Abstract Purpose: PI3K pathway activation occurs in concomitance with RAS/BRAF mutations in colorectal cancer, limiting the sensitivity to targeted therapies. Several clinical studies are being conducted to test the tolerability and clinical activity of dual MEK and PI3K pathway blockade in solid tumors. Experimental Design: In the present study, we explored the efficacy of dual pathway blockade in colorectal cancer preclinical models harboring concomitant activation of the ERK and PI3K pathways. Moreover, we investigated if TP53 mutation affects the response to this therapy. Results: Dual MEK and mTORC1/2 blockade resulted in synergistic antiproliferative effects in cell lines bearing alterations in KRAS/BRAF and PIK3CA/PTEN. Although the on-treatment cell-cycle effects were not affected by the TP53 status, a marked proapoptotic response to therapy was observed exclusively in wild-type TP53 colorectal cancer models. We further interrogated two independent panels of KRAS/BRAF- and PIK3CA/PTEN-altered cell line– and patient-derived tumor xenografts for the antitumor response toward this combination of agents. A combination response that resulted in substantial antitumor activity was exclusively observed among the wild-type TP53 models (two out of five, 40%), but there was no such response across the eight mutant TP53 models (0%). Interestingly, within a cohort of 14 patients with colorectal cancer treated with these agents for their metastatic disease, two patients with long-lasting responses (32 weeks) had TP53 wild-type tumors. Conclusions: Our data support that, in wild-type TP53 colorectal cancer cells with ERK and PI3K pathway alterations, MEK blockade results in potent p21 induction, preventing apoptosis to occur. In turn, mTORC1/2 inhibition blocks MEK inhibitor–mediated p21 induction, unleashing apoptosis. Clin Cancer Res; 21(24); 5499–510. ©2015 AACR.

This file contains information about protein immunoblotting, histopathological analysis, and cell biological assays in cultured cells.

PDF file - 93K, Distribution of the PAM50 intrinsic subtypes based on RORP score groups.

Analysis of angiogenic islet upon genetic inactivation of p110α, p110β and p110Î' ; Supplemental Figure 4 Legend

Analysis of GDC-0941 effects on cell proliferation ; Supplemental Figure 2 Legend

PDF file 2251K, Supplementary Figure S2. PI3K, but not AKT or mTOR, is upstream of the ERK signaling pathway. Related to main Figure 2

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Supplementary Figure S1; Supplementary Appendix.

Breakdown of MAP2K1, RAF1, ARAF, FGFR3-TACC3 fusion and CDKN2A loss patients

Supplementary Figure S1. Distribution of HER2 expression (measured by HERmark) in all patients (left) and in 3+ IHC cohort patients (right). All patient: n=324; IHC3+: n=232.

Supplementary Table S1. Patient Demographics and Disease Characteristics. Supplementary Table S2. Treatment-Related Adverse Events of Grade 3 or Higher Observed in either Cycle 1 or Cycle greater than or equal to 2. Supplementary Table S3. Adverse Events in greater than or equal to 10% of Patients Regardless of Attribution. Supplementary Table S4. Adverse Events of Grade 3 or Higher Regardless of Attribution. Supplementary Figure S1. Trellis plot of individual and fitted tumor volumes to day 21 following treatment with taselisib (GDC-0032). Supplementary Figure S2. PI3K pathway suppression was evaluated in KPL-4 tumor xenografts following a single oral dose of 1, 5 and 25 mg/kg taselisib or MCT (0.5% methylcellulose/0.2% Tween-80) vehicle at the time points indicated. Supplementary Figure S3. Schematic showing the decision-making related to selection of recommended dose for future studies. Supplementary Figure S4. Mean plasma concentration vs. time following single dose on day 1 (A) and multiple dose on day 15 (B). Supplementary Figure S5. Duration of treatment of patients treated via PIK3CA mutation status and dose level. Supplementary Figure S6. Antitumor activity observed with taselisib treatment. Supplementary Figure S7. Example of patient with partial response upon taselisib treatment and changes in circulating tumor DNA (ctDNA).

PDF file - 624K, Relationship between sonidegib area under the plasma concentration-time curve on day 15 and the incidence of grade 3/4 creatine kinase elevation.

PDF file - 6224K, Inhibition of MEK-ERK pathway signaling in tumor biopsies.

PDF file - 59K, Pharmacodynamic Parameters

Clinical activity in patients with and without measurable disease at baseline

Supplemental Methods. Supplemental Table 1: ââ,¬â€¹Genomic Data Characterization by Center. Supplemental Table 2: ââ,¬â€¹Gene Panels Submitted by Each Center. Figure S1: Number of putative germline SNPs per sample, before and after uniform germline filtering. Figure S2ââ,¬â€¹. Distribution of total somatic mutation burden per sample stratified by sequencing panel. Figure S3: ââ,¬â€¹Log-scale comparison of mutation frequencies at hotspot sites between GENIE (data aggregated from all sequencing panels) and cancerhotspots.org (CHS) using a binomial test. Figure S4:ââ,¬â€¹ Comparison of mutation frequencies at hotspot sites in each GENIE sequencing panel with cancerhotspots.org (CHS) using a binomial test.

Supplementary Figure 1: Early adaptive resistance limits the efficacy of CDK4/6 inhibition. High-throughput drug screen identified PI3K-mTOR inhibitors as sensitizers to CDK4/6 inhibitors. Supplementary Figure 2: Determinants of sensitivity to the combination CDK4/6 and PI3K inhibition. Supplementary Figure 3: Early adaptation to CDK4/6 inhibition is mediated by non-canonical cyclin D1-CDK2 interaction. IGF1R inhibition increases sensitivity to CDK4/6 inhibition in MCF-7 cells. Supplementary Figure 4: Palbociclib induced senescence like morphology is reversible. Supplementary Figure 5: Acquired palbociclib resistance through RB1 loss or CCNE1 amplification/expression. Supplementary Figure 6: Body weight of mice during vehicle, BYL719, LEE011 or combination treatment. Supplementary Figure 7: The combination LEE011 and BYL719 is more effective in ER positive PDX than single agent treatments.

PDF file - 50K, Description of Combining SNP6.0 and 250K Platforms