On December 11, 2023 Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), reported that its research collaborators presented data on anti-leukemic activity from the compassionate use of luveltamab tazevibulin (luvelta), a novel folate receptor-α (FR-α) targeting ADC, in pediatric patients with relapsed/refractory CBFA2T3-GLIS2 (CBF/GLIS) acute myeloid leukemia (AML), commonly known as RAM phenotype AML (Press release, Sutro Biopharma, DEC 11, 2023, View Source [SID1234638443]). Data demonstrated that treatment with luvelta produced meaningful clinical responses, including complete remission (CR); and prolongs overall survival (OS) enabling some patients to receive potentially curative therapies such as hematopoietic stem cell transplant. These patients were treated under the single patient IND mechanism. These data were featured in a poster presentation at the 65th American Society of Hematology (ASH) (Free ASH Whitepaper) Annual Meeting and Exposition (ASH 2023) in San Diego, CA.

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"Treatment with luvelta led to notable response in a significant subset of patients who had exhausted all therapeutic options," said Soheil Meshinchi, M.D., Ph.D., presenter and primary author. "Response varied from deep remissions to disease stabilization with minimal toxicity – mostly in outpatient setting. Luvelta was well tolerated as long-term maintenance therapy with little to no hematopoietic toxicity."

CBF/GLIS subtype AML is a rare and highly lethal form of leukemia found exclusively in infants and young children, with the average age of onset at 18 months 1. There are no therapies specifically approved to target this form of leukemia and it is resistant to conventional chemotherapy, with an induction failure rate of over 80%2. Due to a lack of effective treatment, children diagnosed with the disease have a dismal two-year survival rate of 15%3. Recent studies have shown that FOLR1, which encodes for FolRα, is silent in normal hematopoiesis, but is uniquely induced by the CBF/GLIS fusion4.

Under compassionate use, 25 pediatric patients with relapsed/refractory CBF/GLIS subtype AML were treated with luvelta at doses up to 4.3 or 5.2mg/kg every two to four weeks for a median duration of 15.9 weeks (3-73.1), with the majority of patients receiving at least five doses (68%). Of the 25 treated patients, 19 had ≥5% blasts (morphologic disease, or MD) and 8 had <5% blasts (sub-morphologic disease, or SMD)5. Collective results show that treatment with luvelta produced clinically meaningful and durable responses across a broad range of patients in various settings including in patients with or without prior stem cell transplant and in monotherapy or in combination with cytotoxic therapy. These data were generated by the treating physicians and collected and enabled for presentation by Sutro.

"It is clear from these data that luvelta is providing an ongoing and promising impact on the lives of infants and young children with this rare leukemia," said Bill Newell, Sutro’s Chief Executive Officer. "These results add to the growing body of research supporting the development of luvelta, which has now seen positive clinical results across three different tumor types, including those with potentially low or variable folate receptor-α expression."

ASH Presentation Highlights:

Overall, anti-leukemic activity was seen with luvelta either as a single agent or in combination.
19 patients had ≥5% blasts and 8 patients had <5% blasts5.
A CR/CRh was observed in 8 out of 19 (42%) patients with ≥5% blasts treated with luvelta, with 5 out of 8 CR/CRh patients reaching a minimal residual disease (MRD)-negative CR (63%).
6 out of 8 patients with <5% blasts experienced an MRD-negative CR (75%).
Patients whose leukemia experienced an MRD-negative CR had an improved outcome over those who did not experience an MRD-negative CR.
Treatment with luvelta also enabled some children to bridge to stem cell transplant, which is potentially curative therapy.
Luvelta was well-tolerated as a monotherapy agent and in combination with standard of care therapies with minimal hematopoietic toxicity and can be delivered as outpatient therapy.
As of September 17, 2023, 8 patients remain on treatment, with 5 of the 8 (63%) in continued remission and on luvelta maintenance.
The poster titled, "Anti-leukemic Activity of Luveltamab Tazevibulin (LT, STRO-002), a Novel Folate Receptor-α (FR-α)-targeting Antibody Drug Conjugate (ADC) in Relapsed/Refractory CBFA2T3::GLIS2 AML," will be accessible through the News & Events page of the Investor Relations section of the company’s website at www.sutrobio.com.

About Luveltamab Tazevibulin
Luveltamab tazevibulin, abbreviated as "luvelta" and formerly known as STRO-002, is a FolRα-targeting antibody-drug conjugate (ADC) designed to treat a broad range of patients with ovarian cancer, including those with lower FolRα-expression who are not eligible for approved treatment options targeting FolRα. Developed and manufactured with Sutro’s cell-free XpressCF platform, luvelta is a homogeneous ADC with four hemiasterlin cytotoxins per antibody, precisely positioned to efficiently deliver to the tumor while ensuring systemic stability after dosing. Sutro recently initiated REFRaME, a Phase 2/3 registration-directed study for patients with platinum-resistant ovarian cancer. The company has ongoing trials in patients with endometrial cancer and in combination with bevacizumab in patients with ovarian cancer. The company is also assessing the clinical path forward for CBF/GLIS2 acute myeloid leukemia, a rare subtype of pediatric cancer, as well as non-small cell lung cancer. The U.S. Food and Drug Administration (FDA) has granted luvelta a Fast Track designation for Ovarian Cancer, as well as Orphan and Rare Pediatric Disease designations for CBF/GLIS2 Pediatric AML.