MedPacto, a Korean biotechnology company, said Monday it has launched a phase 2 clinical trial of its investigational drug vactosertib for osteosarcoma in Korea and the U.S.

Osteosarcoma, a rare malignant tumor of the bone and cartilage, occurs most frequently in children and adolescents. For more than five decades, chemotherapy has remained the standard treatment, but its effectiveness in improving survival outcomes has been limited, underscoring the urgent need for new therapies.

The company is conducting studies in both adults and adolescents aged 12 to 17 in Korea and the U.S.

After completing a phase 1 trial in adults, MedPacto recently began recruiting patients for the phase 2 trial.

Enrollment for the adolescent phase 1 cohort is nearly complete, and a transition to phase 2 is expected soon.

To accelerate progress, MedPacto plans to expand the number of clinical sites. In Korea, the trial is currently underway at the National Cancer Center (NCC), Korea Cancer Center Hospital, and Seoul National University Bundang Hospital (SNUBH).

New trial centers will be added at Seoul National University Hospital (SNUH), Asan Medical Center (AMC), and Samsung Medical Center (SMC).

In the U.S., MedPacto said it has received requests for “expanded access” or “compassionate use” of vactosertib from institutions including Johns Hopkins University Hospital and Arkansas Children’s Research Institute, with regulatory procedures now in motion.

The company has previously supplied the drug for compassionate use at Stanford University Hospital, UCLA Medical Center, Oregon Health & Science University, and Case Western Reserve University Hospital, among others, treating a total of 10 osteosarcoma patients.

“Following the promising phase 1 data, interest from clinicians worldwide has grown rapidly,” a MedPacto official said. “We are committed to advancing clinical trials quickly to secure early approval while also pursuing global licensing opportunities.”

Vactosertib is designed to inhibit the TGF-β signaling pathway, which plays a key role in tumor growth and immune suppression. By blocking this pathway, the drug reduces expression of the cancer-promoting gene C-Myc and helps restore a favorable immune environment.

In ongoing studies of relapsed or refractory osteosarcoma, vactosertib monotherapy has shown a partial response rate exceeding 35 percent.

The drug has already been granted orphan drug designation in the U.S. and Europe and has received U.S. FDA fast track status. MedPacto is also in discussions with the FDA to obtain breakthrough therapy designation for vactosertib.