The Achilles' heel of cancer cells
Alterations that confer selective advantage during the evolution of cancer cells might also create vulnerabilities that can be exploited therapeutically. We have shown that P-gp can contribute not only to acquired resistance but also to paradoxical drug sensitivity; and that this collateral sensitivity represents a promising strategy for targeting multidrug resistant cancer. By exploiting the paradoxical hypersensitivity of otherwise resistant cancer, we target the Achilles' heel of cancer cells.
Progress in the prevention, early diagnosis, and treatment of cancer has led to a steady decline in cancer death rates. Still, despite significant progress, resistance to chemotherapy is the main reason why cancer remains a deadly disease. By circumventing resistance mechanisms, the efficacy of first line drugs could be restored. Strategies to circumvent reduced drug accumulation conferred by ABC (“ATP-binding cassette”) transporters such as P-glycoprotein (P-gp) have relied on attempts to develop drugs that bypass extrusion (often with a sacrifice in activity); or the exploration of clinical inhibitors that, although showing promise in vitro, have not translated to the clinic.
Alterations that confer selective advantage during the evolution of cancer cells might also create vulnerabilities that can be exploited therapeutically. We have shown that P-gp can contribute not only to acquired multidrug resistance (MDR) but also to paradoxical drug sensitivity; and that this collateral sensitivity represents a promising strategy for targeting multidrug resistant cancer (Figure 1).
Changes accompanying acquired resistance to Drug A may be beneficial, neutral or detrimental in the presence of Drug B. Cancer cells tend to increase their fitness through the overexpression of efflux transporters that keep the concentration of drug A below a cell-killing threshold. If Drug B is not a transported substrate, resistant cells may be eradicated. However, given the wide substrate specificity of the transporters, cancer cells selected in Drug A often survive despite treatment with Drug B (multidrug resistant cells show increased fitness in both environments). Conversely, resistance against Drug A may be accompanied by decreased fitness in Drug B (Szakacs et al., Chem Rev, 2016).
By exploiting the paradoxical hypersensitivity of otherwise resistant cancer, we target the Achilles' heel of cancer cells. Funded by an ERC Starting Grant (2012), we are developing MDR-selective compounds that have the promise of eliminating multidrug resistant cancer cells.
Targeting Drug-tolerant Persisters: a paradigm shift to conquer therapy resistant breast cancer.
Elucidating the molecular basis of therapy resistance in breast cancer is an unmet clinical need. Based on preliminary results we hypothesize that therapy resistance is linked to a rare population of drug tolerant persister cells (DTPs) that survive treatment through the stabilization of transient drug-induced phenotypes, until mechanisms ensuring stable drug resistance emerge. Profiling the tumor during different stages of therapy is necessary to identify vulnerabilities of this adaptive process.
Our preliminary work has characterized the response of orthotopically transplanted tumor-bearing mice to a series of clinically relevant chemotherapies. While these therapies significantly reduce the tumor size, they are unable to eradicate tumor cells, which give rise to drug-sensitive relapse after the cessation of the treatment (Füredi et al., 2017).
The project will address the following research questions: (1) What is the contribution of phenotypic adaptation vs Darwinian selection? (2) Are cells showing a DTP signature present prior to treatment? (3) Will different clinical protocols induce DTPs with similar signatures? (4) What is the relative contribution of genetic vs non-genetic (epigenetic, transcriptional plasticity) factors, and of the interactions with the microenvironment? (5) What is the relation between the pathways supporting DTPs and the mechanisms underlying resistance to therapy? (6) How can this knowledge be translated to improved patient care?
To address these challenging questions, we will profile individual “tumor histories” at single-cell resolution using in vitro cell lines and organoids derived from genetically engineered mouse models of cancer (GEMMC). We will establish, treat and sample barcoded mammary tumors derived from such organoids to track (epi)genetic and transcriptional alterations along the treatment. Because organoids are engrafted in wild-type mice, scRNA sequencing will also reveal the contribution of immune cells and other niche elements to tumor heterogeneity. To monitor clonal evolution, individual cells in organoids will be transduced with a GFP-positive lentiviral library encoding 20,000 unique barcodes. PDOs will be orthotopically transplanted into the mammary fat pad of wild type FVB mice. Matched samples corresponding to treatment-naïve cells, DTPs and relapse will be collected. In experiments aimed at obtaining therapy resistant tumors, chemotherapy will be continued until the treatment becomes ineffective.
Effective targeting of DTPs will result in a paradigm shift, changing the focus from countering drug resistance mechanisms to preventing or delaying therapy resistance, leading to improved treatments of patients.