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Photo by Rhoda Baer

Adding an experimental compound to chemotherapy is a “promising” treatment approach for certain patients with acute myeloid leukemia (AML), according to researchers.

They tested the compound, CPI-613, in combination with high-dose cytarabine and mitoxantrone in a phase 1 trial of patients with relapsed or refractory AML.

The combination produced similar response rates in the overall patient population (50%), patients age 60 and older (47%), and those with poor-risk cytogenetics (46%).

The most common grade 3/4 adverse events (AEs) were hematologic toxicities, and there was 1 fatal AE—hypotension.

Mortality rates in this trial were similar to those observed in historical controls treated with high-dose cytarabine, mitoxantrone, and asparaginase.

“These data are very encouraging, especially for patients 60 years of age or older who have historically done very poorly with this disease,” said Timothy Pardee, MD, PhD, a professor at Wake Forest Baptist Health in Winston-Salem, North Carolina, and chief medical officer of Rafael Pharmaceuticals, Inc., the company developing CPI-613.

Dr Pardee and his colleagues reported these results in Clinical Cancer Research.

The researchers noted that CPI-613 is designed to target mitochondrial metabolism in cancer cells, and preclinical research showed that CPI-613 sensitized AML cells to chemotherapy.

To investigate this further, the team tested CPI-613 in combination with high-dose cytarabine and mitoxantrone in the phase 1 trial. The study included 66 patients with relapsed or refractory AML, as well as a patient with advanced-phase chronic myeloid leukemia (CML) who was mistakenly enrolled.

The patients’ median age was 60 (range, 21-79), and 54% were age 60 and older. Their median percentage of marrow blasts was 43%. Forty percent of patients had poor-risk cytogenetics, and 49% had intermediate-risk cytogenetics.

Most patients (72%) had no prior salvage therapy, 13% had 1 prior line of salvage, 10% had 2 prior lines, and 4% had more than 2. Thirty-one percent of patients had refractory disease.

Seven percent of patients had previously received high-dose cytarabine and mitoxantrone, and 25% had previous salvage including high-dose or intermediate-dose cytarabine.

Treatment

Patients received CPI-613, given over 2 hours, on days 1 to 5 of cycle 1. Doses ranged from 500 mg/m2 to 2750 mg/m2.

Starting on day 3, patients received 5 doses of cytarabine at 3 gm/m2 (for patients younger than 60) or 1.5 gm/m2 (for older patients) in 500 mL normal saline, over 3 hours, every 12 hours.

Patients also received 3 daily doses of mitoxantrone at 6 mg/m2 in 50 mL normal saline, given over 15 minutes, after the first, third, and fifth doses of cytarabine.

Patients were initially assigned to receive 1 cycle of treatment. Those with at least 5% blasts after the first cycle could receive a second course—either a full course or a 3-day course. And patients who responded to the first course could receive up to 2 cycles of the 3-day course.

Safety

There were 2 dose-limiting toxicities when CPI-613 was given at the 2750 mg/m2 dose. One of these toxicities was grade 3 diarrhea that didn’t respond to anti-diarrheals, and the other was grade 3 nausea that didn’t respond to antiemetics.

Because of these events, 2500 mg/m2 was deemed the maximum-tolerated dose. However, the recommended phase 2 dose is 2000 mg/m2.

The most common AEs—occurring in at least 50% of all patients who received CPI-613 (n=67)—included hemoglobin decrease (67%), hyperglycemia (67%), neutropenia (67%), thrombocytopenia (67%), hypomagnesemia (66%), leukopenia (66%), lymphopenia (66%), hypoalbuminemia (65%), hypokalemia (60%), hypocalcemia (57%), and diarrhea (55%).

All cases of neutropenia, thrombocytopenia, leukopenia, and lymphopenia were grade 3/4. Other common grade 3/4 AEs (occurring in at least 20% of patients) included hemoglobin decrease (62%), febrile neutropenia (28%), hypophosphatemia (24%), and hypokalemia (23%).

The only grade 5 AE was hypotension.

The mortality rate was 12% (n=8) at 30 days and 19% (n=13) at 60 days. The researchers said this was similar to the historical experience with high-dose cytarabine, mitoxantrone, and asparaginase. Mortality rates with this regimen were 13% at 30 days and 22% at 60 days.

Efficacy

Sixty-two patients were evaluable for response. Of the 5 patients who were not evaluable, 1 didn’t complete the first cycle of treatment, 1 was the CML patient, and 3 died before assessment.

The overall response rate was 50% (31/62). This included 26 patients with a complete response (CR) and 5 patients who had a CR with incomplete count recovery (CRi).

The rate of CR/CRi was 47% (15/32) in patients older than 60 years of age, 46% (11/24) in patients who had poor-risk cytogenetics, and 53% (8/15) when CPI-613 was given at the recommended phase 2 dose—2000 mg/m2.

The median overall survival (OS) was 6.7 months for all evaluable patients and 13.2 months for patients who achieved a CR/CRi.

The median OS was 6.9 months for patients age 60 and older, which was not significantly different from the median OS in younger patients (P=0.9642).

This study was sponsored by Wake Forest University Health Sciences and the National Cancer Institute.


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