The US Food and Drug Administration (FDA) has granted orphan drug designation for biopharmaceutical firm Epizyme‘s first-in-class EZH2 inhibitor, tazemetostat, to treat malignant rhabdoid tumours (MRTs).

EZH2 is a histone methyltransferase (HMT) that is understood to play a potentially oncogenic role in several cancers.

Last December, the company started a Phase II trial in adults and a Phase I trial in children with genetically defined tumours, including MRTs.

The existing MRT treatment consists of surgery, chemotherapy and radiation therapy, which are associated with limited efficacy and significant treatment-related morbidity.

"In an ongoing phase I study, tazemetostat has demonstrated encouraging clinical activity and an acceptable safety profile in patients with these severe types of cancer."

MRT is defined by loss of INI1 protein as measured by immunohistochemistry, while other rhabdoid tumours, such as MRT of ovary, are characterised by loss of the protein SMARCA4 and have shown sensitivity to tazemetostat in preclinical models and in the Phase I trial.

The company noted that the FDA orphan drug status applies to both INI1-negative MRT, as well as SMARCA4-negative MRT of ovary.

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The drug is also being evaluated in an ongoing five-arm Phase II trial in patients with non-Hodgkin lymphoma.

Epizyme chief medical officer Dr Peter Ho said: "Malignant rhabdoid tumours are rare and aggressive cancers with poor outcomes.

"There have not yet been any targeted drugs developed specifically to treat these patients.

"In an ongoing phase I study, tazemetostat has demonstrated encouraging clinical activity and an acceptable safety profile in patients with these severe types of cancer.

"We believe tazemetostat has the potential to become an important targeted therapy for patients with MRT and we are working aggressively to execute our clinical development programme."

The ongoing Phase II adult and Phase I paediatric trials in patients with genetically-defined solid tumours include patients with rhabdoid tumours, other INI1-negative tumours, and synovial sarcoma.

Interim data from the company’s registration-supporting Phase II clinical trial of tazemetostat in adult patients with genetically defined solid tumours, including MRT, other INI1-negative tumours and synovial sarcoma, are expected to be presented at a medical conference in later this year.