Helen Thackray
Analyst · Cowen and Company
Thanks, Anthony. As we announced today, the FDA has lifted their partial clinical hold on the BCX9930 program, and our pivotal trials in PNH can resume enrollment, along with our proof-of-concept trial in renal indications. This is an important step forward toward our goal of bringing a safe and effective Factor D inhibitor to patients with PNH and complement-mediated renal diseases.
We will reinitiate enrollment using a step-up approach and a dose level of 400 milligrams twice daily, together with encouraging hydration and more frequent safety testing for the first few months in each patient. After review of the data and investigating the elevations in serum creatinine we reported in April, we've arrived at the hypothesis for the mechanism contributing to these observations and our proposal for how to address it. The hypothesis is that crystals are forming in the kidney when the concentration of the drug is highest in the urine, and that this can be mitigated by lowering drug levels in the urine.
We will test this by lowering the dose from 500 milligrams twice daily to 400 milligrams twice daily and encouraging adequate fluid intake to achieve dilution of the drug as it is excreted in the kidney. If we are correct in our hypothesis and these steps successfully address the problem, this will mitigate the risk of elevated serum creatinine in patients receiving BCX9930.
The evidence in support of this hypothesis comes from clinical observations and laboratory studies. As we shared in May, the clinical evidence suggested that the serum creatinine elevations occurred only at the 500-milligram dose level and were likely dose related. In addition, our recent clinical pharmacology studies have shown that a large fraction of the administered dose of BCX9930 is excreted by the kidney.
Importantly, New laboratory studies have found BCX9930 drug solubility is lowered over the typical pH range of human urine, and recent nonclinical studies have also demonstrated dose-related crystal deposition in the renal tract in kidneys in animals. Understanding that, suggests a mechanism contributing to the rise in serum creatinine. It is likely to be a physical one, where crystals form in the urine, in the kidney, when urine concentration of the drug reaches a threshold level.
The crystals cause an inflammatory response with resulting damage to the kidney cells. This would explain how kidney function is affected, and why a rise in serum creatinine is observed with BCX9930 at 500 milligrams. It could further explain why it is happening only in some patients and at the 500-milligram dose level, when intrarenal drug levels exceed a threshold for crystal formation.
This mechanism of injury is avoidable. We believe that the key is to avoiding risk of adverse kidney effects are to reduce the load of drug excretion by lowering the dose and to maintain more dilute urine to further lower the concentration of excreted drug by encouraging adequate fluid intake, especially at the time of drug administration. That dose reduction, together with the dilution effect of hydration, is designed to maintain adequate levels of the drug circulating in the blood for efficacy while reducing the concentration on elimination in the kidney to avoid crystal formation.
Of course, we also need to maintain strong clinical efficacy. As a reminder, the data from our Phase I PNH program supports studying 400 milligram twice daily. When C5 inhibitor-naive patients were taking this dose 400 milligrams in the Phase I program, the hemoglobin rose from baseline by a robust amount, a mean of 4.3 grams per deciliter, and no transfusions were required. This clinical observation was consistent with our PK/PD work showing that 400 milligrams twice daily provided plasma levels above the exposure needed to achieve near complete inhibition of the alternative pathway of complement.
Given that evidence, we believe that 400 milligrams twice daily will achieve similar efficacy results to those we saw in Phase I.
So what comes next? If we are correct in our hypothesis, and if the steps we are taking are the right ones to resolve the elevation in serum creatinine while maintaining strong clinical efficacy, we will be able to confirm this in the clinic.
Our next steps are to lower the dose for patients already on study. While in parallel, we reopened the studies to enrollment. To do this, we will proceed with regulatory submissions for the amended protocols in the REDEEM clinical trials. We've included simple hydration instructions for all patients. And for new patients, we've included a revised regimen to get the 400-milligram dose level with a short initial step up in dose.
We are also amending the RENEW trial with similar measures and initiating the steps to reopen to enrollment at the 400-milligram dose in that trial. In terms of testing our hypothesis, we will assess patients in the first months of reopening enrollment in the REDEEM and RENEW trials. And we will observe patient outcomes closely to determine if the data on safety at 400 milligrams supports continuing to invest through the completion of the pivotal studies, provided we can recruit patients in a timely manner and the initial data are supportive of safety and efficacy we'll proceed. If the data are not supportive, we will discontinue the 9930 program and redirect our efforts and investment elsewhere in our pipeline.
So how will we know this? As we resume enrollment at 400 milligrams, we'll look for absence of the early rise in serum creatinine in new patients enrolling in the study. You will recall that over the first few months of enrollment in REDEEM-1 and REDEEM-2 and in about 1/3 of the first 15 patients, we saw a rapid rise in serum creatinine at 500 milligrams. As we enroll patients at 400 milligrams, this will give us a good basis for comparison to inform our next step.
Let's look at it like this. If about the same small number of patients are treated without similar observations, this will build confidence that the hypothesis is correct and the protocol adjustments are sufficient to address it. By monitoring for serum creatinine at more frequent intervals in the first 3 months, we will gather the information we need to determine if our hypothesis is correct and if our revised amendments sufficiently resolve the problem.
On an individual patient level, more frequent monitoring will allow us to identify any changes in the near term and react swiftly if warranted, both for each individual safety on trial and for any appropriate decision on continuing the program. It's clear to us that the need for better treatment options in these diseases is significant. Throughout our investigation, we have received unwavering encouragement from our investigators and patient organizations in both the hematology and nephrology communities to find a path forward for BCX9930 if there is one.
We are pleased that the FDA has removed the partial clinical hold following their review of our data, our investigation findings and our proposed protocol adjustments. Because of this high unmet need in PNH and other complement-mediated diseases and because we believe making a limited additional investment now to test this hypothesis is warranted by the potential value if the program is successful.
We continue to pursue our goal of bringing a safe and effective Factor D inhibitor to the market for these patients. We are working hard to achieve this goal, and we will make the decisions on where to invest in our pipeline based on sound evidence and where we can create the most value.
Now I'll hand the call back to Jon.