Report of the Relapsed/Refractory Cohort of SWOG S0919: A Phase 2 Study of Idarubicin and Cytarabine in Combination with Pravastatin for Acute Myelogenous Leukemia (AML)

Abstract

Inhibition of cholesterol synthesis and uptake sensitizes acute myeloid leukemia (AML) blasts to chemotherapy. A Phase 2 study of high dose pravastatin given in combination with idarubicin and cytarabine demonstrated an impressive response rate [75% complete remission (CR), CR with incomplete count recovery (CRi)]. However, this population was a favorable risk group as eligible patients had to have a CR/CRi lasting ≥3 months following their most recent chemotherapy. Therefore, the study was amended to treat patients with poor risk disease including those with CR/CRi < 6 months following their last induction regimen or with refractory disease. Here, we present results in this poor risk group. This trial included a significant number of patients with poor risk cytogenetics (43%) and poor risk molecular mutations. The response rate was 30% and approximately one-fourth of patients were able to proceed to allogeneic hematopoietic stem cell transplant (HSCT). The median overall survival for patients proceeding to allogeneic HSCT is 27.1 months. Although this trial did not meet criteria for a positive study based on the response rate (p=0.062), these results are encouraging given the poor risk population and suggest that targeting the cholesterol pathway may have therapeutic benefit in AML.

Introduction:

The treatment of relapsed/refractory acute myeloid leukemia (AML) remains challenging and novel therapies are needed. AML blasts frequently overexpress the genes for the LDL receptor and 3-hydroxy-3-methylglutaryl coenzyme reductase (HMG-CoAR) and therefore import and synthesize cholesterol at higher levels than normal myeloid progenitors.¹ Patients with AML and high white blood cell counts sometimes have marked hypocholesteremia at the time of diagnosis suggesting increased cholesterol metabolism and this typically resolves when patients achieve a complete remission (CR).^{1, 2} These observations suggest that AML cells may require high levels of cholesterol for their survival and that abnormalities in cholesterol homeostasis are necessary for AML cell survival.² In addition, inhibition of cholesterol synthesis and uptake sensitizes AML blasts to chemotherapy.² Thus, targeting the cholesterol pathway represents a potential therapeutic approach.

A previous Phase 1 trial demonstrated encouraging results with high dose pravastatin in combination with IA (idarubicin and intermediate dose cytarabine).¹ This led to a Phase 2 trial of this combination in patients with relapsed AML.³ The response rates in this trial were impressive: 75% CR/CR with incomplete count recovery (CRi). However, this population was a favorable risk group as eligible patients had to have a CR/CRi lasting ≥3 months following their most recent chemotherapy. Therefore, this study was amended to treat patients with poor risk AML (CR/CRi < 6 months following their last induction regimen or refractory disease). Here, we report the results in this poor risk group.

Methods:

Patients were treated at SWOG institutions from April 2013 through November 2014. The protocol (registry: ClinicalTrials.gov Identifier: NCT00840177) was approved by each institution’s review board and signed informed consent was obtained from all registered patients. The procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008. Pravastatin was supplied by Bristol Meyers Squibb (New Brunswick, NJ, USA). Eligibility included: age ≥18 years, relapsed/refractory AML, cardiac ejection ejection fraction ≥45%, CR/CRi following the most recent chemotherapy < 6 months, and no prior hematopoietic stem cell transplant (HSCT). Patients receiving 1 induction course with 7+3 (cytarabine + anthracyline) and a day 14 bone marrow with ≥ 5% blasts were eligible. Treatment consisted of pravastatin (1280 mg by mouth on Days 1–8), idarubicin 12 mg/m²/day intravenous (IV) days 4–6, and cytarabine 1.5 g/m²/day continuous IV infusion days 4–7. Patients achieving a CR could also receive 2 cycles of consolidation with oral pravastatin 1280 mg by mouth days 1–6, idarubicin 12 mg/m²/day IV days 4–5, and cytarabine 1.5 g/m²/day continuous IV infusion days 4–5. CR and CRi were defined by International Working Group (IWG) criteria.⁴ Toxicity was graded and defined according to CTCAE version 3.0 for routine toxicity reporting and according to version 4.0 for serious adverse event reporting. The attribution of toxicities was decided by the treating physician.

Statistics

Thirty-seven patients were to be accrued. If ≥12 patients achieved CR or CRi, the regimen would be considered sufficiently effective (critical level of 5% if the true CR rate is 20%) and power of 87% (if the true CR rate is 40%). These numbers are based on a stratification system described by Estey et al.⁵ Study data were analyzed by Hongli Li, M.S. and Megan Othus, Ph.D., leukemia committee biostatisticians at the SWOG Statistical Center (Seattle, WA). All authors had access to primary clinical trial data.

Results:

Patient characteristics are listed in Table 1. Forty-six patients with a median age of 57 years (range 23–75) were enrolled. Twenty-four patients (52%) were male and the median white blood count (WBC) was 2600/uL (range 200–450,000). The median time from diagnosis to registration was 4.3 months (range 0.7–49.5). At the time of registration, 65% of patients were primary refractory and 35% had relapsed. The number of prior treatment regimens included: 1 (46% of patients), 2 (37% of patients), 3 (7% of patients), and 4 (11% of patients). Prior salvage therapy included: 7+3 (cytarabine plus an anthracycline), single agent clofarabine, high dose cytarabine, MEC (mitoxantrone, etoposide, cytarabine), aurora kinase inhibitor (AMG-900), FLAG (fludarabine, high dose cytarabine, granulocyte colony stimulating factor) +/− anthracycline (idarubicin), 5-azacitidine, and CLAG (cladribine, high dose cytarabine, granulocyte colony stimulating factor) +/− anthracycline (mitoxantrone). Forty-two percent of patients were considered to have either treatment-related AML (n=4; 9%) or had a prior history of myelodysplastic syndrome (n=15; 33%). Cytogenetic risk defined by NCCN criteria⁶: 43% poor, 52% intermediate, and 4% missing. Molecular mutation data was not required at study entry. However, most sites collected this data. The frequency of various mutations included: FLT3 [7/36 patients: 6 internal tandem duplications (ITD), 1 tyrosine kinase domain (TKD)], NPM1 (3/33 patients), c-kit (1/4 patients), WT1 (0/3 patients), CEBPalpha (3/31 patients with single mutations); IDH1 (4/23 patients); IDH2 (2/23 patients), JAK2 (0/3 patients), DNMT3A (4/24 patients), p53 (1/3 patients), ras (3/5 patients), and RUNX1 (1/2 patients). Table 2 outlines Grade 3–5 treatment-related toxicities. No myositis or unexpected toxicities were observed. Figure 1 outlines the distribution of patients with respect to subsequent transplant and consolidation therapy after salvage therapy on trial. One evaluable patient received 1 cycle of consolidation therapy on protocol. Eleven patients were able to proceed to transplant (10 with allogeneic HSCT and one with NK transplant).

Table 1.

Patient Characteristics (n=46)

Median Age	57 years (range 23–75)
Gender
Male	52% (n=24)
Female	48% (n=22)
Median time from initial diagnosis to registration	4.3 months (range 0.7–49.5)
Disease status
Primary refractory	65%
Relapse	35%
Median WBC at registration	2600/uL (range 200–450,000)
Cytogenetic risk by NCCN criteria
Poor	43%
Intermediate	52%
Missing	4%

Table 2. Treatment-related toxicities (Grade 3–5).

(n=46; the numbers are below are the numbers of patients with the specified grade toxicities during protocol treatment)

	Grade 3	Grade 4	Grade 5
Hematologic
Hemoglobin	15	6	0
Leukocytes	0	17	0
Lymphopenia	2	7	0
Neutropenia	1	15	0
Platelets	1	17	0
Non-hematologic
Transaminase	3	0	0
Alkaline phosphatase	1	0	0
Infectious colitis	1	0	0
Creatinine	1	0	0
Diffuse capacity of the lung for carbon monoxide (DLCO)	0	0	1
Diarrhea	8	0	0
Dyspnea	1	0	0
Fatigue	2	0	0
Febrile neutropenia	26	5	0
Gastrointestinal infection	1	0	0
Gastrointestinal pain	4	0	0
Genitourinary Infection	1	0	0
Hypoalbuminemia	6	0	0
Hypocalcemia	1	1	0
Hypokalemia	3	0	0
Hyponatremia	1	0	0
Hypophosphatemia	2	0	0
Hypotension	0	0	1
Hypoxia	3	0	0
Bacteremia	1	8	2
Lung, hemorrhage	1	1	0
Lung infection	7	1	0
Mucositis	2	1	0
Muscle pain	2	0	0
Nausea	3	0	0
Neurologic infection	0	1	0
Opportunistic infection	2	0	0
Rash	1	0	0
Renal failure	0	1	0
Typhlitis	1	0	0
Ulceration	1	0	0
Weight Loss	2	0	0

Figure 1.

Distribution of patients going on to allogeneic HSCT and consolidation after initial treatment on trial (please see separate attached figure).

The response rate was 30% CR/CRi (95% CI: 17.7%, 45.8%). The p-value comparing 30% to 20% (the null response rate) is 0.062 at a one-sided level of 0.05. The estimated median overall survival is 4.1 months (95% CI: 2.8, 6) with the median follow-up among those last known alive being 15.6 months (range 0.8–27.2 months). The median relapse-free survival is 2.6 months (range 0.5–12.8 months). No clinical factors: age, WBC, cytogenetic risk, disease status (relapsed vs. refractory, time from diagnosis, AML onset (de novo vs secondary) were associated with response. Response rates in subgroups with particular mutations included: 1/1 patient with a p53 mutation, 3/6 patients with FLT3 mutations, 2/4 patients with DNMT3a mutations, 2/4 patients with IDH1 mutations, 2/2 mutations with IDH2 mutations and 1/3 patients with ras mutations. The median survival for patients proceeding to allogeneic HSCT is 27.1 months with a median follow-up time of 18.9 months among those last known alive. Relapse free and overall survival curves for patients proceeding to allogeneic HSCT are shown in Figures 2 and 3.

Figure 2.

Relapse-free survival for patients on trial who subsequently went on to allogeneic HSCT.

Figure 3.

Overall survival for patients on trial who subsequently went on to allogeneic HSCT.

Discussion:

The CR/CRi rate in this poor risk relapsed/refractory population did not meet criteria for a positive study but is still encouraging given the poor risk population and suggests that targeting the cholesterol pathway may have therapeutic impact. In particular, a recent clinical trial of idarubicin/cytarabine (IA) in combination with either fludarabine (F) or clofarabine (C) in patients with relapsed/refractory AML, the CR/CR without platelet recovery rate was 38% for CIA and 30% for FIA.⁷ Our regimen included significantly less chemotherapy and still had a comparable response rate, which is encouraging, and suggests that pravastatin may have a role in therapy. In addition to working on the cholesterol pathway in AML, it is also possible that pravastatin may have had a therapeutic advantage in patients with FLT3 mutations in this trial. A publication by Williams, et al. suggests that statins inhibit FLT3 glycosylation in human and murine cells and prolong survival of mice with FLT3 mutated (internal tandem duplication, ITD) leukemia.⁸ The FLT3 status was not known in all of the patients on this trial. However, 3/6 patients with FLT3 mutations achieved CR/CRi suggesting that further exploring this hypothesis in future trials would be worthwhile. In the FLT3 group, the response rates seen in this trial compare favorably to that of other trials with conventional therapy or FLT3 inhibitors in patients that are primary refractory or have had a previous remission duration ≤ 12 months (19–26% CR/CRi).⁸ The results in this trial also compare favorably to that seen with other agents in this particular disease group. As mentioned, CR rates for patients refractory to induction or who relapse within 12 months are typically on the order of 10–30%.⁹ Other agents such as the antibody drug conjugate, SGN33a (vadastuximab) have demonstrated encouraging results (33% CR/CRi) rate.¹⁰ However, many patients had declined/or were ineligible for intensive therapy and CR duration must have been > 3 months in those patients who had relapsed.

The median survival of 27.1 months in this trial for those patients proceeding to allogeneic HSCT is also encouraging, given the patient population. However, these patients had rapidly relapsing disease unless they were able to quickly proceed to allogeneic HSCT, further highlighting the importance of transplant in relapsed/refractory AML. Further interpretations about this trial are limited by the trial’s small size and uncontrolled structure. Ultimately, a randomized phase 3 trial with chemotherapy versus chemotherapy plus pravastatin is needed to definitely address the benefit of statin therapy. In addition, although the response rate was encouraging, it was significantly lower than the 75% seen in the previous cohort of good risk patients with CR/CRi < 6 months suggesting that inhibition of cholesterol synthesis alone is not able to fully overcome the poor prognosis of refractory disease. This suggests that using cholesterol modifying therapy in the upfront setting may have more potential benefit and this is currently being explored in patients with newly diagnosed AML arising out of MDS.

A previous Phase 1 trial suggested that the highest serum bioavailability of pravastatin is reached at doses > 1280 mg/day.¹ Higher doses were not used in the current trial given the concern regarding tolerability; however, given the low toxicity profile, this could be further explored. In addition, previous studies with lovastatin have suggested that the maximum effect of statin blockade is observed after 7 days of lovastatin administration.¹¹ This schema was not used in the Phase 1 or 2 trials with pravastatin given the concerns about delaying chemotherapy in patients. Thus, such an approach may also improve outcomes.

Future avenues of research could include: (1) evaluating other cholesterol lowering medications in combination; (2) evaluating the newer statins which are more potent inhibitors;(3) loading with pravastatin for a longer time prior to chemotherapy; (4) including maintenance therapy with pravastatin for patients in CR1 or post-transplant; (5) combining pravastatin with novel therapies (i.e. antibody based therapies such as SGN-33a, IDH inhibitors). Integration of laboratory correlatives as part of any future trials should also help give us better insight into the biology and pathways affecting response and outcome.

Highlights.

• AML cells require high levels of cholesterol for survival

• Targeting the cholesterol pathway represents a potential therapeutic option for AML

• Pravastatin plus chemotherapy has activity in relapsed/refractory AML