MARLBOROUGH, Mass. — Sumitomo Pharma America said preliminary data from an ongoing first-in-human Phase 1/2 trial showed its investigational cancer therapy SMP-3124LP was generally well tolerated and showed early signs of clinical activity in patients with heavily pretreated advanced solid tumors.
The findings were presented in a poster at the 2026 American Society of Clinical Oncology Annual Meeting.
SMP-3124LP is an investigational, selective checkpoint kinase 1 inhibitor delivered through a PEGylated liposome formulation. The therapy is designed to treat cancers marked by high replication stress.
“Historically, the development of CHK1 inhibitors has been hampered by significant low blood counts and a narrow therapeutic window, which has limited their clinical utility for patients,” said Timothy A. Yap, MBBS, PhD, professor of investigational cancer therapeutics at The University of Texas MD Anderson Cancer Center and lead investigator of the study. “By using this liposomal delivery method, we are attempting to address the primary obstacles that have previously stalled the CHK1 inhibitor mechanism of action. For patients who have already navigated multiple lines of therapy, this approach may offer the potential for meaningful clinical benefit and disease control without the overwhelming burden of side effects common to older therapies.”
The Phase 1 portion of the trial enrolled 61 patients with selected advanced solid tumors across four intravenous dose levels: 20, 40, 60 and 90 mg/m2, given every two weeks. Sumitomo Pharma America said the study population was heavily pretreated, with 37.7% of participants having received more than four prior lines of therapy.
As of April 3, 2026, 56 patients were evaluable for efficacy. The study reported a disease control rate of 48.2%, including five partial responses and 22 cases of stable disease.
Partial responses were observed in two patients with platinum-resistant ovarian cancer, two patients with squamous cell carcinoma of the anus and one patient with colorectal cancer harboring an FBXW7 mutation. Two additional patients with platinum-resistant ovarian cancer achieved stable disease with tumor shrinkage of 20% or more, including one patient who had an 88% cancer antigen-125 response.
Sumitomo Pharma America said SMP-3124LP was generally well tolerated and had a manageable safety profile. No dose-limiting toxicities were observed at the 20 mg/m2 or 40 mg/m2 dose levels. Dose-limiting toxicities, including Grade 4 thrombocytopenia and Grade 3 febrile neutropenia, were reported at higher doses of 60 mg/m2 and 90 mg/m2.
The company said blood-related side effects were generally transient and did not lead to treatment discontinuations. Infusion-related reactions were reported in 41% of patients, all of which were Grade 1 or 2 and manageable with standard supportive care or adjusted infusion rates.
Pharmacokinetic data also supported the therapeutic approach, the company said, with a long half-life of 24 to 28 hours and low volume of distribution consistent with liposomal formulation. Dose-proportional increases in exposure were observed across all tested dose levels.
“We are proud to present our first-in-human data for SMP-3124LP at ASCO—where the most rigorous advancements in oncology are shared—as it reinforces our focus on addressing some of the most persistent challenges in cancer treatment,” said Tsutomu Nakagawa, Ph.D., president and CEO of Sumitomo Pharma America.
“With SMP-3124LP, we are developing a technology platform at SMPA based on liposomal delivery of targeted therapies in an effort to maximize the therapeutic window and minimize toxicities,” said Jatin Shah, M.D., chief medical officer of oncology at Sumitomo Pharma America. “These are the first data in this first-in-human study of SMP-3124 where we have demonstrated the potential ability to deliver selective CHK1 inhibition with less myelosuppression, which has been the major AE limiting the ability to target CHK1 directly to the tumor while sparing the patient’s healthy cells. These data are a reflection of our efforts toward realizing sustainable and effective therapeutic options for those facing the complexities of difficult-to-treat cancers, including advanced solid tumors.”
CHK1 is involved in the DNA damage response pathway and helps cancer cells repair DNA under high replication stress. Sumitomo Pharma America said SMP-3124LP is intended to use liposomal technology to widen the therapeutic window for CHK1 inhibition, which has historically been limited by toxicity to healthy bone marrow.
