Estimation of radioiodinated PYK as an imaging agent for assessment of EGFR-TK activity

Objectives In the previous presentation, we reported a radioiodinated PHY as EGFR-TK imaging agent. We developed a new radioiodinated quinazoline derivative which morpholinopropoxy is introduced at 6 position of quinazoline and estimated it as EGFR-TK imaging agent.

Methods PYK, 4-(3-iodophenoxy)-7-ethoxy-6-(3-molpholinopropoxy)quinazoline, was synthesized. ¹²⁵I-PYK was synthesized by no carrier added iododestannylation method and purified by HPLC. The binding characteristics (Bmax and Kd) were analyzed in A431 cell membrane fraction. The selectivity was evaluated in the blocking study with various TK inhibitors. The biodistribution study of ¹²⁵I-PYK was conducted in A431 bearing mice.

Results The radiochemical yield of ¹²⁵I-PYK was about 88% and the radiochemical purity was greater than 98%. In vitro binding assay showed Kd and Bmax of ¹²⁵I-PYK were 51.3 nM and 27.0 pmol/mg protein, respectively. The binding of ¹²⁵I-PYK to A431 cell membrane was significantly inhibited by EGFR-TK inhibitors (PD153035 and gefitinib). Genistein and RG13022 (protein tyrosine kinase inhibitor) slightly inhibited the ¹²⁵I-PYK binding. However, the ¹²⁵I-PYK binding was not blocked by HNMPA (insulin receptor TK inhibitor) and AG17 (PDGFR-TK inhibitor). Biodistribution study revealed high tumor uptake of ¹²⁵I-PYK (6.44 %ID/g) at 1 hr postinjection. The tumor to blood and muscle ratios were 11.45 and 7.50, respectively.

Conclusions These results indicated that radioiodinated PYK is superior to radioiodinated PYH and is useful as EGFR-TK imaging agent. Further investigations are needed to estimate the usefulness of radioiodinated PYK for the prediction of response to therapy with EGFR-TK inhibitors such as gefitinib