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When the first reports emerged of "cytokine storm" in patients with severe COVID-19, all eyes turned to cancer research. Oncologists have years of experience reigning in "cytokine release syndrome" (CRS) in patients treated with chimeric antigen receptor (CAR) therapies for advanced blood cancers.
There was hope that drugs used to quell CRS in patients with cancer would be effective in patients with severe COVID. But the promise of a quick fix with oncology medications has yet to be fully realized.
Part of the problem is that the two conditions, while analogous, are "not the same," said Nirali Shah, MD, head of the hematologic malignancies section in the pediatric oncology branch at the National Cancer Institute.
"You have to understand the underlying pathophysiology, what triggers the inflammation," Shah said.
CAR T-related CRS is caused by activated T cells in patients with cancer who often do not have an infection, she explained. In contrast, cytokine storm in COVID-19 is triggered by a viral pathogen that can drive "out of control" inflammation. These differences may explain why drugs work in the first instance, but not in the second, she added.
Drugs that inhibit interleukin-6 (such as tocilizumab, sarilumab, and siltuximab) are used with great success to dampen down the CRS in patients receiving CAR therapy for blood cancers. And although trials of these agents in patients with COVID are still ongoing, initial results are disappointing.
The first global, phase 3 randomized controlled trial of tocilizumab in severe COVID-19 failed to meet its primary endpoint of improved clinical status, and it did not meet its secondary endpoint of improved mortality at week 4.
In its recent recommendations, the NIH noted a lack of data to support the efficacy of IL-6 inhibitors in COVID-19, and recommended against their use, except as part of a clinical trial.
Trimming the Tree vs Cutting It Down
As researchers have begun to decode the immune process underlying severe COVID-19, they have turned to other cancer drugs to tame cytokine storm.
For years, the pair have been studying lymphoid tumors. Staudt is chief of the lymphoid malignancies branch at the NCI, and Wilson is head of the lymphoma therapeutics section. In past work, Staudt discovered that inhibiting an enzyme called bruton tyrosine kinase (BTK) dampens macrophage function.
When the pandemic began, Staudt and Wilson realized that singling out just one cytokine like IL-6 may not be enough. They thought that a more effective approach may be to target macrophages with a BTK inhibitor called acalabrutinib (Calquence), which would inhibit multiple cytokines at the same time.
Staudt likens the immune response to a tree, with the macrophages composing the tree trunk and the limbs made up of individual cytokines.
"Targeting macrophages is getting at the trunk of the problem," he said. "You're only cutting off the limbs with tocilizumab."
In just 3 days, Staudt and Wilson went from concept to approval to launching a prospective, observational study. The study took place at five centers in the US, and included 19 patients hospitalized with COVID-19; the results were published in Science Immunology. Over a treatment course of 14 days, the majority of patients treated off-label with acalabrutinib improved, some within 24 hours. Eight of 11 patients on supplemental oxygen were discharged on room air. Four of eight patients on ventilators were extubated, with two of these discharged on room air. Two patients on ventilators died. No discernible toxicity was noted.
Analyses also showed increased BTK activity and elevated IL-6 levels in monocytes — precursors of macrophages — in patients with severe COVID-19, compared with healthy volunteers.
"We showed that the target of acalabrutinib was active in the immune cells of patients with severe COVID-19," Staudt said. "So we have the target. We have the drug to hit the target. And we have an apparent clinical benefit."
Those three things were compelling enough to launch the CALAVI phase 2 trial, an open-label randomized controlled trial, sponsored by AstraZeneca and the NCI, that is being conducted in the US and internationally. It is testing acalabrutinib with best supportive care (BSC) vs BSC alone in people hospitalized with COVID-19. The trial is scheduled to be completed on November 26.
Preliminary insights from this trial are expected soon. "These are not insights that we will likely publish, but they are important insights that will lead to the launch of a definitive double-blind randomized phase 3 trial, which we hope to launch in the next month or so," Wilson said.
Targeting Inflammation and Infection Simultaneously
Other scientists are investigating inhibitors of janus kinase (JAK), a family of enzymes that play a key role in orchestrating immune responses, particularly cytokines. Interest in JAK inhibition to control hyperinflammation in cancer goes back at least 15 years, and drugs that act as JAK inhibitors are already approved for use in the treatment of myelofibrosis (ruxolitinib [Jakafi], fedratinib [Inrebic]) and also for rheumatoid arthritis (upadacitinib [Rinvoq], baricitinib [Olumiant].
"It wasn't a huge leap for those of us with a lot of understanding of JAK inhibitors to propose taking them into the clinic to treat patients with COVID-19," commented John Mascarenhas, MD, the leader of clinical investigation in the myeloproliferative disorders program at the Icahn School of Medicine at Mount Sinai in New York City.
Mascarenhas is also principal investigator of the PRE-VENT trial, which is comparing the investigational JAK2 inhibitor pacritinib plus standard of care to standard of care alone in patients hospitalized with severe COVID-19, with and without cancer. The trial is sponsored by CTI BioPharma (manufacturer of pacritinib), and is taking place at 10 sites in the US.
In a move that may raise eyebrows, PRE-VENT skipped phase 1 and 2 and went straight to phase 3. Pacritinib has yet to receive FDA approval and has mostly been studied in myelofibrosis, an intensely inflammatory disease.
The decision was based on trials of pacritinib in hematologic malignancies and also on results from a phase 2 study in China that found possible clinical benefit for the JAK 1/2 inhibitor ruxolitinib in 43 patients hospitalized with severe COVID-19, although results were not statistically significant, Mascarenhas explained.
Recent results from Lilly's ACTT-2 study have provided further support for the role of JAK inhibitors in treating cytokine storm. ACTT-2 is a phase 3 double-blind placebo-controlled RCT sponsored by the NIH and NIAID comparing the JAK 1/2 inhibitor baricitinib plus the antiviral remdesivir to remdesivir alone in patients hospitalized with COVID-19. In September, Lilly announced that the trial met its primary endpoint of decreased time to recovery in patients who received baricitinib in combination with remdesivir.
But pacritinib's mechanism of action may take things a step further. The drug selectively inhibits JAK2 and spares JAK1, which is important for antiviral activity in the immune system. Also, in vitro data suggests pacritinib may simultaneously reduce inflammation and fight off the virus by selectively inhibiting two additional enzymes and two other receptors.
"The rationale to me is very strong for using pacritinib," Mascarenhas said. "I think this approach was bold but appropriate."
The main safety concern with pacritinib could be bleeding, especially among patients on anticoagulants, Mascarenhas said. Because some patients with severe COVID-19 tend to develop blood clots, anticoagulation has become the standard of care at many institutions.
Because the trial is just beginning — only a minority of the total planned population of 358 patients has been enrolled — no interim results are available.
Right Drug, Wrong Time?
IL-6 inhibition could still have a role to play in COVID-19, but the trick could be in the timing. Most of the trials so far have studied tocilizumab in patients with severe COVID-19, many of whom were already on ventilators. At that point, it may be too late to reverse the damage that has already taken place.
One of the main reasons tocilizumab works so well in CRS after CAR T therapy is that oncologists have learned how to use it early, often within 24 hours of fever onset. Oncologists use the American Society for Transplantation and Cellular Therapy (ASTCT) consensus grading system, which helps them identify CRS when it is easier to control.
But applying the ASTCT grading system to COVID-19 is problematic. "Almost by definition, patients hospitalized with COVID-19 have low oxygen levels, which throws off the scale," said Joshua Hill, MD, an infectious disease specialist at Fred Hutchinson Cancer Research Center in Seattle, Washington, who has research expertise in infectious complications after CAR T therapy.
"The key is to intervene earlier to prevent damage to the lungs and other end organs. We don't have anything magical that will reverse that damage," Hill said.
Results from the phase 3 trial EMPACTA trial (sponsored by Genentech) seem to bear this out. EMPACTA is evaluating use of tocilizumab in hospitalized patients with less severe COVID-19 who do not yet require mechanical ventilation. The trial is notable for being the first global phase 3 trial to demonstrate efficacy for tocilizumab vs placebo in hospitalized patients with COVID-19 pneumonia, and for including a high percentage of racial/ethnic minorities (85% of 389 participants), who have been hard hit by the pandemic and have historically been underrepresented in drug trials.
Last month, Roche announced that EMPACTA met its primary endpoint. Results showed that patients hospitalized with COVID-19 pneumonia who received tocilizumab plus standard of care were 44% less likely to go on mechanical ventilation or die, compared with those who received placebo plus standard of care (P = .0348), although there were no statistically significant differences in death by day 28 between tocilizumab and placebo (10.4% vs 8.6%, P = .5146).
However, earlier administration of tocilizumab raises another issue. IL-6 and its pathway are important for clearing viral infections. Using tocilizumab in the context of an ongoing infection could raise safety issues.
Also, tocilizumab sticks around in the body for a relatively long time. In the treatment of rheumatoid arthritis, it is dosed once a month, and it carries a black box warning for reactivation of tuberculosis.
Whereas results from EMPACTA showed similar rates of infection associated with tocilizumab and placebo (10% vs 11%), at least one other study has found increased rates of superinfection in patients with severe COVID-19 who received tocilizumab. Overall, though, the drug was associated with decreased risk of death in the latter study.
A phase 2 trial called COVIDOSE is tackling the safety issue. COVIDOSE is evaluating whether low-dose tocilizumab is effective in noncritical COVID-19 patients, with the idea that lower doses could be safer. Early results published as a preprint before peer review indicated that low-dose tocilizumab (ranging from 40 mg to 200 mg) was associated with clinical improvement in 32 noncritical patients hospitalized with COVID-19.
Five patients (15.6%) developed bacterial superinfections, and five (15.6%) died by 28-day follow-up, although there wasn't a perfect "overlap" between these groups of patients. Bacterial superinfection was not the cause of death in all five patients who died, and not all patients who died developed bacterial superinfections, according to senior author Pankti Reid, MD, MPH, who commented via email. Reid is an assistant professor of medicine at The University of Chicago.
Results from COVIDOSE also showed that treatment with tocilizumab did not seem to affect the ability of patients to develop antibodies against COVID-19. The results set the stage for a larger randomized controlled trial (still ongoing) to determine the optimal dose of tocilizumab.
Still, Hutchinson Cancer Center's Hill urges caution.
Many of these immunomodulators have been used only in the context of a clinical trial, or only for patients with terminal cancer and no other treatment options. In patients with cancer, these drugs have been studied and have shown an "acceptable safety profile," according to the NCI's Shah.
But this is a different situation, and when it comes to repurposing them to relatively healthy patients with COVID-19, Hill emphasized the need for careful research.
"We're always very concerned about giving drugs that suppress the immune response if people have active infections," Hill said.
"Often times we think it makes things worse, and it typically does," he cautioned.
Mascarenhas reports institutional research funding from CTI Biopharma.
Hill, Staudt, Wilson, and Shah have disclosed no relevant financial relationships.
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Cite this: Cancer Researchers Cross Over to COVID-19 Clinical Trials - Medscape - Oct 13, 2020.