Abstract 4119: Anti-KRAS antibody aggregates KRAS in the cytoplasm of live ex vivo cultured human colorectal adenocarcinoma cells and prevents its trafficking to the plasma membrane
Authors: Cheah Peh Yean , Lam Kuen Kuen , Low Yee Syuen , Lo Michelle , Wong Michelle , Tang Choong Leong , Tan Emile , Chok Aik Yong , En Issac Seow , Wong Siew Heng 
Published: April 2023

Worldwide, colorectal cancer (CRC) is the third highest incidence cancer and a leading cause of cancer mortality. Metastasis to distal organ is the major cause of cancer mortality. However, chemotherapeutic treatment of metastatic CRC has a dismayed success rate of less than 30%. Patients who are resistant to chemotherapy and who are KRAS wildtype are sometimes offered anti-EGFR as a second line therapy. Nevertheless, only about ½ of these patients respond and those who do inevitably develop resistance within months due to selection for downstream KRAS mutations. Moreover, most (80%) sporadic CRCs are microsatellite-stable and are refractory to immune checkpoint blockade therapy. Hence, there is an unmet need to identify novel therapeutics for CRC. KRAS is a gatekeeper gene in colorectal tumorigenesis but is ‘undruggable’ due to its structure not being easily amenable to inhibitor docking. Focus has been diverted to develop small molecule inhibitors for its downstream effectors such as ERK/MAPK and AKT. Despite intense research efforts for the past few decades, however, no small molecule inhibitor has been in clinical use for CRC. Recently developed Sotorasib inhibitor specific for KRAS G12C mutations (rare in CRC) is not effective for CRC. Antibodies have high affinity to their target proteins without having to bind to specific pocket and are fully human in nature and hence less toxic. Antibody targeting KRAS itself is thus an attractive alternative. We developed a transient ex vivo patient-derived matched mucosa-tumor primary culture to assess whether anti-KRAS antibody can be internalized to bind and inactivate KRAS. We showed that anti-KRAS antibody can enter live matched mucosa-tumor cells and specifically aggregate KRAS in the cytoplasm, thus hindering its trafficking to the inner plasma membrane. The mis-localization of KRAS reduces KRAS dwelling time at the site where it tethers to activate downstream effectors. We previously showed that expression of SOX9 was KRAS-mutation-dependent and possibly a better effector than ERK in CRC. In the present study, we showed that anti-KRAS antibody treated tumor cells have less intense SOX9 cytoplasmic and nuclear staining compared to untreated cells suggesting down-regulation of KRAS signaling. Our results demonstrated that anti-KRAS antibody can be internalized and specifically inhibits KRAS function in live tumor cells. With an efficient intracellular antibody delivery system, this can be further developed as combinatorial therapeutics for CRC and other KRAS-driven cancers.

Citation Format: Peh Yean Cheah, Kuen Kuen Lam, Yee Syuen Low, Michelle Lo, Michelle Wong, Choong Leong Tang, Emile Tan, Aik Yong Chok, Issac Seow En, Siew Heng Wong. Anti-KRAS antibody aggregates KRAS in the cytoplasm of live ex vivo cultured human colorectal adenocarcinoma cells and prevents its trafficking to the plasma membrane. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4119.