Pharma Strategy Blog

Commentary on Pharma & Biotech Oncology / Hematology New Product Development

Posts by MaverickNY

MET and KRAS amplification mediate resistance to MET inhibitors

By on September 17, 2010

Here's an interesting paper that was just published in Cancer Research that describes some factors driving acquired resistance to MET inhibition with small molecules.

MET inhibitors have gained a lot of attention recently (see Comoglio et al's review in the references for a good overview) and we have covered this topic a few times on this blog both in terms of the biology and also on promising inhibitors such as ArQule/DaiichiSankyo's ARQ-197, which is the leading compound in this field.

Acquired resistance is a common and limiting problem for chronic therapy with many tyrosine kinase inhibitors (TKI), not just MET inhibitors. After initial excitement at seeing some responses though, they appear to stop working. The big question is why, and what underlying mechanisms may be at play?

Of course, while the issue may be a universal one, the resistance mechanisms are not and will differ with each class of TKI and potentially even tumour types or combinations.

Background

The MET gene is disregulated in a number of different tumour types and those cells exhibiting MET amplification may offer a suitable target for drug inhibition.  Doing so results in impairment of cell growth and apoptosis.

You can read more about the biology of the c-MET pathway here.

Acquired Resistance to MET

In this important research, the authors decided to see if they could define some of the underlying mechanisms of MET resistance:

"To predict mechanisms of acquired resistance, we generated resistant cells by treating MET-addicted cells with increasing concentrations of the MET small-molecule inhibitors PHA-665752 or JNJ38877605."

The results?

They found that cells progressively amplified KRAS, which resulted in increased expression and activation of wild-type (wt) KRAS and in activation of the mitogenactivated protein kinase (MAPK) pathway:

"We show that amplification of wt MET and KRAS is found in cells of diverse histotypes, resistant to different inhibitors.

Moreover, unexpectedly, we observed that resistance to treatment was reversible and that the alterations leading to resistance were lost after drug withdrawal."

This is a very important finding because it may well be helpful for designing future clinical studies, either in combination or in sequence, to reduce the potential for resistance emerging with MET inhibitors, thereby improving the potential for better long term outcomes with treatment.

"Our results suggest that MET and KRAS amplification is a general mechanism of resistance to specific MET inhibitors given that similar results were observed with two small inhibitors and in different cell lines of different histotypes."

Impact

My favourite part of this story was not just the identification of potential mechanisms of MET resistance, but some hints of how the learnings from the data could be applied:

"Because specific anti-RAS drugs are not available, we tested the ability of compounds acting downstream RAS (such as U0126, PD325901, and sorafenib) to impair cell viability. We observed that cells resistant to MET inhibitors that underwent KRAS amplification are indeed sensitive to these drugs."

Clearly, our ability to not only predict potential mechanisms of resistance, but also devise strategies for overcoming or preventing it, is crucial for improved clinical development with these agents as well as providing a clear rationale for other inhibitors still in research.

Where there's a viable target, there's a way forward.

 

References

ResearchBlogging.org Cepero, V., Sierra, J., Corso, S., Ghiso, E., Casorzo, L., Perera, T., Comoglio, P., & Giordano, S. (2010). MET and KRAS Gene Amplification Mediates Acquired Resistance to MET Tyrosine Kinase Inhibitors Cancer Research DOI: 10.1158/0008-5472.CAN-10-0436

Comoglio, P., Giordano, S., & Trusolino, L. (2008). Drug development of MET inhibitors: targeting oncogene addiction and expedience Nature Reviews Drug Discovery, 7 (6), 504-516 DOI: 10.1038/nrd2530

Incyte's INCB018424 looks promising in myelofibrosis

By on September 16, 2010

Just before the American Society of Hematology (ASH) meeting last December, I posted an overview of the JAK2 pathway and pipeline inhibitors in development. Things have changed a bit since then, with TargeGen's inhibitor, TG101348, being licensed by sanofi-aventis and the advent of new phase I/II data being published this week in the New England Journal of Medicine on the leading compound in this category, INCB018424 (Incyte/Novartis).

Background

I loved this simple overview from Verstovsek et al., which is hard to improve on for simplicity and logic:

"Myelofibrosis is a Philadelphia chromosome–negative myeloproliferative neoplasm associated with cytopenias, splenomegaly, poor quality of life, and shortened survival. About half of patients with myelofibrosis carry a gain-of-function mutation in the Janus kinase 2 gene (JAK2 V617F) that contributes to the pathophysiology of the disease. INCB018424 is a potent and selective Janus kinase 1 (JAK1) and JAK2 inhibitor."

Here's what the pathway looks like, for those interested:

Picture 3Source: Cell Signal

Currently, there are no approved therapies for the treatment of myelofibrosis, so using a targeted inhibitor is a worthwhile approach to determine whether any clinical benefit will result.

The Patients

In this study, patients were preselected for one of the following characteristics:

  • JAK2 V617F−positive or JAK2 V617F−negative primary myelofibrosis
  • post–essential thrombocythemia myelofibrosis
  • post–polycythemia vera myelofibrosis.

In all, 153 patients were given INCB018424 as oral therapy for a median duration of more than 14.7 months.  The initial dose-escalation phase established 25 mg twice daily or 100 mg once daily as maximum tolerated dose (MTD).

Additional doses were also examined, with a clear rationale emerging for a 15 mg twice daily starting dose.

The Results

Skimming through the results section, my attention was immediately drawn to the following:

"61 of 140 patients with an enlarged spleen at study entry (44%) had an objective response (clinical improvement), based on a reduction of 50% or more in palpable splenomegaly within the first 3 months after therapy."

Interestingly, the response rates were highest in patients who took their therapy BID, whereas none of the patients who took INCB018424 once daily showed any clinical improvement.

The researchers went onto note:

"A total of 28 patients who received 25 mg twice daily or 15 mg twice daily (the most active regimens for splenomegaly reduction) were transfusion-dependent at enrollment. After a median treatment duration of 12 weeks, 4 patients (14%) had transfusion independence (clinical improvement according to the International Working Group) for a median duration of 20 months."

One of the many problems people with myelofibrosis experience is a poor quality of life, so it was reassuring to see some real improvement in practical real life tests.

A small proportion of the patients underwent the 6-minute walk test, with the following improvement in their ability to walk as follows:

  • 34 m after 1 month
  • 57 m after 3 months
  • 71 m after 6 months

I couldn't find the baseline, but we can reasonably assume that it was 34 m or less, judging from this positive trend.

When considering the patients with (n=61) and without (n=11) the JAK2 V617F mutation, there was no difference in response between the groups in the patients who received the most effective doses (ie 15 mg twice daily or 25 mg twice daily). The response rates were 51% and 45%, respectively.

In addition, people with primary myelofibrosis (n=37) had a response rate of 49%, while those with polycythemia vera (n=22), 45%, suggesting that the overall response rates were in the general 45-51% range, irrespective of the type of myelofibrosis.

With regards to serious adverse events, 59 people were affected by JAK2 therapy, of whom 12 had serious adverse events that were considered to be at least possibly related to treatment. Additionally, 3 patients had transformation to AML, but whether this was treatment related, or part of the natural disease progression, wasn't clear from the article.

Insights

The improvements in clinical benefit (response rates, reduction in splenomegaly and exercise endurance) look promising enough for phase III trials to begin. Understanding the mechanisms behind the inflammatory responses and reduction in splenomegaly will be important as more research is undertaken.

In the previous post on JAK2, we discussed how inhibiting JAK2 may influence or block cytokine signalling, which is thought to be responsible for the myelofibrosis. In this study, normalisation of the inflammatory cytokines was noted with INCB018424, suggesting that JAK1 and JAK2 inhibitors may possibly have clinical efficacy in inflammatory diseases such as rheumatoid arthritis (RA).  

Indeed, a trial with another JAK2 inhibitor, INCB028050, from Incyte is ongoing in RA and has already completed recruitment.  The results from this trial may offer proof of concept for JAK2 and cytokine normalisation in inflammatory disease.

The future though, may well involve some form of combination rather than single agent therapy, as the accompanying editorial pointed out:

"One disappointing finding in the trial was the minimal effect on the burden of the V617F-mutated clone; however, this was not entirely unexpected considering the lack of specificity of INCB018424 for mutated protein. Yet, one may question whether the disappearance of the V617F-mutated clone is a reasonable end point for JAK1 and JAK2 inhibitors without causing excessive toxicity, given the essential role of JAK1 and JAK2 in the normal immune system and hematopoiesis."

It is very good news to see that a single agent JAK2 inhibitor has some early efficacy, so we can hope that the phase III trials (COMFORT I and II) will also be positive and confirm the initial phase II results when the data is available in the first half of 2011. In the long run, though, combination approaches may well produce even better outcomes.

 

References

ResearchBlogging.org Vannucchi, A. (2010). From Palliation to Targeted Therapy in Myelofibrosis New England Journal of Medicine, 363 (12), 1180-1182 DOI: 10.1056/NEJMe1005856

Verstovsek, S., Kantarjian, H., Mesa, R., Pardanani, A., Cortes-Franco, J., Thomas, D., Estrov, Z., Fridman, J., Bradley, E., Erickson-Viitanen, S., Vaddi, K., Levy, R., & Tefferi, A. (2010). Safety and Efficacy of INCB018424, a JAK1 and JAK2 Inhibitor, in Myelofibrosis New England Journal of Medicine, 363 (12), 1117-1127 DOI: 10.1056/NEJMoa1002028

 

Sisyphus, oncology R&D and Pharma

By on September 15, 2010

Loved this cartoon from Hugh Macleod at Gaping Void that just arrived in my mail box:

Sisyphus-1008ww
Source: Gaping Void

In many ways, this is what drug development can look like on a day to day basis. Scientists repeating experiments, project teams holding endless meetings etc, that sometimes it's hard to see which in a portfolio of agents might actually make it through to market and which will fail along the journey.

Still, eventually, some of those small rocks reach enough critical mass (data) and actually do tip over the edge to be successfully commercialised.  

After all, that's what we all live for – the few that make it to market and make a real difference to the lives of people with cancer.

Celebrate Sisyphus today – it's not the fancy silver lures or cool new toys that makes the difference in the end, but the steadfast daily grind through R&D that eventually pays off big time for everyone.

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Biotech is booming in Boston

By on September 14, 2010

Yesterday I was on my way back from Marblehead and the Tufts Cycle for Life event and stopped by Boston for meetings.

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While standing on the pavement contemplating my schedule, I checked out my industry news feeds to see what was happening.

Beantown was hopping around me yesterday!

Ariad

Announced the phase II trial of it's multi-kinase inhibitor, AP24534, which targets the T315I mutation in CML and is now named ponatinib. The drug also inhibits FLT3-ITD and the FGFR pathway.  

According to Ariad: 

"The PACE (Ponatinib Ph+ ALL and CML Evaluation) trial is designed to provide definitive clinical data for regulatory approval of ponatinib in this setting."

The goal will be to focus on the refractory setting after failure of Sprycel or Tasigna:

"The PACE trial is a global, single-arm clinical study of oral ponatinib in 320 patients with chronic phase, accelerated phase, or blast phase CML, as well as Ph+ ALL. Patients resistant or intolerant to dasatinib (Sprycel) or nilotinib (Tasigna), or with T315I mutation of BCR-ABL, will be enrolled in the trial."

Originally, this would have meant ponatinib would be used in 3rd line after imatinib, the dominant front-line therapy, and then either dasatinib or nilotinib in 2nd line.  However, as the 2nd generation therapies move up to first-line, with nilotinib already approved in this indication and dasatinib due to be reviewed by the FDA soon, this could well mean that ponatinib could be used in 2nd line in the future should it garner good data and approval from the FDA.  

This is a particularly promising agent because it is the leading compound being evaluated for the T315I mutation in CML, which none of the existing drugs target.

Genzyme

While all attention is on the seemingly never ending dance between Sanofi-Aventis and Genzyme over the possible buyout deal and price, an interesting press release from the biotech firm quietly announced the divesting of the genetic testing business to Lab Corp:

"LabCorp will purchase the business in its entirety, including all testing services, technology, intellectual property rights, and its nine testing laboratories. LabCorp is committed to offer employment to the unit’s approximately 1900 employees upon closing, including senior management. The agreement is subject to customary closing conditions, including the Hart-Scott-Rodino Antitrust Improvements Act of 1976, with the goal of closing before the end of the year."

This comes after the announcement late last week that 1,000 jobs will be lost over the next 2 years, which was rolling over the local news channels over the weekend. The mood in MA was less the buoyant as a result.  The fallout from the manufacturing problems and subsequent fines are clearly having a major impact on the troubled biotech.  I wonder what will be next to go? 

Ironwood

Last but not least, a more uplifting development yesterday was the announcement by Ironwood and Forest Labs regarding positive top-line results from the first of two Phase 3 clinical trials assessing the efficacy and safety of their investigational drug, linaclotide, in patients with irritable bowel syndrome with constipation (IBS-C).

According to the press release:

"The two co‐primary endpoints required by the European Medicines Agency (EMA) were met in this study, showing statistical significance and clinically relevant improvement for linaclotide treated patients both for abdominal pain/abdominal discomfort responder and IBS degree of relief responder over the three‐month period. Significant improvement was also achieved for all pre‐specified main secondary endpoints (stool frequency, stool consistency, straining, and bloating).

The safety results were consistent with those observed in previous linaclotide clinical trials, with diarrhea being the most common adverse event in linaclotide‐treated patients."

This is very good news indeed for people suffering with the condition, especially as two huge global drug makers (GSK and Novartis) both tried, but failed, to bring a drug to market and keep it there.

Bear in mind that IBS is a debilitating and inconvenient condition that affects a lot lot of people, perhaps as many as 30 million suffer from the effects.  It might sound a little dramatic, but IBS has unfortunately become a sort of sword-in-the-stone challenge to big Pharma. Ironwood may well be the young 'Arthur' for millions of people suffering with IBS.

If the safety and efficacy data hold up with the regulatory authorities, an approval for linaclotide would be very good news indeed for people suffering from this condition. 

 

Photo Credit: Werner Kunz 

I did it!

By on September 11, 2010

Heartfelt thanks to all my friends who sponsored my 25 mile cycle ride in aid of the Tufts Floating Hospital for Children's Cancer Center in Boston.  I did it !! The picture shows me with my friend Marian Cutler. (I'm on the left in the Boston Red Sox cycling shirt)

Cycle for Life 2010

Thanks to everyone's generous donations, I raised over $1500, the team I was riding with, Staley's Riders, over $6000 and the event raised nearly $150,000 in total.  A lot can be done towards children's cancer care with this money.

Aiyana My pedal pal from Tufts was the adorable one year old Aiyana, who was recently diagnosed with Acute Lymphoblastic Leukemia (ALL) a month after her first birthday.  I sincerely hope she makes it through her treatment.

The Cycle for Life is a well organized event, that starts in picturesque Marblehead, on Devereux Beach, 15 miles north of Boston.  The route was a bit tough in places (rather a lot of hills), but this year the weather today was kind – sunny, with a light wind – much nicer than the pouring rain others faced last year!

Thanks again for all the support and contributions to a worthwhile cause. 

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PIK3CA, MEK and mutant KRAS in cancer

By on September 10, 2010

One of the current challenges with developing new targeted agents in oncology is the tendency to rush various agents, whether monoclonal antibodies (mAB) or tyrosine kinase inhibitors (TKIs) into the clinic before we know how they might best work or in what potential combinations based on the precise underlying biology.

Another challenge I see is old school chemotherapy approaches permeating new development thinking. By this, I mean the traditional concept of testing therapies in advanced, metastatic and highly refractory disease where the tumour burden is high and the chances of getting a decent response is low.

This is one reason I love the I-SPY neoadjuvant concept in breast cancer. Testing a range of compounds prior to surgery based on the potential drivers of the cancer will let us know very early which agents are working or not and which could potentially be selected for subsequent adjuvant treatment after surgery.

Background

Recently, I reading a couple of papers (see references below) on phase I and II trials with a MEK inhibitor (PD-0325901), but it was a little bit with a sinking feeling because the trial design was rather old fashioned and traditional, ie take a bunch of solid tumours in phase I, see what (mixed) signals you get:

"PD-0325901 showed preliminary clinical activity. The maximum tolerated dose, based on first cycle dose-limiting toxicities, was 15 mg BID continuously. However, 10 and 15 mg BID continuous dosing and 10 mg BID 5 days on/2 days off schedules were associated with delayed development of RVO; thus, further enrollment to this trial was stopped."

Where RVO was retinal vein occlusion.

Next, do a phase II in a big (ie large potential patient numbers), advanced, metastatic and highly refractory cancer.  Predictably, the results were unsurprising:

"PD-0325901 did not meet its primary efficacy end point."

If we looked at those results in isolation, we might be tempted to dismiss the idea that the MEK inhibitor doesn't work and abandon it.

A different way of thinking

That said, I was much more encouraged by another article from another group that looked at the problem completely differently with exactly the same MEK agent.  If you think about it, a focused sniper rifle strategy is often going to be more effective than a bludgeoning blunderbuss.

They looked at the basic evidence that:

"Mutational activation of PIK3CA, which commonly co-occurs with KRAS mutation, provides resistance to MEK inhibition through reactivation of AKT signaling"

And then set out to look at this relationship more clearly in animal models:

"to determine the MEK dependence of tumors with mutational activation of the pathway. These studies indicate that many KRAS mutant tumor cell lines are, contrary to the prevailing view, sensitive to the MEK inhibitor PD0325901, and hence, dependent on the RAF/MEK/ERK signaling arm.

Resistance to MEK inhibitors in the relevant cell lines is not an intrinsic feature of KRAS oncogenic function but instead mutational activation of PIK3CA is present in most, but not all, MEK resistant KRAS mutant cancers."

It's hard to argue with that logical approach.

Findings

The article is well worth reading and nicely put together, but here are the main findings of the research:

  1. A subset of KRAS mutant cells depends on MEK/ERK signaling
  2. Coexistent KRAS and PIK3CA mutations prevent cyclin D degradation and sensitivity to MEK inhibition
  3. Selective knockout of mutant PIK3CA allele confers MEK/ERK dependence
  4. Sustained cyclin D expression and bypass of MEK inhibitor–induced G1 arrest correlates with MEK antagonist efficacy
  5. Combined inhibition of both MEK/ERK and PI3K/AKT pathways suppresses the growth of tumors with coexisting KRAS and PIK3CA mutations

 

Implications for the future

The thoughtful approach behind Halilovic et al's data is particularly interesting:

"Mutational activation of KRAS is a common event in human tumors. Identification of the key signaling pathways downstream of mutant KRAS is essential for our understanding of how to pharmacologically target these cancers in patients.

We show that PD0325901, a small-molecule MEK inhibitor, decreases MEK/ERK pathway signaling and destabilizes cyclin D1, resulting in significant anticancer activity in a subset of KRAS mutant tumors in vitro and in vivo."

KRAS mutant tumours are particularly relevant to colorectal cancer.  Recently, we have seen that patients with colorectal cancer who have wild type, but not mutant, KRAS are more much more likely to respond to treatment with EGFR therapy ie Erbitux and Vectibix, allowing for careful patient selection and exposure.

What about melanoma where mutant RAS may stop the activity of RAS inhibitor such as PLX4032? Could adding a MEK inhibitor help overcome the problem in some cases, or perhaps that would be too simple? We don't know, but I'd love to see some research data in appropriate xenograft models in this area.

The problem is that there is currently no therapeutic agent that directly inhibits KRAS function, so the Halilovi data have very important implications for tumours driven by mutant RAS.

What the new data tells us:

"These data suggest that tumors with both KRAS and phosphoinositide 3-kinase mutations are unlikely to respond to the inhibition of the MEK pathway alone but will require effective inhibition of both MEK and phosphoinositide 3-kinase/AKT pathway signaling."

Bingo!  Now that's a much more elegant approach to defining which patient populations are most likely to respond based on preclinical research before attempting clinical trials and randomly exposing patients who had no hope of responding to the systemic side effects of a treatment.  

Personally, I would dearly love to see more clinical trial selection based on logical, well researched preclinical data rather than a scattergun let's hope and see approach.

We need to get smarter and faster at well designed research that points us in the right direction to increase the chances of better success and improved outcomes.  It will also conserve precious R&D dollars and focus it where it's needed most.

 

References

ResearchBlogging.org Halilovic, E., She, Q., Ye, Q., Pagliarini, R., Sellers, W., Solit, D., & Rosen, N. (2010). PIK3CA Mutation Uncouples Tumor Growth and Cyclin D1 Regulation from MEK/ERK and Mutant KRAS Signaling Cancer Research, 70 (17), 6804-6814 DOI: 10.1158/0008-5472.CAN-10-0409

Haura, E., Ricart, A., Larson, T., Stella, P., Bazhenova, L., Miller, V., Cohen, R., Eisenberg, P., Selaru, P., Wilner, K., & Gadgeel, S. (2010). A Phase II Study of PD-0325901, an Oral MEK Inhibitor, in Previously Treated Patients with Advanced Non-Small Cell Lung Cancer Clinical Cancer Research, 16 (8), 2450-2457 DOI: 10.1158/1078-0432.CCR-09-1920

LoRusso, P., Krishnamurthi, S., Rinehart, J., Nabell, L., Malburg, L., Chapman, P., DePrimo, S., Bentivegna, S., Wilner, K., Tan, W., & Ricart, A. (2010). Phase I Pharmacokinetic and Pharmacodynamic Study of the Oral MAPK/ERK Kinase Inhibitor PD-0325901 in Patients with Advanced Cancers Clinical Cancer Research, 16 (6), 1924-1937 DOI: 10.1158/1078-0432.CCR-09-1883

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Selective cell death mediated by small conditional RNAs

By on September 9, 2010

Cancer cells are characterized by genetic mutations that deregulate cell proliferation and suppress cell death. To arrest the uncontrolled replication of malignant cells, conventional chemotherapies systemically disrupt cell division, causing diverse and often severe side effects as a result of collateral damage to normal cells. Seeking to address this shortcoming, we pursue therapeutic regulation that is conditional, activating selectively in cancer cells.

via www.pnas.org

This was an interesting paper that caught my eye in PNAS last night.  Further reading demonstrated that the process uses small RNA molecules. The idea behind this approach was that the small RNA molecules can be programmed to attack only specific cancer cells; then, by changing shape, those molecules cause the cancer cells to self-destruct.

Normal cells die after a period of time and are replaced by new ones, a process called programmed cell death or apoptosis.  In a tumour, the cells continue to proliferate and form a mass, growing new blood vessels to feed the structure via angiogenesis.  

One of the things that has absorbed researchers for years is how to stop that process and induce cell death in cancer cells without killing a lot of normal cells at the same time.  To do this, we need to find ways of distinguishing cancerous from normal cells, thereby inducing a more targeted and selective approach to destruction and reducing unwanted side effects.  ]

This is not as easy as it sounds though!

In the PNAS study, the researchers took small conditional RNAs, which are less than 30 base pairs in length and are hairpin shaped molecules as shown in the photo below.

Picture 7

The press release from Caltech described the concept as thus:

"The researchers' method involves the use of two different varieties of small conditional RNA. One is designed to be complementary to, and thus to bind to, an RNA sequence unique to a particular cancer cell—say, the cells of a glioblastoma, an aggressive brain tumor.

In order to bind to that cancer mutation, the RNA hairpin must open—changing the molecule from one form into another—which, in turn, exposes a sequence that can spontaneously bind to the second type of RNA hairpin. The opening of the second hairpin then reveals a sequence that binds to the first type of hairpin, and so on. 

In this way, detection of the RNA cancer marker triggers the self-assembly of a long double-stranded RNA polymer."

Essentially, this is a clever way to use small conditional RNAs to the trick cancer cells into self-destructing by selectively forming long double-stranded RNA polymers that mimic viral RNA.

The researchers tested the RNA concept in the lab in xenograft models derived from three types of cancers: glioblastoma, prostate carcinoma, and Ewing's sarcoma so far, with some success:

"The molecules caused a 20- to 100-fold drop in the numbers of cancer cells containing the targeted RNA cancer markers, but no measurable reduction in cells lacking the markers."

Now clearly this approach has a long way to go before we see it in clinical trials, but there's nothing like starting off your day with exciting new technology approaches that may have application in the near future.

We need more creative research like this in oncology!

 

Photo Credit: Caltech

 

ResearchBlogging.org Venkataraman, S., Dirks, R., Ueda, C., & Pierce, N. (2010). Selective cell death mediated by small conditional RNAs Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1006377107

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Wnt signaling and cancer

By on September 8, 2010

In April at the AACR annual meeting, Bert Vogelstein talked about 12 critically aberrant pathways in cancer and we have talked about a few of these on this blog this year. Today, I want to take a look at another one of those key pathways, Wnt (pron. wint).

Background

Wnt is well known for it's network of proteins playing key roles in both development and cancer.  In simple terms, the process begins when Wnt proteins bind to cell-surface receptors of the Frizzled family, causing the receptors to activate the Dishevelled (dvl) family proteins, leading to a change in the amount of B-catenin that reaches the nucleus.

The basic pathway is described in the schematic below:

Picture 6Source: Cell Signal

Previously, we have discussed the simplicity of Hh signalling driving medulloblastoma and KRAS mutations (WT, wild-type) being critical for deciding EGFR therapy in colorectal cancer, but in pancreatic ductal adenocarcinoma (PDAC) things are a lot more complex.  Morris et al., noted that:

"Analysis of PDAC mouse models driven by targeted pancreatic expression of oncogenic KRAS suggest that both temporal and spatial control of Hh and Wnt–B-catenin activity are involved in specifying a cell lineage that can progress to PDAC."

For those of you interested in more detailed biology associated with PDAC, I urge you to check out Hezel et al's excellent review on the topic (see reference link below).

Wnt–B-catenin signalling in PDAC

An interesting observation in the literature is that the KRAS mutation is nearly universal (>95%) in human PDAC. Furthermore, Morris et al., observed that:

"Wnt–β-catenin signalling is frequently activated in PDAC and contributes to tumour cell proliferation and biology.  Genetic models that allow Wnt–β-catenin deregulation reveal that this pathway can transform pancreatic cells but is insufficient to drive PDAC initiation."

So what else is going on?

In their review, the authors specifically look at:

  • the ability of KRAS to alter cell fate in the pancreas
  • how the timing and location of Hh and Wnt–B-catenin signalling contribute to PDAC development.

It's well worth a read with lots of helpful schematic diagrams to illustrate the underlying biology.

Clearly, we have a long way to go before we know more about the molecular basis of what is happening in this disease.  Some of the many factors that still need to be elucidated include:

  • which components of the complex pathway are activated in cancer
  • how they interact
  • whether there are differences in the tumour epithelium and the microenvironment
  • determine which Hh and B-catenin targets are ‘mission critical’ for maintaining proliferation, viability and differentiation
  • how can we block the critical signalling proteins?

Wnt in multiple Myeloma

Other research has focused on the role of Wnt in multiple myeloma (see Guiliani et al., in the references).  Their results results supported the link between the production of Wnt antagonists by multiple myeloma cells and the presence of bone lesions in multiple myeloma patients. They also demonstrated that myeloma cells do not inhibit canonical Wnt signaling in human bone microenvironment.

Targeting different parts of the Wnt pathway has, however, produced some interesting results. Studies with an orally bioavailable GSK-3a/B dual inhibitor increased markers of cellular differentiation in vitro and bone mass in vivo, proving that we have much to learn about this complex pathway before a likely pharmacologic agent will emerge commercially.

Wnt inhibitors in the pipeline

While several inhibitors of Notch and Hedgehog pathways have reached the clinical trial stage, drugable targets for Wnt inhibitors seem to have have proven elusive so far. I haven't come across too many agents inhibiting Wnt, although I was amused to hear from a friend that one is called Soggy-1.  

The Novartis Institute of Biomedical Research (NIBR) reported on XAV939 in a Nature article.  XAV939 selectively inhibits B-catenin-mediated transcription and acts via tankyrase inhibition. Huang et al., (2009) succinctly noted:

"The development of targeted Wnt pathway inhibitors has been hampered by the limited number of pathway components that are amenable to small molecule inhibition."

Given that few first generation inhibitors hit the mark first time, we may have to test quite a few different generations of Wnt inhibitors or even inhibitors of different parts of the pathway in combination, before a successful strategy finally emerges from R&D pipelines in the future.

 

ResearchBlogging.org

Morris JP 4th, Wang SC, & Hebrok M (2010). KRAS, Hedgehog, Wnt and the twisted developmental biology of pancreatic ductal adenocarcinoma. Nature reviews. Cancer PMID: 20814421

Giuliani, N., Morandi, F., Tagliaferri, S., Lazzaretti, M., Donofrio, G., Bonomini, S., Sala, R., Mangoni, M., & Rizzoli, V. (2007). Production of Wnt Inhibitors by Myeloma Cells: Potential Effects on Canonical Wnt Pathway in the Bone Microenvironment Cancer Research, 67 (16), 7665-7674 DOI: 10.1158/0008-5472.CAN-06-4666

Hezel, A. (2006). Genetics and biology of pancreatic ductal adenocarcinoma Genes & Development, 20 (10), 1218-1249 DOI: 10.1101/gad.1415606

Huang, S., Mishina, Y., Liu, S., Cheung, A., Stegmeier, F., Michaud, G., Charlat, O., Wiellette, E., Zhang, Y., Wiessner, S., Hild, M., Shi, X., Wilson, C., Mickanin, C., Myer, V., Fazal, A., Tomlinson, R., Serluca, F., Shao, W., Cheng, H., Shultz, M., Rau, C., Schirle, M., Schlegl, J., Ghidelli, S., Fawell, S., Lu, C., Curtis, D., Kirschner, M., Lengauer, C., Finan, P., Tallarico, J., Bouwmeester, T., Porter, J., Bauer, A., & Cong, F. (2009). Tankyrase inhibition stabilizes axin and antagonizes Wnt signalling Nature, 461 (7264), 614-620 DOI: 10.1038/nature08356

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MET, HGF and EGFR inhibition in cancer

By on September 7, 2010

Hepatocellular Growth Factor (HGF) and MET receptor tyrosine kinase signalling play important roles in development as well tumorigenesis.  In a Nature review article, Comoglio noted:

"Signals generated by the tyrosine kinase receptor Met elicit a complex biological response including cell dissociation, migration, protection from apoptosis, proliferation and differentiation."

They are also involved in liver regeneration and repair (Huh et al., 2004).

Background

HGF and MET have been shown to be active in a wide range of different cancers from bladder cancer to Wilms Tumours, although it is not yet clear in which tumours the pathway is critical to survival or merely over-expressed as a consequence of events.  

The pathway is fairly complex, but here is a simple version:

Picture 2
Source: Angion Biomedica

There is a more detailed pathway schematic in Eder et al's paper (see reference below) for those interested.

Activation of HGF or MET, results in downstream signalling of the RAS-ERK and PI3K-mTOR pathways. The EGFR ligand has been excluded from this schematic for simplicity, but you can imagine how they can interact and thus dual inhibition of both will essentially reduce the risk of either cross-talk or feedback between the two, which reactivates the downstream pathways unless inhibited.

Inhibitors in the Pipeline

This year we have discussed several MET inhibitors on this blog, namely:

  • Pfizer's crizotinib, which is a weak MET inhibitor, but potent ALK inhibitor
  • Combination of MET and EGFR inhibition previously with ARQ-197 (Arqule/Daiichi-Sankyo) in early lung cancer

I did some research on MET inhibitors in the pipeline and was surprised to find that there are over 30 of them in development, with nearly a dozen in the clinic already.  ARQ-197 is clearly leading the pack and moving into phase III soon, as I classify PF-2341066 as an ALK inhibitor, since that's where it's most active.

Here are some of the active compounds I recently came across, although not all of them may still be actively pursued:

Picture 3
Most of the others in the clinic are in more generic phase I allcomer solid tumour trials, as companies look for safety and efficacy signals before determining which tumour types to focus on for major development.

Several compounds appear to specifically target both HGF and MET, eg MetMAB (Roche) and AMG102 (Amgen), whereas others target purely c-MET eg ARQ-197 and some are multi-kinase Inhibitors, eg XL880 and MK-2461, so it remains to be seen which approach will ultimately work best with these agents, and in what combinations for different tumour types.

Single agent vs combination?

Undoubtedly, the data so far suggests that dual inhibition with an EGFR inhibitor such as erlotinib will be more effective than single agent targeting of MET alone. 

A recent paper in Cancer Research on MET, HGF and EGFR inhibition with SGX523 (SGX Pharma and Lilly) therefore piqued my interest.  I actually thought this compound had been discontinued, following unexpected toxicities two years ago (see here and here), principally compromised kidney function, but it may have been revived by the research group, as the two latest published papers are from late 2009 and last month and Lilly acquired the biotech company in 2008.

The authors looked at a SCID mouse model with the goal of predicting efficacy.  Indeed, they concluded that:

"Our findings also indicate that simultaneously targeting the MET and EGFR pathways can provide synergistic inhibitory effects for the treatment of cancers in which both pathways are activated."

Looking at the data though, most of the tumour suppression occurred when SGX523 was combined with erlotinib than either alone as a single agent, suggesting this approach may have more utility in the clinic.

References:

ResearchBlogging.org

Zhang YW, Staal B, Essenburg C, Su Y, Kang L, West R, Kaufman D, Dekoning T, Eagleson B, Buchanan SG, & Vande Woude GF (2010). MET Kinase Inhibitor SGX523 Synergizes with Epidermal Growth Factor Receptor Inhibitor Erlotinib in a Hepatocyte Growth Factor-Dependent Fashion to Suppress Carcinoma Growth. Cancer research, 70 (17), 6880-90 PMID: 20643778

Buchanan SG, Hendle J, Lee PS, Smith CR, Bounaud PY, Jessen KA, Tang CM, Huser NH, Felce JD, Froning KJ, Peterman MC, Aubol BE, Gessert SF, Sauder JM, Schwinn KD, Russell M, Rooney IA, Adams J, Leon BC, Do TH, Blaney JM, Sprengeler PA, Thompson DA, Smyth L, Pelletier LA, Atwell S, Holme K, Wasserman SR, Emtage S, Burley SK, & Reich SH (2009). SGX523 is an exquisitely selective, ATP-competitive inhibitor of the MET receptor tyrosine kinase with antitumor activity in vivo. Molecular cancer therapeutics, 8 (12), 3181-90 PMID: 19934279

Comoglio PM (2001). Pathway specificity for Met signalling. Nature cell biology, 3 (7) PMID: 11433311

Huh CG, Factor VM, Sánchez A, Uchida K, Conner EA, & Thorgeirsson SS (2004). Hepatocyte growth factor/c-met signaling pathway is required for efficient liver regeneration and repair. Proceedings of the National Academy of Sciences of the United States of America, 101 (13), 4477-82 PMID: 15070743

Comoglio PM, Giordano S, & Trusolino L (2008). Drug development of MET inhibitors: targeting oncogene addiction and expedience. Nature reviews. Drug discovery, 7 (6), 504-16 PMID: 18511928

Eder JP, Vande Woude GF, Boerner SA, & LoRusso PM (2009). Novel therapeutic inhibitors of the c-Met signaling pathway in cancer. Clinical cancer research : an official journal of the American Association for Cancer Research, 15 (7), 2207-14 PMID: 19318488

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Mechanisms of castration resistance in prostate cancer

By on September 6, 2010

Over the last few weeks I've received quite a few questions relating to castration resistance and how it happens.  After all, while we have several therapies now approved once androgen deprivation therapy (ADT) fails, if we could keep men hormone sensitive for longer, then overall outcomes would likely improve.

Writing about prostate cancer is always a tough topic for me after my Dad passed away 10 years ago from the disease. He was sadly diagnosed in stage IV so there wasn't much that could be done really. It took only 18 months or so for a series of hormone therapies to fail and he developed castration resistant prostate cancer (CRPC). He subsequently declined chemotherapy on the grounds that he wanted to go with dignity on his own terms, nor did he want to put my Mother through hell either.  I rather respect that kind of mature and sensible approach in the face of a very difficult situation.

Ever since then though, I've always wondered what could we do inhibit androgen receptor (AR) signalling better and how could we improve on the therapies we have?After all, bicalutamide and similar therapies are not particularly effective agents because eventually, they all stop working and cycling through multiple therapies is very much the norm.

A new paper in Clinical Cancer Research attracted my attention recently (see journal link below).  The authors took a look at various possible methods of castration resistance and defined the main ones from the literature as:

"(i) AR activation by androgens converted from adrenal androgens or synthesized intratumorally via the de novo route

(ii) hypersensitivity of ARs due to overexpression of AR proteins and/or changes in cofactor expression levels

(iii) promiscuous activation of AR signaling by various ligands following AR mutation

(iv) constitutive activation of AR signaling by truncated ARs lacking ligand-binding domains."

A prior article by Harris et al., in Nature Reviews Urology defined 6 potential pathways slightly differently, including:

"(1) Tissue and tumoral steroidogenesis contribute to synthesis of testosterone and DHT, and might lead to persistence of tissue-level androgen despite castration.

(2) Mutations in the AR allow activation by alternate ligands or increased affinity for androgens.

(3) Amplification increases AR abundance.

(4) Ligandindependent activation of AR through ligand-independent modifications or cross-talk with other pathways, including phosphorylation of AR leading to hypersensitization and increased nuclear translocation.

(5) Change in the balance of coactivators and corepressors augment AR activity.

(6) Bypass pathways functioning independently of AR activity through upregulation of antiapoptotic molecules, such as Bcl-2."

These were also described graphically in the following picture, with the source referenced below:

17,20 lyase pathway

Source: Medscape

A lot of people have been asking how the 17,20 lyase inhibitors work. 17,20-lyase is essential for androgen and testosterone synthesis in both the adrenal glands and CRPC tissue, so the inhibitors have been developed to target this mechanism in both organs.

There are a number of 17,20 inhibitor in the oncology R&D pipeline including:

  1. abiraterone (J&J/Centocor) – phase III
  2. TAK-700 (Millennium-Takeda) – phase II
  3. TOK-001 (Tokai) – phase I/II

However, resistance to these therapies have already been observed in clinical trials, so while they may inhibit AR signalling for a period, they may not be the final answer.

The other drug in development that has garnered a lot of attention is MDV2100 (Medivation and Astellas).  This agent works via a completely different mechanism. Rather than acting through the adrenal cortex or CRPC tissues, it may operate in the cell nucleus on the AR regulated genes, essentially acting through the “intracrine” production of androgens from adrenal androgen or intratumorally, blocking the the interaction between androgens and AR.  The first generation agents such as bicalutamide, flutamide and nilutamide are not very effective because they have agonistic activity for CRPC so what is needed is a drug with more complete antagonist AR activity, especially against mutant ARs that develop over time.

What is particularly interesting in the new agents being developed to target advanced prostate cancer is what a poor marker of activity PSA is.  New studies with circulating tumour cells (CTC's) may well ultimately help us learn more about the underlying biology of the disease.

I'm also looking forward to hearing more about TMPRRS2-ERG, a recently discovered fusion by Tomlins et al., (2005) of an androgen-controlled serine protease, TMPRSS2, and the erythroblast transformation-specific (ETS) family gene ERG by chromosomal rearrangement. Together with phosphoinositide-3 kinase (PI3K), this fusion gene is now thought to be involved in the pathogenesis and progression of prostate cancer.

The authors noted:

"By using fluorescence in situ hybridization, we demonstrated that 23 of 29 prostate cancer samples harbor rearrangements in ERG or ETV1."

Once you have a fusion gene identified, you have a potentially druggable target that may play a causal role in cancer.  It will be interesting to see if what happens with this and how long it takes for a new agent to hit clinical trials targeting this aberration in prostate cancer.  

Maybe there is already one out there and I missed it!?

 

References:

ResearchBlogging.org Yamaoka M, Hara T, & Kusaka M (2010). Overcoming persistent dependency on androgen signaling after progression to castration-resistant prostate cancer. Clinical cancer research : an official journal of the American Association for Cancer Research, 16 (17), 4319-24 PMID: 20647476

Harris, William P, Mostaghel, Elahe A, Nelson, Peter S, & Montgomery, Bruce (2009). Androgen deprivation therapy: progress in understanding mechanisms of resistance and optimizing androgen depletion nature clinical practice UROLOGY, 6 (2), 76-85 DOI: 10.1038/ncpuro1296

Tomlins, SA, Rhodes, DR, & Perner, S (2005). Recurrent fusion of TMPRSS2 and ETS transcription factor genes in prostate cancer. Science, 310, 644-648 DOI: 10.1126/science.1117679

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