PURPOSE Acquired resistance to anti-EGFR therapy (EGFRi) in CRC has previously been explained by the model of acquiring new mutations in KRAS/NRAS/EGFR, among other MAPK-pathway members. However, this was primarily based on single-agent EGFRi trials and little is known about the resistance mechanisms of EGFRi combined with effective cytotoxic chemotherapy in previously untreated patients. METHODS We analyzed paired plasma samples from RAS/BRAF/EGFR wild-type mCRC patients enrolled in three large randomized trials evaluating EGFRi in the first-line in combination with chemotherapy and as a single-agent in third-line. The mutational signature of the alterations acquired with therapy was evaluated. CRC cell lines with resistance to cetuximab, FOLFOX, and SN38 were developed, and transcriptional changes profiled. RESULTS Patients whose tumors were treated with and responded to EGFRi alone were more likely to develop acquired mutations (46%) compared to those treated in combination with cytotoxic chemotherapy (9%). Further, contrary to the generally accepted hypothesis of the clonal evolution of acquired resistance, we demonstrate that baseline resistant subclonal mutations rarely expanded to become clonal at progression, and most remained subclonal or disappeared. Consistent with this clinical finding, preclinical models with acquired resistance to either cetuximab or chemotherapy were cross-resistant to the alternate agents, with transcriptomic profiles consistent with epithelial-to-mesenchymal transition (EMT). In contrast, commonly acquired resistance alterations in the MAPK pathway do not impact sensitivity to cytotoxic chemotherapy. CONCLUSION These findings support a model of resistance whereby transcriptomic mechanisms of resistance predominate in the presence of active cytotoxic chemotherapy combined with EGFRi, with a greater predominance of acquired MAPK mutations after single-agent EGFRi. The proposed model has implications for prospective studies evaluating EGFRi rechallenge strategies guided by acquired MAPK mutations, and highlights the need to address transcriptional mechanisms of resistance.

KRAS and NRAS mutations occur in 45% of colorectal cancers (CRC), with combined MAPK pathway and CDK4/6 inhibition identified as a potential therapeutic strategy. In the current study, this combinatorial treatment approach was evaluated in a co-clinical trial in patient-derived xenografts (PDX), and safety was established in a clinical trial of binimetinib and palbociclib in metastatic CRC patients with RAS mutations. Across 18 PDX models undergoing dual inhibition of MEK and CDK4/6, 60% of tumors regressed, meeting the co-clinical trial primary endpoint. Prolonged duration of response occurred predominantly in TP53 wild-type models. Clinical evaluation of binimetinib and palbociclib in a safety lead-in confirmed safety and provided preliminary evidence of activity. Prolonged treatment in PDX models resulted in feedback activation of receptor tyrosine kinases and acquired resistance, which was reversed with a SHP2 inhibitor. These results highlight the clinical potential of this combination in CRC, along with the utility of PDX-based co-clinical trial platforms for drug development.

Designing studies of immunotherapy is limited due to a lack of pre-clinical models that reliably predict effective immunotherapy responses. To address this gap, we developed humanized mouse models of colorectal cancer (CRC) incorporating patient-derived xenografts (PDX) with human peripheral blood mononuclear cells (PBMC). Humanized mice with CRC PDXs were generated via engraftment of autologous (isolated from the same patients as the PDXs) or allogeneic (isolated from healthy donors) PBMCs. Human T cells were detected in mouse blood, tissues, and infiltrated the implanted PDXs. The inclusion of anti-PD-1 therapy revealed that tumor responses in autologous but not allogeneic models were more comparable to that of patients. An overall non-specific graft-vs-tumor effect occurred in allogeneic models and negatively correlated with that seen in patients. In contrast, autologous humanized mice more accurately correlated with treatment outcomes by engaging pre-existing tumor specific T-cell populations. As autologous T cells appear to be the major drivers of tumor response thus, autologous humanized mice may serve as models at predicting treatment outcomes in pre-clinical settings for therapies reliant on pre-existing tumor specific T-cell populations.

In this article, the authors investigate the achievement gap in the context of a particular region and the factors associated with student learning in that region. Data were collected over several years from recent administrations of the mathematics section of the Measurement of Academic Progress in Colorado. Black and Hispanic mathematics achievement and growth were compared to White student achievement and growth. The results indicate that gaps exist not only in mathematics achievement but also in mathematics growth. A statistically significant difference in mathematics growth rates between Black and Hispanic students from different economic backgrounds were found; however, a statistically significant difference in mathematics growth rates by gender was only found in Black and Hispanic third grade students. The authors provide explanations as well as implications of the factors associated with the results with the hope of influencing research and practice.

Purpose: Encorafenib plus cetuximab is an effective therapeutic option in chemorefractory BRAFV600E mCRC. However, there is a need to improve the efficacy of this molecular targeted therapy and evaluate regimens suitable for untreated BRAFV600E mCRC patients. Experimental Design: We performed a series of in vivo studies using BRAFV600EmCRC tumor xenografts. Mice were randomized to receive: 5-fluoruracil, irinotecan or oxaliplatin regimens (FOLFIRI or FOLFOX), encorafenib plus cetuximab (E+C) or the combination. Treatments included long term treatment until progression, with de-escalation strategies replicating maintenance treatments. Transcriptomic changes after progression on cytotoxic chemotherapy or targeted therapy were assessed. Results: Antitumor activity of either FOLFIRI or E+C was better in first-line as compared to second-line, with partial cross-resistance seen between cytotoxic regimen and targeted therapy with average 62% loss of efficacy for FOLFIRI after E+C and 45% loss of efficacy of E+C after FOLFIRI (p<0.001 for both). FOLFIRI treated models had upregulation of EMT and MAPK pathway activation, where E+C treated models had suppressed MAPK signaling. In contrast, with chemotherapy with E+C, EMT and MAPK signaling remained suppressed. FOLFOX or FOLFIRI, each in combination with E+C, were the most active first-line treatments as compared to E+C or to chemotherapy alone. Further, FOLFOX in combination with E+C as first-line induction therapy, followed by E+C +/- 5-FU as maintenance therapy, was the most effective strategy for long term disease control. Conclusions: These results support the combination of cytotoxic chemotherapy and molecular targeted therapy as a promising therapeutic approach in the first-line treatment of BRAFV600E mCRC.