Ladies and gentlemen, thank you for standing by. Welcome to the Onconova Third Quarter 2022 Financial Results and Business Update Conference Call. At this time, all participants are in a listen-only mode. Following management's prepared remarks, we will hold a question-and-answer session. To ask a question at that time, please press star followed by the number 1 on your telephone keypad. If anyone has any difficulty hearing the conference, please press star 0 for operator assistance. As a reminder, this call is being recorded today, November 14, 2022. At this time, I would like to turn the call over to Bruce Mackle of LifeSci Advisors.
Thank you, operator, and welcome everyone to Onconova's third quarter 2022 financial results and business update conference call. Earlier this afternoon, Onconova issued a press release announcing its plans to conduct a phase 1/2 A clinical trial of niraparib combined with letrozole in endometrial cancer and reported its financial results and business progress. If you have not yet seen this press release, it is available in the Investors and Media section of the company's website at www.onconova.com. Following my introduction, we will hear from Onconova's President and CEO, Dr. Steven Fruchtman, Chief Medical Officer, Dr. Mark Gelder, and Chief Operating Officer and Chief Financial Officer, Mark Guerin. These prepared remarks will then be followed by a question-and-answer session.
Before turning the call over Onconova's management team, I'd like to remind everyone that statements made during this call will include forward-looking statements under the Safe Harbor provisions of the Private Securities Litigation Reform Act of 1995, which involve risks and uncertainties that can cause actual results to differ materially. Forward-looking statements speak only as of the date they are made as the underlying facts and circumstances may change. Except as required by Onconova disclaims any obligation to update these forward-looking statements to reflect future information, events, or circumstances. For more information on forward-looking statements, please review the disclaimer in today's press release and the risk factors in the company's SEC filings. With that, I will now turn the call over to Steve.
Thank you, Bruce, and good afternoon, everybody. On today's call, we will focus predominantly on our 2 most recent and exciting pieces of news. These relate to our newly announced plans to advance our lead asset, Narazaciclib, into a phase 1-2A trial in second and third line low-grade endometrioid endometrial cancer and our recent presentation at the ESMO conference, featuring updated data from an investigator-sponsored study of rigosertib. Our CMO, our Chief Medical Officer, Dr. Mark Gelder, will go into more detail on each of these points. I would first like to briefly outline the rationale underlying the upcoming endometrial cancer trial, which will evaluate Narazaciclib in combination with a non-steroidal aromatase inhibitor letrozole. Our decision to pursue this clinical program was driven by 3 key factors.
First, we recognized that endometrial cancer, which arises in the uterine lining, is an indication with a pressing unmet medical need for improved therapies. It is a large addressable patient population and, in fact, is the most common cancer of the female reproductive organs. Low-grade endometrioid endometrial cancer represents the target patient population for our newly announced clinical development program for Narazaciclib. Second, we believe a clinical program evaluating Narazaciclib in combination with letrozole in endometrial cancer has a high probability of technical and regulatory success. This belief is supported by clinical data that demonstrates the benefits of combining an agent that inhibits the CDK 4/6 pathway with letrozole in this indication. As a reminder, Narazaciclib potently inhibits CDK 4 and 6 alongside additional tyrosine kinases that play important roles in cancer cell growth, survival, and metastasis. Clinical data, which Dr.
Gelder will discuss in more detail, substantially de-risk our upcoming trial by providing validation and clinical proof of concept for Narazaciclib's mechanism of action in endometrial cancer. The third and last driving factor behind our decision to conduct our upcoming clinical trial was the opportunity to establish Narazaciclib as a best-in-class therapy when combined with letrozole in recurrent endometrial cancer. While randomized phase II studies establish clinical proof of concept and compendial listings enable the off-label use and reimbursement of CDK4/6 inhibitors such as palbociclib in this setting, these CDK4/6 inhibitors are not FDA-approved in endometrial cancer and have several shortcomings related to safety, their tolerability, and primary and acquired drug resistance. We believe Narazaciclib can overcome these shortcomings based on data that we have generated that Mark Gelder will highlight shortly.
Lastly, before handing the call off to Mark to discuss our efforts in endometrial cancer and recent rigosertib data in more detail, I'll give a very quick update on the status of our trials. Starting with Narazaciclib, I'm pleased to say that safety data from the ongoing phase I solid tumor trials in both the United States and China continue to be encouraging, with the maximum tolerated dose not yet reached in either study, both of which are in their fifth dose escalation cohort. These trials evaluate Narazaciclib administered orally with 2 different schedules, mirroring the administration schemes of approved CDK4/6 inhibitors, which represent multi-billion-dollar drug franchises, although only approved in estrogen receptor-positive, HER2-negative metastatic breast cancer.
Based on the encouraging safety findings to date, we and our partner in China, HanX Biopharmaceuticals, believe we may have the opportunity to dose escalate further in each trial, leaving us better positioned to drive efficacy in subsequent studies. Accounting for the expected addition of dose escalation cohorts, we now anticipate identifying a recommended phase II dose in the first half of 2023. We anticipate the dose administration scheme for Narazaciclib in our phase 1/2A study and our other studies being planned will be once-daily continuous dosing of Narazaciclib. I want to point out that the 2 out of 3 approved CDK4/6 inhibitors are dosed in a 3-week on and 1-week off scheme. This 1 week off requirement potentially permits the tumor cells to proliferate during this week versus continuous repression of the cancer that daily dosing may provide.
The other CDK4/6 agent is typically dosed daily, but due to its half-life, requires twice-daily dosing. It appears that Narazaciclib will be dosed once daily and continuously. Looking forward, we remain interested in several indications for Narazaciclib's development beyond endometrial cancer, as discussed on past earnings calls. While it's too early to provide specifics on our clinical plans for these indications, we can reiterate that CDK4/6 inhibitor-refractory, hormone receptor-positive, HER2-negative metastatic breast cancer is an area of particular focus. We recently identified a principal investigator and breast cancer international key opinion leader to lead the trial and look forward to providing further details as our clinical plans are finalized. We have recently developed very encouraging data in mantle cell lymphoma cell lines with Narazaciclib. This data will be submitted to a major medical meeting.
Shifting gears, I'll now briefly discuss rigosertib. Which, as a reminder, has a multifaceted mechanism of action targeting the RAS and Polo-like kinase 1 pathways and the tumor immune microenvironment. We are utilizing investigator-sponsored trials to advance rigosertib in several indications and are making impressive progress and will continue to present the data at medical meetings, as we most recently did at the ESMO conference. In early 2023, we expect the initiation of an investigator-sponsored phase II trial evaluating rigosertib in combination with the checkpoint inhibitor pembrolizumab in checkpoint inhibitor-refractory malignant melanoma. In addition, the investigator-sponsored trial of rigosertib monotherapy in squamous cell carcinoma of the skin associated with recessive dystrophic epidermolysis bullosa, commonly referred to as RDEB, continues to enroll patients and was recently the subject of a non-dilutive grant to continue this very important clinical trial in these desperate patients.
Initial single-patient data in this ultra-rare genetic disease indicates and continues to show a sustained complete response with the patient now on therapy for over 15 months in complete response, and we have additional patients being enrolled. We believe this impressive response will provide proof of concept. Rigosertib's ability to inhibit Polo-like kinase 1 may have important implications both in RDEB-associated squamous and other more prevalent squamous cell indications, given the central role of the polo-like kinase pathway in various cancers. With that, I'll now turn the call over to Dr. Gelder to speak more about Narazaciclib's upcoming endometrial cancer trial and the recent ESMO presentation on rigosertib nivolumab combination therapy in KRAS-mutated non-small cell lung cancer. Mark?
Thanks, Steve. I'll begin by discussing our lead program, Narazaciclib, which is advancing towards a phase 1/2A study of Narazaciclib and letrozole as combination therapy in second or third-line recurrent metastatic low-grade endometrioid endometrial cancer or otherwise referred to as LGEC. The decision to move forward with a full clinical development program in LGEC has been guided by extensive phase II clinical data demonstrating the safety and clinical benefit of combining a CDK4/6 inhibitor with letrozole in this indication. This includes the results of the ENGOT-EN3 NSGO-PALEO study that was presented by Mirza at ESMO in 2020. This phase II study was a randomized, double-blind, placebo-controlled trial evaluating palbociclib plus letrozole versus letrozole plus placebo in patients with estrogen receptor-positive or ER-positive advanced recurrent endometrial cancer.
Participants received letrozole orally on days 1-28, with either palbociclib or placebo orally on days 1-21 in 28-day cycles until disease progression. Progression-free survival or PFS was significantly improved with letrozole and palbociclib compared to letrozole plus placebo with a hazard ratio of 0.56 and a median PFS of 8.3 months in the palbociclib arm versus 3 months in the placebo arm. This difference in median PFS between groups was statistically significant with a p-value of 0.0376.
In addition, disease control rate at 24 weeks was also improved in the combination therapy group compared to the monotherapy or placebo group with values of 63.6% and 37.8% respectively. Safety data from the trial showed that the toxicity of palbociclib and letrozole combination therapy was manageable, and most patients remained on treatment until disease progression. As anticipated, treatment-emergent grade 3-4 hematologic adverse events with letrozole plus palbociclib were the most common AEs observed, including neutropenia and anemia. Dose reduction and/or discontinuation of palbociclib was required in 36% and 25% of patients respectively. Of note, I want to remind you that we have preclinical data demonstrating in a head-to-head comparison that niraparib causes less neutropenia than palbociclib. To date, significant neutropenia has not been seen in our current phase I dose escalation trial with single-agent niraparib.
Importantly, the promising findings of this randomized phase II trial with palbociclib are consistent with the results of 2 other single-arm phase II trials in patients with estrogen receptor-positive endometrial cancer looking at letrozole in combination with the other 2 approved CDK4/6 inhibitors, ribociclib and abemaciclib. A recent data cut of the abemaciclib plus letrozole trial was presented at the 2022 SGO or Society of Gynecologic Oncology annual meeting in March 2022. The PI of the trial reported on 30 patients enrolled with a median follow-up of 12.5 months, with 9 of the patients still on study. The disease control rate was 73%, and the median progression-free survival was 9.1 months, providing substantial evidence of a clinical benefit in patients with estrogen receptor-positive, recurrent or metastatic endometrial cancer.
In the single-arm trial of ribociclib and letrozole combination therapy, the 12-week progression-free survival rate was 55% in relapsed estrogen receptor-positive endometrial cancer patients, which exceeded the trial's pre-specified success criteria. Collectively, these results strongly suggest Narazaciclib will be able to provide clinical benefit to patients with advanced or recurrent LGEC when combined with letrozole, given its ability to inhibit CDK4 and 6 with similar potency to palbociclib, ribociclib, and abemaciclib. Moreover, we have generated extensive preclinical data that indicates Narazaciclib may offer significant safety and efficacy advantages compared to these other agents. Looking first at efficacy, preclinical data have demonstrated Narazaciclib's ability to suppress the growth of cancer cell lines resistant to palbociclib. In addition, Narazaciclib has displayed potent inhibitory activity against ARK5 and CSF1 receptor, which are not targeted by any of the approved CDK4/6 inhibitors.
With the inhibition of the receptor promoting antitumor immunity, ARK5 playing crucial roles in metastases and cancer cell survival in hypoxic environments, we believe niraparib's ability to inhibit these targets may lead to improved anticancer activity and/or durability of responses. Returning our attention to the safety and tolerability profiles of the approved CDK4/6 inhibitors, let us start with palbociclib and ribociclib. Both of these agents are associated with significant bone marrow suppression, which is a key dose-limiting toxicity that necessitates a 3-week on, 1-week off treatment schedule. With niraparib, we have not seen any clinically meaningful cases of bone marrow suppression, even with continuous daily dosing in our phase I program to date. This highlights a potential safety advantage for niraparib that may also contribute to improved efficacy, since skipping a week of dosing every month may permit continued tumor cell proliferation, as Steve alluded to earlier.
Looking now at abemaciclib, the primary dose-limiting toxicity for this agent is diarrhea. This is a result of its affinity for the kinase GSK-3β, which is 29 times higher than that of niraparib. We believe Narazaciclib will display an improved tolerability profile compared to abemaciclib, allowing it to potentially be administered at a higher, more effective dose. This hypothesis is supported by clinical data from our phase I program, as diarrhea has not been a dose-limiting toxicity or high-grade adverse event that we have seen to date. Taken together, we believe the available clinical and preclinical data with Narazaciclib and currently approved CDK4/6 inhibitors not only point to a high probability of technical and regulatory success for our endometrial cancer program, but also strongly suggest Narazaciclib's successful development would provide patients with a much-needed improved therapeutic option.
We look forward to beginning our multicenter trial, which will start with a dose escalation phase before moving to a phase II expansion cohort with approximately 30 patients and a primary endpoint of 24-week progression-free survival. Our phase 1/2 study in patients with LGEC will be up and running in the first quarter of 2023, and we anticipate interim data in the fourth quarter of 2023. All patients will be treated with a continuous daily dose of both Narazaciclib and letrozole. Next, I'd like to briefly turn the call's focus to rigosertib and discuss the recent ESMO presentation which Steve alluded to earlier. The ESMO presentation featured updated results from an investigator-sponsored phase 1/2A trial evaluating oral rigosertib in combination with the PD-1 checkpoint inhibitor nivolumab in patients with advanced Keytruda checkpoint inhibitor-refractory KRAS-mutated non-small cell lung cancer. Patients with any KRAS mutation were eligible for the trial.
Efficacy data from the first 14 evaluable patients in the study revealed one complete response, 2 partial responses, and 1 patient with stable disease per RECIST criteria. The reported median duration of response was 6.75 months, with 1 partial response patient on study for 10 months and continuing without disease progression. In addition, the patient who achieved a complete response has been on study for 10+ months while maintaining an extracranial complete response. The disease control rate in these highly refractory patients for the dose of rigosertib equal to or above the minimally effective dose of 840 milligrams a day in combination with full-dose nivolumab was 31%. Collectively, these data provide a signal of efficacy that we find highly encouraging, especially when considering 2 key aspects of the trial's patient population. First, there's the treatment history of the trial participants.
Over 80% have failed at least 2 lines of prior therapy, and all patients have failed prior therapy with the checkpoint inhibitor pembrolizumab. This last point is particularly significant as PD-1 is the target of nivolumab. The fact that combining rigosertib with nivolumab led to RECIST-defined objective responses in these patients strongly suggests that rigosertib is synergistically enhancing the efficacy of the checkpoint inhibitor. This hypothesis is consistent with preclinical data we have discussed on past calls and is further supported by the observation of responses in patients who showed low PD-L1 expression at diagnosis, as this feature typically portends resistance to checkpoint inhibitors like nivolumab and suggests a role for rigosertib in targeting the mutated RAS gene. The second key aspect of the trial's patient population I'll discuss relates to the various underlying KRAS mutations in these patients.
Unlike agents that target a particular KRAS variant, such as G12C, the rigosertib-nivo-nivolumab combination has a KRAS mutation-agnostic mechanism of action that positions it to address a broader range of patients. This broad potential is highlighted by data from the phase 1/2-A trial that showed each responding patient with a different underlying KRAS mutation variant. In addition, I should note that 2 of the responding patients had STK11 co-mutations.
Which are generally indicative of a very poor prognosis with currently available treatments. Complementing these efficacy data from the trial are safety results showing that the studied doublet was generally well-tolerated. Looking forward, we are eager to enroll additional patients in the trial and anticipate reporting updated data in the first half of 2023 to inform the continued development of rigosertib/nivolumab combination in KRAS-mutated non-small cell lung cancer. Beyond lung cancer, we are also planning for the initiation of the investigator-sponsored trial in malignant melanoma that Steve referenced earlier. The encouraging lung cancer data we reported at ESMO are actually supportive of our efforts here as well as both trials seek to evaluate rigosertib in combination with anti-PD-1 therapy in patients refractory to checkpoint inhibition. With that pipeline overview complete, I will now turn the call over to Mark Guerin to discuss our financial results. Mark?
Thank you, Mark. I'm happy to report that Onconova finished the quarter ending September 30, 2022, with cash and cash equivalents of $42.6 million. This compares to $55.1 million as of December 31, 2021. Based on our current projections, we believe our cash position will be sufficient to fund our ongoing clinical trials and operations, including the pursuit of corporate development opportunities into 2024, thereby taking us through key catalysts expected across the pipeline. Turning now to our financial results. Research and development expenses for the third quarter of 2022 were $3.6 million, compared to $1.8 million for the third quarter of 2021. General and administrative expenses for the third quarter of 2022 were $2.1 million, and this compares with $2.3 million for the third quarter of 2021.
We reported a net loss for the third quarter of 2022 of $5.4 million, or $0.26 per share on 20.9 million weighted shares outstanding. This compared with the net loss for the third quarter of 2021 of $3.5 million or $0.22 per share on 16 million weighted shares outstanding. My financial review complete, I'll now turn the call back over to Steven.
Thank you, Mark. Before opening up the call for questions, I'd like to briefly review the near-term value drivers we are approaching. Looking first at Narazaciclib, we expect to initiate our phase 1/2A study in endometrial cancer in the first quarter of next year and report preliminary data in the fourth quarter of 2023. In the first half of 2023, we expect to identify a recommended phase II dose for Narazaciclib to inform its further development of multiple indications. With rigosertib, we are expecting additional data from the investigator-sponsored nivolumab combination study in KRAS-mutated non-small cell lung cancer in the first half of 2023. We expect to initiate an investigator-sponsored study in metastatic malignant melanoma evaluating rigosertib in combination with the PD-1 inhibitor pembrolizumab. We are extremely pleased with the results seen in the squamous cell carcinoma trial in head and neck.
These patients have few, if any, therapeutic options that work, and we have already seen a complete response in our trial with single agent rigosertib. We believe this is extraordinary. There is non-dilutive funding to help finance the trial, and we're planning to report on additional patients already entered onto the current trial at the appropriate time at a major medical meeting. As we seek to generate value with these programs, we will continue to devote our internal resources primarily to Narazaciclib while leveraging investigator-sponsored studies and collaborations to facilitate rigosertib's continued progress. In addition, we will continue to assess opportunities to potentially expand our pipeline, guided by a data-driven approach that focuses on assets backed by robust scientific evidence, demonstrating their potential in indications with high unmet medical needs.
We are fortunate to have a robust financial foundation in place as we pursue these various avenues for value creation and are eager to continue our work developing novel solutions for patients with cancers. Finally, I'd like to briefly thank those behind the progress we reported today. The list starts first and foremost with our clinical trial participants and also includes our employees, partners, investigators, and shareholders. With that, we will now open up the line for questions. Operator?
Ladies and gentlemen, if you wish to register for a question for today's question and answer session, you will need to press star, then the number one on your telephone keypad. If your question has been answered and you wish to withdraw your request, you may do so by again pressing star one. If you are using speakerphone, please pick up your handset before entering your request. One moment please for the first question. Charles Zhu with Guggenheim Securities, your line is open.
Hey, good evening, everyone. My first question regarding the Narazaciclib combination with letrozole. How should we think about the cadence of dose escalation in this combination relative to what you guys already did for the single-agent dose escalation? Would you need to escalate in combination just like you did a single agent, or could you possibly start the escalation higher given your prior experience? Thanks.
I'll ask Dr. Gelder. Mark, please.
Yes. This has been discussed extensively, as you can probably imagine. Because of the experience with the other CDK4/6 inhibitors and their combination with letrozole in breast cancer, the current protocol that we will initiate, we're going to start the phase I dose of Narazaciclib at 200 milligrams a day, which is where we are now in the fifth dosing cohort. We don't see any problems with that. We will combine this with letrozole 2.5 milligrams every day, which is the usual approved dose of letrozole.
Got it. Okay, great.
So-
That makes sense. Oh, sorry. Go on.
Dose escalation will proceed in 40-milligram increments. We'll do the 200 plus letrozole. Assuming that's well-tolerated, et cetera, we'll then move to 240 plus letrozole, et cetera. We'll not only be looking at PK and safety, but also the PD marker, the DiviTum assay from Biovica, the TK1 assay.
Got it.
I just wanna add and highlight to make sure everybody knows this. Dr. Gelder, we are very fortunate to have him. I want to highlight his background. Not everybody may know this. Mark is a superbly trained and experienced surgical gynecologic oncologist, having worked at some of the major medical centers in our country, leading their efforts, and that's why we are so pleased to have Mark be our Chief Medical Officer for his expertise in GYN oncology. Just wanted to highlight that for the people on the call.
Great. Maybe 1 more follow-up. Given that the other CDK inhibitors have generated proof of concept data but it doesn't appear that they're approved in this particular setting, what do you think you would need to demonstrate? And what in combination, what do you think would be considered a win? Thank you.
Again, Mark.
We will look carefully at the data from the phase 1/2a study. Based on the data with the available agents, we would expect that a median PFS of 8 to 9 months would be a clear win because when you look at historical data with letrozole or other "antiestrogens" as single agents in this setting, it's generally the PFS is in the 3 to 4 month range.
Great. Thanks for taking the questions.
Ahu Demir with Ladenburg Thalmann. Your line is open.
Good evening. Thank you so much for taking my question. My question is also on Narazaciclib program. Have you shown any data from endometrial cancers as a single-agent activity, and what did it look like, if you could comment on that?
We don't have any data with Narazaciclib as a single agent in endometrial cancer. You know, if you look at the work that's been done in endometrial cancer with the other CDK4/6s, they've all combined with an aromatase inhibitor, letrozole.
I see. My follow-up question is palbociclib showed promising data, proof of concept. It was HR-positive endometrial cancer. Are you planning to target that particular population, or are you going to have a broader endometrial patient enrollment?
Our patient population will be patients with low grade, i.e., grade 1 or grade 2 endometrioid endometrial cancer. Historically, if you look at this population, 97%-99% of them are estrogen receptor-positive. ER positivity is not routinely performed on all patients with endometrial cancer, unlike breast cancer. The actual threshold for quote-unquote endometrial or estrogen receptor positivity is not well established for endometrial cancer like it is for breast cancer. This is why we have decided to move forward with this population after consultation with lots of other experts in this area.
Very helpful. Thank you so much for taking my question.
Mm-hmm.
Robert LeBoyer with Noble Capital Markets, your line is open.
Good afternoon. My question I thought may have been answered by Dr. Guerin, and I thought I may have heard that the dosing regimen is gonna be every day compared with 3 on and 3 off. Is that correct?
Yeah.
This is the-
I'll take that, Rob, if I may. Based on the data we have so far, and we believe for reasons we discussed, we prefer not having the 1 week off scheme that the other FDA drug require 'cause of bone marrow suppression. In the US, our study is every day, and to date, we do not see significant marrow suppression. We believe we're already targeting the key tyrosine kinase 'cause we do see some lowering of the white count, which is anticipated with this class of drugs, but not to the degree that anything needs to be done. We believe and anticipate that we'll have what I'll call the optimal dose, which will be every day and also once a day. Every day dosing to optimize the tumor proliferative effect.
Because of the safety seen to date and in preclinical models as well, we have not seen significant marrow toxicity.
Okay, great. Thank you. Just 1 other financial question is, in the R&D expense line, there was a bit of an increase this quarter over the first half. I was wondering if you could give some guidance as to what it might look like going forward for the next several quarters.
Mark Guerin.
Sure thing, Robert. Yeah, there was an increase in research and development expenses. As you can see, if you look at our 10-Q, a big chunk of that compared to last year at this time was related to manufacturing during the third quarter of 2022. You probably know that our historic quarterly cash burn rate has been around $4-$4.2 million. As we embark on this phase 1, 2A combination study, naturally, that's gonna go up. Our current studies are phase I and/or investigator-sponsored. Once we get back into sponsored studies, our burn will go up on a quarterly basis.
The only guidance that we're comfortable giving at this point is what we said in the press release and in my comment that we believe based on our current cash and our plans that our cash will get us into 2024. Hopefully, that's helpful.
Yes, it is. Thank you very much.
Certainly. I'm showing no further questions in the queue. At this time, I'd like to turn the call back over to the speakers for any closing remarks.
Thank you, operator, and thanks again to all who have joined us today. It's been our pleasure to update you on the progress and newly announced plans to pursue Narazaciclib development in endometrial cancer and to update you on the very encouraging clinical data we have seen and presented with rigosertib at ESMO. We look forward to providing additional updates in the future. As the Thanksgiving holiday approaches, we have much to be thankful for. Special thanks to the brave patients who consent to participating on our experimental studies, and to our investors who support our science in helping to bring new therapeutics to those in need. We wish all of you a very lovely evening, and thank you again.
Ladies and gentlemen, thank you for your participation on today's conference call. This concludes today's event. You may now disconnect.