and here it is...lapatinib resistance due to ER signalling

[Lani]

Would probably imply that lapatinib works better in her2+ER- patients--unless the selective pressure caused the ER- tumor to become ER+ (does this happen?)-- and, that her2+er+ patients should be on the best antihormonal possible (now that is truly controversial and unknown--ie, tam vs ai vs Faslodex) if on lapatinib chronically. Also this would imply the need for concurrent administration of both drugs, a costly affair.

1: Proc Natl Acad Sci U S A. 2006 May 8; [Epub ahead of print] Links

A model of acquired autoresistance to a potent ErbB2 tyrosine kinase inhibitor and a therapeutic strategy to prevent its onset in breast cancer.

Xia W, Bacus S, Hegde P, Husain I, Strum J, Liu L, Paulazzo G, Lyass L, Trusk P, Hill J, Harris J, Spector NL.

Departments of Oncology Biology and Genomic and Proteomic Sciences, GlaxoSmithKline, Research Triangle Park, NC 27709.

The development of acquired resistance to ErbB2 tyrosine kinase inhibitors limits the clinical efficacy of this class of cancer therapeutics. Little is known about the mechanism(s) of acquired resistance to these agents. Here we establish a model of acquired resistance to N-{3-chloro-4-[(3-fluorobenzyl) oxy]phenyl}-6-[5-({[2 (methylsulfonyl)ethyl]amino}methyl)-2-furyl]-4-quinazolinamine (lapatinib), an inhibitor of ErbB2 and ErbB1 tyrosine kinases by chronically exposing lapatinib-sensitive ErbB2-overexpressing breast cancer cells to lapatinib, simulating the clinic where lapatinib is administered on a daily chronic basis. Analysis of baseline gene expression in acquired lapatinib-resistant and parental cells indicates estrogen receptor (ER) signaling involvement in the development of resistance. Using gene interference, we confirm that acquired resistance to lapatinib is mediated by a switch in cell survival dependence and regulation of a key antiapoptotic mediator from ErbB2 alone to codependence upon ER and ErbB2 rather than loss of ErbB2 expression or insensitivity of ErbB2 signaling to lapatinib. Increased ER signaling in response to lapatinib is enhanced by the activation of factors facilitating the transcriptional activity of ER, notably FOXO3a and caveolin-1. Importantly, we confirm that lapatinib induces ER signaling in tumor biopsies from patients with ErbB2-overexpressing breast cancers receiving lapatinib therapy. These findings provided the rationale for preventing the development of acquired resistance by simultaneously inhibiting both ER and ErbB2 signaling pathways. Establishing clinically relevant models of acquired resistance to ErbB2 kinase inhibitors will enhance therapeutic strategies to improve clinical outcomes for patients with ErbB2-overexpressing breast cancers.

PMID: 16682622 [PubMed - as supplied by publisher]

[pattyz]

I totally can't read this/ understand this. My question would be: Since Tykerb/Lapatinib seems to cross bbb, would it then be effective if one is er+ pr- Her2+++ ????? Or NOT????

that's how it would apply to me, with brain mets dx.

pattyz

[al from Canada]

This is a great post Lani,
It only makes sense.... one way to resensitize ER inhibitor resistant BC cells is to give a HER1 inhibitor so it makes sense to give a ER inhibitor for HER type drug resistance. Slamon said some of his best results are with cuncerrent faslodex and herceptin. Lapatinib + an aromitase inhibitor....I sure wish that was available 6 months ago!

Al