CRISPR screens reveal convergent targeting strategies against evolutionarily distinct chemoresistance in cancer.

Resistance to chemotherapy has been a major hurdle that limits therapeutic benefits for many types of cancer. Here we systematically identify genetic drivers underlying chemoresistance by performing 30 genome-scale CRISPR knockout screens for seven chemotherapeutic agents in multiple cancer cells. Chemoresistance genes vary between conditions primarily due to distinct genetic background and mechanism of action of drugs, manifesting heterogeneous and multiplexed routes towards chemoresistance. By focusing on oxaliplatin and irinotecan resistance in colorectal cancer, we unravel that evolutionarily distinct chemoresistance can share consensus vulnerabilities identified by 26 second-round CRISPR screens with druggable gene library. We further pinpoint PLK4 as a therapeutic target to overcome oxaliplatin resistance in various models via genetic ablation or pharmacological inhibition, highlighting a single-agent strategy to antagonize evolutionarily distinct chemoresistance. Our study not only provides resources and insights into the molecular basis of chemoresistance, but also proposes potential biomarkers and therapeutic strategies against such resistance.

PD-1 blockade enhances the effect of targeted chemotherapy on locally advanced pMMR/MSS colorectal cancer.

BACKGROUND: Patients with DNA mismatch repair-proficient/microsatellite stable (pMMR/MSS) colorectal cancer (CRC), which accounts for 85% of all CRC cases, display a poor respond to immune checkpoint inhibitors (i.e., anti-PD-1 antibodies). pMMR/MSS CRC patients with locally advanced cancers need effective combined therapies. METHODS: In this pilot study, we administered six preoperative doses of each 2-week cycle of the anti-PD-1 antibody sintilimab (at a fixed dose of 200 mg), oxaliplatin, and 5-FU/CF (mFOLFOX6) combined with five doses of bevacizumab (the number of doses was reduced to prevent surgical delays) to patients with cT4NxM0 colon or upper rectal cancers. And radical surgery was performed approximately 2 weeks after the last dose of neoadjuvant therapy. The primary endpoint was a pathologic complete response (pCR). We also evaluated major pathologic response (MPR, ≤10% residual viable tumor), radiological and pathological regression, safety, and tumor mutation burden (TMB), and tumor microenvironment (TME) characteristics. RESULTS: By the cutoff date (September 2023), 22 patients with cT4NxM0 pMMR/MSS colon or upper rectal cancers were enrolled and the median follow-up was 24.7 months (IQR: 21.1-26.1). All patients underwent R0 surgical resection without treatment-related surgical delays. pCR occurred in 12 of 22 resected tumors (54.5%) and MPR occurred in 18 of 22 (81.8%) patients. At the cutoff date, all patients were alive, and 21/22 were recurrence-free. Treatment-related adverse events of grade 3 or higher occurred in of 2/22 (9.1%) patients. Among the pCR tumors, two were found to harbor POLE mutations. The degree of pathological regression was significantly greater than that of radiological regression (p = 1.35 × 10-8). The number of CD3+/CD4+ cells in the tumor and stroma in pretreated biopsied tissues was markedly lower in pCR tumors than in non-pCR tumors (p = 0.038 and p = 0.015, respectively). CONCLUSIONS: Neoadjuvant sintilimab combined with bevacizumab and mFOLFOX6 was associated with few side effects, did not delay surgery, and led to pCR and non-pCR in 54.5% and 81.8% of the cases, respectively. Downregulation of CD3/CD4 expression in the tumor and stroma is related to pCR. However, the molecular mechanisms underlying PD-1 blockade-enhanced targeted chemotherapy require further investigation.

Single-Agent Neoadjuvant Immunotherapy With a PD-1 Antibody in Locally Advanced Mismatch Repair-Deficient or Microsatellite Instability-High Colorectal Cancer.

BACKGROUND: PD-1 blockade has been recommended as first-line therapy for nonresectable or metastatic mismatch repair-deficient/microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC). However, the safety and efficacy of neoadjuvant PD-1 blockade immunotherapy for locally advanced dMMR/MSI-H CRC remain unclear. PATIENTS AND METHODS: From June 2020 to June 2022, 11 locally advanced dMMR/MSI-H CRC patients treated at the Sixth Affiliated Hospital of Sun Yat-sen University (Guangzhou, China) were enrolled. All patients received 6 sintilimab (Innovent, LTD) injections (200 mg/injection, every 3 weeks) before radical laparoscopic resection. The patient clinical and pathological data were analyzed retrospectively. RESULTS: dMMR was confirmed by immunohistochemistry for all patients. However, polymerase chain reaction (PCR) or next-generation sequencing confirmed MSI-H for only 90.9% (10/11) of the patients, while 1 patient had microsatellite stable (MSS) disease. After 6 injections of neoadjuvant anti-PD-1 therapy, 90.9% (10/11) of the patients (those confirmed to have dMMR and MSI-H disease) achieved pathological complete response (pCR). The other patient, who achieved major pathological response with residual tumor <1%, had dMMR but MSS disease. No grade 3 or above immunotherapy-related adverse events occurred [Common Terminology Criteria for Adverse Events ; version 5.0]. Overall, 72.7% (8/11) of the patients had grade 1-2 immunotherapy-related adverse events . No operational mortality or complications occurred within 30 days after surgery. CONCLUSION: Single-agent neoadjuvant PD-1 antibody immunotherapy was safe and effective in locally advanced dMMR/MSI-H CRC. Dual confirmation of MMR and MSI status by immunohistochemistry and next-generation sequencing or PCR is necessary for dMMR/MSI-H CRC patients before immunotherapy. The immunotherapy regimen used in this study deserves further validation in phase II and III clinical studies.

Molecular Typing and Clinical Characteristics of Synchronous Multiple Primary Colorectal Cancer.

Importance: Synchronous multiple primary colorectal cancer (sMPCC) is clinically rare, but its incidence has increased over the past decade. However, little is known about the molecular and clinical features of sMPCC, which may differ from those of single primary colorectal cancer (SPCRC). Objective: To evaluate the clinical characteristics and pathogenic variations in lesions and the molecular typing of sMPCC. Design, Setting, and Participants: From November 2012 to April 2021, patients with colorectal cancer (CRC) treated at the Sixth Affiliated Hospital of Sun Yat-sen University were enrolled in this cohort study. Follow-up ended on January 31, 2022. Main Outcomes and Measures: The primary outcome was mismatch repair (MMR) status of each lesion in all patients examined using immunohistochemistry (IHC). Microsatellite instability (MSI) and tumor mutation burden (TMB) were also calculated. Results: A total of 13 276 patients with CRC were enrolled, and 239 patients with sMPCC (mean [SD] age, 63.3 [12.2] years; 173 men [72.4%]) with available clinical data were evaluated. Seventy-eight patients with sMPCC and 94 with SPCRC also underwent next-generation sequencing (NGS)-based molecular testing. The deficient MMR (dMMR)/MSI-H frequencies in sMPCC were significantly higher than those in SPCRC, which was confirmed by both IHC (50 of 239 patients vs 872 of 13 037 patients) and NGS (17 of 78 patients vs 5 of 94 patients). According to the MMR/MSI status of different lesions in patients with sMPCC, they were further divided into 3 subgroups: all dMMR/MSI-H, dMMR/MSI-H and proficient MMR (pMMR)/microsatellite stability (MSS), and all pMMR/MSS. The EGFR and PIK3CA variants were more common, whereas TP53 variants were less prevalent in patients with sMPCC than in those with SPCRC. Moreover, higher tumor mutation burden was associated with higher MSI in patients with sMPCC rather than in those with SPCRC. Conclusions and Relevance: In this cohort study of sMPCC, the incidence of dMMR/MSI-H in patients with sMPCC was significantly higher than that in patients with SPCRC. These findings suggest that sMPCC can be classified into 3 subgroups according to the MMR/MSI status of each lesion, which might be applied to guide personalized therapies for better disease management.