Steve Kelsey
Analyst · SVB Securities. Your line is now open
Thank you, Mark. As we have stated previously based on extensive preclinical studies of RMC-6236, our working assumption is that the on-target effects of inhibiting wild-type RAS in normal tissues will ultimately determine the maximum tolerated dose in people. We have consistently represented that we believe RAS-mediated toxicities will be predictable, manageable, monitorable, and reversible. We have also presented preclinical data suggesting that the slower clearance of RMC-6236 from tumors compared with normal tissues may enhance the therapeutic index for RMC-6236 and contribute to achieving meaningful anti-tumor activity for tolerated exposures. Meaningful clinical activity includes both reduction in tumor size and durable inhibition of tumor growth, represented most frequently as progression-free survival in clinical trials. In the clinical program to date, patients have been treated in five dose cohorts ranging from 10 milligrams daily to 120 milligrams daily. To calibrate you, based on measured drug exposures in these patients, the 10 and 20 milligram doses fall at the lowest end of exposures we evaluated pre-clinically and were associated with some degree of tumor growth inhibition in xenograft models. Drug exposures seen in patients treated at 40, 80 and 120 milligrams daily are similar to those associated with more significant anti-tumor effects in preclinical studies. These included dose-dependent tumor regressions and delay in time to tumor growth in in vivo studies of several RAS-mutant cancer models. But with these doses in patients, we haven't yet reached the exposure levels achieved at the dose we studied the most pre-clinically, that is 25 milligrams per kilogram daily. 36 patients have been evaluated for initial safety and tolerability in the clinical trial so far. As shown in the table of drug-related adverse events on Slide 11, treatment across all dose cohorts has been generally well-tolerated. Some patients have exhibited predicted on-target normal tissue effects, presumably due to inhibition of wild-type RAS. These are primarily grade one or two skin rashes similar to those observed with EGFR inhibitors and the range of mild to moderate severity gastrointestinal toxicities usually nausea or diarrhea. The frequency and severity seem to be dose-dependent and thus far have been manageable with standard supported care. One patient required a brief dose hold for skin rash and resume dosing at reduced dose. Skin rash and gastrointestinal toxicity are recognized consequences of suppressing RAS signaling in normal tissues based on a wide experience in the field with other drugs and drug candidates, including EGFR, MEK, ERK and SHP2 inhibitors. Skin rash has been historically viewed as a biomarker of pharmacologic activity by some of these drugs. Therefore, the clinical findings further support our belief based on PK data that we are achieving exposures of RMC-6236 in patients that are in an active range without inducing unacceptable toxicity. Among all 36 patients evaluated so far, one related serious adverse event has been observed. This patient with metastatic pancreatic cancer and a KRASG12D mutation entered the study with extensive abdominal disease, including a large and deeply invasive tumor implant in the serosal wall of the large intestine. About one week into treatment at 80 milligrams daily, the patient experienced an unfortunate bowel perforation that occurred at the invasive tumor site, accompanied by radiographic evidence of tumor reduction at that location and other metastatic sites. No evidence or clinical symptoms of colitis or colonic ulceration were seen preceding the event or observed on subsequent imaging. Based on abdominal CT scans and the opinions of the clinical investigators, we believe that this event is likely attributable to shrinkage of the tumor by RMC-6236 in the heavily infiltrated bowel wall even within the short treatment period rather than to a direct toxic effect of RMC-6236 on the normal bowel wall. Similar events attributed to tumor shrinkage in the bowel wall have been occasionally described on treatment with BRAF inhibitors and with chemotherapy. We have treated patients with RMC-6236 in a higher-dose cohort, 120 milligrams, without observing additional serious adverse events so far and expect to continue dose escalating even further towards a recommended Phase II dose. Let me provide some information on the anti-tumor activity we have seen in the study. Consistent with study eligibility criteria, patients with a range of tumor types in which KRASG12X mutations are common have been enrolled, including major epithelial cancers, such as non-small cell lung cancer, pancreatic, colorectal and other tumors, including ovarian cancer, appendiceal and bile duct cancers. The KRAS mutations in those tumors cover the range of KRASG12 mutations: G12(D,V,A, S, R) with D being the most heavily represented so far. And this is consistent with the epidemiology of RAS mutations in human cancers. Patients enrolled in this study have been previously treated with the standard of care and/or other regimens with an overall median of three prior therapies as is typical for an oncology dose escalation Phase I study. At the 10-milligram and 20-milligram dose levels, radiographic imaging showed either stable disease with some tumor reduction or disease progression as the best response. Interestingly, in several patients at these lower dose levels, we have measured significant reductions in tumor variant alleles in ctDNA. For instance, in one patient with a KRASG12V non-small cell lung cancer treatment at 20 milligrams daily was associated with initial stable disease and 100% clearance of all RAS-mutant alleles and all other concurrent tumor variant alleles. These earliest signs were consistent with our expectations at these low dose levels and were encouraging. We would like to show you more detail regarding early and preliminary treatment-related activity at the 40, 80 and 120-milligram dose levels. We are focusing on non-small cell lung cancer and pancreatic cancer since those are the two histologies most likely to be sensitive to a RAS inhibitor monotherapy based on the G12C experience. We will report on other tumor types, including colorectal cancer, in future updates. The waterfall plot of tumor volumes on Slide 12 shows our experience so far with the nine pancreatic cancer patients and three non-small cell lung cancer patients that have been treated at 40 milligrams daily or higher and are efficacy-evaluable. All 12 of these patients have exhibited stable disease or better as their best response and remain on study from approximately 1.5 to 4.5 months as of the data cutoff date. 10 of 12 patients have shown some degree of tumor volume reduction by RECIST. One patient with a KRASG12D non-small cell lung cancer achieved a partial response on first restaging scan and was subsequently confirmed with a follow-up scan. One pancreatic cancer patient with a KRASG12D mutation also achieved a thus far unconfirmed partial response, a case study I will describe more fully in a moment. Even at this early stage with short follow-up, small patient numbers and doses below the anticipated recommended Phase II dose, we believe that these data compare favorably with chemotherapy regimens for advanced pancreatic cancer, where disease control rates rarely exceed 60% and the response rates are low. The durability of disease control is of high importance for conferring clinical benefits and ultimately regulatory approval, particularly in advanced pancreatic cancer. Follow-up continues on all of these patients, as we've noted. In some cases, tumors continue to reduce in size beyond the first response evaluation. Let me now describe to you a particular case that is still ongoing and requires further data collection while the patient's treatment continues, but even at this stage, provides a view into the therapeutic potential of RMC-6236. As described on Slide 13, this patient is a 76-year-old male with metastatic pancreatic cancer harboring the KRASG12D allele and associated gene copy number loss in tumor suppressor genes CDKN2A and N2B as well as the associated putative tumor suppressor MTAP. After both neoadjuvant and postsurgical adjuvant chemotherapy, he developed metastatic disease in the lungs and progressed following the third course of chemotherapy. He received RMC-6236 at 80 milligrams daily, which as noted earlier, we project to be in the midrange for anti-tumor activity and is below the anticipated recommended Phase II dose. The patient is tolerating the drug well. At baseline, the patient had three distinct lesions: one in the right lung and two in the left lung that are being followed radiographically. These lesions are identified on the upper row of the three CT images on Slide 14. All three lesions underwent significant reduction over 12 weeks of therapy. At six weeks, all three tumor lesions were reduced in size with an overall 17% reduction in tumor size by RECIST. On the 12-week scans shown in the second row of CT scans, target lesion one has disappeared and target lesion two is considerably reduced. The single non-target lesion is barely detectable. In addition, the density of the residual tumor has changed. RECIST quantifies response by measuring only the unidimensional longest axis for each target lesion and does not consider density or three-dimensional volume. As the first target lesion has been assigned a minimum measurement of 5 millimeters, this patient has formally achieved a 70% tumor reduction and a clear partial response by RECIST, even though volumetrically the reduction in tumor burden appears greater. He continues on study, and the partial response needs to be confirmed with a follow-up scan. We must emphasize that it is too early to project the frequency or durability of responses or comparative results across tumor types and genotypes. The numbers are small, the dose levels are likely to be below the recommended Phase II dose, and follow-up is short. Nevertheless, the totality of data across these 12 patients reinforces our growing conviction about the potential for RMC-6236 to exhibit promising clinical anti-tumor activity in patients with advanced RAS-mutant tumors at doses that are well tolerated. And now I will turn the call back to Mark.