PC-002 (Sepantronium Bromide) Enhances the Antitumor Efficacy of Anti-CD20 Antibody By CD20 Upregulation
Authors: Jiang Vernon , LI Xiang , He Na , Lv Yan , Wang Haiyue , Zhang Ming , Zhai Heiyan , Yang Zhen , Yang Yi , Guo Dagang , Cao Zhixiang , Chen Yiyou 
Published: December 2024

Introduction:
Anti-CD20 monoclonal antibodies have become a standard therapy for B-cell lymphoma, such as diffuse large B-cell lymphoma (DLBCL) and Burkitt's lymphoma (BL). However, despite the high response rate of anti-CD20 monoclonal antibody, many DLBCL and BL patients suffer recurrent disease within 5 years. One potential mechanism of anti-CD20 antibody resistance is loss or down-regulation of CD20 expression. It has been reported that CD20 up-regulation was observed following c-Myc inactivation [1]. PC-002 down-regulates Myc protein by blocking the deubiquitination activity of USP7 [2]. Therefore, the aim of this study is to define whether PC-002 can upregulate CD20 expression by inhibiting c-Myc protein and enhance the antitumor efficacy of anti-CD20 antibody.
Material and Methods:
The DLBCL and BL cells (SU-DHL-10 and RAMOS) were treated with PC-002 in vitro. Then expression of CD20 mRNA was assayed by qRT-PCR. Next, P493 cells with tet-off Myc transgene were used to further confirm the effect of PC-002 on CD20 expression. P493 tet-off cells were treated with tetracycline to suppress the expression of c-Myc (Myc-off). PC-002 was used to treat Myc-on (without tetracycline) and Myc-off P493 cells, then expression of CD20 mRNA was assayed by qRT-PCR. Furthermore, mouse xenografts (RAMOS, SU-DHL-4, SU-DHL-10 and OCI-LY7) were established to evaluate the efficacy of YM155 (2 mg/kg, 168-hour-infusion) in combination with anti-CD20 antibody, including Rituximab, Ripertamab and Ofatumumab in vivo. In addition, a murine DLBCL bone metastasis model was established by injecting RFP/luciferase-expressing NAMALWA (NAMALWA-RFP/Luc) cells via the caudal artery. The bone metastasis model was used to examine the efficacy of the PC002/anti-CD20 treatment. Tumor growth was monitored with an in vivo small animal imaging system.
Results:
PC-002 upregulated CD20 mRNA expression in a dose-dependent manner in BL and DLBCL cells. Such effect was diminished in Myc-off P493 cells. PC-002 in combination with anti-CD20 antibody Rituximab resulted in complete arrest of tumor growth in SU-DHL-10 xenograft models. More strikingly, 4 out of 6 mice in this group showed complete tumor regression by day 21. In contrast, neither agent alone could suppress tumor growth. Similar result was observed in OCI-LY7 xenograft model. The combination effect was further extended to other anti-CD20 antibodies, including Ripertamab and Ofatumumab. Mice with RAMOS or OCI-LY7 xenograft showed more pronounced tumor regression after receiving antibody-PC-002 combination treatment, compared to either agent alone. To further mimic clinical disease of bone metastasis, NAMALWA cells were stably transfected with RFP/Luc reporter and established bone metastasis model via tail artery inoculation.
PC-002 and Rituximab combination demonstrated superior efficacy compared to either drug alone. Moreover, the up-regulation of CD20 after PC-002 treatment in RFP/Luc cells was confirmed by whole transcriptome analysis. These results indicate that PC-002 enhances the efficacy of anti-CD20 antibody by downregulating c-Myc, and support the planned clinical investigation of the combination of PC002 with an anti-CD20 antibody such as rituximab in patients with relapsed/refractory c-Myc driven Burkitt lymphoma or diffuse large B-cell lymphoma.
Conclusion：
In conclusion, our preclinical data highlight the potent anti-tumor effects of PC-002 in combination with anti-CD20 antibody in patients with DLBCL and BL, and warrant the planned clinical investigation of the combination of PC002 with rituximab in patients with relapsed/refractory c-Myc driven Burkitt lymphoma or diffuse large B-cell lymphoma.
References:
1. Yu D, Dews M, Park A, Tobias JW, Thomas-Tikhonenko A. Inactivation of Myc in murine two-hit B lymphomas causes dormancy with elevated levels of interleukin 10 receptor and CD20: implications for adjuvant therapies. Cancer Res. 2005 Jun 15;65(12):5454-61. doi: 10.1158/0008-5472.CAN-04-4197. PMID: 15958595; PMCID: PMC1490323.
2. Li, X., et al., YM155 inhibits neuroblastoma growth through degradation of MYCN: A new role as a USP7 inhibitor. European Journal of Pharmaceutical Sciences, 2023. 181.