Resistance to lapatinib, a tyrosine kinase inhibitor of HER2, is a significant clinical problem and to date the mechanisms of acquired lapatinib resistance remain largely unknown. In order to study acquired lapatinib resistance we established an in vitro cell line model through continuous culture of HCC1954 cells with 1 μM lapatinib. After 6 months the resulting HCC1954-L cells where significantly less sensitive to lapatinib with an IC50 of 2.6 ± 0.3 μM compared to aged-matched parental cells (IC50 0.42 ± 0.02 M; p = 0.004). In addition, lapatinib treatment had no significant effect on the growth of HCC1954-L xenograft tumors in mice, indicating the utility of HCC1954-L cells as an in vivo model of acquired lapatinib resistance.

Array CGH analysis was performed on the sensitive and resistant cell lines. Chromosomal aberrations were detected in 15 regions in the HCC1954-L cells, including increased amplification of the region of chr17q12 known to contain HER2 and STARD3. Immunoblotting was performed to assess whether the increased amplification corresponded with increased expression of the proteins. HCC1954-L cells exhibited a small but significant increase (1.2 fold) in HER2 protein expression (p=0.02) compared to parental cells. Increased gene amplification of HER2 was also confirmed by FISH analysis. While STARD3 protein expression was undetectable in in parental HCC1954 cells, HCC1954-L cells expressed high levels of STARD3 protein. Knockdown of STARD3 using siRNA resulted in a 20% decrease in cell growth compared to scrambled control treated cells, suggesting that STARD3 amplification and expression plays a role in the proliferation of HCC1954-L cells.

In summary, we have developed a robust model of acquired lapatinib resistance which exhibits increased amplification and expression of HER2 and STARD3.

Citation Format: Martina McDermott, Lee Anderson, Liam Shields, Neil O'Brien, Allison Prendergast, Susan Kennedy, William Gallagher, Radoslaw Zagozdzon, Annette Byrne, John Crown, Dennis Slamon, Norma O'Donovan. Increased co-amplification of HER2 and STARD3 in a cell line model of acquired lapatinib resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5634. doi:10.1158/1538-7445.AM2013-5634