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- [00:02]
Podcast Host
Welcome to the American Society of Hematology Conversations with Blood Authors Podcast. This blood podcast episode is hosted by Dr. James Griffin from the Dana Farber Cancer Institute in Boston. He discusses gastrin for the treatment of graft versus host disease of the stomach with Dr. Robert Zizer. He also discusses bone marrow failure, somatic rescue by p53 inactivation and enhances leukmogenesis in germline ER CC6L2D disease with Dr. Stefan Boettcher.
- [00:36]
Dr. James Griffin
Hello everyone, my name is Jim Griffin, I'm one of the podcast editors for Blood. I'm in the Division of Hematologic Malignancies at the Dana Farber Cancer Institute in Boston. We have two very interesting papers to discuss on this podcast. The first is entitled Gastrin for the Treatment of Acute Graft versus Host Disease of the Stomach and this will be presented by Dr. Robert Zeitzer, Department of Internal Medicine at the University of freiburg in Germany. Dr. Zeitzer thank you very much Dr.
- [01:09]
Dr. Robert Zeitzer
Griffin for introducing my topic. For a large fraction of patients with acute leukemia, the only chance of cure is to undergo an allogenic hematopoietic stem cell transplantation and in recent decades the number of patients undergoing this therapeutic intervention has more than doubled worldwide. Acute graft versus host disease accounts for 25% of deaths after this therapeutic intervention in patients with so called steroid refractory acute graft versus host disease have a reported mortality rate of 50% within three years after diagnosis. So the current treatment of horizontal Cu Gravel's host disease is immunosuppression. A major concern with this broad immunosuppression is that we might reduce the anti leukemia effect of the transplanted immune system and we might increase the risk for infections. Therefore, non immunosuppressive therapies including tissue regenerative approaches are urgently needed. We have previously shown that the enteroendocrine hormone called glucagon like peptide 2 has tissue regenerative activity in the lower GI tract of mice and also in patients with stereotrefactory acute GVHD and the phase two trial has been completed here. In this study we explored the tissue protective effect of the enteroendocrine hormone gastrin for acute gravel cell disease of the stomach. The stomach is an area of the gut that that receives less attention compared to the lower GI tract. In the context of gvhd, gastrin is produced by specialized enteroendocrine cells, so called G cells in the gastric antrum in response to multiple physiological inputs e.g. gastric distension or an increase of intraluminal ph, protein intake and others. We observed that acute gravel source disease could caused a loss of gastrium reducing G cells and so called parietal cells. These parietal cells are responsible for the acid release in the stomach. Therefore, we observed that GVHD causes an increased PH of the stomach which is interesting and potentially clinically relevant because currently our strategy in GVHD patients is often that we give proton pump inhibitors and we should rethink that given that GBHD PER C already increases the PH of the stomach. We found that substituting the hormone gastrin with a formula called pentagastrine reduced the loss of these parietal cells. It normalized the PH in the stomach, increased stomach stem cell marker expression and the abundance of LRG5 positive cells. It also led to changes in the stomach microbiome. Gastrin also increased the viability of stomach and small intestinal organoids in vitro. This was interesting because the small intestine also carries receptors for gastrin. Although it's called gastrin and has effects on the stomach, it also had effects on the lower GI tract. To have a genetically defined system, we also used gastrin deficient mice which experienced more severe acute gravel Zoe's disease in the intestine and liver compared to wild type mice and that was rescued by pentagastrine treatment in patients developing acute gvhd. We found that low gastrin levels in the stomach biopsies are connected to reduced survival in independent patient cohorts. Gastrin expression in the stomach correlated with acute GVHD severity and tissue damage scores. So overall our study delineates the protective role of gastrin in acute GVHD of the stomach in mice and in patients. These findings have two clinical implications. First of all, the diagnostic low numbers of G cells correlated with more severe acute GVHD in the stomach. This can have diagnostic utility, particularly given that the upper GI endoscopy currently has very low predictive value for acute gvhd. A second clinical implication is that this procedure finding provides a rationale for clinical trials testing pentagastrine either for prevention or for the treatment of acute gvhd. While the drug has previously been used in the diagnostic setting could be potentially repurposed for acute gravy associates disease and we hope that our findings motivate the translation into clinical application.
- [05:53]
Dr. James Griffin
Thank you very much. Dr. Zeitzer, you mentioned that you've also studied a GLP2 drug and that that had positive results in a small clinical trial. Could you expand on that what's the future of that drug and how might it compare with gastrin for the treatment of GI tract GBHD?
- [06:12]
Dr. Robert Zeitzer
In this clinical trial, the GLP2 analogone abraglutide was given to patients who had failed corticosteroid treatment for lower GI GVHD treatment. And it was combined with oxolitinib, which is currently the standard second line treatment. And we observed response rates that were higher compared to historical controls of patients with lower GI GVHD that received only ruxolitinib. This was not a randomized trial, but it was a phase two trial. It showed safety of the drug and it showed that in comparison to historical controls, response rates were higher. So the next step will be to perform a randomized clinical trial where ruxolitinib combined with placebo is compared to ruxolitinib plus arpaglutide. Arboglutide is already in the approval process for short bowel syndrome and we hope that this will be continued and brought into a randomized clinical trial for GVHD as well.
- [07:11]
Dr. James Griffin
Thank you. Does penegasterin have any effect on the immune response, particularly on T cell activity or T cell mobility?
- [07:20]
Dr. Robert Zeitzer
Yes, we tested that. It's a very important point. So there are no gastrin receptors on immune cells, neither on T cells nor on dendritic cells, macrophages, monocytes and so on. Nevertheless, there could be an indirect effect. So we tested that in two different leukemia models and we found that the anti leukemic immune response was fully maintained in mice despite treatment with Pentagost 3.
- [07:45]
Dr. James Griffin
Do you have any ways potentially of predicting which patients might get stomach GBHD after a transplant?
- [07:53]
Dr. Robert Zeitzer
We see that the gastrin level in the serum of the patient is connected to the risk to die after transplant. So patients with a low gastrin level have a higher chance to die of any complication except for relapse after allotransplant. So non relapse mortality is higher in these patients. Now, if that is a cause or consequence, we couldn't clarify because it's a clinical observation that we made here. But it could serve as a biomarker and as a prognostic marker for patients undergoing allogenic stem cell transplantation, indicating to the physician that these patients have to be watched, particularly because their risk for death after allo is particularly high.
- [08:37]
Dr. James Griffin
Just one last question. You mentioned that pentagastrin previously been used as part of a diagnostic test. What are the side effects of Panagastrin?
- [08:46]
Dr. Robert Zeitzer
The side effects of Panagastrin is Increased acid secretion in the stomach. This is what it's currently used for to test that there have been descriptions of stomach ache, diarrhea, and some patients had reported psychiatric changes. So panic attacks have been reported as a rare event after gastrin. Apart from that, it's relatively well tolerated, so very few side effects. You should not forget it's an endogenously produced intestinal hormone that has a very short half life and therefore very limited systemic activity.
- [09:23]
Dr. James Griffin
Thank you very much and good luck with your future studies with these agents.
- [09:28]
Dr. Robert Zeitzer
Thank you.
- [09:28]
Dr. James Griffin
Our next paper is entitled Bone marrow somatic rescue by p53 inactivation and enhanced leukemogenesis in germline ERCC6L2 or excision repair cross complementing L2 gene disease. This is going to be presented by Stefan Buescher of the Department of Medical Oncology and Hematology and the University of Zurich in Zurich, Switzerland. Dr. Boucher, thank you very much.
- [09:57]
Dr. Stefan Boettcher
Dr. Griffin, maybe I can start with giving a little bit of background on this inherited bone marrow failure syndrome. So ERC6L2 disease is rather relatively recently described inherited bone marrow failure syndrome. It is caused by germline BI D mutations in this gene. And the affected patients have mild to moderate cytopenias, most commonly thrombocytopenia and anemia, but also pancytopenia can be present in those patients. It's an interesting disease. It's a bit special because unlike other inherited bone marrow failure syndromes, ERC6L2 disease really does not really have any recurrent extra hematopoietic manifestations. And this, together with the rather mild hematological phenotype, is the reason why patients often get a diagnosis later in life, adolescence, in early adulthood, or even later adulthood. But what's really striking about ERC6L2 disease and also the reason why we became interested in this disease, is really the strong association with somatic TP53 mutations in human hemopathic stem and progenitor cells and HSPC. So basically TP53 mutant clonoparesis and also high propensity for myeloid malignancy development. So, based on the published data, the lifetime risk of AML and MDS in those patients is at least 30 to 40%. And interestingly, these myeloid malignancies have an erythroid predominance phenotype. Almost all patients that develop AML have acute erythroid leukemia. So this was really the reason why we wanted to study this disease and in general, studying inherited bone marrow failure syndromes. Is not easy. And that's also true for ERC6L2 disease. And this is because primary patient material is difficult to obtain. The diseases are rare after all. And importantly, really, the biology works here against us because the HSPCs carrying such material mutations as in ERC6L2, they have a fitness defect and it makes it hard to work with these cells. So that being said, we had to first develop in vitro and in vivo model systems. And really, I don't want to go into much detail, but we managed to generate those model systems that quite nicely recapitulated key aspects of ERC6L2 disease. HSPC have reduced fitness, even HSPC attrition, there's impaired hematopoietic differentiation, and that leads also to cytopenias in vivo. And on a mechanistic level, we found that deficiency in ERC6L2 really has at least two distinct effects. First, it causes replication stress and subsequent DNA damage, and this in turn activates a P53 response and that results in cell cycle arrest and apoptosis. And secondly, and this is not very well understood, it also reduces the expression of master hematopoietic regulators GATA1 and RUNX1, which impasse hematopoietic differentiation. And these both effects together they cause the bone marrow phenotype. The interesting observation from the clinics is that if there are additional somatic TP53 mutations on top of ERCC6 L2 deficiency, this completely rescues produce the bone marrow phenotype that is caused by ERC6L2 deficiency alone. So double mutant HSPCs, they gain a clone advantage over single mutant ERC6L2 cells, RUNGS1 and GUTTER1 expression is restored and this improves hematopoietic output and differentiation to baseline levels, basically. And also mice engrafted with such double mutant cells have then also normal blood counts. But what's important really to understand, the TPV3 deficiency does not rescue replication stress and DNA damage, it just bypasses the p53 response. Unfortunately, those HSPCs accumulate genomic alterations and this eventually drives myeloid malignancy developments. So in summary, basically the TP50 mutant chip observed in ERC602 disease is A. Is sort of a prototypical example of a maladaptive somatic gene rescue event as we know it from inherited bone marrow failure syndromes. So it improves hematopoiesis, however at the expense of increased risk of myeloid malignancy development.
- [14:21]
Dr. James Griffin
Thank you. This is really a fascinating genetic defect. How common is this disease It's a very rare disease.
- [14:28]
Dr. Stefan Boettcher
I think a little over 100 patients have now been reported in the literature as far as we know has been observed and patients have been diagnosed in multiple ethnicities, multiple regions of this world. There was a founder mutation in Europe, in Finland, so it's also relatively more prevalent in the Finnish populations. But overall it's a very rare disease. It might be a little bit under diagnosed because of, of the, as I mentioned before, lack of extra hematopoietic manifestations and the rather mild hematological phenotype.
- [15:07]
Dr. James Griffin
You mentioned that this gene, ERCC6L2 is ubiquitously expressed in other tissues. Are there any effects of the mutation in tissues outside of metapoiesis?
- [15:19]
Dr. Stefan Boettcher
Yeah, Dr. Griffin, this is a really great question as really, it's one of the really things that are not very well understood. As you said, it's ubiquitously expressed and it's very striking that really the phenotypic readout really only happens in the hematopoietic system. This is not really well understood and this should be definitely addressed in future questions. But in short, it's not known why the phenotype is restricted to the blood forming system.
- [15:47]
Dr. James Griffin
And you show very elegantly that the mutant cells are susceptible to replication stress. Are there any other kinds of cellular stress that also have a problem in these mutant cells?
- [15:59]
Dr. Stefan Boettcher
This is also a very good question and also is one of the puzzles that we have about this disease. So the disease is not manifesting early in life, although one would expect that especially in early postnatal life when a massive hematopoietic expansion occurs. That's all sorts of stress signals. War would lead to a more profound hematological phenotype, which is obviously not the case. However, also in our study we had to use various external stressors that we believe also occur in, in the human body and that is reactive oxygen species nutrient deficiency. But we also tested, of course this is a modern artificial system, also DNA damaging drug drugs. And in such a setting the, the hematopoietic phenotype was really exacerbated. So yes, ERC6L2 deficient cells are more susceptible and gain a even more severe deficit when there is hematopoietic stress.
- [17:04]
Dr. James Griffin
One more question. You made the very interesting observation that in this bone marrow failure syndrome, p53 loss actually restores hematopoiesis. Are there any other bone marrow failure syndromes where p53 plays a similar role?
- [17:20]
Dr. Stefan Boettcher
P53 pathway inactivation has been implicated in actually many inherited bone marrow failure syndromes and I believe telomere biology disorders are probably a prime example where it becomes particularly obvious how important p53 pathway inactivation as a somatic gene rescue event is in these diseases. Where in TBDs it cannot only be TP53 which is mutated by loss of function mutations, but it can also be other forms of p53 pathway inactivation that do not affect the TP53 gene itself. It can be for example MDM4amplification. It can also happen so p53 pathway attenuation if you will by activating negative regulators of the p53 pathway. So mutations in ppm1D have been reported in telomere biology disorders and all these different genomic somatic genomic alterations all converge on the common pathway of P53 activation. Why as far as we know, in essence BRC6R2 disease. Really we have not yet observed these other types of p53 pathway activation, but solely TP53 direct mutation inactivation is also very interesting observation that the mechanistic basis for which has to be clarified.
- [18:47]
Dr. James Griffin
Just one question about treating these patients. Do they tolerate cytotoxic chemotherapy normally if they develop withroblastic leukemia?
- [18:56]
Dr. Stefan Boettcher
Yes, so far in the published cases and again there are not that many. The cohorts are still growing, there are not that many patients been reported. But in the ones that have been reported there is no excessive toxicity to DNA damaging agents. I recall one report not from our institution where a patient that had also developed breast cancer and received irradiation suffered from excessive toxicity of the radiotherapy, but also at our institution we transplanted already patients with ERC6L2 disease and the perit transplant patient course was was very favorable and we did not observe excessive toxicity. So unlike other bone marrow failure syndromes such as Ficoni anemia, this seems not to be the case in ERC6L2 disease.
- [19:47]
Dr. James Griffin
Very interesting. Wish you the best of luck with your future studies on these patients.
- [19:52]
Dr. Stefan Boettcher
Thank you very much Dr. Griffin and thanks for having me on the podcast.
- [19:56]
Dr. James Griffin
Thank you.
- [19:58]
Podcast Host
Thank you for listening to this episode of Conversations with Blood Authors. To read the articles, visit bloodjournal.org this episode is copyrighted by the American Society of Hematology.