WASHINGTON – An investigational, oral, small molecule designed to boost innate antiviral immunity safely cut the incidence of various viral respiratory infections in elderly people during a winter season by nearly a third when administered once daily in a placebo-controlled, multicenter, phase 2 study of 952 patients. Based on these and other findings the drug, RTB101, is now undergoing testing in a phase 3 study, Joan Mannick, MD, said at an annual scientific meeting on infectious diseases.
Mitchel L. Zoler/MDedge News
Dr. Joan Mannick
At a dosage of 10 mg once daily, RTB101 was “well tolerated, upregulated innate antiviral gene expression, and reduced the incidence” of laboratory-confirmed respiratory tract infections caused by several different viruses, said Dr. Mannick, who disclosed that she is a cofounder and chief medical officer of resTORbio, a Boston-based company that’s developing the drug.
During 16 weeks of treatment during the winter virus season, once-daily dosing led to cuts in the rates of respiratory infections compared with placebo by rhinovirus and enterovirus, respiratory syncytial virus, coronavirus, influenza virus, metapneuomovirus, and parainfluenza virus, especially in patients whom the results identified as having the best drug responses: those who were at least 85 years old, and those who were at least 65 years old and also had asthma. Enrolled patients who were at least 65 years old and had other risk factors – current smoking, chronic obstructive pulmonary disease, or diabetes – had notably less robust responses to treatment, and the phase 3 study is not enrolling elderly people who currently smoke or have chronic obstructive pulmonary disease, Dr. Mannick said in an interview.
RTB101 inhibits the active site of the “mechanistic target of rapamycin” (mTOR) protein, the key player of the TORC1 protein complex that appears to downregulate innate antiviral immunity when active. Hence inhibiting mTOR and TORC1 activity should boost innate antiviral immunity. Once-daily dosing with 10 mg of RTB101 appears to mimic the normal daily cycle of high and low levels of TORC1 activity seen in younger adults but which is missing the elderly who generally have persistently elevated levels of TORC1 activity, Dr. Mannick explained.
The study she reported enrolled a total of 952 people at any of 10 sites in the Southern Hemisphere or 17 Northern Hemisphere study sites. The researchers randomized patients to receive either RTB101 or placebo at either of two once-daily dosages or either of two twice-daily regimens. The best drug performance was among the 356 patients treated with 10 mg once daily or placebo. Those who received the active drug at this level had a 19% incidence of any laboratory-confirmed respiratory tract infection, while those who received placebo had a 28% incidence, a 30.6% relative risk reduction with RTB101 treatment that was statistically significant.
The actively-treated patients showed upregulation for 19 of 20 “antiviral” genes assessed in the study compared with upregulation of just five of these genes in the those who received placebo. Two post hoc analyses showed that the people who received 10 mg once daily had about half the rate of all-cause hospitalizations compared with those on placebo, and among those who had respiratory infections treated patients had alleviation of their moderate or severe symptoms in about half the time compared with patients on placebo.
The 10-mg daily dosage of RTB101 is less than 1% of the maximum-tolerated dose in people, and the safety data collected in the current study showed adverse events occurring at similar rates in the patients who received the active drug and those who got placebo. Discontinuations because of adverse events occurred in 5% of people who received RTB101 and in 6% of those on placebo.
The researchers are planning to run a cost-effectiveness study to see whether the observed prevention of respiratory tract infections and their consequences can offset the cost of taking RTB101 daily for 16 weeks, Dr. Mannick said.