Mark Gelder
Analyst · Guggenheim Securities
Thanks, Steve. I'll start with a quick update on narazaciclib's Phase I solid tumor program. I'm going to focus on the program's U.S. study, referred to as study 1901. This study is evaluating the continuous once-daily dosing regimen that we plan to utilize with narazaciclib moving forward. The trial recently completed the fifth dose cohort. This was a cohort of patients who took 200 milligrams a day by mouth on a continuous daily basis, days 1 through 28, each cycle being 28 days. We expect, it will advance to the sixth dose escalation cohort, which will evaluate the safety, tolerability, PK and PD of a 240-milligram dose of narazaciclib orally once daily. We expect to move to the sixth dose escalation cohort after the Safety Monitoring Committee has reviewed the data from the fifth dose cohort. Data from the trial continues to be highly encouraging with anticipated on-target effects of narazaciclib observed, but in the absence of any clinically meaningful cases of neutropenia or diarrhea. This is important, since as Steve pointed out, neutropenia is the dose-limiting toxicity for 2 out of the 3 approved CDK4/6 inhibitors, while diarrhea is the primary dose-limiting toxicity for the third one abemaciclib. These early clinical findings are also notably consistent with narazaciclib's differentiated kinase inhibitory profile as well as its preclinical data that showed reduced neutropenia when directly compared to the most widely prescribed CDK4/6 inhibitor, palbociclib. On our last earnings call, you heard Steve and I speak about how narazaciclib's differentiated inhibitory profile positions it as a potentially best-in-class therapy when combined with letrozole in patients with recurrent or metastatic low-grade endometrioid endometrial cancer, or LGEEC. We also announced that we plan to begin exploring this hypothesis in a Phase I/IIa trial, which has received IRB approval at New York University Langone Health. We expect the study to be open for enrollment later this quarter as planned and are very pleased that it remains on track for a preliminary data readout in the fourth quarter of this year. Several other sites are on track to be open and up and running in the coming weeks. As a reminder, the scientific rationale for the narazaciclib, LGEEC study comes from a randomized, placebo-controlled Phase II study as well as a couple of different single-arm clinical trials of the currently available CDK4/6 inhibitors, palbociclib, ribociclib and abemaciclib in patients with estrogen receptor positive endometrial cancer. These trials all demonstrated the improved anticancer activity of CDK4/6 inhibitors when combined with letrozole, when compared with letrozole plus placebo in the low-grade endometrioid endometrial carcinoma patient. It was these trials that support the compendia listing of the 3 currently available CDK4/6 inhibitors that enabled our off-label use and reimbursement in this setting today. However, I think it's important to realize that none of the currently available CDK4/6 inhibitors are FDA approved for the treatment of low-grade endometrioid endometrial cancer, and they are limited by the shortcomings related to safety, tolerability and treatment resistance as we've discussed before. Given narazaciclib's ability to inhibit CDK4 and 6 with similar potency to palbociclib, ribociclib and abemaciclib, we believe our Phase I/II trial has a high likelihood of technical and regulatory success. Moreover, we believe our preclinical and Phase I findings suggest that narazaciclib may offer significant safety advantages compared to currently available agents and its ability to target additional proteins related to antitumor immunity, metastasis, cancer cell survival, et cetera, may lead to improved efficacy. We therefore believe that narazaciclib has the potential to substantially improve the treatment paradigm for patients with recurrent low-grade endometrioid endometrial cancer and look forward to evaluating this hypothesis in our Phase I/IIa trial. Looking beyond low-grade endometrioid endometrial cancer, we are planning to initiate a clinical program of narazaciclib in one or more additional indications by the end of this year. And while we can't provide too much detail on these plans since they are still being finalized, I can say that other refractory tumors of the female reproductive tract as well as breast cancer are under consideration. Protocols for these clinical trials are currently being prepared for review, and we have identified key opinion leaders to service the principal investigators of the additional studies being planned. To conclude my section on narazaciclib, I want to briefly preview 2 posters on preclinical data that will be presented at the upcoming American Association of Cancer Research, or AACR meeting next month in Orlando. The first of these posters will feature results that demonstrate narazaciclib's single-agent activity against mantle cell lymphoma in vitro and in a chicken embryo chorioallantoic membrane xenograft model. And importantly, narazaciclib's activity against mantle cell lymphoma cell lines was found to be superior to that palbociclib and ribociclib and similar to that of abemaciclib. Moreover, when narazaciclib was combined with ibrutinib, a BTK inhibitor approved for the treatment of mantle cell lymphoma, synergistic increases in antitumor activity against both BTK inhibitor-resistant and BTK inhibitor-sensitive cell lines were observed. The second poster that will be presented at AACR next month will compare the differential cellular targets that are engaged by narazaciclib compared to the FDA-approved CDK4/6 inhibitors. In addition, results from a cell-based memory cell carcinoma model show that stronger induction of apoptosis with narazaciclib would deserve compared to palbociclib as well data that will show narazaciclib combining with autophagy inhibitors to sensitize breast cancer cells to cell death. While the conference embargo policy prevents me for saying much more about the data featured in these 2 posters at this time, we look forward to having further discussions with the scientific and clinical community at the AACR meeting next month. Shifting gears, I'll now discuss our investigator-sponsored rigosertib programs with a focus on the exciting early clinical data in the RDEB-associated squamous cell carcinoma, which was reported back in February. As those familiar with Onconova may recall, RDEB is caused by insufficient type VII collagen protein expression. This deficiency in type VII collagen leads to extreme skin fragility, chronic blistering and wound formation in these RDEB patients, many of whom go on to develop squamous cell carcinoma frequently metastatic that are driven by overexpression of PLK-1. Unfortunately, all of the currently available treatment, including targeted therapy, immunotherapy, conventional chemo therapy, radiation therapy, et cetera, provide only limited benefit for RDEB-associated squamous cell carcinoma patients, who have a cumulative risk of death of 70% by age 45. To address the unmet needs of patients with RDEB-associated squamous cell carcinoma, we are working with multiple investigators on a Phase II program evaluating the safety and efficacy of rigosertib monotherapy in this patient population. Last month, we announced that the trial's second evaluable participant achieved a complete clinical response of all cancer skin lesions after only 4 cycles of therapy. This patient remains on study with additional scans scheduled to monitor metastatic disease. The announcement of the second patient followed data that showed a complete clinical response in the program's first evaluable participant who has remained in complete remission with no signs of metastatic disease for more than 24 months while remaining on rigosertib. The studies remain open and are continuing to enroll patients, and we are actively looking for additional sites to participate in the program. While data from an [indiscernible] must always be taken with caution. The results from rigosertib's RDEB-associated squamous cell carcinoma program have far exceeded our expectations as well as those of the trial's investigators. They have confirmed rigosertib's activity against PLK-1 in the clinic as well as its ability to drive durable clinical responses in patients who have failed prior therapy. As Steve mentioned, the next step for the program is now to engage with the FDA to align on the optimal regulatory path for the program, given our data to date and the lack of effective treatments that are currently available for patients with RDEB-associated squamous cell carcinoma. In addition, RDEB is a catastrophic pediatric illness, and this reality as well as the potential enrollment of pediatric patients in the clinical program will be some of the topics to be discussed with the FDA. Taking a broader view, we believe the results from rigosertib's RDEB-associated squamous cell carcinoma program may have a positive read-through into other more prevalent cancers characterized by PLK-1 over expression. This is a hypothesis being explored in preclinical studies, though I should note that any effort to advance rigosertib's clinical development and additional indications would be enabled by investigator-sponsored trials so that we can continue to dedicate our primary focus and resources on narazaciclib. Lastly, I'd like to touch on the status of the 2 investigator-sponsored trials evaluating rigosertib in combination with a PD-1 checkpoint inhibitor. These trials are supported by preclinical data published by Dr. Ann Richmond's group at Vanderbilt University as well as results recently presented at the AACR targeting RAS conference recently held in Philadelphia, Pennsylvania. This data showed how rigosertib can stimulate an anticancer immune response via activation of the NLRP3 inflammasome. Collectively, these preclinical data provide a strong mechanistic rationale for the aforementioned trials, which aim to leverage rigosertib's immunotherapeutic effects to overcome checkpoint inhibitor resistance. The first of these trials I'll mention is designed to evaluate rigosertib plus pembrolizumab in checkpoint inhibitor refractory metastatic melanoma. I am pleased to say that this trial has recently been posted on clinicaltrials.gov, now has an NCT number, 05764395, and should be open for patient accrual at Vanderbilt University Medical Center later this quarter. We look forward to providing additional updates as this trial progresses. The second rigosertib checkpoint inhibitor combination study I'll mention is the Phase I/IIa trial evaluating rigosertib plus nivolumab in KRAS-mutated non-small cell lung cancer patients who have failed prior therapy with a checkpoint inhibitor. We remain on track to report additional data from this trial in the first half of this year. This announcement will likely include updated data from the 2 patients who remained on study as of its readout at ESMO last year as well as data from additional patients who were not yet enrolled and/or evaluable for efficacy as of the ESMO data cutoff date. After seeing these data, we plan to discuss them with the study investigators to determine the optimal next steps for this program. And now with that, I'll pass the call off to Mark Guerin.