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New antibody-drug conjugate approved in the US

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On June 10, 2019, the U.S. Food and Drug Administration (FDA) granted accelerated approval to Polivy (polatuzumab vedotin-piiq), in combination with the chemotherapy bendamustine and a rituximab product (BR), to treat adult patients with diffuse large B-cell lymphoma (DLBCL) that has progressed or returned after at least two prior therapies. Polivy is composed of a humanized anti-CD79b IgG1 antibody conjugated to the antimitotic agent monomethyl auristatin E (MMAE). The antibody’s target is highly expressed on B cells of patients with lymphoma. The biologics license application for Polivy was granted FDA’s Breakthrough Therapy and priority review designations. The drug also has European Medicines Agency (EMA)’s PRIME designation, and US and EU Orphan Drug designations for DLBCL. EMA is reviewing a marketing authorization application for Polivy.

The drug’s efficacy was evaluated in a study of 80 patients with relapsed or refractory DLBCL who were randomized to receive Polivy with BR or BR alone. Efficacy was based on complete response rate and duration of response (DOR), defined as the time the disease stays in remission. At the end of treatment, the complete response rate was 40% with Polivy plus BR compared to 18% with BR alone. Of the 25 patients who achieved a partial or complete response to Polivy plus BR, 16 (64%) had a DOR of at least six months and 12 (48%) had a DOR of at least 12 months.

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The Antibody Society maintains a comprehensive table of approved mAb therapeutics and those in regulatory review in the EU or US. Located in the ‘Web Resources’ section of our website, the list is updated regularly and can be downloaded in Excel format. Information about other antibody therapeutics that may enter regulatory review in 2019 can be found in ‘Antibodies to watch in 2019’.

 

Back in business: gemtuzumab ozogamicin

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Roughly 17 years ago gemtuzumab ozogamicin was first approved by the FDA for the treatment of patients over the age of 60 with CD33-positive relapsed acute myelogenous leukemia (AML), and who were not considered candidates for other cytotoxic chemotherapy.

The drug, also known as Mylotarg, was the result of a long-lasting collaboration between Wyeth (acquired by Pfizer in 2009) and CellTech (acquired by UCB in 2004), dating all the way back to 1991. Nine years later it was approved as a single agent under an “accelerated” approval based on the surrogate response rate endpoint that was observed in 142 patients with AML across 3 clinical trials. The approval made Mylotarg the first ADC to hit the US market at the time.

However, things turned quickly for the product. One year into its approval it required a black box packaging warning related to the increased risk of veno-occlusive disease. Initially, the warning was aimed at patients who did not receive bone marrow transplantation, but later the increased frequency of veno-occlusive disease was also observed in Gemtuzumab-treated patients after bone marrow transplantation.

A confirmatory, post-approval clinical trial commenced in 2004, per FDA guidelines for accelerated approval. Results of the randomized Phase 3 SWOG S0106 trial showed a significantly higher fatal induction toxicity rate in gemtuzumab combination therapy group versus the control group receiving only chemotherapy (16/283 = 5.7% versus 4/281 = 1.4%; p =  0.01).

Following the results of SWOG S0106 and the post-marketing experience with the drug, Pfizer decided to withdraw Mylotarg from the market in 2010 at the request of the FDA. The discontinuation was an upset in the ADC field. Upon the withdrawal brentuximab vedotin and trastuzumab emtansine were the only two approved ADCs for years to come. However, the potential of ADC therapeutics has seen a revival and around 60-70 products are in clinical trials at the moment.

Not only the ADC field itself bounced back after this blow, but also gemtuzumab ozogamicin made a recent comeback. Early this year Pfizer resubmitted Mylotarg for regulatory review and both the FDA and the EMA accepted to review the application based on added data from the Phase 3 randomized, open-label ALFA-0701 trial. In this study Mylotarg was evaluated as an addition to the standard induction chemotherapy using an alternative fractionated dosing schedule in 280 adult, de novo, AML patients between 50 and 70 years old. Additionally, a meta-analysis of patient-level data from over 3000 patients in five randomized Phase 3 trials were evaluated.

Now, seven years after discontinuation, gemtuzumab ozogamicin is back in business in the US. The FDA has approved the lower recommended dosage range and the alternative treatment schedule. The authorization now covers single uses or in combination with chemotherapy in a patient population that now also includes adults with newly diagnosed CD33-positive AML, and adults and children 2 years and older with relapsed or refractory CD33-positive AML.

First approval for inotuzumab ozogamicin in the European Union

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The European Commission has granted a marketing approval for the antibody-drug conjugate (ADC) inotuzumab ozogamicin (BESPONSA) as monotherapy for the treatment of adults with relapsed or refractory CD22-positive B-cell precursor acute lymphoblastic leukemia (ALL). Inotuzumab ozogamicin is a CD22-targeting humanized IgG4 antibody conjugated to the drug calicheamicin via an acetyl butyrate linker. The approval of BESPONSA was supported by results from the Phase 3 INO-VATE ALL trial (ClinicalTrials.gov number NCT01564784), which compared the effects of either inotuzumab ozogamicin or standard intensive chemotherapy in adults with relapsed or refractory ALL Results of this study were published in The New England Journal of Medicine in 2016. A biologics license application for inotuzumab ozogamicin for the treatment of adult patients with relapsed or refractory B-cell precursor ALL is undergoing a priority review by the US Food and Drug Administration (FDA); the goal date for their decision is in August 2017.

As of July 1, inotuzumab ozogamicin is the seventh antibody therapeutic to be granted a first marketing approval in any country in 2017, following the approvals of brodalumab, avelumab, ocrelizumab, dupilumab, durvalumab, and sarilumab. The Antibody Society maintains a comprehensive table of approved antibody therapeutics and those in regulatory review in the EU or US. As of July 1, 2017, marketing applications for a total of 10 antibody therapeutics that have not been approved in any country are undergoing review in the EU or US. In addition, a marketing application for the ADC gemtuzumab ozogamicin, which was approved in 2000 by the US FDA and subsequently withdrawn from the US market, is undergoing review in the EU and US.

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Increased clinical pipeline of Antibody Drug Conjugates in 2016

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The antibody-drug conjugate (ADC) clinical pipeline has continued to grow in 2016. Last month two ADCs entered the clinic: Genmab’s MMAE-conjugated HuMax-AXL-ADC is now in Phase 1/2 development for five different types of solid tumors (ovary, cervix, endometrium, lung and thyroid). Additionally, a PBD-conjugated ADC for multiple myeloma (SGN-CD352A), was added to Seattle Genetics’ clinical pipeline.

In total, 32 clinical trials involving ADCs were initiated in 2016 and a significant progression of the pipeline into Phase 2 and 3 clinical trial was observed that year. During last year, 14 novel ADCs entered Phase 1, now totaling 37 Phase 1 ADCs. Three ADCs initiated Phase 1/2 development in 2016, increasing the total number of ADCs in this stage to 8. Four ADCs (AGS-16C3F, Anetumab Ravtansine, SAR566658, Rova-T) progressed towards Phase 2 (11 ADCs are now in Phase 2) and two drugs (IMGN853, SGN-CD33A) entered Phase 3 trials, doubling the number of ADCs in this clinical phase.

This year, a market approval could become a reality for inotuzumab ozogamicin. Currently, a marketing authorization application for acute lymphocytic leukemia (ALL) is being reviewed by EMA. Another possible approval is the re-approval for Mylotarg using a different dosing regimen.

Phase I Data for Enfortumab Vedotin and the World ADC Awards

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During the annual congress of the European Society of Medical Oncology (ESMO) in Copenhagen, interim clinical data for enfortumab vedotin (ASG-22ME) and ASG-15ME (Seattle Genetics and Agensys/Astellas) in patients with metastatic urothelial cancer were presented. Both enfortumab vedotin and ASG-15ME are investigational ADCs making use of the microtubule-disrupting toxin MMAE conjugated to anti-Nectin-4 and a SLITRK6-targeting antibody respectively. Nectin-4 and SLITRK6 are highly expressed in urothelial cancers, particularly bladder cancer but also include carcinomas of the ureter and renal pelvis.

There is a high unmet need for patients with metastatic urothelial cancer. In 2016 approximately 77,000 people will be diagnosed and more than 16,000 will die from urothelial bladder cancer. For patients diagnosed with locally advanced or metastatic the average five-year survival is only approximately 15%.

The clinical trial data showed that each agent demonstrated anti-tumor activity in patients previously treated with platinum-based chemotherapy, checkpoint inhibitors, taxanes and those with liver metastases and were generally well-tolerated.

Of the 49 patients evaluable for response to enfortumab vedotin treatment, 18 patients (37%) had an objective response, including one patient (2%) achieving a complete response and 17 patients (35%) who achieved a partial response. The preliminary estimate of median progression-free survival is 16.6 weeks. The recommended phase II dose is 1.25 mg/kg.

Of the 48 patients evaluable for response upon ASG-15ME treatment, 18 patients (38%) showed an objective response, including one patient (2%) who achieved a complete response and 17 patients (35%) achieving a partial response. The preliminary estimate of median progression-free survival is 16.1 weeks.

Both agents demonstrated encouraging anti-tumor activity and safety in these patient groups, and these data support the scheduled advancement to later stage development.

 

In other ADC-related news this month, during the 7th World ADC conference in San Diego the winners of the 3rd World ADC Awards were announced. The World ADC Awards showcase excellence within antibody drug conjugate research and reward the innovation, leadership, and devotion shown by the best companies, teams, and individuals in the industry. Across eight categories winners were awarded which in full can be viewed here (http://worldadc-awards.com/awards-2016/winners/).

The award for Best ADC Platform Technology was won by the Fleximer platform developed by Mersana Therapeutics. Winner of the Most Promising Clinical Candidate
was the ADC Rovalpituzumab tesirine (developed by Abbvie-Stemcentrx). BSP Pharmaceuticals took the prize for Best Contract Manufacturing Provider and ADC Therapeutics won Best New Drug Developer. John Lambert was awarded for his Long Standing Contribution to the field.

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