified for the remainder of the study to allow only the 4-day schedule.

In the EU, Dinutuximab beta is approved for high-risk NB patients at the recommended dosage of 100 mg/m2 per course as either an 8-hour short-term i.v. infusion over 5 consecutive days (STI), or as a long-term i.v. infusion over 10 consecutive days (LTI). A pharmacokinetics study of LTI dinutuximab beta showed that this regimen results in higher plasma exposure at time points preceding subsequent antibody infusions after cycle 1, allowing for a persistent activation of antibody effector mechanisms over the entire treatment period. Moreover, LTI led to a less toxic profile compared with STI regimen. Data on Dinutuximab dosage and safety are based on studies enrolling primary refractory or relapsed NB or first-line NB children with either complete response or at MRD. OS is the most common primary malignant bone tumor in AYA, thus we expect to include older patients than NB patients, that notably experience greater toxicity from antitumor therapies. Moreover, the present trial will enroll patients who have experienced OS R/R and have already received at least one line of standard treatment. Furthermore, so far, PK data are lacking for the adolescent population. For these reasons, the patients enrolled in this study with OS R/R will received Dinutuximab beta (Qarziba) 14 mg/mq/day, for 5 days (total dose: 70mg/sqm/cycle) i.v. continuous infusion. Each cycle will last 28 days.