NEWPORT BEACH, CALIF. – The combination of oral rigosertib and azacitidine is proceeding to a phase 3 trial in patients with myelodysplastic syndromes (MDS), but it isn’t clear if the combination will continue to be developed for acute myeloid leukemia (AML).
In a phase 1/2 trial, oral rigosertib plus azacitidine produced a 90% response rate in higher-risk MDS patients who were naive to hypomethylating agents (HMAs), a 54% response rate in higher-risk MDS patients who had failed HMA therapy, and a 50% response rate in patients with AML.
Genitourinary toxicities were initially a concern in this trial, but researchers found ways to mitigate the risk of these toxicities, according to Richard Woodman, MD, chief medical officer and senior vice president of research and development at Onconova Therapeutics, the company developing rigosertib.
Dr. Woodman and his colleagues presented results from the phase 1/2 trial in two posters at the Acute Leukemia Forum of Hemedicus.
Results in AML
The researchers reported phase 1 results in 17 patients with AML. Eleven patients had AML, according to investigator assessment, and six patients had refractory anemia with excess blasts in transformation, according to French American British criteria, as well as least 20% excess blasts at baseline.
The median age of the patients was 73 years, and 53% were men. Two patients had received no prior therapies, six patients had relapsed disease, and nine were refractory to their last therapy.
Patients received oral rigosertib at escalating doses twice daily on days 1-21 of a 28-day cycle. The recommended phase 2 dose was 840 mg daily (560 mg in the morning and 280 mg in the afternoon), but there were two expansion cohorts in which patients received 1,120 mg daily (560 mg twice a day or 840 mg in the morning and 280 mg in the afternoon). The patients also received azacitidine at 75 mg/m2 per day subcutaneously or intravenously for 7 days starting on day 8.
Patients received a median of three treatment cycles. Fifteen of the 17 patients (88%) discontinued treatment, most because of progressive disease (n = 5), toxicity (n = 4), or death (n = 3).
Twelve patients were evaluable for response, and six (50%) responded. One patient achieved a morphologic complete remission (CR), three achieved a morphologic leukemia-free state, and two had a partial response.
The most common treatment-emergent adverse events (TEAEs) were fatigue (53%), diarrhea (53%), nausea (53%), constipation (47%), back pain (41%), pyrexia (41%), and pneumonia (35%). Grade 3 or higher TEAEs included pneumonia (35%) and anemia (24%).
These results haven’t provided a clear way forward for oral rigosertib and azacitidine in AML. Dr. Woodman said the researchers will have to review past studies and evaluate how AML patients (with at least 20% blasts) have responded to intravenous rigosertib, consult experts in the field, and then decide how they will move forward with oral rigosertib and azacitidine in AML.
Results in MDS
Dr. Woodman and his colleagues presented data on 74 patients with higher-risk MDS. The median age was 69 years, and 59% were men. Most patients were high risk (n = 23) or very high risk (n = 33), according to the Revised International Prognostic Scoring System.