Greetings and welcome to the SELLAS Life Sciences Group corporate update call. At this time, all participants are in a listen-only mode. If anyone should require operator assistance during the conference, please press star zero on your telephone keypad. It is now my pleasure to introduce your host, Bruce Mackle, at LifeSci Advisors. Thank you, Bruce. You may begin.
Thank you, Operator. Good morning and welcome to SELLAS's corporate update call. Before we begin, please note that today's call contains forward-looking statements, the accuracy of which depends on future events outside SELLAS's control and therefore could cause actual results to differ materially from those forward-looking statements. The forward-looking statements are made as of the date of this call only. Additional information regarding the risks and uncertainties and other important factors, any of which could cause SELLAS's actual results to differ from those contained in these forward-looking statements, can be found under the section titled: Risk Factors in SELLAS's annual report on Form 10-K filed on March 16, 2023, and in its other SEC filings. With that, I would like to turn the call over to Dr. Angelos Stergiou, President and Chief Executive Officer of SELLAS. Please go ahead, Angelos.
Thank you, Bruce. Good morning, everyone. I stand before you today with great enthusiasm and excitement because, as I had stated back in January of this year, 2024 should be a transformational year for our two promising assets, Galinpepimut-S or GPS, and our highly selective CDK9 inhibitor SLS009, as they are progressing through clinical development with several near-term and potentially value-creating clinical milestones which I will talk about shortly. We remain steadfast in our belief that the true value of our company lies in the groundbreaking science of the positive impact it can have on patients' lives and, in turn, to you, our valued shareholders.
Today, I will discuss the important steering committee update around the GPS phase III REGAL study with you, as well as the phase IIa study of SLS009 in relapsed refractory AML, which showed a remarkable 50% response rate in the selected 30 mg twice-a-week cohort, exceeding the targeted 20%, and importantly, a 100% response rate in several patients with identified biomarkers. Let me begin with a couple of updates on the phase III REGAL trial of GPS in AML. As you may be aware, the phase III REGAL trial is designed to provide reliable evidence about the effects of GPS maintenance monotherapy for its key primary endpoint of overall survival. In our REGAL study, patients are randomized to receive either GPS treatment or best available treatment or BAT.
In our previous AML phase II study, in the same CR2 patient population as our phase III trial, we observed a clinically and statistically significant survival benefit in patients who received GPS, an almost 16-month differential survival benefit, 21 months versus 5.4 months, with a p-value of 0.02 and a substantial difference in leukemia-free survival. I am delighted to announce that the enrollment for the REGAL study has been successfully completed in accordance with the predetermined statistical analysis plan, and accordingly, we have stopped further patient screening. Also last week, on March 22nd, the steering committee convened to review blinded data from the REGAL trial due to study enrollment completion. As you may recall, the steering committee provides scientific oversight and guidance of the practical aspects of the ongoing REGAL study and, among others, reviews blinded trial results without jeopardizing its integrity as they become available.
I am pleased to inform you that the committee, comprised of Drs. Hagop Kantarjian, Javier Pinilla-Ibarz, and Yair Levy, was able to objectively and thoroughly evaluate the information available to them, and the committee's expertise and insights have been invaluable in guiding the direction of the trial. The data the steering committee reviewed was as of the March 1st, 2024 cutoff date. As of that date, 123 patients were enrolled, of which 66 patients stopped receiving study treatments. In the trial, patients are recorded as having stopped the study treatment in cases of death for any reason, relapse, intolerable toxicity, or treatment completion. Discontinuation of treatment for intolerable toxicities is a remote possibility in this trial. Regarding the GPS arm, we are pleased to report that we have not observed any intolerable toxicities in any patient population across all our clinical studies thus far.
Although toxicities are commonly observed with therapies used in the control arm, physicians are allowed to modify the treatment regimen in any way they deem necessary. This includes the option for observation, which, for the purpose of the trial, is considered a valid treatment option. Therefore, almost all patients who are off treatment, 66 as of March 1st, have most likely either relapsed or passed away. The most frequent cause of death in this patient population is relapse. Due to regulatory reasons, as the study sponsor, we lack specific information on the outcomes of these 66 patients, including data on how many of them relapsed but have not passed away yet. We do know, however, that second or later relapse in AML, unfortunately uniformly, results in death even with the best therapy available.
As we do not have any insight into the actual number of deaths, we cannot confirm that the number of events required for interim analysis, 60, has been already reached. The committee believes the high number of patients who completed participation in the study signals that the interim analysis requiring 60 events may be imminent. The steering committee expressed its satisfaction with SELLAS' overall REGAL study conduct and complimented our company for addressing such a debilitating and high unmet medical need as no drugs are approved in the AML CR2 maintenance setting. The determination of the relevant survival outcomes, including the interim analysis, belongs to the Independent Data Monitoring Committee, the IDMC, which is now scheduled to meet in late April. During this meeting, the IDMC will analyze the accumulated data and assess the safety and efficacy of the treatment.
Statistical significance in the REGAL phase III study will be achieved by an estimated hazard ratio for OS, overall survival, of 0.636, corresponding to an overall survival of 12.6 months versus eight months for GPS versus BAT, respectively. The IDMC must not disclose event rates and clinical data to us, so we will not know in advance when the 60 deaths have been reached. Once the IDMC meeting concludes, we will promptly share the information with you. In addition to our phase III REGAL study in the maintenance setting, I am thrilled to share with you the remarkable strides we have made in our SLS009 program. Our highly selective CDK9 inhibitor continues to demonstrate strong and clinically compelling and positive data. As we communicated before, the SLS009 completed the first-in-human dose escalating phase I trial in the second half of the last year.
Based on the results of the trial, we initiated the phase IIa dose ranging trial in relapsed refractory AML at the end of June last year. The phase IIa trial is taking place only in the U.S. initially and in a small number of centers with strong scientific and clinical expertise and investigator credentials, as we want to focus not only on dose selection, safety, and efficacy but also gain a deeper scientific understanding that would help us in patient identification and target patient population enrichment as well. As of March 15th, I am delighted to report that we have enrolled more than 20 patients, thus exceeding our original publicly communicated plans and expectations. The results to date have been extremely encouraging and may represent an important advancement for SLS009. As a reminder, our ongoing phase IIa trial is in AML patients relapsed on and/or refractory to venetoclax-containing regimens.
This patient population represents arguably the most pressing unmet medical need in AML, and almost all AML patients in the U.S. are at some point during their journey treated with venetoclax combinations. However, those are not curative treatments that eventually all patients relapse or do not respond in the first place. After patients stop responding to venetoclax combinations, they have low response rates to other approved therapies, significantly below 20%. Commercially, the median overall survival is well reported to be approximately 2.5 months. The goals of our phase IIa study, in addition to safety, are as follows: first, assess the efficacy of SLS009 as an add-on therapy measured by response rate with 20% as the target response rate at the optimal dose level and overall survival with target median survival over three months. Second, determine the optimal dosing regimen.
Third, identify biomarkers for target patient population identification and enrichment for further trials. With the usual caveat that this is a trial in progress, I will now share key top-line data with you, beginning with safety. We have achieved our goal of ascertaining feasibility and safety of SLS009 administration concurrently with venetoclax and azacitidine. There were no dose-limiting toxicities at any of the studied dose levels and no treatment-related high-grade extramedullary toxicities, while the hematologic toxicities profile was consistent with venetoclax azacitidine treatment alone thus far. In terms of efficacy, we have observed the following response rates with the March 15th cutoff date: in the 45 mg once-a-week safety cohort, the dose level below the recommended phase II dose, 10% response rate. In the 60 mg once-a-week cohort, 20% response rate. In the 30 mg twice-a-week cohort, 50% response rate.
Thus, not only meeting but exceeding the target 20% response rate at the selected dose level, 30 mg twice-a-week, and that's very exciting. In addition to objective responses, we have observed a strong anti-leukemic activity defined as 50% or more bone marrow blast reduction in the majority of patients across all dose levels. Based on the totality of safety and efficacy data, we have selected the 30 mg twice-a-week as the optimal dosing regimen going forward. Importantly, the design of the study and the collected results adhere closely to the FDA advice as stipulated in the FDA Project Optimus. Median survival has not been reached in any of the dose levels in the trial, which, of course, is extremely promising. The first enrolled patient is still in CR, alive, and leukemia-free nine months after enrollment. Finally, the discussed response rates were observed in unselected patient populations.
During the course of the trial, we identified biomarkers that are currently undergoing testing as predictive markers in the most recent portion of the trial. Patients with identified biomarkers exhibited significantly higher response rates. In all patients with a specific biomarker across all dose levels, the response rate was 57%, and at the optimal dose level, 30 mg twice-a-week, the response rate was a stunning 100% across several patients. These biomarkers are well established as having a negative prognostic value in AML patients, and to date, there are no approved drugs or active biomarker targeted clinical trials, to our knowledge. We have also identified a proposed biological basis and mechanism of action for SLS009 activity in patients with those biomarkers. The relevant biomarkers are present in multiple hematologic and solid cancer indications.
The proportion of patients with the relevant biomarkers in those additional indications is high, ranging up to 50% of approximately 50% of patients. In our AML trial, based on our research, it appears that the reported already high percentage of patients may be significantly higher than that reported in previous publications. We hope to implement this information in the next stage of expansion of clinical development. While I'm unable to publicly identify the biomarkers, as you can appreciate, due to IP and proprietary business considerations, it is important to note that those biomarkers are recognized by regulatory bodies such as the FDA, among others. Now switching to finance and our recently completed financing, we're extremely pleased to have significantly strengthened our financial position with the additional $20 million that was priced at the market last week.
This funding will enable us to reach a number of important upcoming milestones, notably the interim analysis for our phase III REGAL study, further SLS009 phase II data in Q2, and potential expansion of this study while further pursuing regulatory and BD licensing efforts. We're extremely excited about the ability to potentially quickly move into a registrational study with our CDK9 inhibitor based on the predictive biomarkers we have identified and the unprecedented responses we have seen thus far in these patients, as well as explore various regulatory paths in the U.S. and Europe in addition to other cancer indications that these biomarkers express. This financing gives us additional firepower, if you will, to execute on our objectives. In addition to these groundbreaking achievements, we remain steadfast in our commitment to the goals I had outlined in January.
Our organization has undergone a streamlined transformation, and we are dedicated to progressing our licensing and business development initiatives, which I hope to update you on soon. Our team is tirelessly working towards forging strategic partnerships and collaborations, and we're actively seeking partnership and licensing opportunities with other biotech and pharma companies. These collaborations could not only provide additional resources but also validate the potential of our technology in the eyes of the market. Importantly, they could lead to significant strategic outcomes, including co-development and co-commercialization or beyond. As I mentioned, we're deploying internal resources as well as working closely with Stifel Financial Corp. on that front. At this point, I would like to thank, before all else, our patients and their families, and once more thank all our investigators, study nurses, and study personnel for their confidence in and support for product candidates GPS and SLS009.
In conclusion, we have placed great emphasis on bringing about the next stages of value creation on behalf of SELLAS' shareholders. On behalf of the entire SELLAS team, we want to express our gratitude for your continued support and confidence in our company, a matter that I and we collectively do not take lightly. Thank you once again, and we look forward to sharing further updates with you.
This concludes today's conference. You may disconnect your lines at this time. Thank you for your participation.