FDA Grants Fast Track Designation to AMB-05X for Tenosynovial Giant Cell Tumor

AMB-05X has been granted fast track designation for the treatment of patients with tenosynovial giant cell tumor of the knee by the FDA.

The FDA has granted fast track designation to AMB-05X for the treatment of patients with tenosynovial giant cell tumor (TGCT) of the knee, according to AmMax Bio.1

AMB-05X is a potent monoclonal antibody targeting CSF1R. Through its binding to the regulatory cytokines CSF1 and IL-34, CSF1R is involved in the regulation of macrophages and related cells in multiple biological processes against multiple organ systems.

Currently, AMB-05X is under investigation in multiple phase 2 trials for patients with TGCT. Interim data from a phase 2 trial (NCT04731675) examining 5 patients showed that AMB-05X elicited clinical benefit, including tumor reduction per RECIST v1.1 criteria and improvements in patient-reported functional outcomes for this patient population.2 Additionally, AMB-05X was well tolerated and while there were a limited number of non-serious grade 1/2 adverse events (AEs), no serious AEs were observed.

“We are very pleased to receive fast track designation for AMB-05X from the FDA, which clearly reflects the significant unmet need facing thousands of patients suffering from TGCT and its numerous associated co-morbidities,” said Larry Hsu, PhD, chief executive officer of AmMax Bio, in a press release. “Physicians have shown tremendous enthusiasm for a locally injectable form of CSF1R inhibitor to address this localized disease in the joint. AMB-05X is designed to be administered via an intra-articular injection at the site of the tumor to minimize the systemic exposure and the associated serious safety concerns.”

TGCT is a serious and locally aggressive tumor where the current standard of care is surgical resection. However, this treatment carries significant risk to patients, including complications from infections and prolonged postoperative care, and frequent relapse. Because of this, experts are looking for a safe and efficacious pharmacological therapy that can be used alongside surgery.

In the multicenter, phase 2 trial, 11 patients with TGCT of the knee were enrolled and given an AMB-05X injection once every 2 weeks for 12 weeks for a total of 6 treatments.3

Enrollment in the trial was open to patients aged 18 years old with a confirmed diagnosis of TGCT of the knee joint, measurable disease based on RECIST v1.1, and adequate hematologic, hepatic, and renal function. Patients must have had a stable prescription of analgesic regimen and negative urine drug screen at the time of screening and baseline.

Additionally, women of childbearing potential must have a negative pregnancy test and patients must follow contraception guidelines.

Patients who had previously received treatment with another investigational drug within 4 weeks or 5 half-lives of baseline, received prior CSF1, CSF1R, oral tyrosine kinase inhibitors, had a history of extensive knee surgery, or had metastatic TGCT were excluded from the study.

The primary end points of the trial were treatment-emergent AEs and tumor response based on RECIST v1.1. Secondary end points of the study included tumor volume reduction, mean change in range of motion of the knee, mean change in patient-reported outcomes, mean change in stiffness, mean change in pain, and quality of life.

  1. AmMax Bio announces AMB-05X granted FDA fast track designation for the treatment of tenosynovial giant cell tumor (TGCT). News release. AmMax Bio. September 8, 2022. Accessed September 7, 2022. https://bit.ly/3QoWcW8
  2. AmMax Bio announces positive interim phase 2 results of AMB-05X for the treatment of tenosynovial giant cell tumor (TGCT). News release. AmMax Bio. October 20, 2021. Accessed September 8, 2022. https://bit.ly/3Ql5Vgd
  3. An open-label study of intra-articular AMB-05X injections in subjects with tenosynovial giant cell tumor of the knee. ClinicalTrials.gov. Updated July 29, 2022. Accessed September 8, 2022. https://clinicaltrials.gov/ct2/show/NCT04731675
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