15 November 2022, Shanghai – Abbisko Therapeutics Co., Ltd. (“Abbisko Therapeutics”hereafter) today announced that preliminary Phase Ib results of its CSF-1R inhibitor ABSK021

for advanced tenosynovial giant cell tumor (“TGCT”) will be published at the 2022 Connective Tissue Oncology Society (“CTOS”) annual meeting to be held from November 16 to November 19, 2022 in Vancouver, Canada. The data are in relation to the excellent antitumor efficacy and the safety profile of ABSK021 in the treatment of patients with advanced TGCT and will be published under the title of “PRELIMINARY PHASE IB RESULTS OF ABSK021 FOR ADVANCED TENOSYNOVIAL GIANT CELL TUMOR: SIGNIFICANT ANTITUMOR ACTIVITY AND FAVOURABLE SAFETY PROFILE ” in a poster presentation with the poster number of “P 164 ”.

About ABSK021

ABSK021 is a novel, orally available, highly selective, and highly potent small molecule inhibitor of colony-stimulating factor 1 receptor (“CSF-1R”), independently discovered and developed by Abbisko Therapeutics. It is also the first highly selective CSF-1R inhibitor discovered by a Chinese company that has advanced into clinical trial. A number of studies have shown that blocking the colony-stimulating factor 1 (“CSF-1”)/CSF-1R signaling pathway could effectively modulate and change macrophage functions, and potentially treat many macrophage-dependent human diseases.

Abbisko Therapeutics has completed a Phase Ia dose escalation study for ABSK021 in the U.S., and has a Phase Ib multi-cohort expansion trial ongoing in both the U.S. and China. In July 2022, ABSK021 was granted the breakthrough therapy designation by the Center for Drug Evaluation (“CDE”) of the National Medical Products Administration of the People’s Republic of China (“NMPA”) for the treatment of TGCT that is not amenable to surgery. In October 2022, ABSK021 was further approved by the CDE of NMPA for a randomized, double-blind, placebo-controlled and multicenter Phase III clinical study in patients with TGCT.

In addition to TGCT, Abbisko Therapeutics is actively exploring the potential of ABSK021 in treating many types of solid tumors in clinic, and has collaborated with Sperogenix (Shanghai) MedTech Co., Ltd. in exploring its potential for treating amyotrophic lateral sclerosis and other central nervous system diseases. As at the date of this press release, no highly selective CSF-1R inhibitor has been approved in China.

About Phase I trial of ABSK021 (NCT04192344)

NCT04192344 is an open-label, first-in-human Phase I study currently ongoing in China and the U.S. for ABSK021. The trial includes the following two parts, (i) a Phase Ia dose escalation study on patients with advanced solid tumor; and (ii) a Phase Ib dose expansion study to further evaluate the preliminary antitumor efficacy among selected tumor types, including TGCT, and 50mg QD was selected as the current recommended dose for expansion (“RDE”) for TGCT patients enrolled in Phase Ib trial. For TGCT cohort, the primary endpoint is the objective response rate (“ORR”) under RECIST 1.1, and the secondary endpoints include overall tolerability, improvement of motion range and patient report outcome of pain and stiffness.

Safety and efficacy data of 27 patients enrolled in the Phase Ib clinical trial have been updated up to September 2022.

Results

1) Conclusion

• ABSK021 has demonstrated significant antitumor efficacy with a preliminary ORR of 68.0% (17/25, 95% CI: 46.50%-85.05%), including one complete response and 16 partial responses

confirmed by independent review committee (“IRC”) within six months.

• The safety profile of ABSK021 was favorable with no apparent hepatotoxicity. The mean treatment duration was 6.8 months, and 85.2% of patients are still on treatment.

• Range of motion, stiffness and pain preliminarily indicated a trend of alleviation after the treatment of ABSK021 in patients with TGCT.

• The changes of PD biomarkers indicated significant CSF-1R inhibition.

• This is the first result of an oral CSF-1R inhibitor with encouraging preliminary efficacy and safety results in Chinese patients with advanced TGCT, which supports the further evaluation of ABSK021 in a Phase III study.

2) Safety

• As of September 2022, the overall median treatment duration was 205 days (n=27, range: 69-280). 26 patients have been on treatment for no less than 3 months. One patient has been on treatment for less than 3 months due to the impact of COVID-19.

• Most treatment-emergent adverse events (“TEAEs”) were grade 1 or 2 events. No hair color changes or serious liver injury cases were reported.

• CPK and transaminase elevations were asymptomatic and quickly recovered after drug interruptions.

3) Efficacy

• Tumor regression was observed in almost all evaluated patients.

• The ORR was 68.0% (17/25, 95% CI: 46.50%-85.05%), including one complete response and 16 partial responses within six months. The median duration of response was not reached.

• Flexion range of knee at week 13 was assessed in nine patients with an average improvement of 27 degrees (range: 5-58) from baseline along with a similar trend of stiffness and pain alleviation.

• Treatment with ABSK021 led to significant PD changes in TGCT patients, such as an increase in plasma CSF-1 level and a reduction of non-classical monocytes with treatment, showing the inhibitory effect of ABSK021 on the CSF-1R signal pathway.

About TGCT

TGCT is a locally aggressive neoplasm which usually affects synovial joints, mucous sacs, and tendon membranes, resulting in swelling, pain, stiffness, and decreased activity of the affected joints which seriously affect the patient’s quality of life1. According to the 2013 World Health Organization classification, TGCTs were classified as localized TGCT and diffuse TGCT. Diffuse TGCT encompasses formerly known nodular tenosynovitis and pigmented villonodular synovitis (PVNS). Overexpression of CSF-1 occurs in most TGCTs. Surgical resection is the standard treatment for TGCT. However, not all patients are suitable for surgical treatment. It is difficult to remove tumors of diffuse TGCT patients by surgery, which may possibly lead to severe joint damage, total synovectomy, joint replacement, or even amputation, and the risk of surgical complications can be high. It has been reported that more than 50% of patients with diffuse TGCT will undergo recurrence after surgical resection2. For TGCT patients not amenable to surgery, there is currently no approved drug available in China.

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