Authors:

Fei Teng¹, Huanhuan Guo¹, Hongjun Li¹, Lizhi Qin¹, Hanjing Mao¹, SonnyYao¹, Xiaoli Zi¹, Lisa Zheng¹, Yi Gu¹, Xueming Qian¹.

¹Suzhou Transcenta Therapeutics Co., Ltd, Suzhou, China

Background:

LIV-1 is a member of the zinc transporter family and an estrogen-regulated gene in metastatic breast cancer. While normal tissue expression is limited, LIV-1 was found to be overexpressed in a high prevalence in breast cancer (93%), as well as in melanoma (82%), prostate (72%), ovarian (48%) and uterine (30%) cancers[1]. LIV-1 is considered as one of the attractive cell surface targets for developing ADC therapeutics. To develop next generation LIV1 targeting ADC, we generated 48D6, a proprietary novel humanized anti-LIV-1 mAb with high affinity, specificity, internalization ability, unique epitope and improved pharmacokinetics profile in mice. In vitro studies indicated that breast tumor cells, such as MDA-MB-468 and MCF-7, are more sensitive to Topo I inhibitor than MMAE. Therefore, we generated two Topo I inhibitor-based ADCs (ADC-1 and ADC-2) using glycotransferase mediated site-specific conjugation. Both ADC-1 and ADC-2 have a drug-to-antibody ratio (DAR) of 4 but with two different Topo I inhibitor payloads. A MMAE based ADC (ADC-3) with the same site-specific conjugation and DAR4 was also synthesized as the control. ADC-1 and ADC-2 displayed similar and specific cytotoxic activities against human LIV-1-expressing tumor cells in vitro, as compared to SGN-LIV1A analog (DAR4) or ADC-3. In the human LIV-1 transfected MDA-MB-468, a triplenegative breast cancer (TNBC) tumor model, ADC-1 or ADC-2 demonstrated dosedependent anti-tumor activities and inhibited tumor growth more potently than the SGN-LIV1A analog or ADC-3. At 3 mg/kg the tumor growth inhibition (TGI)% are: ADC-1 92.4%, ADC-2 94.7%, ADC-3 68.5% and SGN-LIV1A analog 57.0% on Day 30; At 3 mg/kg, the overall response rate (ORR, 50% reduction of tumor volume from baseline) of SGN-LIV1A analog or ADC-3 was 0%, while ORRs of ADC-1 and ADC-2 were 40% and 70%, respectively. At 6 mg/kg, on Day 42 ADC-1 and ADC-2 had ORR of 90% and 100% respectively, and CR rate of 90% and 100% respectively. And the body weight of mice didn’t change significantly at either 3 or 6 mg/kg for ADC-1 or ADC-2. The enhanced anti-tumor activities of ADC-1 and ADC-2 are likely contributed by the high affinity binding of 48D6 to LIV-1 and high cytotoxicity of Topo I inhibitor in breast tumor cells. These data warrant further investigation of the lead LIV-1 targeting ADCs (ADC-1 and ADC-2) as potential next-generation therapeutic agent in LIV-1 positive breast cancer and other solid tumors.

Conclusions:

48D6 is a novel humanized anti-LIV1 antibody binding to a unique epitope.

ADC-1 and ADC-2 are novel LIV-1 ADCs with 48D6 site-specifically conjugated with Topo I inhibitor payloads. With higher affinity and specificity, they can be internalized by the tumor cells and kill the tumor more efficiently.

Although the cytotoxicity activity of ADC-1 and ADC-2 were similar to that of SGNLIV1A analog in vitro, they exhibited much more potent tumor inhibition than SGNLIV1A analog in vivo and both ADCs regressed the tumors completely.

Both ADC-1 and ADC-2 have strong bystander effect to overcome tumor heterogeneity.

By site-specific conjugation, ADCC activity and other Fc functions of antibody were depleted, which may reduce Fc mediated non-specific binding and cytotoxicity.

As potential next-generation therapeutic agent for LIV-1 expressing solid tumors, ADC-1 and ADC-2 are being further developed for clinical testing.