Pioglitazone Did Not Affect PPAR-Γ, STAT5, HIF2α and CITED2 Gene Expression in Chronic Myeloid Leukemia Patients with Deep Molecular Response

Preliminary reports demonstrated that pioglitazone, an antidiabetic drug that is agonist of peroxisome proliferator-activated receptor gamma (PPAR-γ) was able to reduce expression of STAT5 and its downstream targets HIF2α and CITED2, which are key guardians of the quiescence and stemness of chronic myeloid leukemia (CML) leukemia stem cells (LSCs). Leaving quiescence would turn the LSCs more sensitive to imatinib (IM) and cause an erosion of the LSCs. This was demonstrated in vitro and in vivo in CML patients that achieved complete molecular response after pioglitazone use. This was the rational for the design of EDI-PIO trial (Pilot Study of Imatinib Discontinuation in Patients with Chronic Myeloid Leukemia with Deep Molecular Response - Evaluation of Pioglitazone in Treatment-Free Remission) (NCT02852486). In this trial, pioglitazone was given in association with IM, with the aim to pull out the LSCs from the quiescence and sensitizing them to IM effect, increasing treatment-free remission (TFR) rates after treatment interruption.

Aims: to evaluate PPAR-γ, STAT5, HIF2α and CITED2 gene expression before and after pioglitazone use in CML patients with criteria for IM discontinuation

Patients and methods: EDI-PIO is a prospective, phase II trial. Inclusion criteria: CML in chronic phase, treated with IM for at least 3 years, with stable deep molecular response (MR4.5) for at least 2 years. Patients received pioglitazone 30 mg/day, orally, for 3 months before IM discontinuation. BCR-ABL levels were measured by real-time quantitative PCR monthly in the first year after discontinuation, every two months in the second year, and then every 3 months during the subsequent follow-up. Imatinib was reinitiated at molecular relapse (loss of major molecular response or confirmed loss of MR4.0). Total RNA was extracted from peripheral blood leukocytes, pre and post pioglitazone, and at 3 and 6 months after IM discontinuation. After cDNA synthesis, an aliquot was used for gene expression analysis by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR), using specific primers for PPAR-γ, STAT5, HIF2α and CITED2. The relative gene expression was calculated using the equation, 2^-ΔΔCT. GAPDH was used as control gene. Statistical analysis was performed using ANOVA. Treatment-free remission (TFR) was calculated from IM discontinuation until molecular relapse, reintroduction of IM by any cause, progression to advanced phases or death to any cause.

Results: The study is closed for enrollment. Between June 2016 and January 2019, 32 chronic phase CML patients were recruited, of which 30 patients were included in gene expression analysis. Median age was 55 years at trial initiation; 56.7% were men, 50% low risk Sokal and the median time of IM treatment was 117 months (41-191). The median follow-up time was 20 months. TFR was 60% at 24 months. Eleven patients relapsed and IM was reintroduced, but none presented hematologic relapse or progression to advanced phases. There was no significant difference in STAT5, PPAR-γ, HIF2α and CITED2 expression pre and post pioglitazone, at 3 and 6 months after IM discontinuation. No difference was found in the comparison of the relapsed vs. non-relapsed group.

Conclusions: pioglitazone did not affect STAT5, PPAR-γ, HIF2α and CITED2 gene expression in this group of pts with deep molecular response. The ACTIM trial demonstrated a reduction in STAT5 expression in bone marrow cells 6 months after pioglitazone exposure, but pioglitazone was given to pts with MMR, without MR4.0. There was no difference in gene expression in the groups with or without molecular relapse. TFR rates remains similar to those reported in other discontinuation trials.