Therapeutic potential of dual CDK12 and 13 inhibition in colorectal cancer.

Abstract

e15601 Background: To date, studies on cyclin-dependent kinase inhibitors in colorectal cancer (CRC), such as targeting CDK4/6 with Palbociclib, have shown little to no clinical benefit. However, tumor profiling of CRC has shown that mutations and amplifications in CDK 12 and 13 are prevalent in 5 to 10% of CRC patients, suggesting that CDK12/13 inhibition may be a potential target for patients with CRC. Methods: To study the effects of inhibiting CDK12 and 13 in CRC, a total of 11 patient-derived organoids (PDO) were first established from patients undergoing biopsy or resection of their primary or metastatic CRC. In vitro drug sensitivity assays were performed by treating each PDO with THZ531, a selective dual CDK12/13 inhibitor; 5-flurouracil, oxaliplatin and SN38 as a standard of care; or Palbociclib (CDK 4/6 inhibitor) at seven different drug concentrations (0.0064 μM - 100 μM) with five replicates at each concentration. Viability was assessed 72 hours following the addition of each drug using CellTiter-Glo (Promega) and IC50s were calculated. Results: Targeting CDK12/13 with THZ531 demonstrated dose dependent activity in the majority of CRC PDOs, with IC50 values ranging from 0.06 μM to 4.2 μM. In comparison, targeting CDK4/6 with Palbociclib was ineffective, with IC50 values ranging from 2.5 μM to 17 μM (p = 0.0003, 95% CI 3.7 to 10.4). Inhibition of CDK12/13 was also more effective than standard of care chemotherapy with either 5- FU or oxaliplatin (mean IC50 values were 4.2 μM and 21.4 μM for 5-fluorouracil and oxaliplatin, p < 0.05) and was comparable to irinotecan (mean IC50 was 0.07 μM for SN38). Finally, no significant correlation was found between sensitivity to THZ531 and microsatellite status, mutations in RAS and BRAF, or grade of the original patient tumor. Conclusions: We identify dual CDK12/13 inhibition as a promising therapy to treat CRC. Further studies will focus on characterizing mechanisms of action, evaluating efficacy and toxicity in vivo, and determining biomarkers of response based on actionable genomic alterations.