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Despite their similar functions, each current and emerging therapy for treating hemophilia has a unique safety profile, and each needs to be weighed apart from agents both within and outside its pharmacologic class, a hemophilia specialist said.
“My view is that each new molecule coming to the hemophilia space, including variant factor molecules, needs to be scrutinized separately, without class assumptions or extrapolations, and it’s clear that thrombosis risk has become a priority safety consideration,” said Dan Hart, MBChB, MRCP, FRCPath, PhD, from Barts and the London School of Medicine and Dentistry.
He reviewed the comparative safety of standard and novel therapies for hemophilia at the annual congress of the European Association for Haemophilia and Allied Disorders.
Factor inhibitors
Inhibitors occur in both hemophilia A and hemophilia B, and are primarily seen in patients with childhood exposure to factor concentrates. Inhibitors, which include anti–factor VIII and factor IX alloantibodies, are more common among patients with severe hemophilia and those with more disruptive factor VIII and factor IX mutations.
“There can be transient vs. persistent inhibitors, and arguably the more you look, the more you find, but clinically we never miss high-titer inhibitors that have a big impact on individuals and the subsequent decisions about management,” he said.
Hamster vs. human
It’s currently unclear whether there is an immunologic advantage for previously untreated patients to be started on factor VIII concentrates derived from recombinant human cells lines, or from products derived from Chinese hamster ovary (CHO) or baby hamster kidney (BHK) cell lines, Dr. Hart said.
“We need to ensure that we’re not selective about comparator choice for new products in the absence of head-to-head studies,” he said.
Route of administration matters
Inhibitors appear to be a more common occurrence among patients who received factor concentrates subcutaneously, compared with intravenously, Dr. Hart noted, pointing to a 2011 study indicating a background annual risk of 5 cases of inhibitor development per 1,000 treatment years in previously treated patients who received intravenous therapy (Blood. 2011 Jun 9;117[23]:6367-70).
In contrast, in a phase 1 trial of subcutaneous turoctocog alfa pegol, 5 out of 26 patients had detectable N8-GP–binding antibodies after 42-91 exposure days. Of these patients, one developed an inhibitor to factor VIII, and anti–N8-GP antibody appearance was associated with a decline in factor VIII plasma activity in four of the five patients. In addition, five patients reported a total of nine bleeding episodes requiring treatment during prophylaxis. As a result of this trial, further clinical development of the subcutaneous version was suspended. (J Thromb Haemost. 2020 Feb;18[2]:341-51).
Other subcutaneously administered factors are currently in development, Dr. Hart noted.
Nonfactor inhibitors?
“The nonfactor agents do have the risk of generating antibodies: Monoclonal antibodies outside the hemophilia setting provoke antidrug antibodies,” he said.
Although there is no consensus regarding which assay can best monitor antidrug antibodies (ADA), enzyme-linked immunosorbent assay (ELISA) can detect neutralizing antibodies and other antibodies.
In the hemophilia setting, surrogate markers for loss of drug efficacy include longer activated partial thromboplastin time (ATTP) or a drop in serum drug levels. Worsening bleeding phenotype can also be a marker for loss of efficacy, albeit an imperfect one.
Emicizumab (Hemlibara), the first nonfactor monoclonal agent to make it to market, has the largest dataset available, and evidence suggests a rate of neutralizing antibodies with this agent of less than 1% in the HAVEN clinical trial series, but 5.2% in the single-arm STASEY trial.
“We shouldn’t assume that other biophenotypics will have a similar ADA rate, and this needs to be evaluated for each molecule, as it will need to be for other monoclonals” such as anti–tissue factor pathway (TFPI) antibodies, Dr. Hart emphasized.
Pegylation
Pegylated compounds include polyethylene glycol, an inert polymer, covalently bound to the therapeutic protein to extend its half-life, and theoretically, reduce immunogenicity.
Many patients may already have exposure to pegylated products in the form of peginterferon to treat hepatitis C, consumer products such as toothpaste, cough medicine, and cosmetics, and, more recently, in vaccines against COVID-19.
Safety considerations with pegylated agents in hemophilia include concerns about accumulation of polyethylene glycol (PEG), although “some of the preclinical models looking at excretion of PEG are difficult to interpret in my view, and people debate about whether studies are long enough, but it’s undoubtedly the case that toxicology dosing is order of magnitude higher than the routine dosing in hemophilia,” he said.
After more than 5 years of experience with pegylated products there is no clinical evidence of concern, although “it’s not clear, actually, what we’re looking for, whether it’s a clinical parameter, or imaging or histological parameter.”
Patients may also not have lifelong exposure to pegylated products, as it is unlikely that they will stay on the same product for decades, Dr. Hart said.
Thrombosis
As of June 30, 2020, more than 7,200 persons with hemophilia have received emicizumab, and there have been 23 reported thrombotic events, 19 of which occurred in the postmarketing period. Of the reported cases, six patients had a myocardial infarction, and all of these patients had at least one cardiovascular risk factor.
The antithrombin agent fitusiran was associated with one fatal thrombotic event in a phase 2, open-label extension trial, leading to a pause and resumption with mitigation protocols, but that trial has since been paused again because of additional, nonfatal thrombotic events.
Nonfatal thrombotic events have also occurred in clinical trials for the investigational anti-TFPI monoclonal antibodies BAY 1093884 and concizumab, but none have thus far been reported in phase 3 trial of marstacimab.
“We need renewed efforts for prospective reporting and independent review of all adverse events of all agents, old and new: This will need some guidance nationally and internationally, and I think the relevant trial [serious adverse events] need to be reported in peer review literature, and clinicaltrials.gov updated in a timely manner, regardless of whether that strategy was successful or unsuccessful,” Dr. Hart said.
Risk with longer-acting agents?
In the question and answer following his presentation, Christoph Königs, MD, PhD, from University Hospital Frankfurt, asked whether there was potential for increased thrombosis risk with second-generation extended half-life (EHL) molecules in clinical trials.
“As we edge towards normalization of hemostasis, clearly the other non–hemophilia dependent issues of thrombosis risk come into play,” Dr. Hart acknowledged. “I think it will be an inevitability that there will be events, and we need to understand what the denominators are – hence my pitch for there being a renewed effort to try and collate sufficient data that we can really define events happening with people treated with standard half-life [products] through into the novel agents,” he said.
Dr. Hart disclosed grant/research support and speaker bureau activities for Bayer, Octapharma, Takeda, and others. Dr. Königs has reported no relevant disclosures.
Despite their similar functions, each current and emerging therapy for treating hemophilia has a unique safety profile, and each needs to be weighed apart from agents both within and outside its pharmacologic class, a hemophilia specialist said.
“My view is that each new molecule coming to the hemophilia space, including variant factor molecules, needs to be scrutinized separately, without class assumptions or extrapolations, and it’s clear that thrombosis risk has become a priority safety consideration,” said Dan Hart, MBChB, MRCP, FRCPath, PhD, from Barts and the London School of Medicine and Dentistry.
He reviewed the comparative safety of standard and novel therapies for hemophilia at the annual congress of the European Association for Haemophilia and Allied Disorders.
Factor inhibitors
Inhibitors occur in both hemophilia A and hemophilia B, and are primarily seen in patients with childhood exposure to factor concentrates. Inhibitors, which include anti–factor VIII and factor IX alloantibodies, are more common among patients with severe hemophilia and those with more disruptive factor VIII and factor IX mutations.
“There can be transient vs. persistent inhibitors, and arguably the more you look, the more you find, but clinically we never miss high-titer inhibitors that have a big impact on individuals and the subsequent decisions about management,” he said.
Hamster vs. human
It’s currently unclear whether there is an immunologic advantage for previously untreated patients to be started on factor VIII concentrates derived from recombinant human cells lines, or from products derived from Chinese hamster ovary (CHO) or baby hamster kidney (BHK) cell lines, Dr. Hart said.
“We need to ensure that we’re not selective about comparator choice for new products in the absence of head-to-head studies,” he said.
Route of administration matters
Inhibitors appear to be a more common occurrence among patients who received factor concentrates subcutaneously, compared with intravenously, Dr. Hart noted, pointing to a 2011 study indicating a background annual risk of 5 cases of inhibitor development per 1,000 treatment years in previously treated patients who received intravenous therapy (Blood. 2011 Jun 9;117[23]:6367-70).
In contrast, in a phase 1 trial of subcutaneous turoctocog alfa pegol, 5 out of 26 patients had detectable N8-GP–binding antibodies after 42-91 exposure days. Of these patients, one developed an inhibitor to factor VIII, and anti–N8-GP antibody appearance was associated with a decline in factor VIII plasma activity in four of the five patients. In addition, five patients reported a total of nine bleeding episodes requiring treatment during prophylaxis. As a result of this trial, further clinical development of the subcutaneous version was suspended. (J Thromb Haemost. 2020 Feb;18[2]:341-51).
Other subcutaneously administered factors are currently in development, Dr. Hart noted.
Nonfactor inhibitors?
“The nonfactor agents do have the risk of generating antibodies: Monoclonal antibodies outside the hemophilia setting provoke antidrug antibodies,” he said.
Although there is no consensus regarding which assay can best monitor antidrug antibodies (ADA), enzyme-linked immunosorbent assay (ELISA) can detect neutralizing antibodies and other antibodies.
In the hemophilia setting, surrogate markers for loss of drug efficacy include longer activated partial thromboplastin time (ATTP) or a drop in serum drug levels. Worsening bleeding phenotype can also be a marker for loss of efficacy, albeit an imperfect one.
Emicizumab (Hemlibara), the first nonfactor monoclonal agent to make it to market, has the largest dataset available, and evidence suggests a rate of neutralizing antibodies with this agent of less than 1% in the HAVEN clinical trial series, but 5.2% in the single-arm STASEY trial.
“We shouldn’t assume that other biophenotypics will have a similar ADA rate, and this needs to be evaluated for each molecule, as it will need to be for other monoclonals” such as anti–tissue factor pathway (TFPI) antibodies, Dr. Hart emphasized.
Pegylation
Pegylated compounds include polyethylene glycol, an inert polymer, covalently bound to the therapeutic protein to extend its half-life, and theoretically, reduce immunogenicity.
Many patients may already have exposure to pegylated products in the form of peginterferon to treat hepatitis C, consumer products such as toothpaste, cough medicine, and cosmetics, and, more recently, in vaccines against COVID-19.
Safety considerations with pegylated agents in hemophilia include concerns about accumulation of polyethylene glycol (PEG), although “some of the preclinical models looking at excretion of PEG are difficult to interpret in my view, and people debate about whether studies are long enough, but it’s undoubtedly the case that toxicology dosing is order of magnitude higher than the routine dosing in hemophilia,” he said.
After more than 5 years of experience with pegylated products there is no clinical evidence of concern, although “it’s not clear, actually, what we’re looking for, whether it’s a clinical parameter, or imaging or histological parameter.”
Patients may also not have lifelong exposure to pegylated products, as it is unlikely that they will stay on the same product for decades, Dr. Hart said.
Thrombosis
As of June 30, 2020, more than 7,200 persons with hemophilia have received emicizumab, and there have been 23 reported thrombotic events, 19 of which occurred in the postmarketing period. Of the reported cases, six patients had a myocardial infarction, and all of these patients had at least one cardiovascular risk factor.
The antithrombin agent fitusiran was associated with one fatal thrombotic event in a phase 2, open-label extension trial, leading to a pause and resumption with mitigation protocols, but that trial has since been paused again because of additional, nonfatal thrombotic events.
Nonfatal thrombotic events have also occurred in clinical trials for the investigational anti-TFPI monoclonal antibodies BAY 1093884 and concizumab, but none have thus far been reported in phase 3 trial of marstacimab.
“We need renewed efforts for prospective reporting and independent review of all adverse events of all agents, old and new: This will need some guidance nationally and internationally, and I think the relevant trial [serious adverse events] need to be reported in peer review literature, and clinicaltrials.gov updated in a timely manner, regardless of whether that strategy was successful or unsuccessful,” Dr. Hart said.
Risk with longer-acting agents?
In the question and answer following his presentation, Christoph Königs, MD, PhD, from University Hospital Frankfurt, asked whether there was potential for increased thrombosis risk with second-generation extended half-life (EHL) molecules in clinical trials.
“As we edge towards normalization of hemostasis, clearly the other non–hemophilia dependent issues of thrombosis risk come into play,” Dr. Hart acknowledged. “I think it will be an inevitability that there will be events, and we need to understand what the denominators are – hence my pitch for there being a renewed effort to try and collate sufficient data that we can really define events happening with people treated with standard half-life [products] through into the novel agents,” he said.
Dr. Hart disclosed grant/research support and speaker bureau activities for Bayer, Octapharma, Takeda, and others. Dr. Königs has reported no relevant disclosures.
Despite their similar functions, each current and emerging therapy for treating hemophilia has a unique safety profile, and each needs to be weighed apart from agents both within and outside its pharmacologic class, a hemophilia specialist said.
“My view is that each new molecule coming to the hemophilia space, including variant factor molecules, needs to be scrutinized separately, without class assumptions or extrapolations, and it’s clear that thrombosis risk has become a priority safety consideration,” said Dan Hart, MBChB, MRCP, FRCPath, PhD, from Barts and the London School of Medicine and Dentistry.
He reviewed the comparative safety of standard and novel therapies for hemophilia at the annual congress of the European Association for Haemophilia and Allied Disorders.
Factor inhibitors
Inhibitors occur in both hemophilia A and hemophilia B, and are primarily seen in patients with childhood exposure to factor concentrates. Inhibitors, which include anti–factor VIII and factor IX alloantibodies, are more common among patients with severe hemophilia and those with more disruptive factor VIII and factor IX mutations.
“There can be transient vs. persistent inhibitors, and arguably the more you look, the more you find, but clinically we never miss high-titer inhibitors that have a big impact on individuals and the subsequent decisions about management,” he said.
Hamster vs. human
It’s currently unclear whether there is an immunologic advantage for previously untreated patients to be started on factor VIII concentrates derived from recombinant human cells lines, or from products derived from Chinese hamster ovary (CHO) or baby hamster kidney (BHK) cell lines, Dr. Hart said.
“We need to ensure that we’re not selective about comparator choice for new products in the absence of head-to-head studies,” he said.
Route of administration matters
Inhibitors appear to be a more common occurrence among patients who received factor concentrates subcutaneously, compared with intravenously, Dr. Hart noted, pointing to a 2011 study indicating a background annual risk of 5 cases of inhibitor development per 1,000 treatment years in previously treated patients who received intravenous therapy (Blood. 2011 Jun 9;117[23]:6367-70).
In contrast, in a phase 1 trial of subcutaneous turoctocog alfa pegol, 5 out of 26 patients had detectable N8-GP–binding antibodies after 42-91 exposure days. Of these patients, one developed an inhibitor to factor VIII, and anti–N8-GP antibody appearance was associated with a decline in factor VIII plasma activity in four of the five patients. In addition, five patients reported a total of nine bleeding episodes requiring treatment during prophylaxis. As a result of this trial, further clinical development of the subcutaneous version was suspended. (J Thromb Haemost. 2020 Feb;18[2]:341-51).
Other subcutaneously administered factors are currently in development, Dr. Hart noted.
Nonfactor inhibitors?
“The nonfactor agents do have the risk of generating antibodies: Monoclonal antibodies outside the hemophilia setting provoke antidrug antibodies,” he said.
Although there is no consensus regarding which assay can best monitor antidrug antibodies (ADA), enzyme-linked immunosorbent assay (ELISA) can detect neutralizing antibodies and other antibodies.
In the hemophilia setting, surrogate markers for loss of drug efficacy include longer activated partial thromboplastin time (ATTP) or a drop in serum drug levels. Worsening bleeding phenotype can also be a marker for loss of efficacy, albeit an imperfect one.
Emicizumab (Hemlibara), the first nonfactor monoclonal agent to make it to market, has the largest dataset available, and evidence suggests a rate of neutralizing antibodies with this agent of less than 1% in the HAVEN clinical trial series, but 5.2% in the single-arm STASEY trial.
“We shouldn’t assume that other biophenotypics will have a similar ADA rate, and this needs to be evaluated for each molecule, as it will need to be for other monoclonals” such as anti–tissue factor pathway (TFPI) antibodies, Dr. Hart emphasized.
Pegylation
Pegylated compounds include polyethylene glycol, an inert polymer, covalently bound to the therapeutic protein to extend its half-life, and theoretically, reduce immunogenicity.
Many patients may already have exposure to pegylated products in the form of peginterferon to treat hepatitis C, consumer products such as toothpaste, cough medicine, and cosmetics, and, more recently, in vaccines against COVID-19.
Safety considerations with pegylated agents in hemophilia include concerns about accumulation of polyethylene glycol (PEG), although “some of the preclinical models looking at excretion of PEG are difficult to interpret in my view, and people debate about whether studies are long enough, but it’s undoubtedly the case that toxicology dosing is order of magnitude higher than the routine dosing in hemophilia,” he said.
After more than 5 years of experience with pegylated products there is no clinical evidence of concern, although “it’s not clear, actually, what we’re looking for, whether it’s a clinical parameter, or imaging or histological parameter.”
Patients may also not have lifelong exposure to pegylated products, as it is unlikely that they will stay on the same product for decades, Dr. Hart said.
Thrombosis
As of June 30, 2020, more than 7,200 persons with hemophilia have received emicizumab, and there have been 23 reported thrombotic events, 19 of which occurred in the postmarketing period. Of the reported cases, six patients had a myocardial infarction, and all of these patients had at least one cardiovascular risk factor.
The antithrombin agent fitusiran was associated with one fatal thrombotic event in a phase 2, open-label extension trial, leading to a pause and resumption with mitigation protocols, but that trial has since been paused again because of additional, nonfatal thrombotic events.
Nonfatal thrombotic events have also occurred in clinical trials for the investigational anti-TFPI monoclonal antibodies BAY 1093884 and concizumab, but none have thus far been reported in phase 3 trial of marstacimab.
“We need renewed efforts for prospective reporting and independent review of all adverse events of all agents, old and new: This will need some guidance nationally and internationally, and I think the relevant trial [serious adverse events] need to be reported in peer review literature, and clinicaltrials.gov updated in a timely manner, regardless of whether that strategy was successful or unsuccessful,” Dr. Hart said.
Risk with longer-acting agents?
In the question and answer following his presentation, Christoph Königs, MD, PhD, from University Hospital Frankfurt, asked whether there was potential for increased thrombosis risk with second-generation extended half-life (EHL) molecules in clinical trials.
“As we edge towards normalization of hemostasis, clearly the other non–hemophilia dependent issues of thrombosis risk come into play,” Dr. Hart acknowledged. “I think it will be an inevitability that there will be events, and we need to understand what the denominators are – hence my pitch for there being a renewed effort to try and collate sufficient data that we can really define events happening with people treated with standard half-life [products] through into the novel agents,” he said.
Dr. Hart disclosed grant/research support and speaker bureau activities for Bayer, Octapharma, Takeda, and others. Dr. Königs has reported no relevant disclosures.
FROM EAHAD 2021