Inhibitor drug 'primes' the body for anticancer immunotherapy

Combining a histone deacetylase inhibitor drug with immunotherapy agents is safe and may benefit some patients with advanced cancers that have not responded to traditional therapy, according to a Phase 1 clinical trial conducted by US researchers and published in the journal Clinical Cancer Research.

During the study, 33 patients with advanced solid tumours received the histone deacetylase inhibitor drug entinostat for two weeks. Then some patients received the immunotherapy agent nivolumab, a checkpoint inhibitor, in combination with the entinostat, while others received both nivolumab and a second checkpoint inhibitor agent, ipilimumab, after the initial dosing with entinostat.

Checkpoint inhibitors, such as nivolumab and ipilimumab, release important ‘brakes’ that permit the immune system to fight the cancer cells. Meanwhile, the epigenetic inhibitor drug entinostat has been shown in preclinical models and laboratory studies (which led to this current clinical trial) to drive changes in the chemical environment of cells to make them more amenable to immunotherapy. Study co-author Evanthia T Roussos Torres, an adjunct professor at Johns Hopkins University and assistant professor at the University of Southern California, said entinostat functioned as an immune system-priming agent prior to using immunotherapy in solid tumours that traditionally are nonresponsive to checkpoint inhibition therapy.

The study’s objective response rate, or percentage of patients whose cancer responded to therapy, was 16%. One patient with triple-negative breast cancer had a complete response, meaning a total shrinkage of the cancer. The median progression-free survival, or time until disease progression or death, was 6.1 months, and median overall survival was 10.6 months. Stable disease, considered the best response, was observed in 44% of participants. Clinical benefit rate, or the percentage of patients who achieved stable disease, or partial or complete response, was 60%.

Because the cancer types included in the study are not felt to have high response rates to immune checkpoint therapy, these preliminary results are very promising. Treatment-related adverse events were mostly low grade, and included fatigue, nausea, anaemia and diarrhoea.

“One of the major findings of our study is that this is a safe and tolerable combination of therapies,” Prof Roussos Torres said. “There aren’t very many trials investigating dual immune checkpoint inhibition in combination with other novel therapeutics. We determined a safe, tolerable dose with this combination that had very few adverse effects. That is significant.”

The researchers collected blood and tumour samples from patients before and after the two weeks of entinostat to assess the impact of the entinostat on the immune system, and also after the addition of the immune checkpoint agents to evaluate the effect of each of the treatments on the immune environment. The study team found a significant increase in the ratio of CD8/FoxP3 gene expression in tumours following checkpoint inhibitor treatment but not after entinostat treatment alone. This suggests that the combination therapy helped increase both cytotoxic immune system T cells — immune cells that directly kill cancer cell — as well as decrease immune system T regulatory cells — immune cells that modulate the immune response — which equalled a stronger immune response, Prof Roussos Torres said.

The most robust increases in CD8/FoxP3 ratio were observed in two patients with HR-positive breast cancer who experienced a partial response and stable disease. Three additional patients who experienced stable disease had adenocarcinoma, a cancer of glandular tissue.

The complete response in a patient with breast cancer was described as “a promise that there may be a role for this combination of therapies in breast cancers”, said senior study author Roisin M Connolly, an adjunct professor at Johns Hopkins and Chair in Cancer Research at University College Cork and Cork University Hospital.

“Immunotherapy hasn’t been as big a blockbuster to date in advanced breast cancer as in other cancers, such as lung cancers or melanoma,” Prof Connolly said. “This study paves the way for novel combination therapies that have the potential to improve response rates to immune checkpoint inhibitors in traditionally less-responsive tumour types.”

This drug combination is being investigated further in a group of 24 patients with HER2-negative breast cancer. Dr Vered Stearns, Director of the Women’s Malignancies Disease Group at Johns Hopkins’ Sidney Kimmel Comprehensive Cancer Center, said, “We are excited to have completed accrual to these ongoing studies in advanced HER2-negative breast cancer, and expect to report on these findings later this year.”

Image credit: ©stock.adobe.com/au/royaltystockphoto

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