Histone Deacetylase Inhibitors in Myelodysplastic Syndrome
Authors: Selene Insija Ilyas , Jose Jemin Aby , Sardar Muhammad , Shah Zunairah , Shafqat Madeeha , Faridi Warda , Malik Mustafa Nadeem , Yasir Muhammad , Khalil Muhammad Jahanzeb , Aslam Shehroz , Qureshi Anum , Rafiyath Shamudeen , Anwer Faiz 
Published: October 2019

Abstract
Background
Myelodysplastic Syndrome (MDS) represents a heterogeneous group of diseases with clonal proliferation, bone marrow failure and increase risk of progression to acute leukemia. Histone deacetylase inhibitors (HDACi) modulate the epigenetics of cancer cells to promote differentiation and programmed cell death. Our aim is to study the efficacy and safety of HDACi in patients with MDS/ acute myeloid leukemia (AML). HDACi can be a safer alternative in patients with high risk MDS who are not eligible for stem cell transplantation or high intensity chemotherapy.
Methods
A comprehensive literature search was done using following 5 databases: (Pubmed,Embase,Web of Science,Cochrane library,Clinical Trials.Gov) in accordance with the PRISMA guidelines. We included 21 trials (Phase II/III ) with a total 1654 patients,of which 1030 patients recieved HDACi and were evaluable for respone. Our primary objective was to determine efficacy of HDACi based regimen in terms of overall response rate (ORR) and composite complete response rate (CCR). A meta-analysis was done for regimen that were evaluated in more than one trials to report ORR and CRR.CMA software V.3 was used to run metaanalysis to calculate the response and the heterogenity among studies were assesed by using I2 test.A random -effect model was applied.
Results:
The pooled analysis (95% CI) with 1030 evaluable patients in MDS/ AML showed an overall response rate of 37.1% (32.3-42.3 : I2= 86.105 )with composite response (comp CR=CR+Cri+mCR) of 30.8%(26.8-35.1) .The median overall survival of those who received HDACi ranges from 8 -25 months.The Base line Characterstics,Outcome and Toxicity of HDACi in MDS/AML are summarized in Table 1.
In the meta-analysis (n=57) of two trials (Garcia et al, 2007 & Luger et al. 2013), combination regimen of Mocetinostat- Azacytidine had an ORR of 54%(95% CI: 10.2-92.3) and composite complete response (CCR) of 18.9% (95% CI :9.3-34.7) in patients with MDS/AML. Combination of Vorinostat-Cytarabine-Idarubicin had an ORR of 50.7% (95% CI :40.7-96.5) and CCR of 30.1% (95% CI: in 111 patients with MDS/AML in a meta-analysis of trials by Prebet et al. 2013 and Manero et al. 2012. The meta-analysis of 3 trials evaluating Vorinostat-Azacitadine regimen (Craddock et al. 2017; Sekers et al. 2017 & Montalbano et al. 2016) had an ORR 38.3%( 95 % CI :18-63) CCR of 29%(95% CI: 11-58) in a total patient population of 274 patients. The regimen of Valproate- Deictibine/Cytarabine was evaluated in 3 separate trials with a total patient population of 156 which showed an ORR of 41.6% (95 % CI :20.9-65.6)and a CCR of 28.3%(95% CI 18.9-42.7) in the metanalysis. The meta-analysis of 3 trials evaluating a three-drug regimen of Valproate-Azacytadine-All trans retinoic acid(ATRA) showed an ORR of 32.2%(95% CI :24.2-41.3) and CCR of 23.7%(95 %CI 13.1-39.0) in 144 MDS/AML patients. In a trial by Manero et al (2017), the combination of Pracinostat and Azacitadine had an ORR of 67.5% (95% CI :51.7-80.01) CCR of 60%(95% CI 44.3-73.8) in 51 AML/MDS patients. A single trial evaluating regimen of Panobinostat and Azacitadine (n=40) had an ORR of 37.5% and CCR of 27.5%. Combination of Panobinostat and Decitabine in a trial by Geoffry et al in 2017 (n=52), the ORR was 21.2% and CCR of 19.2%.The Overall response rate and Composite response rate of HDACi in MDS/AML are mentioned in Table 2 and Table 3.
Conclusion:
Most of the HDACi like Mocetinostat,Valproic acid ,Pracinostat when used in combination with either Hypomethylating agents(Azacytidine ,decitabine) or purine analogs (cytarabine/idarubicin) produced a good response.Pracinostat in combination with azacytidine showed the best ORR among the studies but there was only single study mentioning this combination.Single agent studies with resposne were also not evaluable.Most of MDS patients get resistant to hypomethlating agent thus there is need to explore newer agents and HDACi agents is a promising group.

Disclosures
No relevant conflicts of interest to declare.