Targeted therapies including BRAF and MEK inhibitors (i.e. Dabrafenib, Trametinib) have achieved unprecedented success in melanoma patients with advanced disease. However, adaptive drug tolerance (ADR), distinct from ‘classical’ genetic alterations leading to permanent resistance through cellular reprogramming, is believed to be responsible for about 50% of patients’ deaths, underscoring the critical need to overcome ADR.
ADR undergoes two distinct stages in vitro before gaining permanent resistance to targeted therapies, which are termed early and late tolerance. During the process, it is possible to reverse gained resistance. Once permanent resistance is established, melanoma cells can’t be re-sensitised to the drug.
Calcium ions (Ca2+) play a crucial role in regulating multiple cell activities, including cell migration, proliferation, and gene transcription. We determined mRNA levels of ten different Ca2+ pumps, channels, and regulators in early and late tolerant WM164 melanoma cells. Interestingly, only two are upregulated at both states of ADR, with one exceeding ten times higher levels compared to drug-sensitive parental cells. Indeed, genetic silencing prevented the development of the dabrafenib-induced late tolerant state. Employing an assay to study store operated Ca2+ flux, we observed reduced store operated Ca2+ entry in early tolerance, indicating a shift from store operated Ca2+ entry towards a Ca2+ channel mediated Ca2+ influx.
In summary, our preliminary data illustrated the importance of Ca2+ channels in the development of early tolerance to targeted therapy in melanoma in vitro, which can provide a novel target to resolve drug resistance during targeted therapy improving therapy outcomes. Based on this, our research will investigate the relationship between Ca2+ channel expression and development of ADR, along with related cell signalling pathways. We will evaluate the potential of inhibiting Ca2+ channels to prevent and/or reverse ADR in both in vitro and in vivo during targeted therapy.