# Presentation: 679575

## 1845-1923

**1845-1923**

## High Spatial ResolutionCT, MRI, Optical, & US

**MRI Imaging**
**High Density, Internalizing Receptors**
**Transferrin receptor w. Transferrin MION**
**Optical Imaging**
**Physiologic measurements**
**Volume, flow, Hb O****2**
**Fluorescent-labeled ligands**
**Ultrasound Imaging**
**Physiologic measurements**
**Targeting with a single, site-directed bubble.**

## The Advantage of Radionuclides for Targeted Imaging, especially Low Density Sites (<20 nM)

| If 10 mCi at a specific activity of >1000 μCi/nmol: 10 nmol/70 Kg  | <0.2 nM |
| --- | --- |
| For Gd MRI:.
 Iron oxide (T2) increases sensitivity. | 10-100 μM |
| For iodinated contrast media | >100 μM |
| Optical imaging and Ultrasound | ? |

## George Charles de Hevesy

**The first to identify the radioisotope tracer principle.  **
**In 1923, he used 10.6 hour lead-212 to study the uptake of solutions in bean plants, noninvasively. Used small, non-toxic amounts given the sensitivity of the radioactivity techniques. **
**The first experiment in animals used Bi-210 to label and follow the circulation of Bi-containing antisyphilitic drugs in rabbits.**
**In a later book with Fritz Paneth, the tracer method was introduced as the use of radioelements as indicators.**

## The first practical application of a radioisotope was made by George de Hevesy in 1911.

**The first practical application of a radioisotope was made by George de Hevesy in 1911.**
**He suspected that meals that appeared regularly might be made from leftovers.**
**To confirm these suspicions de Hevesy put a small amount of radioactive material into the remains of a meal.**
**When the same meal was served, it was radioactive!**

**History has forgotten the landlady, but George de Hevesy went on to win the Nobel prize in 1943 and the Atoms for Peace award in 1959.**

## Imaging the In Vivo Distribution of a Gamma Emitting Radioisotope

## Unprecedented Progress

**1937 Discovery of the element Tc**
**1947 Isolation of Tc-99**
**1958 Technetium Generator**
**1970 Instant DTPA, HSA, & RBC Kits**
**1978 Crystal structures of potential Tc radiopharmaceuticals**
**2002-present**
**Smaller, neutral, more polar inert chelates**
**Maximal effective specific activity**
**Tc labeled molecules ~300 MW**

## 1934 photo of Livingston and Lawrence with the 27” cyclotron at LBL

## In 1938, Glenn Seaborg and Emilio Segre discovered Technetium-99m.

## Walter Tucker Powell Richards

## Mechanism: TcO4-  + stannous ion = reduced Tc + chelating agent or particle = final product 

**Kit components = stannous salt (reducing agent)**
** ****& chelating agent or particle**

## RS-[123I]IQNB on 5/11/83

## Market Analysis and Future Prospects

**U.S. sales of diagnostic radiopharmaceuticals reached $1.53 billion in 2004 and are expected to rise to $3.20 billion by 2010. **
**This growth will be based on introduction of new products, strong demand for cardiology procedures and increased sales of oncology products, particularly FDG for PET imaging. **
**Nuclear cardiology sales of $1.06 billion in 2004 will increase to $1.89 billion by 2010.**
**FDG sales for oncology as well as cardiology and neurology will increase from $249 million in 2004 to $522 million by 2010. **
**In addition, new PET radiopharmaceuticals in the pipeline for specialized applications should add to these sales estimates. **

## Market Analysis and Future Prospects

**U.S. sales of therapeutic radiopharmaceuticals were still on the threshold in 2005, with total sales of $57 million. **
**Rapid growth is anticipated over the next 5-6 years. By 2012, therapeutic product sales should reach $1.9 billion, with high continuing growth beyond that time. **
**This will be based on the introduction of new therapeutic radiopharmaceuticals for treating lymphoma, colon cancer, lung cancer, prostate cancer, bone cancer and other persistent cancers. These agents will be used in conjunction with traditional therapies, enhancing their effectiveness, with better specificity and reduced side effects.  Individualized Medicine!**

## DEVELOPMENT OF Enzyme/Receptor Targeting in humans

_**DATE**__**	**__**PET**__**	**__**	**__**	**__**	**__**SPECT**_
**1977****	****	****[****18****F]FDG**
**1983****	****	****[****11****C]N-MeSpip****	****	****[****123****I]IQNB**
**1984*****	****[****18****F]Cyclofoxy**
**1985****	****	****[****11****C]Raclopride****	****[****99m****Tc]NGA**
**1985****	****	****[****11****C]Carfentanil**
**1985****	****	****[****11****C]Flumazenil**

**How many radiotracers have changed clinical care?**
**How many have been used in combination with pharmaceuticals?**

## The Principle of PET: Coincidence Detection of Two 511 KeV Gamma Rays is Used to Determine the Position

## PET RADIONUCLIDE PRODUCTION

_**T**__**1/2 **__**(**__**min**__**)**__**	**__**E**__****__**+ **__**(kev)**__**	**__**	**__**Nuclear Reaction**_
**82****Rb****	****1.3****	****3350****	**** ****82****Sr generator**
**11****C****	****20 ****	****960****	****14****N (p,********)****  ****   ****w. 6 ppm O****2**
**13****N****	****10 ****	****1190****	****16****O (p,********)**
**15****O****	****2.05 ****	****1720****	****14****N (d,n)    ****w. 2% O****2**
**18****F****	****109.6 ****	****635****	****20****Ne (d,********)  ****w. 0.5%F****2**
**18****F****	****109.6****	****635****	****18****O (p,n)**
**76****Br****	****966****	****3980****	****75****As (********,3n)**
**64****Cu****	****762****	****571****	**** ****64****Ni (p,n)**
**124****I****	****5976****	****2134****	****124****Te (p,n)**

## FDG:1976 to 2002

## Imaging Saturable Sites with MRI

**Relatively High Capacity, Internalizing Sites.**
**Mion-Transferrin**
**Substrates For Enzymes.**
**FDG**
**High Capacity, Non-internalizing Binding Sites.**
**A Gd complex of polyDTPA polyneogalactosyl dextran.**
**Low Capacity, Non-internalizing Binding Sites.**
**Gd antibodies targeted to solid tumors.**
**Gd labeled antibodies targeted to endothelial sites.**

## In Vivo MR Imaging: MR image of a mouse with TfR+ and TfR- flank tumors

-  **(a) The T1-weighted coronal SE image (3.5 min; 0.3x0.3x3 mm****3**** resolution). TfR- tumors (right arrowhead) and TfR+ tumors (left arrowhead) have similar signal intensity. **
**(b) Corresponding T2-weighted gradient echo image showing significant difference (8 min; same resolution). TfR-mediated cellular accumulation of the superparamagnetic probe decreases signal intensity as expected using T2- and T2*-weighted imaging pulse sequences on cellular internalization. **
**(c) Composite of a T1-weighted spin echo image obtained for anatomic detail with superimposed R2 changes after Tf-MION administration displayed in a color map.**

## Other Imaging Modalities for desialylated glycoproteins binding to the high capacity (~500 nM) hepatic binding protein

**[Gd]DTPA-*****galactosyl*****-Dextran**

**Post-injection: 3.8 min**
**Liver: 66 % Enhancement**

## How can targeted imaging accelerate drug discovery?

- William C Eckelman PhD
- Bethesda MD

## Definitions: Molecular Imaging

- The term molecular imaging can be broadly defined as the in vivo characterization and measurement of biologic processes at the cellular and molecular level. [Weissleder & Mahmood, Radiology 2001].
- MI techniques directly or indirectly monitor and record the spatiotemporal distribution of molecular or cellular processes for biochemical, biologic, diagnostic, or therapeutic applications [Thakur & Lentle, Radiology 2005].

## Targeting ProteinsThe Magic Bullet

- Paul Ehrlich used the English expression “magic bullet” for the first time in his Harben Lectures. The German word “Zauberkugel” appears earlier in his thoughts and publications, based on his view of “sidechains”, the precursor of our concept of receptors, and on the desirable property of drugs that must not harm the host, but attach the parasitic invader.
- Royal Institute of Public Health (London:Lewis, 1908), Experimental Researches on Specific therapy. On immunity with special references to the relationship between distribution and action of antigens, 107.

## The Magic Bullet

-  Ehrlich’s first magic bullet was Salvarsan or arsphenamine, discovered in 1909, which provided the only cure for syphilis.
-  Ehrlich also thought of attaching toxins to antibodies whereby the antibody would carry the deadly freight to the site of the invading parasite. His idea lives on in the development of immunotoxins.

## Both the lock and the key are necessary in Targeted Imaging

- 99mTcDTPA or GdDTPA in GFR measurements is a key without a specific target (lock). GFR is a nontargeted process.
- [18F]FP-TZTP is a M2 muscarinic agonist, which is transported non specifically across the BBB, but binds specifically to the M2 receptor (the lock).
- Doxorubicin in liposomes is not a targeted drug although the therapeutic effect is increased by improvement in liver tox profile.

- Emil Fischer, 1894

## Imaging & “Molecular Targeting”

- Interactions between a probe and a protein target using pre-genomic techniques.
- “Biochemical probes” such as iodide (~50 years), receptor binding radiotracers and monoclonal antibodies (~25 years) from autopsy, linkage and drug efficacy, etc.
- Interactions between a probe and a protein target using post-genomic techniques.
- Molecular biology, proteomics, genomics, antisense, reporter genes, protein-protein interactions. More targets (500      2000-3000)

## Why is Targeted Imaging becoming more important in Drug Development?

- As the pharmaceutical industry turns to targeted drugs, targeted imaging is well positioned to “biomark” the drug potential.
- Target identification is dependent upon clinical research, i.e., “humanomics” should be the study of choice.

- Lindsay MA. Finding new drug targets in the 21st century. DDT 2005: 23/24: 1683.

## The Druggable genome

- Russ & Lampel. The Druggable genone: an update. DDT 2005: 23/24: 1607.

**Nucl Horm R**

## Measuring Targeting with Imaging for targets of differing density

**In Vitro B/F = B****max****/K****i**
**Imaging requires B/F ratio  ~5, Drugs do not**

## Measuring the In Vivo Binding Parameters of [18F]-Fallypride in Monkeys Using a PET Multiple-Injection Protocol.

|  | Bmax  (nM) | Bmax/KD
(theory) | LRR (DVR) | DA OCC
AMP | Koff
min-1 |
| --- | --- | --- | --- | --- | --- |
| putamen | 27 | 900 | 22 | 19% | 0.043
0.028 |
| caudate | 23 | 767 | 24 | 18% | 0.043
0.029 |
| v. striatum | 14 | 467 | 4 | 18% | 0.030
0.025
0.026 |
| thalamus | 1.8 | 60 | 2 | 24% | 0.056
0.035
0.054 |
| amygdala | 0.9 | 30 | 2 | 39% | 0.042
0.036
0.052 |

- Mukherjee 2005

## Measuring occupancywith Imaging for a successful treatment

## Specific binding of [18F]Cyclofoxy was lower by 29 to 32% in Methadone Maintained Patients.

**Control**

**Methadone**
**Maintained**
**Patient**

**Specific binding of [****18****F]Cyclofoxy was lower by 29 to 32% in Methadone Maintained Patients.**

**Kling et al.,  *****J Pharm Exp Therap*****, 295: 1070-1076, 2000**

**Thalamus****	****	****  32  ± 15**
**Amygdala****	****	****  24  ± 30**
**Caudate****	****	****  24  ± 19**
**Ant. cingulate cortex****	****  29  ± 20**

**Notes:**
Four [18F]cyclofoxy PET image slices from a normal control (top) and a methadone maintained patient (bottom). These levels show amygdala, basal ganglia, thalamus, and cortex. Subjects chosen had nearly average binding (V) values for each group. Images are averages of data collected from 30-90 min postinjection. For purposes of display, images were smoothed to a resolution of ~9 mm and are scaled so that the highest color corresponds to five times the occipital background level.  This study shows that methadone blocks the binding of [18F]Cyclofoxy to a relatively small extent, leaving opiate receptors available for other functions.

## Measuring Occupancy with Imaging for Multi-target drugs

- A single target drug with a multi-target radiotracer.
- A multi-target drug with a single target radiotracer.

## M100907 as measured using [11C]NMSP PET in humans 

- Measure possible 5-HT2A receptor occupancy by measuring frontal cortex to cerebellum ratio.
- Measure possible D2 receptor occupancy by measuring striatum to cerebellum ratio.
- Is the Occupancy related to plasma concentration?
- Is the Occupancy time course related to plasma concentration?

## [11C]NMSP Binding at 5-HT2A & D2 receptors

**Notes:**
A PET brain scan before and after administration of M100907, a potential antipsychotic.  The radioligand [11C]NMSP binds to both the 5HT2A receptor and the dopamine D2 receptor as evidence by increased radioactivity in the frontal cortex indicating 5HT2A receptor binding and increased radioactivity in the caudate putamen indicating dopamine D2 receptor binding. After administration of 18 mg M100907, decreased radioactivity can be seen in the frontal cortex, but not in the caudate putamen.  This is an indication that M100907 is an atypical antipsychotic. 

## Schizophrenia and Antipsychotic Drugs

- M100907 (aka MDL 100907) is a potent and selective 5-HT2A receptor antagonist, but does not bind to the D2 receptor.
- Therefore, it has the profile of an atypical antipsychotic agent.
- [11C]NMSP can be used to monitor 5-HT2A and D2 receptor density changes.

**J Clin Pharmacol Suppl 1999**

## Sensitivity/Identifiabilityfor Drug Changes

**Measuring endogenous transmitter changes**

## Measuring increased dopamine.22.3% (±2.7)  in schizophrenia vs. 15.5% (±1.8) in controls.Schizophrenia is associated with elevated amphetamine-induced synaptic dopamine.

_**Breier A, Su TP, Saunders R, Carson RE, Kolachana BS, de Bartolomeis A, Weinberger DR, Weisenfeld N, Malhotra AK, Eckelman WC, Pickar D.**_**	****Proc Natl Acad Sci U S A. 1997 Mar 18;94(6):2569-74.**

**Notes:**
The effect of pharmaceuticals that alter the release of neurotransmitter from the synaptic vesicles can be measured using an infusion paradigm where steady state is reached, the drug is administered, and the effect on endogenous neurotransmitter release can be measured indirectly.  In this experiment, [11C]Raclopride, a D2 dopamine receptor binding antagonist, is infused to steady state and monitored using. PET The upper curve is radioactivity in the caudate putamen and the lower curve is radioactivity in the cerebellum, which contains very few D2 dopamine receptor. In this case, amphetamine is administered at 50 min.  The increased dopamine in the synaptic cleft competes with the [11C]Raclopride for the limited number of D2 receptors.  The result is that fewer [11C]Raclopride molecules are bound.  The interesting result of a study in schizophrenia is that schizophrenic patients release more dopamine than normal subjects for the same amount of amphetamine administered. This approach tests the dopamine system rather than testing only the pos-synaptic receptor density.

## Measuring increased acetylcholine. [18F]FP-TZTP as a probe for AChE inhibitors such as donepezil, rivastigmine, & tacrine. Increased ACh and 15% decrease of [18F]FP-TZTP in Ctx.

**Control**

**Physostigmine**

**Carson RE, Kiesewetter DO, Jagoda E, Der MG, Herscovitch P, Eckelman WC. Muscarinic with [****18****F]FP-TZTP: control and competition studies.**
**J Cereb Blood Flow Metab. 1998 Oct;18(10):1130-42.**

**Notes:**
In a similar experiment in monkeys, [18F]FP-TZTP can be used as a probe for potential acetylcholine esterase (AChE) inhibitor. [18F]FP-TZTP binding to the M2 receptor subtype can be monitored in vivo using PET before and after injection of a potential AChE inhibitor.  Compared to the baseline study, physostigmine causes a  20-30% decrease binding in the cortex due to the decreased metabolism of acetylcholine in the synaptic cleft.

## Individualized Medicine

## Current Individualized Medicine

**Metastatic pheochromocytoma (Pheo) can be detected using [****123****I]MIBG (or it that is not available [****131****I]MIBG can be used) prior to therapy with [****131****I]MIBG. **
**The mechanism of localization is based on the neuroendocrine character of this disease with the the norepinephrine transporter (NET) being the key biochemical parameter.  **
**Up to 73% of PHEO cells in vitro express somatostatin receptors so patients with Pheo have been assessed with somatostatin receptor imaging (with either [****123****I]Tyr3-octreotide or [****111****In]DTPA-octreotide). **
**Since the presence of NET and SSR appear to be inversely related and dependent on cell differentiation, imaging both pathways can be instrumental in choosing therapy.**

## Current Individualized Medicine

**The American College of Radiology has recently set practice guidelines for [****90****Y]ibritumomab tiuxetan (Zevalin) and [****131****I]tositumomab (Bexxar), which are approved by the FDA for radioimmunotherapy of non-Hodgkin’s lymphoma.**
**Both antibodies are directed against the CD20 antigen, which is found on the surface of normal and malignant B lymphocytes. **
**The preliminary imaging studies are to determine dosimetry or assess biodistribution before the radiotherapeutic is administered. The package insert for these two radiotherapeutics has guidelines for interpreting the imaging study and these guidelines must be met before the therapy can commence.**

## Targeted Drugs Targeted Imaging

**Trastuzumab for HER2 (aka ErbB2 & Neu)**
**A cell surface glycoprotein with TK activity**
**HER2 amplification/over-expression is predictive for response in breast caner.**
**Overexpression became an entry criteria and higher objective response was related to level of overexpression.**
**Imaging study was developed with Ab fragment to match the Ga-68 half life.**

**tra STUH zoo mab; Herceptin**

## Imaging HER2 Receptor in response to HSp90 Inhibitors

**17-allylaminogeldanamycin (17-AAG) is the first Hsp90 inhibitor to be tested in a clinical trial.**
**Induce proteasomal degradation of HER2 by binding to Hsp90 chaperone protein.**
**Label the F(ab’)****2 **** of the anti-HER2 antibody Herceptin with Ga-68.**

**Smith-Jones et al. Nat Biotech  2004**

## MicroPET images (coronal)  of mice with BT-474 tumors with Ga-68-DOTAcHF at 3 h before and 24 h after 17-AAG

**Tumor & kidney**

**Taken from Smith-Jones et al. Imaging the pharmacodynamics of HER2 degradation in response to Hsp90 inhibitors. Nat Biotechnol. 2004;22:701-6**

## Slide 47

## Targeted Drugs

**Imatinib is an inhibitor of BCR-ABL TK.**
**The Philadelphia chromosome and BCR-ABL have prognostic significance for chronic myeloid leukemia (CML).**
**Also, inhibits TK of the oncogene c-KIT  in GIST.**
**Imatinib-resistant mutants led to BMS 354825.**

**im MA ta nib; Gleevec**

## In Vivo Proteomics:FDG: Before and after Gleevec

- Taken from Demetri et al.

## Cancer is not a single gene disease, yet .....

**Imatinib (Gleevec)-effective in GIST and CML. Mutants appeared, but further TK inhibitors have high affinity for all mutants.**
**Trastuzumab (Herceptin)-best in high expressors of HER2.**
**Gefitinib (Iressa)-EGFR TK.**
**Shrinks tumor, but no change in survival in NSCLC. Population specific.**
**Erlotinib (Tarceva) & Cetuximab (Erbitux)-MAb**
**Angiogenesis Inhibitors**

**DDT 2004:9:1042-1044  **

- _[Golsteyn ](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15808815)__[RM.](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15808815)_** DDT 2005 10(6):381.**

## Drivers for Targeted Imaging

- Expansion of SPECT/CT complementing the continued expansion of PET/CT.
- Development of the parallel field of small animal imaging.
- The pharmaceutical company’s need to increase their success rate from 17% for established targets and 3% for post-genomic targets.
- The FDA’s need to encourage biomarker development, especially for human use.

## Magnitude of the opportunities

- Failures in Phase II or Phase III are often due to newly identified toxicity or absence of targeting.
- 2000 drugs have failed to target sufficiently and are accumulating at a rate of 150-200 per year.

- Kola & Landis Nat Rev DD 2004:3:711-716

- Arth   CV   CNS   Inf   Oncol  Eye  Metab Uro	Women ALL

**Percentage of success**

## Efficient “Molecular Targeting” Discovery & Development

- Streamlining drug discovery: finding the right drug against the right target to treat the right disease.
- For Targeted Imaging probes: finding the right molecular probe against the right target to monitor the right disease.

## Molecular Probe Design

- Develop Molecular Imaging Probes that target a protein that changes early in the disease.
- Develop molecular tracers that are based on a reductionist concept where the drug-organism interplay can be reduced to a drug-target interplay.
- Collaborate with or join the Pharmaceutical Industry

## Opportunities

- University Faculty
- Chemistry dept
- Pharmacology dept
- Radiology dept
- Radiopharmaceutical companies
- Pharmaceutical companies
- Drug development using imaging

## Slide 56

## Target-based drug discovery: Is something wrong? 

- Physiologic targets
- For example, blood pressure measurements *in vivo * using potential drugs, e.g., the ACE inhibitors.
- Targeted Drugs
- Gene Targets, e.g., single gene disease
- Mechanistic Targets (receptors, enzymes)
- Combitorial chemisty, HTS, rationale drug discovery
- Underestimation of the complexity of the physiology and lack of relevant disease model.
- Targeted Imaging could play a major role.

**Sams-Dodd, DDT 2005:10:139**

## Other Imaging Modalities for desialylated glycoproteins binding to the high capacity (~500 nM) hepatic binding protein

**[Gd]DTPA-*****galactosyl*****-Dextran**

**Post-injection: 3.8 min**
**Liver: 66 % Enhancement**

**Mattrey, Hall Vera  UCSD**

## Comparison of HER2 status between primary tumor and disseminated tumor cells in primary breast cancer patients.

-  **RESULTS: In 46 of 137 (34%) breast cancer patients, CK-positive cells were detectable in BM. DTC with HER2 positivity were found in 20 (43%) of these patients. **
**The HER2 expression on DTC was heterogeneous in 7 of 17 (41%) patients. **
**Concordance rate of HER2 status between primary tumor and DTC was 62%. In 12 of 20 patients with HER2 negative tumors HER2 positive DTC were detected.**
**HER2 positive DTC can be detected in patients with HER2 negative primary tumors.**** **** **

- _[Solomayer](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Solomayer+EF%22%5BAuthor%5D)__[ EF](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Solomayer+EF%22%5BAuthor%5D)_** et al.**** Breast Cancer Res Treat. 2006 Mar 22; [Epub ahead of print] **

## HER2-positive circulating tumor cells (CTC) indicate poor clinical outcome in stage I to III breast cancer patients.

**We detected one to eight CTCs in the peripheral blood of 17 of 35 patients (48.6%) presenting no overt metastasis. **
**As a positive control, 7 of 7 (100%) patients with metastatic disease presented positive. **
**The presence and frequency of HER2-positive CTCs correlated with a significantly decreased disease-free survival (P < 0.005) and overall survival (P < 0.05).**
** ****Interestingly, in 12 patients with HER2-positive CTCs, the primary tumor was negative for HER2 as assessed by immunohistochemical score and fluorescence in situ hybridization. **
**This study provides some evidence of a prognostic effect of HER2-positive CTCs in stage I to III breast cancer.**** **

- _[Wulfing](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wulfing+P%22%5BAuthor%5D)__[ P](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wulfing+P%22%5BAuthor%5D)_** et al****. Clin Cancer Res. 2006 Mar 15;12(6):1715-20. **

## Predictive Factors for Outcome in a Phase II Study of Gefitinib in Second-Line Treatment of Advanced Esophageal Cancer Patients.

- Gefitinib has a modest activity in second-line treatment of advanced esophageal cancer.
- However, the patient outcome was significantly better in female patients and in patients demonstrating high EGFR expression or SCC histology.
- The selection of esophageal cancer patients for future studies with EGFR-TKIs based on the level of EGFR expression in their tumors or SCC histology should be considered.

- _[Janmaat](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Janmaat+ML%22%5BAuthor%5D)__[ ML](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Janmaat+ML%22%5BAuthor%5D)_** et al.**** J Clin Oncol. 2006 Apr 1;24(10):1612-9. **

## What makes a probe a targeted molecule?

- Does the probe bind to the target?
- If there are a limited number of sites, increased mass should decrease probe binding.
- Is the delivery dependent on flow, permeability, or protein concentration?
- What does flow dependence look like?
- What does permeability dependence look?
- Is the probe sensitive to target change?

## Epidermal growth factor receptor inhibitors in cancer treatment.

**The epidermal growth factor receptor (EGFR) is a cellular transmembrane receptor with tyrosine kinase enzymatic activity which plays a key role in human cancer. EGFR-dependent signaling is involved in cancer cell proliferation, apoptosis, angiogenesis, invasion and metastasis. **
**Cetuximab (Erbitux(R)), a chimeric human-mouse monoclonal immunoglobin (Ig)G(1) antibody, which blocks ligand binding and functional activation of the EGFR, is currently registered in the USA, Switzerland and the European Union for the treatment of advanced, irinotecan-refractory colorectal cancer. Gefitinib, (Iressa((R))), a small molecule EGFR-selective inhibitor of tyrosine kinase activity which blocks EGF autophosphorylation and activation, has been the first EGFR-targeting drug to be registered in 28 countries worldwide, including the USA, for the third-line treatment of chemoresistant non-small cell lung cancer patients.**

- _[Ciardiello](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Ciardiello+F%22%5BAuthor%5D)__[ F](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Ciardiello+F%22%5BAuthor%5D)_. **Future Oncol. 2005 Apr;1(2):221-234. **

## Antiangiogenic cancer therapies get their act together: current developments and future prospects of growth factor- and growth factor receptor-targeted approaches

**The identification of surrogate markers that can monitor the activity and efficacy of antiangiogenic drugs in patients belongs to the most critical challenges to exploit the full potential of antiangiogenic therapies. The opportunities and obstacles in further development of growth factor- and growth factor receptor-targeted antiangiogenic approaches for advanced cancer, including malignant melanoma, will be discussed herein with particular reference to selected ongoing clinical trials. **

- _[Gille](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Gille+J%22%5BAuthor%5D)__[ J](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Gille+J%22%5BAuthor%5D)_**. Exp Dermatol. 2006 Mar;15(3):175-86.**

## Triage for Breast Cancer