Roy S. Herbst, MD, PhD
An antibody that targets the programmed death ligand 1 (PD-L1) to unleash the body’s immune system has demonstrated a 21% response rate in a phase I study of patients with multiple solid tumors, setting the stage for an advance in immunotherapy with broad implications for treatment.
MPDL3280A produced durable responses with no dose-limiting toxicities and a favorable adverse event profile in heavily pretreated patients, according to Roy S. Herbst, MD, PhD, a professor of Medicine at Yale Cancer Center and chief of Medical Oncology at Smilow Cancer Hospital at Yale-New Haven in Connecticut.
“This therapy has the potential to be used in almost every tumor type,” Herbst said in an interview. “It’s just the tip of the iceberg so far. We’re still figuring out exactly what the right biomarker is going to be to predict the most responsive population.”
Herbst previewed the findings during a press conference Wednesday in advance of the Annual Meeting of the American Society of Clinical Oncology (ASCO), scheduled for May 31-June 4 in Chicago, where full data will be presented.
In the study, MPDL3280A was administered intravenously every 3 weeks to patients with metastatic tumor types including non-small cell lung cancer (NSCLC), melanoma, colorectal cancer, gastric cancer, and renal cell carcinoma. Responses were assessed with computed tomography scans every 6 weeks for 6 months and then every 12 weeks.
In all, 29 of 140 evaluable patients (21%) exhibited tumor shrinkage according to RECIST criteria, with the highest overall responses in patients with NSCLC and melanoma. Of the 29 responders, 26 patients continued responding as of their last assessment. Responders were on the study from 3 months to more than 15 months.
In a biomarker analysis, responses were better among patients with higher levels of PD-L1 expression. The response rate among PD-L1-positive patients was 36% (13 of 36 patients), compared with 13% (9 of 67 patients) who were PD-L1-negative.
The role that PD-L1 expression might play as a biomarker is still being explored, Herbst said. Methods of measuring the protein, the nature of the tumor samples used to analyze its expression, and the levels that would predict a response to therapy are among the questions that remain unanswered.
For the safety analysis, results were available for 171 patients. A total of 43% of patients experienced grade 3/4 adverse events (AEs), most commonly hyperglycemia (5%), fatigue (4%) and increased alanine aminotransferase levels (3%). However, investigators determined that 13% of the grade 3/4 AEs were attributable to the drug, and there were no treatment-related deaths, Herbst said.
Moreover, only 2% of the participants (4 patients) experienced grade 3/4 AEs that were deemed to be immune-related, and only one patient discontinued treatment because of an immune-related AE.
“We didn’t see any high-grade pneumonitis, which makes us feel very optimistic that this drug, because it’s hitting only the PD-L1, is probably sparing some of the mechanisms that would allow for the lung to become inflamed,” Herbst said in the interview.” We saw a couple episodes of hepatitis and liver inflammation but really, it’s a very mild toxicity profile.”
Findings Generate Excitement
MPDL3280A is the latest example of the checkpoint blockade anticancer strategy pioneered with the development of ipilimumab (Yervoy), which unlocks the power of the immune system by targeting CTLA-4. The FDA approved the melanoma drug in 2011.
One of the highlights of the ASCO meeting last year was research into BMS-936558, now called nivolumab, which targets PD-1. Research into the agent also will be presented at this year’s meeting.
Herbst said the efficacy demonstrated thus far in attacking PD-L1 and other immune checkpoints “gives us the opportunity to open up a whole new avenue of therapy in cancer.”
Tumor cells express PD-L1, which in turn binds to the T-cell receptors PD-1 and B7.1, Herbst said. “As long as there’s PD-L1 on the surface of the tumor, the T cell PD-1 sees it as a friend,” he said. “It is cloaked and it doesn’t recognize the tumor as a foreign body and it doesn’t kill it. But as soon as that PD-L1 goes away—by blocking it with an antibody—the tumor becomes visible, the target can be lit up, you go after it, and the T cell attacks and kills it.”
Herbst said the therapeutic strategy could apply to a variety of cancers. “Any tumor type that has mutations is going to have the potential to be immunogenic and to work in this way to activate the immune system,” he said, adding that “a lot of patients don’t have a driver mutation that’s easily targetable.”