Pharma Strategy Blog

Commentary on Pharma & Biotech Oncology / Hematology New Product Development

Posts from the ‘Melanoma’ category

New mechanisms of resistance to MET inhibition

By on April 12, 2011

A very apt quote from Jeff Engelman’s group caught my eye this week:

“Unfortunately, cancers invariably develop resistance, and overcoming or preventing resistance will ultimately be key to unleashing their full therapeutic potential.”

MET is the receptor tyrosine kinase for hepatocyte growth factors (HGF) and inhibition has been implicated in metastases and migration of cancer cells (Rong et al., (1994), Takayama et al., (1997)), but more recently, it has also been observed that some tumour types have MET oncogenic addiction, including gastric cancer (Smolen et al., 2006).

MET Inhibition - source: Ma et al., (2007) BJC

Qi et al., (2011) went on to explain how they were looking at strategies for overcoming resistance to MET inhibitors, using PHA-665752 and PF-2341066, as an example in highly sensitive gastric cell lines.  They investigated the possibilities in vivo and in vitro. The results, however, were unexpected:

“To our surprise, we observed at least two mechanisms of resistance that arose simultaneously.  Both resulted in maintenance of downstream PI3K (phosphoinositide 3-kinase)-AKT and MEK (MAP/ERK kinase)-ERK signaling in the presence of inhibitor.”

Many of you will be aware of activation loops from other kinases, such as imatinib (Gleevec) in CML (T315I) and GIST (D842V) or erlotinib (Tarceva) in lung cancer (T790M), and adaptive pathways e.g. with BRAF inhibitors such as PLX4032 (vemurafenib) in melanoma, so this phenomenon is not uncommon.

With the MET inhibitors tested in the current research, the group found:

  1. A mutation in the MET activation loop, Y1230
  2. Activation of the epidermal growth factor receptor (EGFR) pathway due to increased expression of transforming growth factor alpha (TGFa)

What do these results mean?

The data suggests that combining MET and EGFR inhibitors in gastric cancer may be a viable therapeutic strategy, but consideration must also be given to approaches that inhibit Y1230 mutant MET as well, in order to shut off the escape routes.

It is hard to argue with the authors conclusion that:

“These results also underscore the notion that a single cancer can simultaneously develop resistance induced by several mechanisms and highlight the daunting challenges associated with preventing or overcoming resistance.”

Given the positive results seen with trastuzumab (Herceptin) in patients with HER2-positive gastric cancer, part of me is also wondering what incremental value there would be efficacy-wise, if MET and EGFR inhibitors were used in combination with trastuzumab?  We know that the blocking the driver mutation, the adaptive pathway and the ligand is important.  Some further preclinical research in this area may shed light on the matter.

References:

ResearchBlogging.orgQi, J., McTigue, M., Rogers, A., Lifshits, E., Christensen, J., Janne, P., & Engelman, J. (2011). Multiple Mutations and Bypass Mechanisms Can Contribute to Development of Acquired Resistance to MET Inhibitors Cancer Research, 71 (3), 1081-1091 DOI: 10.1158/0008-5472.CAN-10-1623

Ma, P., Tretiakova, M., Nallasura, V., Jagadeeswaran, R., Husain, A., & Salgia, R. (2007). Downstream signalling and specific inhibition of c-MET/HGF pathway in small cell lung cancer: implications for tumour invasion British Journal of Cancer, 97 (3), 368-377 DOI: 10.1038/sj.bjc.6603884

Rong S, Segal S, Anver M, Resau JH, & Vande Woude GF (1994). Invasiveness and metastasis of NIH 3T3 cells induced by Met-hepatocyte growth factor/scatter factor autocrine stimulation. Proceedings of the National Academy of Sciences of the United States of America, 91 (11), 4731-5 PMID: 8197126

Takayama H, LaRochelle WJ, Sharp R, Otsuka T, Kriebel P, Anver M, Aaronson SA, & Merlino G (1997). Diverse tumorigenesis associated with aberrant development in mice overexpressing hepatocyte growth factor/scatter factor. Proceedings of the National Academy of Sciences of the United States of America, 94 (2), 701-6 PMID: 9012848

Smolen GA, Sordella R, Muir B, Mohapatra G, Barmettler A, Archibald H, Kim WJ, Okimoto RA, Bell DW, Sgroi DC, Christensen JG, Settleman J, & Haber DA (2006). Amplification of MET may identify a subset of cancers with extreme sensitivity to the selective tyrosine kinase inhibitor PHA-665752. Proceedings of the National Academy of Sciences of the United States of America, 103 (7), 2316-21 PMID: 16461907

What can Zebrafish tell us about metastatic melanoma?

By on March 30, 2011

This week’s Nature is chock full of interesting articles on various cancer related topics so it was quite hard to pick just one to discuss in a blog post.   Nevertheless, two on Zebrafish was very striking, since the Letters discusses how models have revealed oncogenes and potential new drug targets in a particularly difficult to treat tumour type, i.e. melanoma.

Zebrafish, source: wikipedia

We now know that in melanoma, the BRAF V600E mutation drives signaling and proliferation of the MAPK pathway and that resistance also develops to treatment with targeted therapies such as PLX4032 and other inhibitors after six months or so.  The question then is what factors are driving the resistance and are other (druggable) oncogenes involved?

A multinational group of researchers from Boston, Rome and Paris used Zebrafish melanoma models to explore events in a:

“Recurrently amplified region of chromosome 1 for the ability to cooperate with BRAF(V600E) and accelerate melanoma.”

In doing so, they discovered something very interesting:

“SETDB1, an enzyme that methylates histone H3 on lysine 9 (H3K9), was found to accelerate melanoma formation significantly in Zebrafish.”

Chromatin was also found to be involved in tumorigenesis associated with SETDB1.

Histone methylation has been mooted as a promotor of cancer in other tumour types such as renal cell carcinoma and others, thus this study lends support to that theory.

In the second letter, White et al., (2011) report that DHODH inhibition with either leflunomide and NSC210627 led to a marked decrease in melanoma growth, both in vivo and in a xenograft model.  They used the Zebrafish to successfully identify:

“Small molecule suppressors of neural crest progenitors that give rise to melanoma.”

What do these findings mean?

SETDB1 is focally amplified in a number of malignancies, which means that it would be interesting to see if it also promotes histone methyltransferase activity in other cancers too.

The results from the Letters to Nature suggest that both DHODH and SETBD1 could be valid new targets for therapeutic intervention if drugs could be designed and developed to shut down the activity and prevent acceleration of the disease.  Future new logical combinations or sequencing of therapies in melanoma could therefore emerge from these important research findings.

In addition…

If you haven’t taken a look yet, this weeks Nature magazine is well worth reading for several other useful articles on cancer that are related to research including vaccines, biomarkers, liver cancer, genome sequencing in multiple myeloma, FAS and NF-kB signalling in lung cancer.  There is also a whole Outlook section (open access) on Cancer Prevention that is relatively easy to read, even for the layman that is worth checking out.

References:

ResearchBlogging.orgCeol, C., Houvras, Y., Jane-Valbuena, J., Bilodeau, S., Orlando, D., Battisti, V., Fritsch, L., Lin, W., Hollmann, T., Ferré, F., Bourque, C., Burke, C., Turner, L., Uong, A., Johnson, L., Beroukhim, R., Mermel, C., Loda, M., Ait-Si-Ali, S., Garraway, L., Young, R., & Zon, L. (2011).  The histone methyltransferase SETDB1 is recurrently amplified in melanoma and accelerates its onset.  Nature, 471 (7339), 513-517  DOI: 10.1038/nature09806

White, R., Cech, J., Ratanasirintrawoot, S., Lin, C., Rahl, P., Burke, C., Langdon, E., Tomlinson, M., Mosher, J., Kaufman, C., Chen, F., Long, H., Kramer, M., Datta, S., Neuberg, D., Granter, S., Young, R., Morrison, S., Wheeler, G., & Zon, L. (2011).  DHODH modulates transcriptional elongation in the neural crest and melanoma Nature, 471 (7339), 518-522  DOI: 10.1038/nature09882

Accelerated approval and cancer drugs

By on March 24, 2011

There is a provocative article in this week’s New England Journal of Medicine asking whether the accelerated approval process should be used for more cancer drugs:

“The striking results of recent phase 1 trials of targeted cancer drugs have provoked serious discussion about shortening the road to drug approval.”

The main thrust of the argument was that it takes on average seven years from entering human trials to approval if phase III trials are included in the oncology drug development process.

“Of the 23 oncologic drugs given accelerated approval between 1993 and 2008, two were ultimately withdrawn from the U.S. market — gemtuzumab because of toxicity and gefitinib because of lack of efficacy.”

The author argues that:

“Phase 3 trials are expensive and time-consuming, usually taking at least 2 to 3 years to reach survival end points. The news of a highly successful new compound in phase 1 or 2 rapidly reaches physicians and patients, creating demand for early access.”

While we have seen some successes with the Accelerated Review process with imatinib (Gleevec), erlotinib (Tarceva), cetuximab (Erbitux), bevacizumab (Avastin) and others, there has also been a flood of promising phase II agents that duly flopped in randomised phase III trials, with Pfizer’s figitumumab, Novartis/Antisoma’s ASA404 and sanofi-aventis’ iniparib to name a few off the top of my head.

One of the challenges here is that companies often take a targeted therapy but strangely test it in an unselected patient population, which will increase the chances of failure in a more rigorous randomised phase III trial.  In an ideal world, several carefully designed adaptive phase II trials would help develop logical combinations and markers of response, thus increasing the chances of success in phase III studies.

The big problem as I see it then, is that while we have exciting new agents likely to be approved in 2011 such as:

  • crizotinib in lung cancer
  • ipilimumab (Yervoy) and PLX4032 (vemurafenib) in metastatic melanoma
  • brentuximab vedotin in Hodgkin Lymphoma
  • abiraterone acetate (Zytiga) in prostate cancer

we don’t always know how to carefully select patients to enable treatment based on the underlying molecular basis of the disease.

Of those mentioned above, with crizotinib (ALK), vemurafenib (V600E BRAF) and brentuximab (CD30) we clearly do, but with abiraterone and ipilimumab the issue of patient selection seems less clear at the moment.  Sadly there are not any biomarkers available to tell us which patients are most likely to benefit from treatment in targeted therapies already approved such as bevacizumab.

The fate of bevacizumab in breast cancer has yet to be determined.  It was approved under the FDA Accelerated Review process based on the initial phase II data, with the assumption that the phase III trials would show an improvement in overall survival.  The AVADO and RIBBON1 trials showed a benefit in progression free survival or PFS (ie a surrogate marker of event free survival), but unfortunately were not positive for overall survival, which is the ultimate measure of disease progression and the condition required to be met under the fast track process.

The FDA are therefore recommending withdrawal based on the lack of overall survival as per the accelerated agreement and Roche offering the counter argument that there was evidence of patient benefit.  That issue will no doubt continue to be debated for much of 2011 until the public hearing later this year.  There is an excellent analysis of the impact of the FDA recommendation on bevacizumab uptake in the US in Oncology Business Review for anyone interested in trends.

Ultimately, we need have a better understanding of the molecular basis of the cancer types and drugs developed to target that aberration in a more carefully selected patient population.  The arguments for and against accelerated review will run and run – probably for longer than the debate about how to pronounce some of the new names!

My position on the accelerated review process?

When it works, it works well.  However, problems can arise when you get phase III trials that do not support the full approval due to a lack of a proven overall survival advantage in the population evaluated.  The FDA can find themselves in an impossible position especially given the high emotions that run in breast cancer, for example.  The onus should be on the company to do further research or trials better defining the patients who are most likely to respond rather than risk exposing thousands of patients to the systemic effects of a drug that may not offer meaningful benefit to the majority.

References:

ResearchBlogging.orgChabner, B. (2011). Early Accelerated Approval for Highly Targeted Cancer Drugs New England Journal of Medicine, 364 (12), 1087-1089 DOI: 10.1056/NEJMp1100548

3 Comments

New mechanisms of drug resistance to BRAF inhibitors in melanoma

By on February 23, 2011

Many of you will have been following the ongoing story of the discovery of activating V600E mutations in BRAF in greater than 50% of melanomas. As a result, BRAF inhibitors such as PLX4032 have emerged in melanoma but ultimately, we have also seen how resistance unfortunately sets in after 6 to 9 months of therapy despite some impressive initial results.  In addition, approximately 20% of patients don’t respond at all – the key question is why?

Previously, we have discussed several mechanism of resistance, namely AKT and MEK, which has lead to new clinical trial combinations of BRAF plus an AKT or MEK inhibitor (e.g. see this trial) to see if this approach can delay the development of resistance and thus improve the time to progression further.   A background on MEK inhibition can also be found here.

A new article published this month in Cancer Research from Paraiso et al., (2011) suggests another possible mechanism of resistance with BRAF inhibition may also be involved, namely loss of PTEN function (see references below).  They looked at what might happen with a new second generation BRAF inhibitor, PLX4720.

In this new research, some interesting findings emerged:

“We identify loss of PTEN expression, observed in >10% of melanoma specimens, as being responsible for increased PI3K/AKT signaling when BRAF is inhibited.

We further show that PTEN loss contributes to the intrinsic resistance of BRAF V600E-mutated melanoma cell lines to PLX4720 by suppressing the expression of the pro-apoptotic protein BIM.”

They essentially found that increased AKT signaling occurs with PTEN loss:

“Treatment of the PTEN+/- cell line panels with PLX4720 increased pPDK1 and pAKT signaling only in the melanoma cell lines lacking PTEN expression.”

They also observed that:

“Loss of PTEN contributes to intrinsic BRAF inhibitor resistance via the suppression of BIM-mediated apoptosis.”

Some of you may be wondering how these findings can be used to design new therapeutic strategies.  However, loss of PTEN function and heightened BIM expression isn’t something that can be changed directly, but rather, indirectly:

“Dual treatment of PTEN- cells with PLX4720 and a PI3K inhibitor enhanced BIM expression at both the mRNA and protein level and increased the level of apoptosis through a mechanism involving AKT3 and the activation of FOXO3a.”

There are some new trials open with either single agents or combination trials in this area, such as the following selection (by no means exhaustive):

  1. GSK2118436 (A BRAF and MEK/ERK inhibitor) – single agent trial interim data was previously presented at ASCO and ESMO last year.  The initial data in melanoma related brain mets presented at ESMO was stunning.
  2. BKM120 (PI3K) and GSK1120212 (MEK) – combination trial in advanced solid tumours with RAS/RAF mutations.
  3. GDC-0941 (PI3K) plus GDC-0973 (MEK) – combination trial in advanced solid tumours.
  4. GSK1120212 and GSK2141795 phase I safety and PK trial.

I think this is one area in oncology where the research into the underlying biology and mechanism of resistance is almost keeping pace with the clinical research, which is great news for patients!   More vibrant data may begin to emerge soon at ASCO in June and ESMO in September, so hopefully we won’t have long to wait for a new update on progress.

A big question that remains to be answered though, is figuring out which patients should get what combination and in what sequence?  Time will tell, but we have a while to go before we understand things better.

References:

ResearchBlogging.orgParaiso, K., Xiang, Y., Rebecca, V., Abel, E., Chen, A., Munko, A., Wood, E., Fedorenko, I., Sondak, V., Anderson, A., Ribas, A., Dalla Palma, M., Nathanson, K., Koomen, J., Messina, J., & Smalley, K. (2011). PTEN loss confers BRAF inhibitor resistance to melanoma cells through the suppression of BIM expression Cancer Research DOI: 10.1158/0008-5472.CAN-10-2954

1 Comment

PLX4032 phase III data in metastatic melanoma announced by Roche

By on January 19, 2011

Some of the most frequently searched words on this blog or those that arrive via organic Google searches centre around:

  • Melanoma
  • Ipilimumab
  • PLX4032

Interestingly, few are searching for RG7204, the Roche code for their compound being developed in partnership with Plexxikon or BRAF, the actual kinase target involved.

As background, you can read up on the past developments with BRAF V600 mutated melanoma here, here and here, including the phase II NEJM data, mechanisms of resistance (MEK or AKT) and how targeting CRAF as well as BRAF can lead to the development of squamous cell lesions in some patients.

This morning, Roche and Plexxikon announced the long awaited results of the phase III study (BRIM3) in newly diagnosed patients with metastatic melanoma:

“RG7204 (PLX4032) met its co-primary endpoints showing a significant survival benefit in people with previously untreated BRAF V600 mutation-positive metastatic melanoma.

Study participants who received RG7204 lived longer (overall survival) and also lived longer without their disease getting worse (progression-free survival) compared to participants who received dacarbazine, the current standard of care.”

The good news is that the survival benefit observed in the Phase II trials appears to be confirmed although the press release was rather short on specifics, presumably because the actual data will be presented at a cancer meeting later this year. However, given the current timing, I’m thinking this may augur well for an ASCO data submission. If so, ASCO is going to be interesting in metastatic melanoma this year with data anticipated from PLX4032 and ipilimumab (BMS).

Clearly, Roche intend filing the positive data with the Health Authorities, and in the meantime, they have announced plans to expand the access to PLX4032:

“Roche is now working closely with global health authorities to expand the recently announced RG7204 Early Access Program (EAP). The global EAP will be extended to include people with previously untreated, BRAF V600 mutation-positive metastatic melanoma.”

Now that we know more about the mechanisms of BRAF V600 resistance in metastatic melanoma, I’m also wondering when we might see some logical new trials evolve with PLX4032 in combination with a MEK or AKT inhibitor or perhaps sequenced, but to me it would make more sense to combine them.  It will be very interesting to see:

  • What the final survival advantage for PLX4032 is over dacarbazine
  • If a BRAF-MEK combination would further improve the OS

Fortunately, Genentech actually have two MEK inhibitors in development, GDC-0623 and GDC-0973 in solid tumours, so this approach is certainly feasible for them.

We’ll have to wait and see, but to put things in context, the phase II trial reported by Flaherty et al., (2010) in the NEJM demonstrated an approx. 6 month survival advantage in favour of PLX4032 before resistance set in.

2 Comments

Six feet under – snowpocalypse 2010

By on December 27, 2010

Maybe two feet under snow really, judging by my back yard, which is largely sheltered and not prone to drifts. It looks like a pristine Winter Wonderland.

For once, the weathermen were right when they said a blizzard was coming.  Twitter and Foursquare are abuzz with people signing in or tweeting about #snowpocalypse2010, #snomageddon or #snomg in jest, but really it’s just a lot of noise about the first snowfall of the season.

The result out front on the street is a big mess though, as the howling wind, drifting snow and snow ploughs have created huge 6ft ridges behind which are parked cars in igloo like humps.  Glad I parked on the left hand side to avoid that conundrum 😉

Still, there is a good two feet plus on the path and pavement, so shovelling it all will be the highest priority today.

Wherever you all are in the world, stay warm and dry.  I’ll leave you with an old post on the ipilimumab data to contemplate some thoughts, since this will be a hot topic of discussion in January with the FDA ODAC meeting scheduled for the beginning of Feb.

It will also soon be time for the annual year in review for 2010 and predictions for 2011 posts coming up.  What were your big events in cancer this year?  Do let me know if you have any predictions for next year in the comments below.

4 Comments

Metastatic melanoma – what’s new on the horizon?

By on November 3, 2010

Metastatic melanoma is quite a hot topic right now with a rich pipeline of products in development after a decade of little or no progress.  Of course, it is a bit like three London buses coming along at once after an hour long wait in the winter weather, but better late than never.

Many of you will remember the recent data from ipilimumab (BMS), an immunotherapy that showed increased survival, albeit with some severe adverse events, from the phase III trial in newly diagnosed metastatic melanoma presented at ASCO in the plenary session earlier this year, followed by a publication in the NEJM.  The FDA filing was subsequently submitted on the basis of the positive data.

Yesterday, BMS announced that the FDA have moved the PDUFA date back 3 months from Dec 25th to March 26th, 2011.  A precise reason for the delay wasn’t given , but the company did say:

“In response to an FDA request, Bristol-Myers Squibb submitted further analysis of data pertaining to the current application for pre-treated advanced melanoma and the agency considers this to be a major amendment to the drug’s BLA.”

I’m not going to speculate on the reasons for the extra review time or what the new data was, but it is an interesting and unexpected development.

Meanwhile, there’s also been a lot of buzz around targeted BRAF inhibition in melanoma lately, specifically around the initial stunning results seen with PLX4032 (Plexxikon & Roche).  So far, it seems that responses of around 6-12 months, with a median of around 8 months are possible with an kinase inhibitor that specifically targets the V600E mutation associated with BRAF, although there two problems:

  1. The responses are not durable as resistance (eg associated with MEK or AKT amplification) sets in.
  2. Inhibiting CRAF as well as BRAF appears to lead to an unwanted excess proliferation of squamous cells, which is reversible on withdrawal of treatment.

In the first case, a couple of recent papers have looked at mechanisms of resistance around BRAF inhibition that give us some clues of where to go next.

Gopal et al., (2010) decided to see what happened with AZD6244 or selumetinib (Array and AstraZeneca), a MEK and MAP/ERK inhibitor, and whether it would have any impact in mitigating BRAF resistance, given the potential close interaction within the RAS-RAF-MAPK pathway and downstream events that could be impacted through cross-talk and feedback loops:

“We analyzed a panel of Braf mutant human cutaneous melanoma cell lines for their sensitivity to growth and survival inhibition by AZD6244. We compared these effects with the baseline activation status of signaling pathways in the cells, and with AZD6244 treatment–induced changes in signaling networks.

These studies have identified the phosphoinositide 3-kinase (PI3K)-AKT pathway as a critical regulator of the efficacy of AZD6244 in Braf-mutant melanomas, including in cells without baseline activation of the pathway.”

In order to determine possible mechanisms of resistance in the cell lines, they compared the effects of AZD6244 treatment on their signaling pathways with effects in sensitive cell lines and found:

“Although all four of these Braf-mutant cell lines showed similar degree and duration of MAPK inhibition and several other proteins, the resistant cell lines increased their P-AKT levels following exposure to AZD6244, which was not observed in the sensitive cell lines.”

They went on to note:

“The functional significance of AKT activation is supported by the fact that inhibition of AKT activity, either by AKT knockdown or concurrent treatment with the mTORC1/2 inhibitor AZD8055, resulted in synergistic cell killing in the resistant cell lines.”

AstraZeneca and Merck have an ongoing partnership with their MEK (AZD6244) and AKT (MK-2206) kinase inhibitors, so combining them in a clinical trial to try and reduce resistance via feedback loops here would be an interesting approach worth trying.  Such a combination trial is currently recruiting in advanced solid tumours, not melanoma per se.  It is, however, a classic catch-all phase I study to see what kinds of cancers might respond and determine the MTD, but I would be very interested to see the data from patients with metastatic melanoma if they are enrolled.

Now, it has been shown in breast cancer cell lines showed that MEK inhibition resulted in cross-activation of the EGFR tyrosine growth factor receptor, but EGFR has not been shown to be relevant in melanoma, so Gopal et al., considered what other receptors might be responsible for mediating the effects.   In the discussion, an interesting snippet caught my eye:

“AZD6244 treatment induced a slight increase of IGF-I secretion by the cells, and knockdown of IGF-I also blocked P-AKT induction by AZD6244.  Supporting a specific role for the pathway in cell survival, recombinant IGF-I treatment blocked AZD6244-induced cell death, but not growth arrest, in the sensitive WM35.”

This might also suggest another useful combination approach to consider in clinical trials.

Previously, it has been shown that targeting BRAF can not only inhibit the important driver in melanoma, the V600E mutation, but it can also stimulate cellular signaling through the MEK-ERK pathway by activating the related family member C-RAF. This may explain the squamous cell proliferation seen in some patients with PLX4032. The more ideal BRAF inhibitor would therefore specifically target BRAF V600E, without activating CRAF at the same time.

Related to the subject of malignant melanoma, Kamata et al., (2010) just published a paper that looked at the relationship between BRAF and CRAF in the disease.  Previously it has been shown that D594A BRAF lacks kinase activity, but can induce the related gene product CRAF in addition to the mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK pathway.  What they found was really interesting.  In a nutshell:

“We show that the aneuploid phenotype is dependent on Craf. Treatment with the MEK inhibitor U0126 did not attenuate the emergence of aneuploidy but prevented the growth of aneuploid cells.  These results provide a previously unidentified link between Craf and chromosomal stability, with important implications for our understanding of the development of cancers with driver mutations that hyperactivate Craf.”

Aneuploidy is an abnormal number of chromosomes and can lead to genetic instability, a key cancer hallmark. It’s an important concept here because Kamata et al., have offered a different reason for the CRAF proliferation observed with some BRAF inhibitors:

“Impaired activity BRAF mutants are frequently coincident with oncogenic RAS mutations in human cancers (26) and in these, albeit rare, cancers, we may expect the hyper-activated CRAF induced by the combination of both oncogenes to enhance the aneuploidy response compared with mutation of either oncogene alone.  Such a situation is likely to be highly detrimental to the individual and, indeed, this mechanism may well account for the highly aggressive melanomas we observed following the combined expression of D594A Braf and G12D Kras in melanocytes.”

All in all, this is a very complex yet fascinating area of research and for those of you interested in this field, I would highly recommend reading the latest papers.

Photo Credit: Wikipedia

References:

ResearchBlogging.org Boni, A., Cogdill, A., Dang, P., Udayakumar, D., Njauw, C., Sloss, C., Ferrone, C., Flaherty, K., Lawrence, D., Fisher, D., Tsao, H., & Wargo, J. (2010). Selective BRAFV600E Inhibition Enhances T-Cell Recognition of Melanoma without Affecting Lymphocyte Function Cancer Research, 70 (13), 5213-5219 DOI: 10.1158/0008-5472.CAN-10-0118

 

Garnett MJ, Rana S, Paterson H, Barford D, & Marais R (2005). Wild-type and mutant B-RAF activate C-RAF through distinct mechanisms involving heterodimerization. Molecular cell, 20 (6), 963-9 PMID: 16364920

Gopal, Y., Deng, W., Woodman, S., Komurov, K., Ram, P., Smith, P., & Davies, M. (2010). Basal and Treatment-Induced Activation of AKT Mediates Resistance to Cell Death by AZD6244 (ARRY-142886) in Braf-Mutant Human Cutaneous Melanoma Cells Cancer Research, 70 (21), 8736-8747 DOI: 10.1158/0008-5472.CAN-10-0902

Kamata, T., Hussain, J., Giblett, S., Hayward, R., Marais, R., & Pritchard, C. (2010). BRAF Inactivation Drives Aneuploidy by Deregulating CRAF Cancer Research, 70 (21), 8475-8486 DOI: 10.1158/0008-5472.CAN-10-0603

4 Comments

What causes resistance to BRAF inhibition in melanoma?

By on August 31, 2010

Last week there was lot of excitement and interest surrounding the blog post on Roche/Plexxikon's data on PLX4032 in metastatic melanoma published in the New England Journal of Medicine. A number of the discussions on Twitter and email centred around what is causing resistance to the BRAF inhibitor?

If we take a look at the BRAF pathway alone, we would get a sense of the flow from the PDGF ligand through RAS, RAF and MAPK, which essentially drives angiogenesis and proliferation, like this 2004 review article:

Picture 5
Source: Nature Reviews Cancer

However, what this sort of simple diagrammatic picture doesn't tell us though, is where cross-talk or feedback loops might interfere with the inhibition to enable cell signalling to continue, thereby guaranteeing the tumour's continued survival despite our efforts to shut it down.

Another way of looking at the problem is to consider how pathways related to RAS signalling might possibly interact with the process, like this:

RASSource: Reaction Biology

When we look at the cell signalling processes this way, we can see that inhibiting PI3-kinase or AKT at the same time as RAF might turn out to be a useful approach.

It was therefore with great interest while browsing my RSS cancer feeds that I spotted a paper by Shao and Aplin in the current Cancer Research journal entitled: "Akt3-Mediated Resistance to Apoptosis in B-RAF–Targeted Melanoma Cells" (see journal link below).

If we use a BRAF inhibitor such as PLX4032 in advanced melanoma, we are effectively trying to kill the cancer cells by inducing apoptosis, or programmed cell death, thereby reducing the tumour growth and proliferation.  However, as the researchers put it very succinctly:

"Melanoma cells are highly resistant to anoikis, a form of apoptosis induced in nonadherent/inappropriate adhesion conditions.  Depleting B-RAF or the prosurvival Bcl-2 family protein Mcl-1 renders mutant B-RAF melanoma cells susceptible to anoikis."

They therefore began looking at different approaches to dealing with anoikis using both inhibitors and RNA interference.

These concepts may help us better understand how mutant B-RAF protects melanoma cells from apoptosis, thereby providing insight into possible resistance mechanisms to B-RAF inhibitors by developing new mutations in AKT. It also paves the way for future therapeutic strategies, either in combination, or in sequence, with a V600E BRAF inhibitor such as PLX4032 and an Akt inhibitor. I'm also wondering what effect a PI3-kinase inhibitor might have, but clearly adding an Akt inhibitor to the mix may well be worth a try in the first instance.

There are a number of AKT inhibitors in development in various companies pipelines. This is where the challenges and hurdles begin if a company doesn't have a relevant inhibitor because traditional R&D focuses on developing one's own pipeline with or without the current standard of care rather than cross-development with other companies with novel combination treatments unless a partnership, particularly with a small biotech, is specifically sought out.

As far as I know, Roche/Genentech or Plexxikon don't have an AKT in their pipelines, but there are some currently in early clinical development with other companies. The PI3K-mTOR-AKT pathway has been discussed in more detail in previous blog posts.

The most interesting and promising compound in this class is probably Merck's MK-2206, currently in phase II development for a number of different tumour types.

Other Akt inhibitors in R&D include:

  • Keryx: perifosine in phase II development for myeloma and colorectal cancer
  • Rexahn: Archexin in phase II trials in pancreatic cancer
  • Nerium: oleandrin in phase I development for metastatic renal and colorectal cancers
  • GSK: GSK2141795 and GSK21110183 are both in phase I trials for either hematologic malignancies or solid tumours

GSK had an earlier Akt inhibitor in phase I, GSK690693, but I believe it may have been terminated due to problems with hyperglycaemia, a common problem associated with PI3K-IGF-1R feedback. This problem has since been addressed and managed in other trials associated with these agents by the simple addition of metformin in the protocol. GSK now appear to be focusing on the follow-on compounds instead.

All in all, it's interesting to see how our knowledge of the biochemical and molecular pathways helps us better understand how cancer works and how we can use the data to devise improved strategies for tackling melanoma in the future. I'll be watching how this field develops with close interest.

 

ResearchBlogging.org Dibb, N., Dilworth, S., & Mol, C. (2004). Opinion: Switching on kinases: oncogenic activation of BRAF and the PDGFR family Nature Reviews Cancer, 4 (9), 718-727 DOI: 10.1038/nrc1434

Shao, Y., & Aplin, A. (2010). Akt3-Mediated Resistance to Apoptosis in B-RAF-Targeted Melanoma Cells Cancer Research, 70 (16), 6670-6681 DOI: 10.1158/0008-5472.CAN-09-4471

Crouthamel, M., Kahana, J., Korenchuk, S., Zhang, S., Sundaresan, G., Eberwein, D., Brown, K., & Kumar, R. (2009). Mechanism and Management of AKT Inhibitor-Induced Hyperglycemia Clinical Cancer Research, 15 (1), 217-225 DOI: 10.1158/1078-0432.CCR-08-1253

2 Comments

Inhibition of mutated, activated BRAF in metastatic melanoma

By on August 25, 2010

Hot on the heels of last week's New England Journal of Medicine article on ipilimumab (BMS) comes another article on metastatic melanoma, this time from Keith Flaherty's group in Pennsylvania and Boston on BRAF inhibition with PLX4032, an exciting compound being developed by Plexxikon/Roche (see link below in the references for the article).

I've written a few posts on this interesting compound recently (e.g. here and here), for those interested in getting up to speed on the concept and data.

The basic concept is that a while back it was noticed that some tumours such as melanoma develop the V600E BRAF mutation and induce resistance or a poorer prognosis, so common sense says why not find a targeted agent to inhibit the activity to see what happened?

In the August 26th edition of the NEJM, Flaherty et al., described the updated phase I results in two phases:

  • 55 patients (49 with melanoma) in the dose escalation phase
  • 32 additional people with metastatic melanoma who had BRAF with the V600E mutation in the extension phase

Now, remember, a phase I trial usually seeks to define the maximum tolerated dose (MTD), which is used in the phase II studies and looks at the general tolerability and side effects.  Efficacy is not the primary end point, but of course, we all secretly look at the activity to see if there is any sign of a response!

First things first.  After some palaver with the crystalline formulation, it was finally settled on a "micro-precipitated bulk powder" since that offered superior bioavailability. I'm paraphrasing a bit and taking liberties here, but no doubt regular readers will sense my excitement and tendency to skip to the bottom line and find out what it all means, although we have all been there with those kind of challenging problems, especially as they add delays and frustrations all around!

Anyway, as a result of these changes, the final recommended dose that emerged for the phase II studies was 960mg BID, with increases in the dose limited by grade 2 or 3 rash, fatigue or arthralgia. These kind of side effects are fairly typical of oral TKI's and very different from what we saw with last week's NEJM article on immunotherapy with ipilimumab in a similar population.

Potentially, the biggest concern is the appearance of squamous-cell carcinoma that appeared in 10 of 32 patients (31%) in the dose escalation cohort.  While normally well differentiated and of low invasive potential, it is something to note.  The authors noted that recent data earlier this year (see references below) suggest BRAF inhibitors can activate the MAP kinase pathway in cells that lack a BRAF mutation and may explain some of the peculiar side effects seen with PLX4032.

Previously, Flaherty et al., reported nine responses in the second PLX4032 cohort and median PFS of 6 months.  For comparison with the updated data, see the last report before reading on. Over half of the people in both cohorts had received 2 or more therapies, so these are a mix of relapsed and refractory patients:

  • In the first cohort of 55 people, there were 16 with the BRAF V600E mutated melanoma and received 240mg or more of PLX-4032.  The efficacy?  Well, there were 10 partial response and 1 complete response (69%).
  • In the extension cohort of 32 people, 24 were partial responders and 2 had a complete response (81%), which is pretty impressive all around.  No wonder Dr Flaherty was very excited when interviewed for an article in the NY Times earlier this year!

My first reaction was slight disbelief, after all, this is a very difficult to treat and highly aggressive disease, thus sadly, people do tend to relapse early. In short, if there were three cancers I absolutely wouldn't want to get, this would be one of them.

On closely checking the data carefully including the 81% response rate in the second cohort (yes, it's correct!), I noticed that the researchers reported across all patients in the phase I study, the median progression free survival (PFS) was now improved to 7 months.  That means that 50% did worse and 50% did better than 7 months, way better than one might expect so early in a trial.  I did double check again and pinch myself, as it was late on Tuesday night when I penned the draft.

If you are interested in this area, do check out the link to the article below because the water plots and anti-tumour responses over time are well worth looking at, especially as some people are clearly achieving responses approaching a year, despite having advanced disease.

"Responses were observed at all sites of the disease, including the bone, liver, and small bowel."

Yes, it is still very early, but how awesome is it to read that?

As an aside, a number of readers have written asking why sorafenib hasn't shown to be effective in melanoma, despite inhibiting BRAF.  Flaherty et al., had an answer for that. They suggested that  because it also inhibits other pathways, it may well be that the non-BRAF effects of the drug mediate side effects that limit the ability to achieve enough drug concentration and thus the drug concentration isn't high enough to effectively inhibit the V600E BRAF mutation.  An interesting theory that also speak to the idea that several specific inhibits may be more effective that more promiscuous multi-kinase inhibitors.

The good news is that for now at least, we seem to be on the right track with PLX4032 and ipilimumab in metastatic melanoma.  It will be interesting to see what the mechanisms of resistance are down the road, and whether we have some options in the works for either combination or sequencing of different targeted agents for this disease.

 

ResearchBlogging.org Flaherty, K., Puzanov, I., Kim, K., Ribas, A., McArthur, G., Sosman, J., O'Dwyer, P., Lee, R., Grippo, J., Nolop, K., & Chapman, P. (2010). Inhibition of Mutated, Activated BRAF in Metastatic Melanoma New England Journal of Medicine, 363 (9), 809-819 DOI: 10.1056/NEJMoa1002011

Heidorn, S., Milagre, C., Whittaker, S., Nourry, A., Niculescu-Duvas, I., Dhomen, N., Hussain, J., Reis-Filho, J., Springer, C., & Pritchard, C. (2010). Kinase-Dead BRAF and Oncogenic RAS Cooperate to Drive Tumor Progression through CRAF Cell, 140 (2), 209-221 DOI: 10.1016/j.cell.2009.12.040

Poulikakos PI, Zhang C, Bollag G, Shokat KM, & Rosen N (2010). RAF inhibitors transactivate RAF dimers and ERK signalling in cells with wild-type BRAF. Nature, 464 (7287), 427-30 PMID: 20179705

Hatzivassiliou, G., Song, K., Yen, I., Brandhuber, B., Anderson, D., Alvarado, R., Ludlam, M., Stokoe, D., Gloor, S., Vigers, G., Morales, T., Aliagas, I., Liu, B., Sideris, S., Hoeflich, K., Jaiswal, B., Seshagiri, S., Koeppen, H., Belvin, M., Friedman, L., & Malek, S. (2010). RAF inhibitors prime wild-type RAF to activate the MAPK pathway and enhance growth Nature, 464 (7287), 431-435 DOI: 10.1038/nature08833

2 Comments

Improved survival with ipilimumab in metastatic melanoma

By on August 19, 2010

The latest New England Journal of Medicine dropped in the mail yesterday afternoon, it has some interesting articles on how palliation plus chemotherapy offers improved survival over chemo alone and a small study on the positive impact of T'ai Chi on fibromyalgia.  My attention, however, was drawn to the ipilimumab data in advanced metastatic melanoma.

We saw the first major presentation of this phase III trial recently at ASCO, and my pre-ASCO notes can be found here. At the BMS investor meeting held during the conference, the executives were clearly very excited about the prospects for the agent.  It would seem that the FDA agrees with them, as it was announced yesterday that Priority review status has been granted in previously treated people with melanoma.  The PDUFA action date is estimated as December 25th, 2010, so I think we can safely assume that it will likely happen a bit before that 🙂

Going back to the NEJM paper, what can we expect?

The complex study design looked at the impact of ipilimumab, which targets CTLA-4 antibodies resulting in anti-tumour effects, with and without gp100, a vaccine based on melanoma vaccine, versus ipilimumab alone in a phase III trial of 674 patients. In short, here's how the median overall survival results stack up:

  • Ipilimumab + gp100:   10.0 months
  • gp100 alone:               6.4 months
  • Ipilimumab alone:      10.1 months

There was no difference in survival between the two ipilimumab groups, suggesting that the gp100 vaccine isn't adding anything to the mix. I'm not really convinced, however, of the arguments for using gp100 as an unconventional control over dacarbazine (DTIC) in patients who had previously failed IL2 therapy.  From this data, we have no idea how ipilimumab stacks up versus dacarbazine in the second-line setting, but given there is no standard of care in the refractory setting for patients who have failed dacarbazine, it presented a tricky issue in trial design. Still, the overall survival advantage in favour of ipilimumab alone speaks for itself.

It will be interesting to see what BMS do with this commercially, if the FDA approve it and they most likely will.  Based on this data, it appears to make sense to market ipilimumab alone without the extra costs and potential toxicities associated with adding gp100.

Four months improvement in advanced refractory melanoma is a relatively big jump, and like many I'm excited to see that, despite the low responses rates seen in the ipilimumab groups (6-11%).  The editorial by Hwu also noted that:

"… the true importance of this drug lies in the long-term benefit that was seen in a subgroup of patients. Follow-up from the earliest cohort of patients that received the anti–CTLA-4 drug shows that ongoing complete responses in some patients with metastatic melanoma can continue past 6 years."

The biggest downside of this trial though, was the side effect profile. Whereas we recently saw few fatal toxic side effects associated with the Provenge vaccine in castrate-resistant prostate cancer, immunotherapy with ipilimumab is an entirely different kettle of fish, as the NEJM article demonstrated:

Grade 3-4 immune related adverse events:

  • 10-15% of ipilimumab treated patients
  • 3% treated with gp100 alone

Deaths in study:

  • 14 related to study drugs (2.1%)
  • 7 associated with immune-related events

Now, we need to remember that people entering clinical trials at Academic centres are not the typical patients seen in the Community setting.  They tend to be younger and have a much better performance status for a start, so it is likely that there will be some nervousness associated with management and complications in older, more frail patients. The authors noted that:

"Adverse events can be severe and long-lasting, or both, but most are reversible with appropriate treatment."

It reminds me somewhat of the situation with another immune-related therapy a few years ago with alemtuzumab (Campath), an monoclonal antibody that binds to CD52 in chronic lymphocytic leukemia (CLL), where the occasionally urgent side effect management and rare complications that can arise (CMV activations, severe infections etc) were so resoundly disliked by the Community, that most avoid using it where at all possible. Urgent medical attention of severe and, potentially fatal, complications is much easier to handle in a hospital than an office setting, especially on a Friday afternoon or over the weekend.

Ipilimumab looks to be an efficacious therapy that extends life, but at a cost.  I can therefore see that it will mostly likely get used in Academic settings, where there is more comfort and familiarity in dealing with the potential complications, especially in advanced, relapsed disease.  I could be wrong in that assessment, but that is what instinct tells me.

Most doctors will try something once, especially in the refractory or salvage setting, but the first sign of potentially fatal complications requiring urgent medical attention creates an environment that is fraught with stress and worry, busy Community practices may well decide it will be easier to refer appropriate patients in that situation.

In an accompanying editorial (see below for reference link), Patrick Hwu summed up the trial and new directions in metastatic melanoma admirably:

"Despite dramatic effects in a subgroup of patients receiving the anti–CTLA-4 drug, the majority of patients with metastatic melanoma do not respond to this agent, and further work is vital to improve these results.

Future efforts should include the rational combination of anti–CTLA-4 agents or alternative checkpoint inhibitors with targeted therapies or other immune agents. Instead of attempting to marginally increase the median survival, the primary goal of these new combination therapies should be to enhance the percentage of long-term survivors, thereby elevating the “tail” of the survival curve."

 

{Disclosure: Long on BMS}

 

ResearchBlogging.org Hodi, F., O'Day, S., McDermott, D., Weber, R., Sosman, J., Haanen, J., Gonzalez, R., Robert, C., Schadendorf, D., Hassel, J., Akerley, W., van den Eertwegh, A., Lutzky, J., Lorigan, P., Vaubel, J., Linette, G., Hogg, D., Ottensmeier, C., Lebbe, C., Peschel, C., Quirt, I., Clark, J., Wolchok, J., Weber, J., Tian, J., Yellin, M., Nichol, G., Hoos, A., & Urba, W. (2010). Improved Survival with Ipilimumab in Patients with Metastatic Melanoma New England Journal of Medicine DOI: 10.1056/NEJMoa1003466

Hwu, P. (2010). Treating Cancer by Targeting the Immune System New England Journal of Medicine, 363 (8), 779-781 DOI: 10.1056/NEJMe1006416

3 Comments
error: Content is protected !!