Phase II study of lamivudine in p53 mutant metastatic colorectal cancer (mCRC).

Abstract

149 Background: Non-coding repeat RNAs in cancers are pervasive and “mimic” viruses with activation of pattern recognition receptors and the innate immune response. Many repeat RNAs replicate in cancer genomes through a reverse transcriptional intermediate analogous to retroviruses. Nucleoside reverse transcriptase inhibitors (NRTIs) block this retroviral life cycle to increases repeat RNAs in p53 mutant colon cancer cell cancer lines. We initiated a Phase 2 study of lamivudine (3TC) in TP53 mutant mCRC. Methods: Two-stage design with target accrual of 20 patients (pts) in stage 1 and total of 32. Eligibility: pts with p53 mutant refractory mCRC with progression on or intolerance to 5FU, oxaliplatin and irinotecan and anti-EGFR if RAS WT. RNA sequencing was performed on pre-treatment (tx) and on tx biopsy to evaluate for repeat RNA expression and expression of other genes linked to 3TC response/resistance. Radiation was allowed. 9 pts were treated with 3TC 150 mg po bid for 28-day cycles, the maximum FDA approved dose of 3TC in HIV. Subsequent pts were treated at 600 mg po bid, previously tested in P1 trials. Tumor assessments were performed every 8 weeks until documented disease progression by RECIST 1.1 criteria or drug intolerance. Results: 29/32 pts have been treated. Median age: 60 yrs. (27-82) 18 males, 11 females. 2/ 9 (22%) pts on standard 3TC dosing had stable disease (SD) on single agent 3TC with a duration of tx of 169 and 167 days, respectively. Both pts had an initial drop in CEA upon initiation of 3TC. Of the next 20 pts on high dose 3TC, 19 were evaluable. 4 had SD, for 110, 159, 130 and 228+ days. 14 pts had tx-related adverse events (TRAE). 1 pt with a definite Grade 1 TRAE (fatigue). No pts with Grade ≥3 TRAEs. We obtained pre-tx fresh frozen biopsies on 24/29 pts. Of those with SD, 4 had biopsies and differential expression identified significantly higher HSATII repeat RNA in pts with SD compared to PD. There was an association of decreased epigenetic gene expression in HSATII repeat RNA high tumors. Conclusions: This proof-of-concept study demonstrates the safety and activity of single-agent 3TC. Repeat RNA levels appear to correlate with clinical benefit and can be measured in biopsies. Further combination studies and correlatives are planned. Clinical trial information: NCT03144804.