Twincretin Meets Primary Endpoints in Pivotal Diabetes Trials

Mitchel L. Zoler, PhD

June 14, 2021

The investigational, novel, injected once-weekly "twincretin" tirzepatide met its primary efficacy endpoint of significantly cutting hemoglobin A1c as well as its secondary weight-loss endpoint in patients with type 2 diabetes when compared with control patients in top-line results from each of five discrete pivotal trials.

The company developing tirzepatide, Lilly, announced these results in a series of four press releases issued during December 2020–May 2021. Scientific reports on the outcomes from four of these trials are scheduled during the American Diabetes Association's Scientific Sessions being held virtually in late June 2021, with results from the fifth on track for a report during the annual meeting of the European Association for the Study of Diabetes in September 2021.

Tirzepatide is a "twincretin" because it combines in a single molecule two different gut-hormone activities. It works as both a glucagonlike peptide–1 receptor agonist (GLP-1 RA) and as an agent that mimics the glucose-dependent insulinotropic polypeptide (GIP).

While diabetologists qualified their comments on these results because of the limited scope and format of the five reports to date, they also expressed enthusiasm over what the press releases said.

Results Give Hope

"It's quite exciting, but of course we would like to go by the data that's presented" at upcoming meetings, commented Robert A. Gabbay, MD, PhD, chief science and medical officer of the American Diabetes Association in Arlington, Va. "The idea of GLP-1 and GIP activities working together has been out there for a while, but without any therapeutic options that leverage this," he said in an interview.

Dr Robert Gabbay

"The preliminary results give us hope that tirzepatide will be a very effective glucose-lowering agent, perhaps the most effective among all options currently available, including insulin," commented Ildiko Lingvay, MD, a diabetologist and professor at the University of Texas Southwestern Medical Center, Dallas.

Dr Ildiko Lingvay

"Tirzepatide might have the added benefit of clinically meaningful weight loss," and "the adverse event profile seems to be in line with what we are accustomed to with the GLP-1 RA class. I look forward to seeing the full results. Tirzepatide promises to be a great addition for type 2 diabetes," Lingvay said in an interview.

A Rare Head-to-Head Against Semaglutide

The five phase 3, randomized controlled trials described by Lilly in its four press releases all belong to the SURPASS series of studies for this agent. Perhaps the most intriguing of the five were results from SURPASS-2, announced in a release on March 4. This trial randomized 1,879 patients from the United States or any of seven other countries to 40 weeks of open-label treatment with one of three different dosages of tirzepatide administered by injection once weekly, or to the control group that received a weekly 1-mg injection of semaglutide (Ozempic), the highest dosage approved for controlling glycemia in patients with type 2 diabetes at the time the study launched.

In SURPASS-2 all three tested dosages of tirzepatide led to a significantly larger reduction, from baseline in A1c, compared with semaglutide, after 40 weeks, according to the Lilly release. Each of the three tirzepatide dosages also led to significantly greater weight loss from baseline, compared with semaglutide, and significantly greater percentages of patients who achieved an A1c of less than 7%, compared with semaglutide.

As an example, the highest tested tirzepatide dosage of 15 mg weekly led to an average A1c reduction from baseline of 2.46% and an average weight loss from baseline of 12.4 kg; 92% of patients achieved an A1c of less than 7%, and 51% had their A1c fall below 5.7% which indicates completely normalization of glycemic control. By comparison, the patients randomized to treatment with semaglutide had an average 1.86% reduction in their A1c level from baseline and a 6.2-kg average cut in body weight from baseline; 81% achieved an A1c of less than 7%, and 20% reached an A1c of less than 5.7%.

There Are Caveats

While these findings are notable as a rare example of an industry-sponsored head-to-head comparison of two new agents, the study comes with a few important asterisks.

First, it was open label, a curious limitation given that both agents are delivered by the same delivery method and schedule. "I cannot conclude based on this study that tirzepatide is superior because it was open label," commented Anastassia Amaro, MD, medical director of Penn Metabolic Medicine at the University of Pennsylvania, Philadelphia.

"The gold standard is the double-blind study. An open-label design is a limitation," agreed Gabbay.

A second caveat is that the Food and Drug Administration recently approved a higher dosage of semaglutide (2.4 g once/week) for treating overweight or obesity in patients with type 2 diabetes and in those without diabetes but a different weight-related condition such as hypertension of hypercholesterolemia. This means that the tested comparator dosage of 1 mg/week is no longer the maximum that most patients treated with semaglutide for glycemic control can receive.

"The inevitable question" about this comparison study is "what about a higher semaglutide dose," and how might tirzepatide perform relative to that, said Gabbay. The recently approved higher dosage of semaglutide "adds an interesting wrinkle."

Lilly has launched a series of studies testing tirzepatide as a treatment for overweight or obesity in people without diabetes, but the results are not expected until sometime in 2022 or 2023.

And there's a third caveat: Semaglutide has already shown its value for cardiovascular risk reduction in patients with type 2 diabetes in the SUSTAIN 6 trial with nearly 3,300 randomized patients followed for 2 years and reported in 2016. The cardiovascular outcomes trial for tirzepatide, SURPASS-CVOT with more than 12,000 patients with type 2 diabetes, is underway but its results are not expected until 2024.

Despite these important limitations, a blinded comparison of tirzepatide and higher-dose semaglutide is unlikely, Amaro predicted. "It's not worth the expense," she said in an interview. A more likely scenario will be that, if tirzepatide enters the U.S. market, decisions on whether to treat patients with it or semaglutide will pivot on factors like the cost for treatment to individual patients based on their insurance coverage and tolerability, suggested both Amaro and Gabbay. "Physicians will need to develop a sense for tirzepatide: Do patients tolerate it and are they happy using it?" Amaro said.

Tirzepatide vs Insulin, or on Top of Insulin

The other four trials in patients with type 2 diabetes reported by Lilly in releases included SURPASS-1, which randomized 478 patients to treatment with tirzepatide or placebo as monotherapy; SURPASS-3, which randomized 1,444 patients to tirzepatide or insulin degludec (Tresiba) on top of background treatment with metformin; SURPASS-4, which randomized 2,002 patients with high cardiovascular disease risk to treatment with tirzepatide or insulin glargine (Lantus) on top of background treatment with one to three different oral drugs; and SURPASS-5, which randomized 475 patients to treatment with tirzepatide or placebo on top of background treatment with insulin glargine and optional addition of metformin. Altogether, the five trials randomized nearly 6,300 patients.

The studies that compared tirzepatide against two different types of insulin, and the third that tested tirzepatide on top of insulin glargine, are especially notable. "It's good to see that the combination [of tirzepatide and insulin glargine] works without causing major adverse events," said Amaro.

"These are fair and helpful comparisons. I applaud Lilly for doing the right kind of comparisons," said Gabbay.

In total, the five studies "provide evidence that tirzepatide will be effective at all stages of type 2 diabetes and can safely be used in combination with other glucose-lowering agents, including insulin," said Lingvay. The studies with active comparator agents "allow us to compare tirzepatide's efficacy against established therapies."

The SURPASS trials were sponsored by Lilly, which is developing tirzepatide. Gabbay had no relevant disclosures. Lingvay has received research funds, consulting and advisory fees, or other support from Lilly as well as from several other companies including Novo Nordisk, which markets semaglutide (Ozempic) and insulin degludec (Tresiba), and Sanofi, which markets insulin glargine (Lantus). Amaro has received research funding from Lilly and from Fractyl, and has been a consultant to and received research funding from Novo Nordisk.

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