Approximately 1 in 5 breast cancers are diagnosed as the high-risk Her2-enhanced subtype (HEBC) predicting an inferior outcome. While the first HER2-blocking drug, trastuzumab (Herceptin), has significantly prolonged patient survival, HEBC become harder to treat when resistance develops. Recent patient trials demonstrated that combination with other mechanistically distinct anti-HER2 drugs pertuzumab or lapatinib improve efficacy over trastuzumab alone, resulting in clinical adoption of the combination therapy. However, as inevitable as for most cancer therapies, acquired resistance to dual HER2 blockade is expected to restrict clinical benefit. To tackle this challenge, a systematic understanding of underlying resistance mechanisms is warranted.
Transposon mutagenesis screens provide a state-of-the-art approach to exploring genetic mechanisms underpinning diverse cancer-related processes. Engineered transposons such as Piggybac can be introduced into cells to cause random mutations, of which some will lead to tumour formation, metastasis or therapy resistance. By tracking an identifiable “marker” left by transposon insertion, impacted genes can be pinpointed by DNA sequencing analysis. This has allowed the unbiased discovery of genes associated with common insertion sites that are potential “drivers” of many cancers based on their over-presentation at experimental endpoint.
A lentiviral-mediated tamoxifen-inducible vector system has been developed to enable transposon mutagenesis in target cells, which is used in this project for enrichment and identification of transposon “hits” related to therapy resistance. In HER2-overexpressing BT474 cells which are intrinsically sensitive to lapatinib, high transduction efficiency has been achieved by lentivirally-mediated introduction of transposon and transposase. Furthermore, a rapid PCR-based method was developed to detect transposon mobilisation upon tamoxifen induction, reassuring the anticipated functionality. Most importantly, transposon mutagenised BT474 cells have started to display resistance to the dual HER2-targeting drugs, trastuzumab and lapatinib, at doses that eliminate the vast majority of parental cells.
This study will gain valuable insights into resistance to dual HER2 blockade as an emerging therapy for HEBC patients, providing an advantage for future clinical translation.