Phosphatase and Tensin Homologue on chromosome Ten (PTEN) is a tumor suppressor and an antagonist of the phosphoinositide-3 kinase (PI3K) pathway. We identified a 576-amino acid translational variant of PTEN, termed PTEN-Long, that arises from an alternative translation start site 519 bp upstream of the ATG initiation sequence, adding 173 N-terminal amino acids to the normal PTEN open reading frame. PTEN-Long is a membrane permeable lipid phosphatase that is secreted from cells and can enter other cells. As an exogenous agent, PTEN-Long antagonized PI3K signaling and induced tumor cell death in vitro and in vivo. By providing a means to restore a functional tumor suppressor protein to tumor cells, PTEN-Long may have therapeutic uses.
Basal-like breast cancers (BBCs) are enriched for increased EGFR expression and decreased expression of PTEN. We found that treatment with metformin and erlotinib synergistically induced apoptosis in a subset of BBC cell lines. The drug combination led to enhanced reduction of EGFR, AKT, S6 and 4EBP1 phosphorylation, as well as prevented colony formation and inhibited mammosphere outgrowth. Our data with other compounds suggested that biguanides combined with EGFR inhibitors have the potential to outperform other targeted drug combinations and could be employed in other breast cancer subtypes, as well as other tumor types, with activated EGFR and PI3K signaling. Analysis of BBC cell line alterations led to the hypothesis that loss of PTEN sensitized cells to the drug combination which was confirmed using isogenic cell line models with and without PTEN expression. Combined metformin and erlotinib led to partial regression of PTEN-null and EGFR-amplified xenografted MDA-MB-468 BBC tumors with evidence of significant apoptosis, reduction of EGFR and AKT signaling, and lack of altered plasma insulin levels. Combined treatment also inhibited xenografted PTEN null HCC-70 BBC cells. Measurement of trough plasma drug levels in xenografted mice and a separately performed pharmacokinetics modeling study support possible clinical translation.
In Canada, as in many developed countries, healthcare conscientious objection is growing in visibility, if not in incidence. Yet the country's health professional policies on conscientious objection are in disarray. The article reports the results of a comprehensive review of policies relevant to conscientious objection for four Canadian health professions: medicine, nursing, pharmacy and dentistry. Where relevant policies exist in many Canadian provinces, there is much controversy and potential for confusion, due to policy inconsistencies and terminological vagueness. Meanwhile, in Canada's three most northerly territories with significant Aboriginal populations, whose already precarious health is influenced by funding and practitioner shortages, there are major policy gaps applicable to conscientious objection. In many parts of the country, as a result of health professionals' conscientious refusals, access to some legal health services - including but not limited to reproductive health services such as abortion - has been seriously impeded. Although policy reform on conscientious conflicts may be difficult, and may generate strenuous opposition from some professional groups, for the sake of both patients and providers, such policy change must become an urgent priority.
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