In this episode, we speak with Chiara Pozzato and Georgia Konstantinidou from the University of Bern, Switzerland about their recent pre-clinical research investigating a new potential treatment approach for KRAS-driven cancers.
The conversation explores the role of FAK signalling in KRAS driven NSCLC and potential approaches to bypass drug resistance against FAK inhibitors: from the molecular mechanisms involved to the impact of their study for the wider cancer research community.
This study, ‘ERK5 suppression overcomes FAK inhibitor resistance in mutant KRAS-driven non-small cell lung cancer’, was published in EMBO Molecular Medicine and was selected for the EACR’s Highlights in Cancer Research, showcasing its significance to the field.
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Our host is Dr. Alexandra Boitor, EACR Scientific Officer.
Episode transcript
Alexandra: Thank you so much for taking the time to tell us more about your recent study published at the end of last year. Georgia, your lab’s research focuses on signalling and lipid metabolic alterations in KRAS induced lung and pancreatic cancer. In this paper you continue, if I understood it correctly, the work you started during your postdoc at the University of Texas, which you’ve published in 2013 in Cancer Discovery. So I suppose the first thing I’d like to ask you is what made you direct your attention towards the focal adhesion kinase signalling in particular?
Georgia: Thank you very much first of all for inviting us to join the podcast and discuss our research on focal adhesion kinase. So during my PhD studies at UT Southwestern Medical Center at Dallas, I was working with the KRAS-driven lung adenocarcinoma model. And while observing the tumours under the microscope, I noticed that they were forming papillary structures.
My initial thought was that these tumours must rely on a prominent and dynamic cytoskeleton. To explore this I performed immunohistochemistry on the tumour tissue using antibodies available in our lab back then, and focal adhesion kinase was among them. The results were intriguing, sparking my curiosity about focal adhesion kinase signalling. From that point on, I became deeply interested in understanding its role in cancer progression.
Alexandra: My understanding is that the research you did as a postdoc showed that FAK inhibition reduces cell proliferation and induces cell death in KRAS driven tumours in the mouse models. And hence set the basis for a phase two clinical trial a few years later, if I’m not mistaken, where heavily pretreated KRAS mutant non-small cell lung cancer patients were treated with Defactinib, an ATP competitive FAK inhibitor.
So my understanding is that the trial had modest results showing a disease control rate of 50%. So what determined you to continue or come back to investigating focal adhesion kinase inhibition now?
Georgia: Actually, I never really stopped. So after completing my postdoc, I moved from the US to Switzerland and established my own lab in 2016. And since then, projects focussed on the regulation of focal adhesion kinase in lung cancer have consistently been part of my lab’s research portfolio. So as you mentioned correctly, in the meantime, the results of the phase two clinical trial using this Defactinib, the orally available efficacy inhibitor in mutant KRAS non-small cell lung cancer patients were published.
And while the clinical trial outcomes were promising, they fell short of the curative effects we observed in the preclinical models. This discrepancy between preclinical and clinical responses highlighted a critical gap in our understanding, and particularly regarding mechanism of resistance.
And then in early 2018, Chiara joined my lab as a PhD student and she focused on unravelling the mechanism of resistance to focal adhesion kinase inhibitors. Her work revived and sharpened our focus on focal adhesion kinase inhibition, pushing us to explore not just how FAK functions in tumour progression, but also why certain cancers can evade FAK targeted therapies.
Now, this ongoing investigation has been key to advancing both our fundamental understanding of focal adhesion kinase signaling and its potential as a therapeutic target.
Alexandra: So focusing the conversation on this most recent publication you had on this topic, the first experiment you did aimed to uncover the mechanisms behind the anti-proliferative and pro-apoptotic effects seen upon FAK inhibition in KRAS mutant lung cancer cells.
To this end you, or actually I guess Chiara nowadays, knocked out FAK expression in bronchial epithelial cells with P53 knock down and then re-expressed wild type and mutant variants of focal adhesion kinase containing point mutations that disrupt the phosphorylation sites of known binding partners or the nuclear localisation of the signal, to see which one would fail to rescue the phenotype? Did I get that right from the paper?
Chiara: Yes, you did.
Alexandra: So this way you identified the phosphorylation of FAK at serine 732 and 910 to be responsible for promoting cancer cell proliferation. Would you like to tell us a bit more about what this means for tumour control?
Chiara: Yes, as you correctly mentioned, the study shows that phosphorylation of FAK at serine 732 and 910 plays a crucial role in promoting the proliferation of cancer cells, particularly in KRAS mutant lung cancer. And our study demonstrates that a genetic and pharmacological inhibition of ERK5 and CDK5 synergistically suppress cancer cell proliferation induced apoptosis and compromise FAK function.
The in vitro data were corroborated by an in vivo study conducted in a mouse model of KRAS driven lung adenocarcinoma, in which we observed suppression of tumour progression and promotion of cancer cell death upon concomitant ERK5 and CDK5 inhibition. Mechanistically, we demonstrated that co-inhibition of this kinases, similarly to FAK inhibition, triggers loss induced DNA damage.
Alexandra: Looking maybe a bit more into the mechanistic insights you’ve just mentioned. Through your in vitro experiments, you found increased P53 and P21 protein levels following a ERK5 and CDK5 concurrent inhibition, supporting an inhibitory role of FAK on P53, which is in line with the results that you got Georgia during your postdoc.
So would this make the tumour response dependent on P53 status? Did you test this hypothesis? I noticed that in the clinical study mentioned earlier it was noticed that the FAK inhibitor activity did not appear dependent on the TP53 status.
Georgia: Yes, that’s correct. Focal adhesion kinase inhibition leads to P53 upregulation in P53 wild type models. And while this might add to the overall anti-tumour effect, especially by promoting loss induced DNA damage. With further studies in my lab, we found that suppressing P53 didn’t really reverse the reduced proliferation or the increases that we observed.
So it seems that P53 isn’t the key driver of these effects. What’s interesting is that we saw the same thing in our in vivo lung cancer mouse model, which actually has a KRAS mutation in P53 deletion. Despite the absence of P53 in this setting, focal adhesion kinase inhibitors still work just as effectively as they did in our cellular models.
This suggests that while P53 upregulation might offer an extra advantage in some cases, it’s not essential for the antitumour effects we are seeing with FAK inhibition. Of course, there’s still more to uncover and we think that we definitely need further studies to understand the P53 independent mechanism at play, which could help us refine FAK targeted therapies even more.
Alexandra: In order to further understand the molecular mechanisms mediating the synergistic effect of ERK5 and CDK5 inhibition, you turned to RNA sequencing. Pathway analysis of the differentially expressed genes highlighted, if I remember correctly from the paper, DNA repair, cell cycle progression, P53 signaling and oxidative phosphorylation as being affected by the combinatorial treatment.
So what determined you to further investigate the effect of CDK5 and ERK inhibition on the oxidative stress?
Chiara: Yes, as you correctly mentioned, RNA sequencing analysis on lung cancer cells treated with CDK5 and ERK5 inhibitors, revealed that the combination treatment altered key molecular pathways involved in DNA repair, cell cycle progression, oxidative phosphorylation and P53 signaling.
The motivation for further exploring oxidative stress stems from its strong connection to reactive oxygen species production, which has a dual role involving cancer progression and treatment. Indeed, many anti-cancer therapies depend on loss generation to induce cancer cell death. In our study, we aim to determine whether the absurd antitumour effect was a result of increased oxidative stress leading to cancer cell death.
Indeed we confirmed that co inhibiting ERK5 and CDK5 significantly increases intracellular loss levels, which correlated with announced DNA damage. Interestingly, we observed these phenotype also in cancer cells treated with FAK inhibitor, reinforcing the idea that targeting ERK5 and CDK5 mimics FAK suppression. And corroborating our findings, the increase in ROS could be reversed by the treatment with an antioxidant agent.
Alexandra: So further on in your experiments, you developed a model mimicking FAK inhibitor resistance to uncover its molecular basis, which I think was very interesting on itself as a model. Would you like to tell us a bit about what you discovered? Like for instance, what are the effects of prolonged FAK inhibition? I guess what I’m trying to ask is where is the connection between ERK5, CDK5 and FAK inhibitor tolerance?
Georgia: We found that prolonged treatment with FAK inhibitors can lead to the development of FAK inhibitor tolerant cancer cells. And what we found is that in these FAK inhibitor tolerant cells, there is an upregulation of ERK5 mediated phosphorylation of focal adhesion kinase at serine 910. This modification seems to dampen the DNA damage response, allowing the tumour cells to survive and evade apoptosis, which is a key mechanism of resistance.
ERK5 plays a really crucial role here. In fact, when we combined FAK and ERK5 inhibitors, we saw significant tumour regression. And this suggests that dual inhibition could be a promising strategy to overcome resistance, especially in KRAS mutant lung cancers.
On the other hand, CDK5 behaves differently. It doesn’t seem to be involved in the resistance process in fact. Instead its role appears to be more about maintaining the initial activity of FAK before resistance develops. So while CDK5 is important for FAK signalling, it’s not a key player when it comes to the tolerance that emerges with prolonged FAK inhibition.
Alexandra: So from the conversation we’ve just had, it sounds like, at least according to the in vitro and in vivo studies you’ve done in preclinical models, this combinatorial approach to treating KRAS small cell lung cancer might be quite promising, especially given what you said earlier, that it doesn’t necessarily apply only to a certain P53 status in tumours.
But do you think this approach could be applicable beyond lung cancer to other KRAS-driven cancers?
Chiara: Yes, we believe that it can be applicable for other KRAS-driven cancers. As a reminder, I would like to mention that previous studies have shown that FAK is a synthetic lethal partner of KRAS. In fact FAK is over expressed in pancreatic ductal adenocarcinoma, which harbour KRAS mutations in 95% of the cases.
In the last years, research on pancreatic cancer revealed that FAK inhibitor resistant tumours have upregulated STAT3 signaling, which is a phenotype that we also observed in our study. So in summary, our research underscores the critical role of FAK in sustaining KRAS mutant lung cancer, and highlights how its inhibition, while initially effective, leads to resistance via ERK5 upregulation.
Given that KRAS mutations drive other aggressive cancers, including pancreatic and colorectal cancers, similar resistance mechanisms may be at play in these malignancies.
Alexandra: So it sounds to me like this is a promising approach to potentially target a broader range of cancers. So I’m curious, what is the next step for this study? You note in your paper there are no ERK5 inhibitors in clinical development at the moment. But I’m wondering if you are planning on somehow trying to take this approach to clinical trials.
Georgia: That’s a great question. The next step for this study is really to address some of the key limitations we have identified. And one major challenge is that despite several promising lead compounds, there are currently no ERK5 inhibitors in clinical development. And this makes it difficult to predict the therapeutic window for combining FAK and ERK5 inhibitors in a clinical setting.
So before we can even think about moving into clinical trials, we need to focus on identifying or developing ERK5 inhibitors that are both potent and selective with favorable pharmacokinetics and safety profiles. This could involve collaborating with medicinal chemists and pharmaceutical partners to optimise existing compounds or discover new ones that are suitable for clinical testing.
And ultimately our goal is to generate robust preclinical data that can pave the way for future clinical trials. And we aim to understand, to demonstrate that targeting both FAK and ERK5 is not only effective but also safe, which will be critical for advancing this combination therapy toward clinical applications.
Alexandra: Thank you very much for having this interesting conversation about your paper with me. I’d like to ask you one more thing in order to sum up our conversation? How would you describe the impact of this study in your own words?
Chiara: The impact of our study is significant in the field of cancer therapy, particularly for KRAS mutant non-small cell lung cancer. The key contributions of our research include, first of all, uncovering the mechanisms of FAK inhibitor resistance by identifying ERK5 as a crucial mediator of FAK driven drug tolerance.
Secondly, we propose a novel co-targeting strategy. Indeed this study lays the foundation for a potential co-inhibitory strategy targeting ERK5 and FAK, as our findings demonstrate that ERK5 inhibition effectively prevents resistance to FAK inhibitors both in vitro and in vivo. We also believe that our research has clinical relevance and therapeutic potential since ERK5 is frequently upregulated in non-small cell lung cancer and associated with poor prognosis.
So this study paves the way to the development of ERK5 inhibitors as a therapeutic strategy. Finally, our study has the potential to extend its implications beyond lung cancer. One key reason is that focal adhesion kinase is over expressed in various primary and metastatic tumours of different origins.
And since the co-inhibition of ERK5 and CDK5 synergistically disrupts FAK signaling, targeting these kinases could be advantagous for tumours with high FAK expression, helping to prevent feedback mechanisms that drive drug resistance.
Alexandra: It sounds like a very promising approach. I hope in a few years we’ll get a chance to meet again and chat about the updates that you have on this study. I’m quite curious how this might develop over time. But for now, I’d like to thank you very much for accepting our invitation to speak on The Cancer Researcher Podcast and for allowing us a glimpse into your research.
It was lovely chatting with you and learning so much about the molecular mechanisms of focal adhesion kinase inhibition in KRAS driven non-small cell lung cancer. So thank you very much.
Georgia: Thank you very much. We really appreciate the opportunity to talk about our work with the broader audience.
Chiara: Yeah, thank you very much for the opportunity.
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