Altered Expression of Pdgfrα and Its Downstream Signalling Components May be Causal in the Development of Imatinib Induced Thrombocytopenia in CML Patients Receiving Imatinib Treatment

Background:

The main regulators of most of the cellular signalling pathways are protein kinases. Among these the receptor tyrosine kinases (RTKs) play important roles in cellular growth and proliferation by transmitting extracellular messages to intracellular signalling circuits. An important component of the intracellular circuits is the (PDGFR/PI3K/Akt/mTOR) pathway. Aberrant functioning of this pathway is known to occur in a number of diseases through various mechanisms. We report here that expression of PDGFRα gene and its downstream signalling components viz. PI3K and AKT is down regulated after imatinib treatment in some CML patients on imatinib therapy and may be a causal in the development of imatinib induced thrombocytopenia in these patients.

Methods:

A cohort of 100 chronic phase CML patients admitted to the Lok Nayak Hospital, New Delhi, India were included in this study. After initiation of imatinib treatment, haematological response of CML patients was monitored regularly for two years, in which development of thrombocytopenia was the primary end point.

Total RNA, from blood samples of CML patients, was extracted using Trizol method. RNA concentration was determined by measuring absorbance at 260 nm. A cDNA synthesis kit (ThermoFisher Scientific, USA) was used for cDNA synthesis according to the manufacturer's instructions. The mRNA expression of all the genes was evaluated by quantitative SYBR Green based real time polymerase chain reaction (qRT-PCR) and results were expressed as fold change (2^-∆∆ct). Results:

Expression of PDGFRα, PI3K and AKT1 genes was significantly downregulated after imatinib treatment with a fold change (Mean + SD) of (2.12 + 0.41, 2.38 + 0.53 and 4.78 + 0.38 respectively) in CML patients receiving imatinib therapy (p < 0.0001). Further, we analysed the expression of PDGFRα, PI3K and AKT1 genes in two groups of CML patients- one that developed thrombocytopenia after imatinib treatment and the other that did not. We observed that there was a differential expression of PDGFRα and AKT1genes in thrombocytopenic and nonthrombocytopenic CML patients. Thrombocytopenic CML patients had a lower expression of PDGFRα and AKT1 genes in comparison to non-thrombocytopenic CML patients and this difference reached a statistical significance with a p-value of 0.02 and 0.04 respectively. Moreover, the expression of PI3K gene was also slightly downregulated in thrombocytopenic CML patients (fold change = 2.21+ 0.47 ) compared to nonthrombocytopenic ones (fold change = -2.55 + 0.57) but this difference did not reach a statistical significance (p=0.14).