RTKs and rational cancer therapy Dr Andrejs Liepins/Science Photo Library

Are we making progress?

In looking at “5-year” survival, we need to remember we are are making a LOT of progress in cancer detection for some cancers

And we need to remember advances in detection when it comes to “survival rates”

How does current chemotherapy work?

KILL dividing cells!

Chemotherapy kills all dividing cells Amanda Dugger 2007 ACS Hero of Hpe

There has to be a better way! Amanda Dugger 2007 ACS Hero of Hpe

Bishop and Varmus Let ’ s go Back to the 1970s

Retroviruses can cause cancer by picking up mutated versions of normal cellular genes Alberts et al. Fig

Many viral oncogenes are kinases, including RTKs Alberts et al.

Different families of RTKs recognize a diverse set of different ligands Alberts et al. Fig

And that was just a few of the RTK families doi: /j.cell

Valberga, Anals. Oncogene 07 Adding complexity, in mammals many RTKs and ligands are encoded by multi-gene families The EGF receptor family The EGF Ligand family

Ligand binding activates RTKs by dimerization Lodish et al. Fig

RTK signaling ultimately leads to activation of a transcription factor Gilbert Fig. 6.14

Most ligands that induce receptor dimerization act as dimers Alberts et al. Fig

EGF and TGF-alpha induce receptor dimerization by an unusual mechanism Garrett et al., Ogiso et al., Cell 2002, 110: 763, 775

“ Neuroblastoma is one of the most common solid tumours of early childhood usually found in babies or young children. The disease originates in the adrenal medulla or other sites of sympathetic nervous tissue. The most common site is the abdomen (near the adrenal gland). Most patients have widespread disease at diagnosis. ” Neu = HER2 was first found in a Neuroblastoma cell line

While HER2 is overexpressed in some neuroblastomas, it is not commonly mutated there

However, it did provide the earliest example of a mutated RTK in a tumor

Her discovery allowed Cori Bargmann to make a bold prediction

"I prefer the clustering model- a series of receptors on the membrane.... all have to bind with growth factor more or less simultaneously.... Only after they are clustered are they able to send along the signal... The insertion of a glutamic acid into the transmembrane domain could trick the neu protein into believing it was surrounded by other neu receptors even when it stood alone"

"I prefer the clustering model- a series of receptors on the membrane.... all have to bind with growth factor more or less simultaneously.... Only after they are clustered are they able to send along the signal... The insertion of a glutamic acid into the transmembrane domain could trick the neu protein into believing it was surrounded by other neu receptors even when it stood alone" She was right!

Activating mutations in RTKs take several forms but all lead to ligand-independent dimerization and thus activation Lodish et al. Fig

A chimeric oncogenic version of the trk RTK isolated from a human colon carcinoma Here ’ s a cool example Lodish et al. Fig

Tropomyosin dimerization dimerizes the receptor even in the absence of ligand Lodish et al. Fig

However, mutational activation of RTKs in human tumors is rare

So why are you telling us all this?

Gene amplification is also a common mechanism of inappropriate gene activation in human tumors Double minute chromosomesTandem duplications Alberts et al. Fig

Kim et al, JKMS 08 HER2 amplified HER2 normal HER2 is Amplified in 30% of Breast Cancers & patients with HER2 amplification have a worse prognosis

HER2 and other RTKs are also amplified in other cancers Met amplified in drug resistance lung cancers EGFR amplified in some glioblastomas and lung cancers HER2 amplified in some bladder cancers Kit amplified in some gastrointestinal stromal tumors

They are enzymes-- what should we do?

An example of an inhibitor (in red and green) designed to block the active site of the insulin receptor tyrosine kinase (in gray)

Iressa, an EGFR inhibitor Illustrates the ups And downs Of this form of therapy aka Gefitinib

Iressa was approved after Phase II trials for “third line” treatment of non-small cell lung cancer Curr Treat Options Oncol :75-81www.iressa-us.com

Iressa was approved after Phase II trials for “third line” treatment of non-small cell lung cancer Curr Treat Options Oncol :75-81 But Phase III clinical trial data From December 2004 raised serious questions about whether it prolongs life.

Data suggested that Iressa benefits a small subset of patients Including “never-smokers” and Patients of Asian descent Curr Treat Options Oncol Feb;8(1):28-37

Data suggested that Iressa benefits a small subset of patients Including “never-smokers” and Patients of Asian descent Curr Treat Options Oncol Feb;8(1):28-37 Why those patients?

It only works on patients with activating mutations in the kinase domain of the EGF receptor

It has been partially replaced by Erlotinib (Tarceva), another EGFR inhibitor approved for “second line” treatment of non-small cell lung and pancreatic cancers

Erlotinib (Tarceva) works, but how well? Median Survival: 6.7 months vs. 4.7 months in placebo control

Other second generation EGFR inhibitors are now in clinical trials EKB-569, HKI-272, CI-1033, and ZD6474 The Oncologist, Vol. 12, No. 3, , March 2007 Covalently bind EGFR Target multiple kinases including HER2 and VEGFR

BUT even when kinase inhibitors work well initially....

Relapses often occur

How could that happen?

Have you heard The one about Natural selection?

Drug treatment selects for mutant cancer cells with Second site mutations in the kinase domain, blocking drug binding, or with other RTKs (e.g., c-Met) gene amplified

Luckily drugs are not the only approach

Herceptin-- The corporate view

Genentech.com

Antibodies have been crafted by natural selection to allow recognition of diverse antigens from bacterial, viral, and parasitic invaders Alberts et al. Fig

The 3-dimensional structure of an antibody Alberts et al. Fig

The antibody-antigen recognition event is exquisitely specific Yellow and blue= heavy and light chains Green=antigen (in this case would be EGF Receptor) Red= amino acids in contact Alberts et al. Fig

Genentech.com Data from Phase III clinical trials of Herceptin

Genentech.com Data from Phase III clinical trials of Herceptin

Herceptin is now approved for treatment of Metastatic breast cancer

However, even more exciting is data on using Herceptin plus chemotherapy for treatment of early breast cancer Breast cancer was half as likely to come back in patients who received Herceptin® for a year after completing chemotherapy than in patients who received chemotherapy alone! New England Journal of Medicine, October 20, 2005

However, even more exciting is data on using Herceptin plus chemotherapy for treatment of early breast cancer FDA News Nov. 16, 2006 The FDA rapidly approved expansion of recommended use

By early 2009 follow-up data and additional trials Confirm a 50% reduction in recurrance And 30% improvement in survival Clin Breast Cancer Dec;8 Suppl 4:S

By early 2009 follow-up data and additional trials Confirm a 50% reduction in recurrance And 30% improvement in survival There are also Ongoing trials in HER2 positive Gastric, uterine And endometrial cancers Clin Breast Cancer Dec;8 Suppl 4:S

But like a freight train, it can run you over.... Cardiac toxicity in a few percent of patients Costs $60,000!

Two anti-EGFR and one anti VEGFR antibodies are also FDA approved

And back to the pathway…. Gilbert Fig Raf inhibitors Mek inhibitors Farnesyl transferase inhibitors largely failures

As metnioned earlier, the RTK-Ras pathway Offers several drug targets for cancer treatment e.g., or the Raf kinase inhibitor Vemurafenib Approved for treatment of Late stage melanoma August 2011) and approved for inoperable hepatocellular carcinoma (Nov. 2007)

BUT……. Tumors develop resistance to raf inhibitors Through many routes! 1)Amplification of mutant B-raf gene 2)Upregulation of PDGF receptor 3)Mutation of N-ras 4)Mutations in B-raf 5)Mutations in Mek

BUT……. Tumors develop resistance to raf inhibitors Through many routes! 1)Amplification of mutant B-raf gene 2)Upregulation of PDGF receptor 3)Mutation of N-ras 4)Mutations in B-raf 5)Mutations in Mek So now we add MEK inhibitors to treat this! Trametinib FDA approved January 2014