[Madrid, Spain = E-Daily Reporter Kim Jinsoo ] “Bladder cancer patients treated with BAL0891 have maintained treatment for over 18 months and have sustained a response for more than seven months even after achieving complete remission (CR).”

Lee Soo-jin SillaJen, Inc.(215600), Executive Director (MD·CMO), met with PharmDaily at the European Society for Medical Oncology (ESMO 2026) conference in Madrid, Spain, and explained the clinical results of the anticancer candidate “BAL0891” as described above.

BAL0891 is a dual inhibitor that simultaneously inhibits TTK and PLK1, both of which are involved in cell division. Executive Director Lee stated, “Development of existing TTK or PLK1 monotherapy inhibitors has faced challenges due to their respective side effects,” adding, “As a compound that simultaneously inhibits TTK and PLK1, BAL0891 is expected to be a ‘first-in-class’ agent.”

At this year’s ESMO conference, SillaJen, Inc. presented interim analysis results from a Phase 1 clinical trial of BAL0891 as monotherapy and in combination with paclitaxel for patients with advanced solid tumors. The trial enrolled patients with advanced solid tumors who had not responded to standard of care treatments. The analysis of 49 evaluable patients revealed that disease control was observed in all treatment groups.

Executive Director Lee stated, “Since complete remission was confirmed in a bladder cancer patient, the response has been maintained for more than seven months, and the therapeutic effect has also persisted for a long time in other patients who showed partial response (PR).”

Executive Director Lee explained, “In Regimen A, which started with a low dose, the disease control rate was over 70 percent, and objective treatment responses were confirmed in other monotherapy studies.”

He continued, “Since the number of patients has increased significantly since the ASCO presentation, the response rates may also change,” emphasizing that “the primary objective at present is to evaluate safety and tolerability and to determine the maximum tolerated dose and the recommended dose for subsequent clinical trials.”

The optimal treatment regimen and indications have not yet been finalized. Executive Director Lee said, “While it would be ideal if sufficient efficacy were demonstrated with monotherapy, we also need to identify patient subgroups that may respond better to combination therapy. Personally, I believe the objective response rate (ORR), which combines complete remission and partial response, is important.”

He continued, “Complete remission has been confirmed in bladder cancer, and partial responses have been observed in breast, uterine, and head and neck cancers. Since there aren’t many cases in each category, it is too early to specify a particular cancer type.”

“First-in-Class” Combination of TTK and PLK1 TTK and

PLK1 are enzymes that regulate cell division. Inhibiting them disrupts the division of cancer cells but can also affect normal cells. In particular, hematological toxicities, such as neutropenia, have been a barrier to the development of existing PLK1 monotherapy inhibitors.

Executive Director Lee said, “Prolonged inhibition of PLK1 can increase the risk of hematological toxicities such as neutropenia,” adding, “While simultaneously inhibiting both targets offers advantages in terms of antitumor efficacy, it can also increase toxicity.”

He further emphasized, “The design—which involves temporarily targeting PLK1 and inhibiting TTK for a relatively longer period—is intended to reduce hematological side effects.”

In fact, the most common adverse reaction in this study was neutropenia. SillaJen, Inc. adjusted the dosing schedule from days 1 and 8 of a 3-week cycle to days 1 and 15 of a 4-week cycle after observing insufficient neutrophil recovery following high-dose administration. The injectable drug G-CSF, which stimulates neutrophil production, was also used as an adjunctive therapy.

Executive Director Lee stated, “Neutropenia is a typical adverse reaction associated with the drug’s targeted action,” adding, “We managed it by adjusting the dosing interval and dosage and using G-CSF.”

He continued, “It cannot be concluded that the combination paclitaxel group experienced fewer adverse reactions than the monotherapy group, as adverse reactions from the combination drugs are also included,” and noted, “There were no cases of death or treatment discontinuation due to treatment-related adverse reactions, and most non-hematologic adverse reactions were mild.”

He explained, “When dose-limiting toxicity (DLT) occurred during the initial monotherapy phase, G-CSF adjuvant therapy had not yet been widely adopted,” and added, “As the study progressed and medical staff gained experience in managing neutropenia, risk management has improved.”

SillaJen, Inc. determined the recommended Phase 2 dose (RP2D) for BAL0891 monotherapy to be 160 mg, based on a comprehensive evaluation of safety, pharmacokinetics (PK), and antitumor efficacy.

Executive Director Lee said, “After considering drug exposure levels, safety, and antitumor efficacy together, we determined that 160 mg is optimal,” adding, “Drug exposure in the body is predictable and reproducible at this dose, which will aid in designing future administration regimens and combination therapies.”

In addition to paclitaxel, SillaJen, Inc. is currently conducting studies on combination therapy with the immunotherapy tislelizumab and on recurrent and refractory acute myeloid leukemia (AML).

Executive Director Lee said, “We plan to continuously assess which cancer types and combination regimens yield the best responses,” adding, “We expect the entire Phase 1 clinical trial to be completed around the third quarter of 2027.”