Evaluation of SRC-family kinases in gastrointestinal stromal tumors

Abstract

9529 Background: Inhibition of KIT oncoproteins by imatinib mesylate (IM) induces clinical responses in most GIST patients. However, many patients develop IM-resistance and novel KIT-Inhibitors show clinical benefit in only a minority of patients. SRC-family kinases (SFK) are important participants in kinase oncoprotein signaling pathways in ALL and CML, and dual-specificity SRC/ABL-inhibitors show promising activity in IM-resistant CML in vitro. However, little is known about SFK functional roles in IM-resistant GIST. Methods: GIST were analyzed for SFK expression and activation by western blotting. Biological consequences of KIT inhibition alone (IM), SFK inhibition (SU6656) and combined KIT/SFK inhibition (PP1, PP2, SU6656+IM) were determined by immunoblotting for protein activation, and—in GIST cell lines—by luminescence assays for cell proliferation. Results: Primary GIST and GIST cell lines showed weak SFK activation compared to Jurkat (T-cell ALL) controls. Variable expression of the SFK proteins FYN, LYN and SRC (but not BLK and LCK) was shown in the cell lines and primary GIST. Expression of SFK proteins HCK and FGR was found in 2 primary GIST only. KIT and KIT signaling pathways (pAKT, pS6, pSTAT3) were affected by IM and combined KIT inhibitors but not by SU6656 at 1μM in GIST882 (IM-sensitive cell line) and GIST48 (IM-resistant cell line). SRC phosphorylation (Y418) was not affected by IM or SFK-inhibitors at 1μM. IM showed superior inhibition of proliferation compared to PP1 and PP2 (1μM) in GIST882 (IM: 67%, PP1: 1%, PP2: 0%) and comparable inhibition in GIST48 (IM:30%, PP1: 29%, PP2: 29%). No effects on proliferation were seen with SU6656 alone or in combination with IM; no antagonistic effects were observed. Conclusions: Our analysis showed expression and weak activation of several SFK in GIST. Expression of heme-associated SFKs in primary GIST may be explained by lymphocellular infiltration. Biochemical inhibition of SFK alone does not have antiproliferative effects in GIST cell lines, and no synergies or antagonisms were found in combination with IM or with combined KIT/SFK inhibitors. Therefore, targeting of SFK may be of less therapeutic value in GIST than in kinase-driven haematological cancers. No significant financial relationships to disclose.