CHICAGO (FRONTLINE MEDICAL NEWS) – Combining two immunotherapies, one inhibiting immune suppression and the other stimulating immune activation, is well tolerated and shows activity for a variety of solid tumor types, according to a phase I trial presented at the annual meeting of the American Association of Clinical Oncology.

Investigators enrolled 51 patients with locally advanced or metastatic solid tumors of any type after progression on standard therapy to a phase Ib dose-escalation study using atezolizumab, a monoclonal antibody checkpoint inhibitor that targets PD-L1, in combination with MOXR0916 (MOXR), an agonist IgG1 monoclonal antibody targeting OX40, a costimulatory receptor. Atezolizumab received Food and Drug Administration approval in May 2016 for use in certain patients with urothelial carcinoma. There were 28 patients in a dose-escalation cohort of the study and 23 in a serial biopsy cohort. The dose of the drug combination was started at 12 mg and escalated to understand pharmacodynamic changes in the tumors.

“The pharmacokinetics of both MOXR0916 and atezolizumab were similar to their single-agent data, suggesting no interaction,” reported Dr. Jeffrey Infante of the Sarah Cannon Research Institute in Nashville, Tenn.

The drug combination was well tolerated through the entire escalation range of MOXR. There were no dose-limiting toxicities, and no maximal tolerated dose was reached. There were also no drug-related deaths or grade 4 toxicities or drug-related treatment discontinuations. One case of grade 3 pneumonitis, successfully managed with methylprednisolone and antibiotics, occurred at the MOXR 40-mg dose on cycle 4 of treatment in a patient with non–small-cell lung cancer, he said.

About half the patients (53%) experienced any form of adverse event on the drug combination, and only 8% were grade 2 or 3. There were very few adverse events of any one type, and they did not appear to cluster among patients on the higher MOXR doses. The most prevalent adverse events were nausea, fever, fatigue, and rash, and each was in the 8%-14% range and almost always grade 1.

Many patients showed efficacy of the regimens out to 6-7 cycles regardless of tumor type, and 8 of the 51 patients were still receiving the therapy past cycle 7 with partial responses.

The stimulatory molecule OX40 is not normally expressed on T cells, but it is expressed when antigen interacts with the T-cell receptor, and it can then interact with its ligand, OX40L. The result is production of inflammatory cytokines such as gamma-interferon, activation and survival of effector T cells, and production of memory T cells. At the same time, OX40 activity blocks the suppressive function of regulatory T cells.

“So a molecule that can be a cancer therapeutic such as an OX40 agonist has dual mechanisms of action,” Dr. Infante said. “It can costimulate effector T cells and at the same time inhibit regulatory T cells. Furthermore, there is a reduced risk of toxicity, potentially, as its activity is linked to antigen recognition.”

There is good rationale for using an OX40 agonist such as MOXR, either for its immune stimulatory function or to deactivate immune suppression by regulatory T cells, or both, said discussant Dr. Jedd Wolchok, chief, melanoma and immunotherapeutics service, Memorial Sloan-Kettering Cancer Center, New York. Dr. Infante’s dose-escalation study was “very nicely designed and showed quite good safety,” Dr. Wolchok said, though one thing he would have liked to have seen was a quantification of regulatory T cells in tumor biopsies.

“This [study] is very important considering that this is an agonist antibody, and the agonist agents need to be dosed very deliberatively, as was done here, to ensure safety of patients,” Dr. Wolchok said, adding that further research needs to target “optimal combinatorial partners” and explore other mechanistic biomarkers.

MOXR was given in this trial at escalating doses on a 3+3 design (0.8-1,200 mg) on the same day as atezolizumab 1,200 mg IV once every 3 weeks with a 21-day window for assessment of MOXR dose-limiting toxicities. MOXR doses of 300 mg maintained trough concentrations sufficient to saturate OX40 receptors. An expansion regimen using 300 mg MOXR with atezolizumab 1,200 mg every 3 weeks is underway and will assess efficacy in the treatment of melanoma, renal cell carcinoma, non–small-cell lung cancer, urothelial carcinoma, and triple-negative breast cancer.

The study was sponsored by Roche. Dr. Infante reported having no relevant financial disclosures. Dr. Wolchok owns stock in Potenza Therapeutics and Vesuvius Pharmaceuticals, has received travel expenses and/or has an advisory role with several other companies, and is a coinventor on an issued patent for DNA vaccines for the treatment of cancer in companion animals.