Abstract PR16: Normal and neoplastic tissues with partial Hus1 impairment show hypersensitivity to cisplatin in vivo

The DNA damage response (DDR) factor HUS1 is vital for proper functioning of the ATR checkpoint pathway. Following DNA damage, HUS1 forms a heterotrimeric complex with RAD9 and RAD1 and works with other checkpoint and scaffold proteins to activate ATR and CHK1 kinases. HUS1 also has separate functions that promote DNA repair. Due to its essential nature and diverse roles in genome maintenance, we hypothesized that HUS1 would be critical in the response of normal and neoplastic tissues to the DNA-damaging chemotherapeutic, cisplatin. Cisplatin is a widely used chemotherapeutic that damages DNA via platinated adducts, which form intrastrand and interstrand crosslinks. To test our hypothesis, we made use of a mouse model whereby a hypomorphic Hus1 allele is combined with a null allele in order to achieve partial impairment (Hus1neo/Δ1n) in vivo. Hus1+ and Hus1neo/Δ1n FVB mice were administered high dose cisplatin intraperitoneally (13.5 mg/kg). Body weights were recorded daily and mice were euthanized when humane intervention criteria were met. Hus1neo/Δ1n mice had reduced 7-day survival (P = .0071) and increased weight loss (P = .0485) when compared to Hus1+ mice. In order to determine if neoplastic tissues had a similar requirement for HUS1 in response to DNA damage inflicted by cisplatin, we combined Hus1 impairment with K-ras oncogene activation in vivo. K-RAS is the most frequently mutated oncogene in non-small cell lung cancer (NSCLC). Mutations in this oncogene, the majority of which occur in codon 12, affect 25–30% of western NSCLC patients. K-RAS encodes for a membrane-bound GTPase that regulates cell growth, differentiation, and survival. In our model, activation of oncogenic K-ras is restricted to the lung and is achieved via a tetracycline-controlled reverse transactivator linked to the CCSP promoter. In the presence of doxycycline, mutant Kras4bG12D is expressed in type II alveolar epithelial cells, and lung tumors develop in a regulatable, predictable manner. Mice with wild-type or partial Hus1 impairment and simultaneous oncogenic K-ras activation were screened for lung tumor development via computed tomography (micro-CT), then treated with maximum-tolerated dose (MTD) cisplatin, and assessed for response according to semiautomated volumetric methods and the clinical standard, RECIST (Response Evaluation Criteria in Solid Tumors). Using either histologic evaluation or micro-CT imaging, mice with partial Hus1 impairment have a decreased tumor burden at 1- and 3- weeks after cisplatin treatment, as compared to mice with wild type Hus1. Overall, this data identifies a role for HUS1 in the response of normal and neoplastic tissues to the DNA-damaging chemotherapeutic, cisplatin. Understanding tissue specific responses to cisplatin is important for determining how therapeutics targeting the DDR will work cooperatively with traditional cytotoxic agents in the treatment of cancer. This abstract is also being presented as Poster B08. Citation Format: Terese E. Noe, Cleo C. Siderides, Aitor Gallastegui, James M. Cheung, Tina Abratte, Kelly R. Hume. Normal and neoplastic tissues with partial Hus1 impairment show hypersensitivity to cisplatin in vivo [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr PR16.