Dietary calcium supplementation enhances efficacy but also toxicity of EGFR inhibitor therapy for colon cancer

The inverse correlation between levels of dietary calcium and colorectal cancer (CRC) incidence has been extensively investigated. However, the impact of supplemental calcium on cancer therapy remains unknown. We used four models of CRC, Caco-2 and HCT116 human cancer cell lines and ApcMin/+ and azoxymethane carcinogen-induced mouse models, to investigate the impact of a Western-style diet low in calcium (0.05%) vs. a similar diet but supplemented with calcium (5%) on therapeutic targeting of the epidermal growth factor receptor (EGFR). We found that calcium supplementation combined with pharmacologic blockade of EGFR results in an additive effect on tumor growth inhibition in all models. Unexpectedly, the combined use of dietary calcium supplementation and EGFR inhibitors also resulted in elevated toxicity suggesting that careful consideration be given when combining dietary supplements with prescribed cancer therapies

Efficacy of EGFR Inhibition Is Modulated by Model, Sex, Genetic Background and Diet: Implications for Preclinical Cancer Prevention and Therapy Trials

Molecule-targeted therapies are being widely developed and deployed, but they are frequently less effective in clinical trials than predicted based upon preclinical studies. Frequently, only a single model or genetic background is utilized using diets that are not relevant to that consumed by most cancer patients, which may contribute to the lack of predictability of many preclinical therapeutic studies. Inhibition of epidermal growth factor receptor (EGFR) in colorectal cancer was used to investigate potential causes for low predictive values of many preclinical studies. The efficacy of the small molecule EGFR inhibitor AG1478 was evaluated using two mouse models, ApcMin/+ and azoxymethane (AOM), both sexes on three genetic backgrounds, C57BL/6J (B6) and A/J (A) inbred strains and AB6F1 hybrids, and two diets, standard chow (STD) or Western-style diet (WD). AG1478 has significant anti-tumor activity in the B6-ApcMin/+ model with STD but only moderately on the WD and in the AOM model on an A background with a WD but not STD. On the F1 hybrid background AG1478 is effective in the ApcMin/+ model with either STD or WD, but has only moderate efficacy in the AOM model with either diet. Sex differences were also observed. Unexpectedly, the level of liver EGFR phosphorylation inhibition by AG1478 was not positively correlated with inhibition of tumor growth in the AOM model. Model-dependent interactions between genetic background and diet can dramatically impact preclinical results, and indicate that low predictive values of preclinical studies can be attributed to study designs that do not account for the heterogeneous patient population or the diets they consume. Better-designed preclinical studies should lead to more accurate predictions of therapeutic response in the clinic

Summary of pair-wise observations of AG1478 inhibitor effect on tumor growth.

<p>SD standard diet; WD, western diet; ↓ corrected p<0.05; trend, uncorrected p<0.05 but corrected p>0.05.</p

Western blot analysis of EGFR signal.

<p>Total EGFR and pEGFR in liver protein lysates from A) APC<i>^Min</i>^/+ and B) AOM mice, separately for each strain and sex. STD = standard diet, WD = western diet, “+”  =  AG1478 treatment and “−“  =  no AG1478 treatment. Below bar graphs are estimated effects and significance based on linear mixed models.</p

Effect of diet, sex and strain on AG1478-mediated tumor number reduction.

<p>A) <i>Apc^Min</i>^/+ small intestinal and colonic tumor number as a percentage of STD without AG1478 treatment for the B6 inbred and AB6F1 (shaded) strains; and B) AOM (A and AB6F1) colonic tumor number expressed as a percent of STD treatment. The raw values for average number of tumors/mouse are displayed below each graph. STD = standard diet, WD = western diet, “+”  =  AG1478 treatment and “−“  =  no AG1478 treatment. Standard Error of the Mean bars are shown for each treatment. Below bar graphs are estimated effects and significance based on linear mixed models.</p

Comparison of diet compositions.

<p>Comparison of diet compositions.</p

Effect of diet, sex and strain on AG1478-mediated tumor size(mm) reduction.

<p>A) <i>Apc^Min</i>^/+ small intestinal and colonic tumor size as a percentage of STD without AG1478 treatment for the B6 inbred and AB6F1 (shaded) strains; and B) AOM (A and AB6F1) colonic tumor size expressed as a percent of STD treatment. The raw values for average size of tumors/mouse are displayed below each graph. STD = standard diet, WD = western diet, “+”  =  AG1478 treatment and “−“  =  no AG1478 treatment. Standard Error of the Mean bars are shown for each treatment. Below bar graphs are estimated effects and significance based on linear mixed models.</p

Dietary calcium supplementation enhances efficacy but also toxicity of EGFR inhibitor therapy for colon cancer

The inverse correlation between levels of dietary calcium and colorectal cancer (CRC) incidence has been extensively investigated. However, the impact of supplemental calcium on cancer therapy remains unknown. We used four models of CRC, Caco-2 and HCT116 human cancer cell lines and Apc(Min/+) and azoxymethane carcinogen-induced mouse models, to investigate the impact of a Western-style diet low in calcium (0.05%) vs. a similar diet but supplemented with calcium (5%) on therapeutic targeting of the epidermal growth factor receptor (EGFR). We found that calcium supplementation combined with pharmacologic blockade of EGFR results in an additive effect on tumor growth inhibition in all models. Unexpectedly, the combined use of dietary calcium supplementation and EGFR inhibitors also resulted in elevated toxicity suggesting that careful consideration be given when combining dietary supplements with prescribed cancer therapies