Abstract C31: DMBA-induced skin tumors in HPV16 E7 transgenic mice are affected by bovine α-lactalbumin made lethal to tumor cells (BAMLET)
Authors: Barman Provaboti , DeAzambuja Katherine Marie , Toyama Joy Ai , Lee Deborah , Chua Kristopher , Elashoff David , Wiley Dorothy J. 
Published: June 2012

Background and Purpose: Human papillomavirus Type 16 (HPV16) infection is necessary but not alone a sufficient causal risk factor for cervical and other anogenital cancers and nearly 25% of head and neck malignancies (1, 2). HPV16 E7 is one of the important oncoproteins that promotes carcinogenesis. Most treatments for cervical precancers are ablative and few therapeutic drugs are available. Human α-Lactalbumin Made Lethal to Tumor Cells (HAMLET), a complex of Human α-Lactalbumin and oleic acid shows promise for treating skin papillomas by differentially inducing apoptosis in transformed cells without adverse effects on normal cells. Bovine α-Lactalbumin Made Lethal to Tumor Cells (BAMLET) has been shown to be biologically equivalent to HAMLET (3) and in vitro studies suggest BAMLET and HAMLET show similar cytotoxic effects in tumor cell lines (4). Further, in vitro studies suggest both a dose- and time-dependent response to BAMLET treatment (3–6). To determine the effect of BAMLET on tumor number, size and histological characteristics in vivo, we compared two groups of BAMLET-treated with normal saline (NS)-treated HPV16 E7 transgenic C57/BL6 mice (TG) and syngeneic mice receiving chemical carcinogen DMBA topically to induce skin tumor.

Methods: For 56 TG and syngeneic mice, in six treatment groups, 100nmol/200μl DMBA was applied topically on the dorsal thoracic flank for up to 20 weeks. BAMLET, 0.7 mM, was applied daily for 7d before and either 11d (18d BAMLET) or up to 23 weeks (24w BAMLET) following DMBA initiation. As a comparison, NS was similarly applied to 10 TG and syngeneic mice for a total of 24 weeks. A series of bivariate zero-inflated repeated-measures Poisson (ZIP) models predicted the number of papillomas based on TG/syngeneic groupings, and treatment group. The fully adjusted model evaluated the effect of the TG, treatment group and duration, and time on study for predicting the number of tumors. Least-squares linear regression (LSLR) was used to estimate the effect of treatment on average tumor size at censoring or death, controlling for the effect of gender, among the transgenic mice.

Results: On average, papillomas developed after 9 weeks of DMBA treatment. Analyses showed TG-mice developed more tumors than did syngeneic mice (p&lt;0.0001), controlling for the effect of time on study (p&lt;0.0001). In the fully adjusted analyses, the number of tumors was most affected by the TG (p&lt;0.0001) and time on study (p&lt;0.0001), but treatment showed no effect: 18d (p=0.9) and 24w (p=0.8) vs. normal saline (NS). Among transgenic mice, time on study was shorter than for syngeneic comparators and was a proxy indicator across treatment groups, confounding the ZIP analyses. Among transgenic mice, BAMLET treatment predicted average tumor size at censoring or death in the LSLR analysis. Specifically, among transgenic mice, the average tumor size was greatest for the 18d (μ=0.24 cm, p=0.003) and 24w BAMLET-treated (μ=0.20 cm, p=0.03) mice when compared to NS-treated controls (μ=0.12 cm).

Discussion and Conclusion: These preliminary data suggest the effect of the transgene is strong on the number of tumors the result from DMBA treatment and on survival. This strong effect suggests we lack the power to detect an effect of BAMLET in transgenic mice. However, some data herein suggest BAMLET may increase average tumor size among HPV16-E7 transgenic mice. In light of positive findings in human clinical studies using the human analogue, HAMLET, understanding whether the effects of α-Lactalbumins and oleic acid complexes are modulated by HPV E6, E7, or E6/E7 oncogenes warrants further exploration.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C31.