xenobiotics. To determine if chronic EGFR inhibition affected males similarly to females, a cohort of 6 8 week old male B6 mice were fed AG 1478 or control diets under identical conditions. Male mice had no significant differences in body weight gain, Celecoxib Celebrex organ weights or cardiovascular function after 90 days of treatment, nor significant differences in cardiac pathology. Aortic valves tended to be larger with AG 1478 treatment, but this did not reach significance. There were also no significant changes in cardiac expression of apoptotic genes by treatment groups. However, the hypertrophy marker Nppb was upregulated in the hearts of AG 1478 treated male mice, despite the fact that mean cardiomyocyte area was unchanged. Unlike females, Erbb2 and Egf transcripts were upregulated compared to controls, suggestive of compensatory changes.
Discussion Consistent with previous reports using TKIs EKB 569 or EKI 785, we demonstrated that dietary delivery of the EGFR small molecule inhibitor AG 1478 effectively represses EGFR kinase activity and tumorigenesis c-Met inhibitor drug in vivo. Employing chronic oral exposure of AG 1478 and EKB 569, TKIs from different chemical classes, we found marked changes in weight gain and cardiac function in B6 female mice. Drug exposure also resulted in pathological changes indicative of cardiotoxicity. Most notably, the number of TUNEL positive cells was increased by nearly threefold in the hearts of AG 1478 treated female B6 mice compared to controls, which was supported molecularly by significantly decreased expression of the anti apoptotic gene Bcl2l1 in cardiac tissue.
Drug treatment also exacerbated diet induced pathological changes in cardiac valves. To our knowledge, this is the first study to extensively evaluate cardiac function and pathology after chronic oral exposure to EGFR TKIs in adult mice, modeling exposure of patients to EGFR TKIs in the oncology clinic. Interestingly, gender may influence response to TKIs, as unlike females, we saw no differences in physiological and pathological parameters by treatment in male B6 mice. Although we detected no significant differences by gender or treatment in cardiac EGFR expression, sexual dimorphism in basal EGF levels has been reported with male mice having higher protein levels in salivary glands and higher transcript levels in pituitary glands compared to females.
Since we found that Egf, Erbb2 and Nppb transcripts were upregulated in the LV of male but not female AG 1478 exposed mice relative to their respective controls, it is possible that increased expression of these genes in the male heart, coupled with higher circulating ligand levels in males, may compensate for reduced EGFR activity and contribute to the observed male specific protection from cardiotoxicity. Results of our studies suggest that EKB 569 may be more toxic than AG 1478. EKB 569 exposure resulted in body weight loss, compared to suppression of body weight gain with AG 1478 treatment. Interestingly, reports from Phase I clinical trials reported anorexia in approximately 20% of patients receiving intermittent doses of EKB 569. Similarly, hearts from EKB 569 treated mice had thinner LV walls and significantly more TUNEL positive cells compared to controls, although AG 1478 caused greater depression in systolic function. Despite milder changes in cardiac contractility, wet lung weights were significantly increase