Highlights from the last EACR meeting - Abstracts of interest for AML

The European Association of Cancer Research (EACR) provides scientific meetings to facilitate communication within the cancer research community. They have a multi-disciplinary approach to provide new insights in cancer research. Of their rich and expansive scientific programme, presented at the last meeting held in Manchester July 2016, there were 2 abstracts of interest for Acute Myeloid Leukemia (AML).

The first one was presented as a poster by M.T. Esposito from the University of East London and colleagues and revealed that PARP inhibitors might represent a new therapeutic approach in AML.

The second one, also presented as a poster, by Z. A. Ahmed from Aga Khan University Hospital-Karachi-Pakistan indicated that monitoring WT1 gene expression during treatment might be a predictive tool for early recurrence or relapse.

153 - Exploiting DNA damage repair defects for effective targeting of acute myeloid leukaemia by PARP inhibitors

Abstract

M.T. Esposito, et al.

Introduction: Inhibitors of Poly-ADP-Ribose Polymerase (PARPi) have been successfully developed and approved by FDA for treatment of ovarian cancer carrying mutations in DNA damage response (DDR) genes BRCA1/BRCA2. In Acute Myeloid Leukemia (AML) patients, these mutations are extremely rare. However, chromosomal rearrangements generate chimeric oncofusion proteins that, by acting as transcriptional regulators, impair DDR gene expression. This prompted us to test the efficacy of using PARPi in AML.

Materials and Methods: PARPi were tested in vitro and in vivo. In vitro experiments were carried out in mouse and human leukemic cell lines. Mouse leukemic cells expressing the oncofusion gene of interest were generated by Retroviral Transduction Transformation Assay (RTTA).

Results: Leukemic cells driven by the oncofusion genes, AML1-ETO and PML-RARa, are sensitive to PARP inhibition whereas cells harbouring MLLAF9 translocation are resistant. Treatment of AML1-ETO and PML-RARa leukemic cells with PARPi induces apoptosis, senescence, cell cycle arrest and differentiation in vitro and significantly prolongs survival in vivo. By using gH2AX and RAD51 as markers of DNA damage and HR (Homologous Recombination) we showed that AML1-ETO and PML-RARa cells accumulate DNA damage and are defective in recruiting RAD51 to DNA damage foci upon PARPi treatment. Further analysis revealed that the expression of a number of genes that are involved in the HR pathway are reduced in AML1-ETO and PML-RARa cells including Rad51, Brca2 and Rpa1. This suggests that AML-ETO and PML-RARa are sensitive to PARPi as result of defective DDR. We showed that HOXA9, a key downstream target of MLL-fusions plays a critical role in promoting expression of HR genes and thus providing evidence by which MLL-AF9 are resistant to PARPi. Depletion of Hoxa9 reduces the expression of Rad51 and Brca2 in MLL-AF9 cells and confers PARPi sensitivity in MLL-AF9 leukemic cells, compromising its ability to form colonies, repair DNA damage and prolongs survival in mouse models. Conversely, HOXA9 overexpression rendered AML1-ETO and PML-RARa cells resistant to PARPi. Likewise, pharmacological suppression of Hoxa9, using GSK3 inhibitor LiCl, can also sensitize MLL-AF9 cells to PARPi and prolongs survival in our mouse model.

Discussion: Our data indicate that PARPi might offer a new therapeutic strategy for patients with AML1-ETO or PML-RARa translocations. More importantly, we showed for the first time that HoxA9 can activate a potential DNA repair back-up pathway. PARPi in combination with pharmacological inhibitors of HOXA9 may represent a novel avenue for tailored therapeutic targeting of the aggressive MLL leukaemia.

Conflict of interest: Ownership: Alan Ashworth: Patents related to the development of PARP inhibitors with AstraZeneca. Advisory Board: Alan Ashworth: Consulting or Advisory Role: Genentech, Sun Pharma, GlaxoSmithKline, Novartis.

307 - Assessment of WT1 expression as a marker of treatment outcome in karyotype normal acute myeloid leukemia patients in Pakistan

Abstract

A. Ahmed, et al.

Background: Currently, there is an effort to predict relapse by follow-up monitoring of MRD and subsequently to begin the treatment of the patients during their clinical and hematological remission prior to overt hematological relapse. Expression of WT1 in AML is known to be independently associated with significant inferior response to therapy and short survival outcome. Follow up monitoring of WT1 gene expression during or after therapy would be a valuable predictive marker for early recurrence or relapse of AML disease. Objective: To demonstrate prognostic relevance of WT1 expression levels monitored at diagnosis and during follow up of chemotherapy for predicting relapse in AML patients.

Methods: For this study, five AML patients registered at the Oncology Clinics of the Aga Khan University Hospital, Karachi were recruited. Blood was collected from these patients and it used to isolate RNA from purified PBMCs. The RNA was reverse transcribed to make cDNA which served as template for quantitative RT-PCR analysis.

Results: The WT1 levels were quantified by RT-PCR in five male patients with AML. Relatively higher level of WT1 mRNA (4,000–9,500 copies/ml) was detected in treatment naive patients, whereas only (100–250 copies/ml) were seen in two patients (one was receiving induction and the other patient was on consolidation therapy). In addition, one patient who received induction therapy showed raised WT1 mRNA levels (7,700 copies/ml).

Conclusion: High WT1 burden (>5,000 copies/ml) in two patients is indicative of early recurrence of the disease along with shorter disease free and overall survival. The low WT1 expression (<200 copies/ml) in two patients after induction and consolidation therapy respectively is suggestive of better prognosis.

No conflict of interest.