New treatment strategies for MSS CRC: Dr. Parikh (2021)

Dr. George  0:00
Hello everyone. I’m Dr Manju George, the Scientific Director at PALTOWN Development Foundation, the nonprofit that supports Colontown. We are very happy to have Dr Aparna Parikh with us, and she’s going to talk about colorectal cancer strategies to make cold tumors hot. And just a little brief introduction about Dr Parikh. She completed her MD from the Indiana University School of Medicine, residency from Mass General, and fellowship at UCSF. She’s board certified in internal medicine as well as medical oncology, and she has a lot of nice papers, the most recent one is in Nature Cancer on radiation therapy and immunotherapy. And we are really excited to have you here with us. Take it away.

Dr. Parikh 0:13
Great. Thank you so much, Manju for inviting me. I want to just thank Manju tremendously for her incredible collaboration with a lot of our work that we’re working on kind of pan- stages of colorectal cancer, and I’ve gotten to know her through our Stand Up to Cancer Colon Dream Team and her advocacy and voice in our adjuvant study. So, you know, there’s lots of different areas where I sort of thought we could talk about today, but in light of our recent paper and some work that our disease group is working on, I wanted to share some of the strategies that we’re looking at in the metastatic setting to make some of these cold tumors hot, in colon cancer, but as well as other GI cancers. But I’m hoping today that we will leave ample time for discussion, and I know Manju had asked me to just briefly also comment on the status of our stage III CtDNA trial, as well as the study that our group is doing, this being led by Ryan Corcoran in the BRAF setting. So I will go through this deck, and we’ll have some questions, and then I’ll give some brief updates, and then we can close with a Q&A which I think would be very much welcome to me as well.

Dr. Parikh  2:06  
So I do apologize if some of you attended AACR, because this is somewhat of a repetition of the talk that I gave there, but I hope we’ll be able to spend a little bit more time in terms of our next steps from these first generation of trials in the setting. So here are my disclosures, and as part of this, I do need to mention that I am discussing Investigational Use of ipi and nivo as well as 3TC in colorectal cancer.

Dr. Parikh  2:39  
So this is a slide that won’t be new at all for this audience, but it’s one of my favorite slides, just in showing the gains that we have had from the 80s. But you know, except for biomarkers, subtypes, really, since 2014 with the pivotal 80405, first line study for the RAS wild type patients haven’t really seen a slope increase where we need it to be, in terms of where we are in 2021 and arriving on 2022 soon. I think it’s always helpful to put in context where our median OSs are for the latest non-biomarker, selected drugs such as rego and lonsurf, where rego was FDA approved first in 2012 and subsequently lonsurf in 2015…

Dr. Parikh  3:33  
Dr. Parikh: …where we see median OS is still less than two months. And except for these biomarkers, which I’m not diminishing the role of these biomarkers, because in summation, these biomarkers do add up. And a lot of exciting work obviously happening in the BRAFV600E and other activating non V600E alterations, The tremendous gains that we’ve seen in MSI disease over the last several years, the HER2, and the trastuzumab deruxtecan data, as well as several other small molecule inhibitors and TKIs for the HER2 setting, and then rapidly evolving G12C, plus, you know, D, V and others in that space too. So not diminishing the importance of predictive biomarkers and the great strides we’re making in those particular settings, but I think it’s really humbling to look at the rego and lonsurf data and put that in context of where we need to go.

Dr. Parikh  4:41  
Personally, if we’re sort of having a DocTalk, I don’t even really use rego, I do use lonsurf, if we don’t have a good trial option because we do see patients, with no great biomarker of who those patients are. But do have patients that do derive benefit for quite some period of time, but in now, kind of seven years sort of being an attending, just with Rego, haven’t seen anything. And as you all know, toxicity is tough. But I do use lonsurf.

Dr. Parikh  5:13  
So this, again, for this audience, isn’t going to be news to any of you, but I think it just goes to show that the PD-1 story in colon cancer has actually been around for some time, as far back as 2010 where we have tried to use PD-1 therapy without efficacy. So if you look at sort of summary of the numerators and denominators, very humbling numerators with a non trivial number in the denominator in terms of MSS patients that were treated with checkpoint inhibition. I think just for time, I’m going to skip over the MSI data, because you guys all know the keynote 177 data, but again, noting which many of us are paying close attention to, including approaches such as using CtDNA in the setting to try to really understand who these patients are that are dropping off early. So when you look at the keynote 177 data, the thing that I always like to point out is in the pembro group that you had a 30% non response rate. And so even for these patients, even though we have made tremendous headway with the MSI patients in pembro, nivo, nivo/ ipi, what are the biomarkers that are predicting lack of response here? And can tools such as CtDNA be used as a guide to predict who those non responders are going to be and potentially salvage an opportunity to switch to chemo sooner rather than later for those patients?

Dr. Parikh  7:01  
So this cancer immunotherapy cycle is, again, not a figure that’s new to the field, and was kind of a figure that initially came out of Ira Mellman and colleagues, but really shows us at the cellular level, what the problem is with these cold tumors and the various checkpoints and opportunities we have to try to engage tumoral responses. So some of the things that we’re going to be talking about too, is not only where we’re looking at removing the brakes of the checkpoint inhibitors, but I think a lot of interest in the TGF beta, the CMS4 colon cancers too, and how we can really help with infiltration into tumors, both enhancing the chemotherapy response, but protect potentially, other signaling pathways such as TGF beta to try to hinder TGF beta signaling and allow for immune trafficking, but also efficacy of chemotherapy. And then what we’re trying to do with some of our approaches here, are there ways for us to kind of stimulate antigen presentation and basically stimulate an in-situ vaccine response to try to get these tumors from here over to the left to the right side of this diagram.

Dr. Parikh 8:32  
So we at MGH have a very radiation heavy group, kind of a phenomenal group of radoncs, led by Ted Hong, who is the NRG chair. And because of that, we entirely recognize that, not only in colon cancer, but rectal cancer, pancreatic cancer, we’re a very radiation bias  sort of group. And do a lot of trials and work, to try to exploit radiation as a tool. And some of this work actually came from the Penn group initially, and the men and colleagues now several years ago, that showed that using radiation and dual checkpoint inhibition may actually activate non-redundant immune mechanisms. We’ve seen several other studies in other tumor types, such as lung cancer, GU cancers as well, showing that low dose radiotherapy may actually help your tumor presentation and prevent the resistance to immunotherapy that is happening. It is very controversial what the right dose of radiation is and whether one time radiation is sufficient or not. I actually think that you may need to give subsequent doses to create that T cell repertoire and  then maintain that T cell response over time, and maybe a one time or a couple dose of radiation isn’t going to be sufficient. But if you look here, with the Minn paper, here, with the preclinical data, looking at the control in the gray here, but combining the control with RT and CTLA4 and RT again responses here in the preclinical colon cell lines. So based on some of that work, and they used sort of an 8 gray times three fractionation schedule, and that’s what we ended up ultimately taking into the clinic.

Dr. Parikh  10:39  
So it’s complex, I think it’s one of these things that we’re really trying to understand what is happening. But we do know that it does seem that radiation is helping promote T cell infiltration, antigen presentation and shaping your T cell repertoire. We see that the responses that are happening to radiation seems to be happening in an interferon dependent manner, so really activating the innate immune response and not just sort of adaptive immunity. There is some evidence, preclinically, that there is actually through the kind of cellular processes and turn around that are happening with the low dose radiation, we’re not exhausting your T cells or burning them out, that you are releasing tumor specific antigens, and with those tumor specific antigens, mounting a direct T cell response to that. And we know actually that RT activates dendritic cells as well. And one of our lab collaborators who works in Nir Hacohen’s labs, Arnav Mehta, is really trying to look at some strategies using TLR9 and others to right now in pancreatic cancer, is where he has funding to try to look at dendritic cell activation with kind of TLR anti- agonist and RT. We know that anti CTLA4 promotes the expansion of T cells, inhibits TREGs and effectively increasing your CD8/ TREG ratio, and that PDL-1 blockade may actually reverse your T cell exhaustion and help mitigate that depression in your CD8 to TREG ratio further. Again, the idea being that we’re trying to get an oligoclonal T cell response here, even though we are going to be getting polyclonal responses. Really, the idea here is, is there a way to figure out a way to get that oligoclonal T cell expansion and response, and then help subsequently, with your T cell infiltration. And can we use these combination approaches to really kind of harness what radiation is able to do? 

Dr. Parikh  12:53  
So, given this, we embarked on a trial. It was a single institution trial funded by BMS, with correlatives supported by Stand Up to Cancer for the colon component. It was a trial that combined colon cancer, pancreatic cancer, as well as MSI disease. We haven’t completed the MSI cohort yet, but did complete the MSS, CRC and pancreatic cohorts. And what we did here is we gave Nivo and IPI at cycle one, day one. And then cycle two, six weeks later, we gave Nivo and IPI again, and we gave 8 gray X 3 to a single lesion that was radiated.

Dr. Parikh  13:44  
And what’s important to note here is that the lesion we radiated was not the lesion that was measured. We are pulling the data to look at the radiated lesion response, but currently what we reported and what the end point of study was to look at response outside of the radiated field. And then we continued Nivo and IPI after that initial 8 gray X 3 to a single lesion beyond that initial treatment. So here were the consort diagrams for both cohorts. For colon, we had 40 patients.

Dr. Parikh  14:24  
I do think it’s important to note from both cohorts we had around a 30% drop off from the start of Ipi+ Nivo to radiation. And so I’ll show you the data for both the all-comer population here, sort of the Intent To Treat, but actually what we call the modified Intent To Treat. So the response of people that actually went on to receive radiation. And what you can see the reasons for discontinuation, toxicity was a few, I think, keeping in mind that when we started to study in like 2016, 2017, IPI and Nivo were still relatively new to the GI space, so we were sort of figuring out how to manage the colitis and others, where we have made a lot of headway in the recent years  within the GI community, how to handle those side effects. But we were still learning how to safely give these drugs at that time. We had nine other patients that had PD (progressive disease). This is a heavily pre treated patient population, so unfortunately, by the time you register the patient and actually start treatment, we had nine patients that dropped off, and ultimately weren’t able to get to radiation.

Dr. Parikh  15:43  
So when you look at the per protocol analysis, these were people that actually ended up getting radiation, so not the all-comer, we see a disease control rate of nearly 40% and an objective response rate of 15%. And what I want to call attention to is the duration of responses in the patients that were deriving benefit. So if you look here at the CRs (complete response) and PRs (partial response) as well as the stable disease patients, and we didn’t put this figure in the paper, but we actually did map out the previous lines of therapy for these patients and how long they were on their last previous line. And I think what was notable to us was that for a number of these patients, the duration of treatment is exceeding a year.

Dr. Parikh  16:35  
And we don’t think that was just sort of biologically selecting patients, because again, when we looked at the previous line of therapy for those patients, it wasn’t quite nearly a year by any means. There was only one patient that had lung only Mets. She wasn’t a PR patient, but she was a stable disease patient, and so sort of lower volume lung only disease that her biology was clearly favorable. But besides her, we don’t think that this was sort of a fluke in terms of biologically selecting favorable patients.

Dr. Parikh  17:15  
All right. So here is just one example of the out of field responses. So this was a patient that I shared with Ted, and we did not pre-specify in the protocol what needed to be radiated. So Ted Hong or his colleague Jen Woo, would sort of pick if there was a lesion that was needed for symptom control or palliation, often would pick that region or another region that was amenable to biopsy, because we had to do a lot of correlatives here. And here what you can see for this particular patient, he radiated the liver. And what you can see here is a really nice response in the lung metastases. So these are the same cuts, and you see improvement, here of this lesion and actually disappearing of some of the other lung nodules that we saw.

Dr. Parikh  18:09  
When we look at the Kaplan Meier curves, just for, I put the PDAC (pancreatic ductal adenocarcinoma) just for reference here, but when you look at the PFS and OS for the patients that actually went on to benefit or not, 5.2 versus 2.4 months, and then the OS 20.9 months versus 7.7 months for patients that were not deriving benefit.

Dr. Parikh  18:36  
One of the questions–this actually we hadn’t done initially– because we sort of assumed it was fine, just based on this and then the reviewers actually asked us to go back and look at TMB, which we did, and not surprisingly, these were all low TMB patients, so TMB albeit controversial, and colorectal cancer was certainly not the reason that was driving this change. We had 41 samples, or we had paired germline and DNA, 17 patients that were actually analyzable with the radiation. There was really no change in TMB before, during after treatment. Profiling is what you would sort of expect–KRAS, P53, APC alterations. We did note, interestingly, some change in sort of DNA damage response genes, but again, numbers are really small, so hard to really draw a lot of conclusions around kind of any DDR signatures as well. But what was interesting is, you know, when we started to look at what was coming out, and sort of the bulk RNA Seq, and one of the other kind of changes that we were seeing is David Ting, who did a lot of the correlative work for this, was noticing that in the responders, they seem to be enriched in these, again, interferon signature response genes. So signifying again, that we’re something is happening with kind of the innate immune system, and perhaps that these patients that were going on to respond were somehow primed to respond to this approach. And what we’re really trying to figure out is, is there a way for us to figure out how can we make more patients sort of primed for this approach? And are there any ways? And I’ll show you what some of those ways are to try to exploit this vulnerability for patients.  We saw some change in antigen presentation, as well as kind of T cell recruitment signatures before and after radiation. And then we saw this differential expression of these non coding RNA repeats and all the biopsies from the responders to non responders, particularly one repeat, which is called HERV-K. And I’ll tell you a little bit about what these repeats are and in the subsequent slide or two.

Dr. Parikh  21:12  
So like I mentioned, HERV-K was one thing that came out, but also LINE-1, which is another repeat. And they’re actually kind of ISH (in-situ hybridization) assays that are easy to do to ascertain HERV-K and LINE-1 status. And again, we saw this, and what we have learned in other cancers, actually urothelial cancer, there was a great paper that I put in reference here, and I can make sure Manju has these slides, that basically showed that HERV-K was associated with response to urothelial cancer, and HERV-K sssociation, or HERV-K is actually been associated with NK (natural Killer) activation. So maybe there’s something with these non coding repeat elements that are actually the ones that are driving these tumors to be primed for responding. Our hypothesis is, and what we’re trying to really understand is, is there a way to exploit these repeats further?

Dr. Parikh  22:09  
So what we saw was that this strategy of CTLA-4 and PD-1 did show some activity in a subset of patients. I’ll show you the schema for our trial that we will have our last patient on this week and have finished this next MSS trial to kind of confirm the signals, and with this next trial, we tried to mitigate some of that toxicity fallout.  But also Nir Hercohen and others have done work that’s showing that perhaps  PD-1 blockade prior to the antigen priming, may paradoxically lead to T cell exhaustion. So independent of toxicity if we expose to the checkpoint inhibition early. can we help with the responses and obviously the ongoing biomarker work that we’re doing.

Dr. Parikh  23:13  
So this was the study that is 30 patients, and patient 30 will come on this week, where we did the exact same thing, 8 gray X 3 (RT), but moved Nivo and ipi up to cycle one day one. And then actually are only continuing with four cycles of IPI, just based on other tumor types, the data that maybe you don’t need the IPI long term.

Dr. Parikh  23:41  
So we’re seeing, it’s too early, we haven’t yet looked at the data. I’m treating a lot of these patients, and so we are seeing some benefit. I don’t think it’s going to be where we would like to be in terms of 40% response rates, but I do think I mean, I know we’re seeing some patients benefiting, and we’ll see what those numbers look like. And now we’re really trying to figure out what our path forward is here, and are there better ways to get more to respond? Or will BMS support a larger study with this approach? Because, as you all know, if you’re in that 20% of patients that you’re driving benefit for a while that’s real and meaningful, and it’s our job now to kind of figure out with biopharma how to support this.

Dr. Parikh  24:34  
So we’re doing a lot of  correlative work with this too. We’re looking at ctDNA. We’re doing single cell RNA sequencing. And the way I like to sort of think about some of these immuno oncology correlatives is it’s the single cell approach is to really understand what is in the tumor so, what is the composition of, NK, CD8s, dendritic cells. And then what’s important is not only in understanding what, but using some of these multiplex approaches to understand where are these different cellular components located, to try to understand what’s what, to try to help us understand what’s happening.

Dr. Parikh  25:15  
So then going back to the repeats. So this was something that also actually came from David Tings lab, and when he was in the cancer center director Daniel Havers lab, as a postdoc, long time ago now, and they started to identify, as well, some other groups these, what it’s being called as the repeatome, and it’s an unexplored facet of the genome. Which, when I first met with, the backstory is, I showed up at MGH, almost six years ago too, and David Ting and I met, and he was like, Hey, we found this stuff. It’s constituting 50% up to 70% of the genome, and we don’t think it’s just junk. And he showed me some data that he had in colon cancer, and we started to put our heads together kind of digging through the data and the repeat landscape. And was there a way for us to try to think about how to harness these repeats, which, interestingly, these repeats we see in embryogenesis, and you see really high levels of these. And then it seems to be pretty quiescent until expression, again, in cancer pathogenesis, but also in aging and autoimmune disease. So there’s something going on. And I think  from a very simplistic standpoint, it makes a lot of sense, like, why would something be there? And it must have some purpose. And if they’re suppressed, they don’t cause problems. But if they are not suppressed, it can lead to problems such as epithelial malignancies.

Dr. Parikh  27:05  
And so this is just to show you that these repeats have actually been around for some time and act like endogenous retroviruses and actually have their own reverse transcriptase (RT). But only in the last few years, are we seeing this, not only in GI cancers, but a lot of other malignancies, in terms of the role of these and how they may actually stimulate immune responses. We know that they represent in the genome, like viruses, they have an RT (reverse transcriptase) so different things like methylation can actually help derepress them. And then you can have this RT that we think helps them reintegrate and expand into the genome.

Dr. Parikh  27:55  
And this is sort of a nice diagram of the RNA to the RNA/DNA. And rdDNA constructs there, and how they eventually are reintegrated and expanded. And can we use something like an RTI (Reverse Transcriptase Inhibitor) to prevent this reintegration and then expansion? This was a Nature Genetics paper, a couple years ago that looked at these repeats and several different malignancies. And Interestingly, esophageal cancer is one of the higher ones, but you see here, colon cancer is another cancer where these repeats seem to be differentially expressed. And like I mentioned, is that we think that these RNA repeats are actually triggering an innate immune response. And with these repeats, we see a lot of these inflammatory cytokines go up. And what you can see here with HSET- 2, which is one of these repeats, you can see a difference here between  TNF, IL-6, expression, IL-12. So seems to be something happening with these and interferon responses.

Dr. Parikh  29:11  
This was a JCI paper. David Ting was a collaborator on this, as well as from Bersani and colleagues a few years ago, looking at these NRTIs. So using 3TC, for example, and to inhibit these tumor spheres of  p53 mutant colon cancer. I won’t go into some of the details of how TP 53 is repressing these repeats, but we do think that actually, these repeats tend to be linked to TP 53 expression. So if you see here, this is LINE-1 in the green. And if you look at TP53 Colon cancer versus wild type colon cancers, the TP53 mutant seem to be enriched in these repeats as well.

Dr. Parikh  29:55  
So David Tang sort of treated some mouse xenografts with 3TC, and you can look here in pretty standard colon cancer xenografts, here in cell lines, looking at what’s happening in TP 53, mutant tumors, as well as wild type tumors. In HCT 116, cell line versus the xenograft what is happening with 3TC and tumor growth here? So showing some activity of this in the mutant patients, but not in wild type.

Dr. Parikh  30:37  
So this led us to write a small grant that was funded by a foundation. You can imagine, it’s really hard to get these funded because biopharma, there’s not a clear R and D sort of path for these. So we tried lots of different avenues, and ultimately, a foundation, the Gateway Foundation, funded this trial, and it was a small study with 3TC alone. And we didn’t really think that 3TC alone was going to, I think we know even going forward, that we’re going to need to look at combination approaches, but we wanted to make this sort of a biomarker driven trial and see that with 3TC alone and doing biopsies, are we actually hitting the target here and engaging these repeats. And so we did the trial. We started initially at the HIV dosing, which is our hepatitis dosing too, which is 300 milligrams daily, and we ended up going up to 1200 milligrams daily. And this was actually based on the initial HIV data, where there were no DLTs at the 1200 but given the efficacy they saw in the  viral space, around 300 that’s what ultimately was approved.

Dr. Parikh  31:56  
And so we had nine patients that were enrolled at 300 and then we went up to 23 more patients with the higher dosing. Really no significant side effects, some fatigue. Hard to sort out was that cancer versus drug, and we had eight out of 32 patients that had disease control and one out of 32 patients that had a mixed response, that one person the mixed response did not meet RECIST criteria for response, but had a really nice CEA  decline, and then had some tumors that were actually regressing, and then others that were growing, but the CEA overall was coming down. So that’s this patient here with the CEA response, and you can see a little bit of CEA response there, and some stability, at least here.

Dr. Parikh  32:47  
And when we looked at the patients that were deriving benefits, again, what we saw was that in the responders versus non responders, the same thing this LINE1 protein which is another, it’s a another one of the proteins that is expressed or formed by these repeats, sort of the LINE-1 leads to LINE-1 protein. And we looked at line one status, and again, looks like differentially expressed in patients that were benefiting versus not. So that study is we are under revisions right now for publication and trying to figure out our path forward with both of these approaches. And I hope we can all continue to work together as a community, because these are hard studies for biopharma to support. But  we’re looking at other options to try to get some of these concepts through, and our priority options for even when we get patients that are interested in supporting trials and things too. So we’re looking at options with 3TC and RT, based on the initial data that I showed you from our RT study. If you use epigenetic drugs and preclinical data, you may be able to get these repeats expressed. They seem to be linked to DNA damage and DNA damage response and as a kind of repair mechanism for double stranded DNA breaks. And so we have brokered some pre clinical contracts with David Ting to look at some of the DNA damage drugs out there, but are really working hard to try to figure out how to exploit these and get patients access to some of these combination strategies.

Dr. Parikh  34:49  
So with that, I think I went a little bit over what I wanted to with the 30 minutes, but wanted to share with you all some of the things that we are working on and where we are headed. So maybe I’ll pause for questions, and I can give you kind of brief non slide updates on the BRAF study as well as the CtDNA studies. Does that sound okay?

Dr George:
Yeah, that sounds good. This is really exciting. Thank you. Dr Parikh, so we have some general questions, so maybe we can go through them quickly, what is the rationale and risk benefit for triplet chemo, like FOLFOXIRI,  in the first line versus sequential doublets?

Dr. Parikh
Yeah. So I think there is a lot of institutional bias around this. And in general, I think taking a step back, of triplet versus doublet as well as I think maintenance versus holidays is a big discussion that I think a lot of people sort of split our hairs around in trying to understand. I do think when you can give FOLFOXIRI safely, I do think that there is, it’s truly synergistic, right? It’s not just additive. And so I do think that there is a survival benefit. And I sort of believe the TRIBE 2 and studies that for patients, and we’ve seen this with pancreatic cancer and others. And, in cholangio, there was a study that just looking at FOLFIRINOX and Gem/Cis, and didn’t show that FOLFIRINOX was better than Gem/Cis. So it’s not always just more is better. But for colon cancer, I think we do have compelling data to say that  in the right patient who we can get through FOLFOXIRI and in experienced hands with dose adjustments and things, you can get people through FOLFOXIRI probably with survival benefit. So I, I’m biased. We’re a pro FOLFIRINOX group, FOLFOXIRI group, have been for years, and so I do believe that there is a survival benefit, but I’m also, I don’t think, not surprisingly, treatment holidays lead to a detriment in PFS, but overall survival benefits are the same. And so I’m a firm believer in quality of life discussions with the patient and what their goals are, and don’t think that with the right patients you’re going to lose survival by both, doing maintenance. But I’m also a believer in good induction.

Dr. George  37:26  
I mean, what would you think, would you give it to a younger patient? I know that many of the  BRAF V 600E mutant patients, they get FOLFOXIRI in the beginning, right? So do you use some criteria to decide who are the patients that you will give FOLFOXIRI up front?

Dr. Parikh
Even older patients that have good performance status, I feel like performance status is in the eyes of the beholder, but we have given FOLFOXIRI or FOLFIRINOX to octogenarians of pancreatic cancer, and have gotten them through. So I’m not shy about it and recognizing that we may have to dose adjust and things along the way, but I think performance status to me more than age.

Dr. George  38:09  
Okay, And then the next question is about re challenging with say, FOLFOX or FOLFIRI for a patient later, like two or three years after they have had those. What do you think about that as part of a statement strategy? So it’s something that you follow? 

Dr. Parikh
Very much. So I think we have good enough benefit if  I think if data that have neuropathy and things are okay, that you can  regain response, particularly to the platinum. So even with FOLFOXIRI, I should mention, I’m not pushing through necessarily six months of FOLFOXIRI, sort of doing four months, get a response, then ,I tend to be pro-FOLFIRI, just because of the neuropathy issue and trying to save the platinum for later. So FOLFIRI Bev or anti EGFR, depending on sidedness and mutational status, and then, giving a holiday at some point in time, and then reintroducing later

Dr. George 39:12  
Okay. And then the next question is about, what are some of the conditions under which you decide to stop the chemo? And then consider local or regional treatments.

Dr. Parikh  39:25  
Yeah, so this is a good question, and it gets debated all the time, because as you may know, that, for example, liver directed therapy hasn’t been survival advantages there. But we are a site that I said for limited disease, depending on locations, particularly if a patient needs a break from chemotherapy, whether it’s toxicity or just fatigue, or is that a good response for some time, and we have shown that we’re not going to get behind. Have certainly used, sbrt to a dominant liver lesion. And as long as we think we have a good handle of lung, we do ablation for small volume liver lung Mets, for example. So it’s really about following the biology and making sure that the systemic disease isn’t going to get ahead of you. And if you feel like you have that window to stay on top of the systemic disease, but you can treat a dominant liver meth that may cause problems imminently, and prevent that from causing problems, in discussion with the patient, sort of understanding that we haven’t [had a lot of trial data] yet. There’s an NRG trial that’s looking at oligomet treatment and radiation and things, but I think we’re all starting to get a sense that oligomet sort of treatment was probably kind of beneficial. So our group, again, recognizing the biases of not a lot of survival data yet to support these, but in the right patients aren’t shy about like organ specific disease control approaches.

Dr. George
Okay, thank you very much for that. There’s one question about trials, but maybe we’ll go to that later. There are some questions in chat. So any insight on overcoming resistance to G12C inhibitors, or ideas on sequencing? Is there any news on if switching to a new G12C inhibitor after failing another one will work?

Dr Parikh
Yeah, I don’t think another G12C inhibitor in of itself, is going to work. I think we are seeing the differences between the G12C inhibitors and which ones are better versus others. But I think the kind of dual, triple pathway blockade approach with looking at better, I think there are better ERK inhibitors that are coming. ERAS is a company that I think has a really exciting ERK inhibitor. I think we’re still looking at some of the SHP2combination approaches. So I think it’s going to be combination strategies, because as far as we know, Dr. Corcorans Lab is doing a lot of work in this, but a lot of the resistance alterations that we’re seeing, and then what they saw in the New England Journal lung cancer paper, aren’t necessarily resistance alterations that are going to be able to be overcome with just another G12C inhibitor. So it’s sort of combination or downstream approaches too.

Dr George
Okay. The next question is, how do experts use CtDNA or NGS testing to know when to re challenge targeted treatments –like CETUX, Ras treatment, BRAF inhibitor, etc? Is it an estimate of how many months between treatment is needed for optimal possible results?

Dr Parikh
It’s a great, great question. And you’ll see people like Len Salz argue from CHRONOS that it’s only a 20% response rate. And the reEGFR inhibitor  challenge of person is really like cost effective and useful? So, I don’t think we really know. I think we do kind of have a timeline of what we would expect, the kind of resistant clones half life of a few months in terms of decaying and six to eight months seems to be that window. What I tend to do at the time of RE, when people are going on either holidays or something else, is I just get, kind of every two months  ctDNA test and see what is happening to those resistance clones.  And, I think what’s so challenging with even just up front  ctDNA testing, is does a small KRAS clone at 0.1%, does that actually portend resistance or not? And the dogma now is  of course, I guess KRAS is a resistance alteration and has detriment to anti EGFR therapy. But if you see that a RAS wild type tumor, and then you see this small clone, is that really clonal? Not clonal? Should you not give that patient anti EGFR therapy,  when you have a limited toolbox of things to try?  Same thing with HER2. I had a patient that had a RAS mutation, but I didn’t have a lot of things to try, but was really and I had a HER2 at 25 to one. Am I going to believe that small CtDNA result and not give them HER2 directed therapy? It’s hard not to, right, when you have an amplification that sort of at 25 to one. So that patient benefited. But again, the purists  would say, KRAS alteration came up, and that’s a known resistance mechanism. Those patients aren’t getting benefit. But you’re not necessarily looking at the fact that, again, that for that particular patient, you had a amplification, it was like at 25 to one, and clearly your driver event here, and that KRS was probably just a sub clone that overall, wasn’t going to hinder benefits. So ctDNA is a great tool, and I’m obviously biased, but it is a tool,and you have to sort of think about what you have in your tool box to care for the patient individually. And luckily for colon cancer, sometimes you have a little bit of time to try one or two things before people fall off.  Unfortunately, you know where you may not. That’s not always the case. And sometimes you just have to make your best clinical judgment, but I think we use it as a tool, but not as the end all be all

Dr George
Like with with clinical judgment, right?

Dr Parikh
Yes, right.

Dr George
So I had two questions about your talk. So the HERV K that repeat element as well as the LINE-1. So are you seeing that before treatment itself, you could look at the tumor and see if there is over expression or not?

Dr Parikh
Yeah, yeah. David Ting did a really great look. He hasn’t published this yet, or we haven’t, but actually, when you look at we did a cohort of just neoadjuvant rectal cancer patients that did not go on to have a clinical complete response. And what he showed was that the patients that were what was left were these HERV K elements. So it’s almost seemed to be a biomarker of non response to just the chemo, too. And so what we’re trying to figure out, can we make these repeats engaged more to try to therapeutically, use them to push these tumors over to response.

Dr George
Yeah. And I was also curious to see that, like with the mutation, with the TP53 mutation, you’re seeing more LINE-1 expression and things like that, right? So, I mean, I would think that ideally, if they, if some of the testing companies, CtDNA, or the tumor testing companies, would also look at these elements that would be kind of nice to see for your trial itself, to select patients who you’d get a better response, right?

Dr.Parikh
Yeah. So we are actually working with some colleagues, actually at the Brigham to look at a LINE-1 blood assay as well, and then we’re trying to validate that with the tumor to sort of figure out. But as you can imagine, biopharma is like, what are these? What do we do with them? And David Ting and I are pitching this constantly, like, hey, we have an ISH, we have an assay. We can sort of, but it’s really hard for them to currently get it, but I think we’re getting there.

Dr George
Okay, thank you for that. So there is a patient with a pole mutation. It is like a S314A, missense variant and the TMB 7.4. So she’s asking, if there is, it will have an effect in choosing immunotherapy, like with the low TMB with pole? What do you think?

Dr Parikh
Yeah, so probably not. Unfortunately, I think I would have to look up this particular polE variant. It may just be a kind of a VUS. But you know, the typically, the PolE ones that we’re seeing response are like hundreds of TMB.

Dr George
Okay, thank you for that. I think that we can go for the updates, and then there is one BRAF-related question, so we can look at that. So you’re going to start with your CtDNA trial, right, first?

Dr Parikh 48:17
Yeah. So the CtDNA trial has had lots of challenges, but we’re not giving up on it yet. Some of the challenges came with being a trial that, just by nature, the Stand Up to Cancer team was only a northeast heavy team, and I don’t think when the team came together it was based on the correlative expertise and clinical expertise, but not necessarily like a cooperative group study. So it was a small number of sites that could activate the study and then COVID hit. And because it was a stage III trial, a lot of our institutions weren’t allowing stage III trials to continue on, because they were trying to improve cure, not necessarily metastatic, where they didn’t seem that there were other options. So we had a really big delay, and we so we’ve had around 40 ish patients at MGH, and it was only the last couple months that MSK and Hopkins and Cornell all came on board. So I think we’ll see now a rapid increase there. But we’re behind, but I think the  Stand Up to Cancer, even though the team is over, is still really committed to the question, and they’re not pulling funding from it, so we’re continuing. And, I think Manju, I had mentioned to you, and there was a lot of controversy around rectal. We were getting close to adding rectal, but people were very concerned that if we added rectal, we would get a lot of challenges about the meaningfulness of the data if we didn’t stratify it. And actually we ran the stats to stratify for rectal, it was going to be.. it’s already a 400 to 500 patient study to try to find 80 patients that are CtDNA positive after treatment and to give you a sense of that, almost 40 ish or so patients we have, it’s good we don’t want to be seeing positive results. We’re not seeing a lot of positive patients, which is good, but it’s not yet enough to sort of show that we’re able to, I don’t have it yet. I can’t tell you yet if we’re seeing a signal of clearance or not, with a small number, but committed to continuing the study. 

Dr. Parikh  50:27  
And then I think, mainly the updates from it that may not be yet, even on the clinical trials.gov was the HER2 edition, which I know I have mentioned to you. We have the cohorts that are just the MSS, getting FOLFIRI if they’re CtDNA positive versus randomized to a little bit more stringent surveillance than you would get under the NCCN guidelines. And then we have a Nivo arm for the MSI positive, HER2 arm for the HER2 amplified positive, and then the BRAF arm for the BRAF positive patients.

Dr. George 51:22  
I think that we are showcasing some of the trials in the COLONTOWN University website. So I think this might be a good trial to showcase. So maybe I’ll reach out to you after the call. So and then about Dr Cocorans trial?

Dr Parikh
Yeah. So no updates since ESMO, we haven’t looked,  so that’s the last update, but we had an expansion that already filled that BMS gave us for additional patients, so we’re looking through all of that now. Still have MSI BRAF spots open, but the BRAF MSS is finished accrual, and so now we’re looking at all their data. I think we’re hoping to repackage it, maybe for GI ESMO.

Dr. George  52:14  
Okay, July, then?  And then this is this question, some BRAF V600E patients in other countries are trying to replicate Dr. Corcoran’s and Dr Morris’s trial: checkpoint inhibitor + BRAF. Prior BRAF or IO, how has it affected the results? I think that he was allowing prior IO, and then, and now you’re not accepting it now…

Dr Parikh
We’re not Yeah, because it actually seemed the patients that were benefiting first were the untreated BRAF patients. So there were a few patients that had prior BRAF therapy that seemed to be benefiting, but it seems like the patients that were deriving the most benefit were not treated patients.

Dr George
Okay, okay, yeah. And then I think we’ve covered those questions. I was really interested in seeing that the 3TC results. I mean, are you planning trials? How can we help?

Dr Parikh
We are pitching it to a bunch of different people. So  we have five or six different schemas with different combinations, with radiation, checkpoint inhibition, with epigenetic drugs. Epigenetic space has been really tough for solid tumors, right? And so the companies that have guatacytabine, AZTEC, and ASA, given the challenges they’ve had, in solid tumors in the past haven’t been too key on a development path for solid tumors. So we’re trying, we’re looking at, potentially, there may be some opportunities just to do, like, via cooperative group, or Stand Up to Cancer, for example, like just in like a neoadjuvant FOLFIRINOX setting for rectal, sort of a proof of concept with 3TC and radiation. But we’re trying. we’re like, looking, we had some concepts brewing with ATM and ATM/ATR inhibitors, plus 3TC and IO, but biopharma is tough.

Dr. George 54:18  
Yeah. So again, in that also, are you seeing the LINE-1 expression in the TP 53 mutant? Like, I mean, actually, with patient selection, you should be able to get patients and I mean feasibility wise, it will be a great study, right?

Dr Parikh
Like, yeah. So I’m hoping, what’ll happen is once, if we can get these revisions out, it’s at a pretty high profile journal right now with kind of some major revisions. And so I’m hoping if that paper comes out in combination with this IPI and  NIVO study, people will kind of believe the story a little bit more, and then we have the tools, like we know how to select for these patients. So we’re not giving up.

Dr George 55:05  
Okay, I think the last question is about promising trials for all wild type MS patients. I mean, for  your patients, what are some of the things that you look for?

Dr. Parikh  55:16  
Yeah, we’re trying to look at some opening some new ADCs that are coming in the Phase I world. I’mnot gonna lie, I’m not too keen. We’re opening them because I think they’re good options to have. But some of the VEGF IO trials, I think we’ll just have to see where these Pembro lenvatinib Rego Nivo approaches. It’s interesting. You wonder if there are certain patients, liver metastases, patients where that may be more beneficial. And so it’s a little bit hand wavy now, but given kind of the responses we’re seeing with the TKI, VEGF combos in HCC, is there something about like liver mets or primary to see if that would allow those patients to benefit more. So very much looking at combination studies. But I think ADCs are another  area that we’re kind of paying attention to, in terms of companies that may have ADC for MSS disease. I think the other challenge with the MSS, which I don’t quite understand why biopharma hasn’t quite adopted is, sort of really looking at subsets of patients, right? We know, there was a TGF beta trial that ended up not showing.. the company ended up not deciding to put in colon cancer as an expansion cohort. But they didn’t select the right patients, right, that are kind of high stromal driven patients. And so I think, as we’re having conversations, trying to really encourage them to think about what the biomarkers are, and if it’s not CMS, is it things like this that can help us select patients.

Dr George
Yeah, it makes sense. So are you looking at the two ADCs, like the HER3 and the TROP2 those ones?

Dr Parikh
Okay, yeah, the TROP2. I think there are some, they’re looking at it potentially in the adjuvant setting too, using CtDNA too. So,yes. So exactly the HER3 and the TROP2.

Dr George
Okay, And then in your talk, you mentioned that you’re not a fan of stivarga, regorafenib- you choose lonsurf. Are you seeing that kind of a difference? Because the trials, they say they’re kind of comparable, but is there a larger number of patients that respond to lonsurf versus Stivarga?

Dr Parikh
I think so. I think I’ve seen true responses with lonsurf, and these are platinum refractory, 5FU refractory patients, Stivarga I’ve had very, very limited actual some disease control. But I’ve again, I just haven’t seen, I’ve seen maybe one true response. And getting getting to dosing at 160 is also really tough.

Dr George
Yes, yes, okay, it’s two o’clock. Thank you so much, this was amazing. The recording will be posted in COLONTOWN University. And thank you so much for your time and all the information. Thank you all for attending.

Dr. Parikh 58:19  
Bye, take care.