Advances reported at 2005 ASCO meeting

By Jerry Call

GIST patients with a particular genetic mutation are more likely to respond to Gleevec than those without the mutation, reported Dr. Michael C. Heinrich at one of plenary sessions of the annual conference of the American Society of Clinical Oncology, held May 14-17 in Orlando, Florida.

The results confirm previous observations and provide a foundation for molecular testing that can predict who will best respond to treatment with Gleevec.

A professor of medicine at Oregon Health & Science University in Portland, Heinrich’s presentation was titled “Correlation of target kinase genotype with clinical activity of imatinib mesylate (IM) in patients with metastatic GI stromal tumors (GISTs) expressing KIT (KIT+).”

The objective of the study he reported on (CALGB 150105/SWOG S0033) was to correlate molecular abnormalities in pre-treatment GIST specimens with clinical response to Gleevec in patients treated in the S0033 phase III NCI trial. Some 344 patients had sufficient tumor samples to be included in this study. This is about 46 percent of the total number of patients in the phase III S0033 trial. The pathology of these 344 patients was reviewed by Dr. Christopher Fletcher of the Brigham & Women’s Hospital. Of the 344 patients, 332 of them were confirmed to have GIST, while 12 patients (3.5 percent) were reclassified as non-GIST sarcomas.

Of the 332 GISTs analyzed, 324 (97.5 percent) were “KIT-positive” GISTs, and eight (2.5 percent) were “KIT-negative” GISTs. Heinrich also noted that 98 percent of KIT exon 9 mutations have a small intestine origin and 98 percent of PDFRA mutations have a stomach origin. The study data showed that both KIT-positive and KIT-negative GISTs have either KIT or PDGFRA mutations in about 87 percent of cases; however, the ratio of KIT to PDGFRA mutations was different. KIT-positive GISTs had KIT mutations 86 percent of the time and PDGFRA mutations in only 1.5 percent of cases. KIT-negative GISTs had KIT mutations in 50 percent of the cases, and PDGFRA mutations in 37.5 percent of the cases.

Kinase genotyping (checking for mutations in the various exons of c-kit and PDGFRA), was done by Heinrich and Dr. Christopher Corless, also of OHSU in Portland. Using gene expression profiling, three different groups (Subramanian et at, Antonescu et al, and Kang et al) have reported different molecular signatures for KIT exon 9, exon 11, and “wild-type” GISTs (no KIT or PDGFRA mutations).

The study looked at c-kit positive patients with KIT exon 11 and exon 9 mutations and patients with no mutations to determine the likelihood of an objective response when comparing low-dose (400 mg.) to high-dose (800 mg.) Gleevec. Note that “objective response” measures tumor shrinkage using RECIST criteria, and does not necessarily equate to how long the therapy will be effective (time to progression).

The study found that there was no effect on dose in patients with an exon 11 mutation. The “odds-ratio” of highdose vs. low-dose in these patients was 1.0 (p=0.96). This means that lowdose patients had the same odds (1.0) of an objective response as high-dose patients. Yet the study also found that the 25 patients with exon 9 mutations were much more likely to have an objective response on 800 mg. Gleevec than those on 400 mg., with an odds ratio of 8.0 — that is, eight times the chance of having a response.

“However,” Heinrich noted, “when adjusting for multiple comparisons, and considering the small sample size, this difference was not statistically significant.” Patients with no mutation (n=33) had an odds ratio of 1.5, but this was not statistically significant (p=0.62).

Heinrich presented data showing that patients with exon 11 mutations had a much longer median time to treatment failure (576 days) compared to patients with exon 9 mutations (308 days) or patients with no mutation (251 days).

The study concluded that there is no effect of Gleevec dose on objective response of KIT exon 11 mutant GIST. However, further study is needed to determine if KIT exon 9 mutant GISTs respond better to highdose imatinib. Also, the study concluded that kinase genotyping is useful for:
— Confirming the diagnosis of GIST, particularly for c-kit negative GIST;
— Predicting response and duration of response to Gleevec;
— The design and interpretation of clinical trials to study new treatments for GIST.

GLEEVEC MAY WORK ON KIT-NEGATIVE GIST

In another presentation (abstract No: 9010), Dr. Martin Blackstein presented data showing the response rate and progression-free survival in KITnegative GIST is not significantly different than KIT-positive GIST (43 percent vs. 49 percent progression-free survival at two years); however, a significant difference in survival was noted for KIT-positive vs. KITnegative GIST (77 percent vs. 57 percent, estimated overall survival at two years).

The conclusions of this study are that Gleevec therapy can provide clinical benefit for patients with KIT-negative GIST and the high incidence of kinase mutations in KIT-negative GIST support a therapeutic trial of Gleevec for all GIST patients regardless of CD117 (KIT) expression. It should be noted that many indications for Gleevec only include patients with KIT-positive GIST — thus patients with KITnegative GIST who could benefit from Gleevec might not be able to get it.

SUTENT BOOSTS SURVIVAL IN GLEEVEC-RESISTANT GIST

Dr. George Demetri reported that the new Pfizer drug Sutent (SU11248 or sunitinib malate) more than doubled survival and significantly reduced tumor growth and spread in patients with Gleevec-resistant GIST.

Demetri, of Dana-Farber Cancer Institute in Boston, presented phase III clinical trial data1 for Sutent, an oral, multi-targeted kinase inhibitor. Sutent inhibits multiple signals including KIT, PDGFRA, PDGFRB, VEGFR1, VEGFR2, VEGFR3, Fms, FLT3, and CSR1R.

This study accrued 312 patients within one year and was conducted at 56 sites in the United States, Australia, Europe and Singapore. One out of every three patients received a placebo. Patients progressing were unblinded and those receiving the placebo were allowed to cross over and receive SU11248.

The primary study objective was to compare time to progression (defined by RECIST criteria) between the two arms. Secondary goals included objective response rates and overall survival, patient-reported outcomes, including pain control, safety monitoring, correlation of drug exposure with efficacy and safety, and evaluation of biomarkers and molecular target studies including kinase genotyping.

The first interim analysis for efficacy was done in January. At that time the primary endpoint (time to progression) was found to be statistically significant between SU11248 and the placebo. After discussions between Pfizer and the independent data and safety monitoring board, treatment was unblinded and all patients receiving the placebo were allowed to cross over.

Patients receiving SU11248 had an 8 percent partial response rate vs. 0 percent for the placebo group. Stable disease was noted in 58 percent of SU11248 patients and in 50 percent of the placebo patients — but it is not clear from the data at what time point this was the case, particularly given the report that patients receiving SU11248 had a significantly longer median time to progression vs. placebo (6.3 months vs. 1.5 months). Progressive disease occurred in 20 percent of SU11248 patients and 39 percent of placebo patients. Some patients were not evaluable (too early or missing).

SU11248 also lengthened overall survival in spite of the placebo group being able to cross over after progression. Finally, although all patients on the placebo were given the option of crossing over to the drug after being unblinded following progression, 46 of the 105 placebo patients did not. No explanation for this group was given.

PET SCAN REVEALS EFFECTS OF SUTENT

Dr. Annick D. Van den Abbeele of Brigham and Women’s Hospital of Boston presented abstract2 on using PET scans to reveal kinase target inhibition with SU11248 in patients who have Gleevec-resistant GIST. The study showed that patients responding to SU11248 had a decrease in standard uptake valve (SUV) of the FDG tracer as soon as seven days after beginning SU11248.

A series of PET scans of a patient on a two-week on, two-week off drug schedule was shown. This patient had a dramatic decrease of activity seven days after starting therapy. Another PET scan taken on the last day of the two-week off drug period showed a rebound in activity, although the activity did not appear to be quite as high as a baseline scan. Another PET scan taken seven days after restarting SU11248 showed reduced activity that was similar to the PET scan taken seven days after beginning therapy.

An interesting question from the audience was whether PET scans were done before the patient stopped Gleevec. The answer was yes, and there was “a tremendous flare” in activity on the PET scan taken after the washout period, just before starting SU11248. This wash-out period flare-up suggests that there was still some response to Gleevec in “Gleevec resistant” patients.

GLEEVEC TOXICITY

Dr. Ronald DeMatteo presented an abstract3 that showed that the toxicity profile of Gleevec for patients with no visible disease is similar to patients with metastatic disease. The notable exception is that doctors are not seeing bleeding in patients with no visible disease, suggesting that bleeding in metastatic patients in probably related more to the GIST tumors themselves rather than Gleevec irritation of the GI tract. The benefit of adjuvant Gleevec has not yet been defined, but researchers hope to have this data within the next year.

GIST MUTATIONS

Dr. Sebastian Bauer from Dana- Farber presented this poster (abstract 9034), KIT hyperactivation in imatinib-resistant GIST: Implications for salvage therapies. Two new Gleevec-resistant GIST cell lines were established from biopsy specimens and used in this study along with an existing GIST882 cell line. GIST882 has a primary KIT mutation in exon 13 (K642E) and is sensitive to Gleevec.

GIST48, one of the new cell lines, has a primary mutation in exon 11 (V560D). This primary mutation would normally be sensitive to Gleevec. But this cell line also has a secondary mutation in exon 17 (D820A) that causes these cells to become resistant to Gleevec.

GIST430 is the second new cell line. It has a primary mutation in exon 11, and a secondary mutation in exon 13 (V654A). This secondary mutation causes Gleevec resistance.

 Levels of KIT protein were equal in all of the cell lines, but KIT activation was three to six times greater in the cell lines with secondary mutations compared to the Gleevec-sensitive GIST882 cells. PKC412 was found to inhibit the cell lines with secondary mutations, but may not inhibit certain Gleevec-sensitive primary mutations.

The study concluded:
— GIST secondary mutations can be associated with KIT hyperactivation and Gleevec resistance.
— Gleevec resistance is not absolute and varies depending on the type of resistance mutation.
— GIST proliferation and survival depend on the absolute (residual) levels of KIT activation after treatment with Gleevec.
— Gleevec resistance may be overcome with alternate KIT inhibitors or by targeting critical downstream signaling proteins, such as PI3K.
— PKC412 effectively inhibits cell lines with secondary Gleevec-resistant KIT mutations but may not inhibit certain Gleevec-sensitive primary mutations.
— The PI3K/AKT pathway is a critical signaling pathway in Gleevecresistant GISTs and appears to be a relevant therapeutic target.
— JAK/STAT signaling seems to play a minor role for cell survival/ proliferation in GIST.

GLEEVEC plus RAD001

Dr. Allan van Oosterom was lead author of the abstract4 on the phase I/II trial combining RAD001 and Gleevec. The original phase of this trial combined 600 mg. Gleevec with weekly 20 mg. doses of RAD001. Only one of 13 patients had progression-free survival of four months or more. So this phase I study was amended to a daily dosing of RAD001 and the interruption of Gleevec for PK sampling was eliminated. The amended protocol compared 600 mg. Gleevec plus either 5 mg/day or 2.5 mg/day of RAD001. Seven of 18 patients demonstrated clinical benefit (four months or more of progression-free survival) and one patient had a partial response. The regimen selected for phase II studies was 600 mg. Gleevec plus 2.5 mg/day of RAD001. The study is continuing.

The study did note that clinical benefit was not apparent in patients with known exon 9 mutations in the primary tumor (n=5). However, one Life Raft Group member with an exon 9 primary tumor resistant to Gleevec, SU11248 and BMS-354824, now appears to be responding (with shrinkage) to Gleevec plus RAD001.

GLEEVEC PRIOR TO SURGERY YIELDS RESULTS

Dr. Jonathan C. Trent of M.D. Anderson Cancer Center in Houston Texas, reported on apoptotic and antivascular activity of imatinib in GIST patients (abstract 9001).

Patients with planned resections of tumors were treated with a short course of 600 mg. Gleevec a day prior to surgery. Before Gleevec, patients had biopsies to acquire baseline tumor samples. The effects of short-term Gleevec administration were examined. The researchers noted both a direct anti-tumor effect of apoptosis (programmed cell death) and an antivascular effect. It is interesting to note that Gleevec was continued to within six hours (yes, hours) of surgery.

SUTENT FATIGUE TIED TO THYROID FUNCTION

Dr. Jayesh Desai presented an abstract5 on a study that found some patients (25 of 64) developed abnormal TSH levels after 5.4 months (median) on SU11248. TSH is a measurement of thyroid function. Nineteen of the 25 patients were treated with thyroid hormone replacement. The study found that the thyroid dysfunction noted may account, in part, for fatigue previously described with SU11248. All patients could be effectively treated with thyroid hormone replacement.

AFTER SURGERY, CONTINUE GLEEVEC

Two abstracts (9037 and 9038) were about the role of surgery and Gleevec. Both found that surgery in patients who were still responding to Gleevec was generally successful as long as Gleevec was continued after the surgery. Surgery in patients with Gleevec-resistant GIST was much less successful. In the 9038 study, six patients with Gleevec-resistant GIST had progression a median 6 months after surgery. The study’s authors found that patients with progressive disease are candidates for treatment with second- line molecularly targeted therapies, since surgery is likely of minimal benefit. The 9037 study recommended that in patients with progressive disease, indications for surgery should be individualized.

‘NEW’ LESIONS MAY NOT BE NEW

Kim M. Linton, MBChB, MRCP, was the first author of a study (abstract 9047) on liver lesions in two GIST patients. In both patients, CT scans taken eight to 12 weeks after the start of Gleevec showed the appearance of new, low-density liver metastases consistent with progressive disease, although other sites of disease had become smaller. Patient 1 had considerable symptomatic improvement despite the CT scan showing “new lesions,” so treatment was continued. All sites of disease remained stable for two years at the same dose of Gleevec.

Patient 2 developed new symptoms so treatment was stopped. Later, it was considered that the development of new low-density liver lesions on the early CT scans may have been due to cystic changes within tumors that were already there but not visible on the initial CT scans. Gleevec was therefore restarted two years later (at a time of rapid progression) and a significant response was seen.

The authors conclude that following Gleevec treatment, a fall in lesion density due to cystic change can result in increased conspicuity of liver metastases, which may look like new lesions but were actually pre-existing. This should not be confused with the development of new lesions.

GLEEVEC CROSSES BRAIN BARRIER?

Dr. Amir Khan gave abstract 9050, “Efficacy of Imatinib in Metastatic GIST to the Brain.” This is the case report of a patient with liver metastases who stopped Gleevec after five months of treatment. Within a month, the patient had multiple lesions in the brain, believed to be GIST. The patient restarted Gleevec at 400 mg. a day and improved within two weeks. An MRI done 10 weeks later showed complete resolution of the lesions. This case and another similar case reported earlier suggest that Gleevec can cross the blood-brain barrier, contrary to earlier reports.

Jerry Call is science coordinator of the Life Raft Group. Life Raft members present at 2005 ASCO conference included Penny Duke, Jim Hughes, Norman Scherzer and Marina Symcox. Penny and Marina represented GIST Support International.

1 Demetri: Abstract 4000, A phase III, multicenter, randomized, double-blind, placebo-controlled trial of SU11248 in patients following failure of imatinib for metastatic GIST.

2 Van den Abbeele: Abstract 9006-Imaging kinase target inhibition with SU11248 by FDGPET in patients with imatinib-resistant gastrointestinal stromal tumors (I-R GIST).

3 DeMatteo: Abstract 9009, Adjuvant imatinib mesylate in patients with primary high risk GIST following complete resection: Safety results from the U.S. Intergroup Phase II trial ACOSOG Z9000.

4 Van Oosterom: Abstract No. 9033, A phase I/ II trial of the oral mTOR-inhibitor everolimus (RAD001) and imatinib mesylate (Glivec/ Gleevec) in patients with GIST refractory to imatinib.

5 Desai: Abstract 3040, Hyprothyroidism may accompany SU11248 therapy in a subset of patients with … GIST and is manageable with replacement therapy.