- Email: [email protected]
Imatinib: resisting the resistance
Leukemia Research 27 (2003) 977–978
Editorial
Imatinib: resisting the resistance
CML is driven by the activated tyrosine kinase (TK) encoded by the BCR-ABL fusion gene. Inhibition of this activity by imatinib (Gleevec, Glivec, STI571) causes hematologic, cytogenetic and molecular remissions in descending frequency, respectively [1]. Unfortunately, as with many agents utilized in the treatment of cancer, including chemotherapeutic drugs, hormones and antibodies, resistance is an almost inevitable outcome. Refractory disease and acquired resistance is most commonly found for patients in accelerated phase and blast crises, being much rarer for patients in the chronic phase of the disease [1]. Resistance to imatinib in the clinic setting has been attributed to amplification of the fusion gene and point mutations in the TK [2]. Eighteen different candidate gleevec resistance mutations (GRMs) have been reported at 14 different sites, all between ABL codons 244 and 396 [2–9]. Fig. 1 in Corbin et al. [10] shows the relative frequency of these mutations. The most frequently reported GRMs are T315I, E255K, M351T and Y253H. Not all cases of evident drug resistance have been explained with GRM and gene amplification. Other mechanisms have been proposed including overexpression of the multiple drug resistance gene, activation of another oncogenic pathway, overexpression of a single-copy BCR-ABL, and binding of imatinib to overexpressed plasma ␣1 acid glycoprotein [4,11,12]. Overexpression of BCR-ABL in the absence of gene amplification has been seen in several patients who relapsed during imatinib therapy [4]. This suggests that a search for mutations in the promoter region of the fusion gene may be fruitful or possibly a trans mechanism may be at work in which expression of the fusion gene is up-regulated due to a defective regulatory pathway. Not all BCR-ABL GRMs are created equal. Some of the mutations discovered in patients with evidence for clinical resistance, particularly V379I and F311L, have not been substantiated by direct demonstration of resistance in biochemical and cellular assays [10]. This might be due to innocuous variants that are coselected along with a real BCR-ABL GRM or imatinib resistance due to some other mechanism. Other mutant BCR-ABL products have been shown to maintain sensitivity to imatinib at higher doses in cell proliferation assays, suggesting that a dose escalation strategy might be useful [5,6,10]. In a very recent report Kantarjian et al. [13] showed that an increased dosage of
imatinib can be helpful in CML patients resistant to standard doses, but they did not evaluate the patients for GRMs. In any strategy to cope with a GRM, it is important to know the patterns of cross-resistance. For example, PD09808 inhibits ABL TK with most of the known BCRABL GRMs, with the notable exception of T315I [14], while the hsp90 inhibitor 17-allylaminogeldanamycin causes the degradation of BCR-ABL containing this mutation with even greater potency than for wild-type BCR-ABL [15]. For these reasons, the advice given to families with inherited disease, “know your mutation,” is valuable in this situation as well. Knowledge of the patterns of cross-resistance will also be valuable in designing multiagent therapies to prevent the emergence of drug resistance [1]. If it is good to know your mutation, then is it good to know your mutation early, before overt resistance and relapse are evident? I think the answer will be yes, but we cannot be sure until prospective analysis for GRMs demonstrates an ability to predict resistance. We do not know how long it takes for a cell with a de novo mutation, or a preexisting rare variant, to expand and produce a relapse in a treated patient. If this process is slow enough we will find patients with low-level GRM for whom we can develop strategies to alter fate. Should we wait until there is evidence of rising BCR-ABL transcript level by molecular methods, or use mutation testing as a primary means of detecting an imminent relapse? I think mutation testing should be withheld until there is some other evidence of potential resistance. Detection and measurement of the BCR-ABL fusion transcript is sensitive down to one leukemia cell in 10,000–1 million normal cells, which is beyond the sensitivity of most methods for the detection of point mutations. When there is clear evidence of an increase in BCR-ABL transcripts during imatinib therapy, then resistance may be suspected and investigated. What level of sensitivity is needed for the early detection of GRMs? The answer to this question awaits evidence. The need to detect point mutations when present in low levels is a challenge to the molecular diagnostician. The most commonly used methods for detection of point mutations are adequate when the mutation is present in 10% of the cells. In this issue of Leukemia Research Liu and Makrigiorgos present a strategy to detect two of the GRMs down to 0.1% for Y253F and nearly to this level for T315I [16]. Thus, methods are now available to begin working on this problem.
0145-2126/03/$ – see front matter © 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0145-2126(03)00096-1
978
Editorial / Leukemia Research 27 (2003) 977–978
We have an even greater challenge ahead if the proposals above prove true. We will need to detect several GRMs (all?) in a sensitive and cost effective manner. Such methods of mutation detection may be valuable in other clinical situations. Among these are early detection of drug resistance to other chemotherapeutic agents for cancer and infectious disease, and detection of minimal residual disease in malignancies using point mutations as a marker. Perhaps it might become feasible to use such tests as early markers of malignancy for screening purposes [17]. One possible scenario is that after a 10-fold increase in BCR-ABL fusion transcripts in an environment selective for imatinib resistance, the majority of such transcripts may have a GRM. In that case enrichment for the mutation by the BCR-ABL specific RT-PCR itself may provide the needed sensitivity. Other complications include the recent finding of multiple GRMs simultaneously in many relapsed patients, with each mutation present in a fraction of the cells [6]. There is still much to learn about resistance to imatinib and how to exploit mutation detection strategies to gain a benefit in the clinic.
[8]
[9]
[10]
[11]
[12]
[13]
References [1] Druker BJ. Inhibition of the Bcr-Abl tyrosine kinase as a therapeutic strategy for CML. Oncogene 2002;21:8541–6. [2] Gorre ME, Mohammed M, Ellwood K, Hsu N, Paquette R, Rao PN, et al. Clinical resistance to STI-571 cancer therapy caused by BCRABL gene mutation or amplification. Science 2001;293:876–80. [3] Roche-Lestienne C, Soenen-Cornu V, Grardel-Duflos N, La¨ı J-L, Philippe N, Facon T, et al. Several types of mutations of the Abl gene can be found in chronic myeloid leukemia patients resistant to STI571, and they can pre-exist to the onset of treatment. Blood 2002;100:1014–8. [4] Hochhaus A, Kreil S, Corbin AS, La Rosée P, Müller MC, Lahaye T, et al. Molecular and chromosomal mechanisms of resistance to imatinib (STI571) therapy. Leukemia 2002;16:2190–6. [5] Roumiantsev S, Shah NP, Gorre ME, Nicoll J, Brasher BB, Sawyers CL, et al. Clinical resistance to the kinase inhibitor STI-571 in chronic myeloid leukemia by mutation of Tyr-252 in the Abl kinase domain P-loop. Proc Natl Acad Sci USA 2002;99:10700–5. [6] Shah NP, Nicoll J, Nagar B, Gorre ME, Paquette RL, Kuriyan J, et al. Multiple BCR-ABL kinase domain mutations confer polyclonal resistance to the tyrosine kinase inhibitor imatinib (STI571) in chronic phase and blast crisis chronic myeloid leukemia. Cancer Cell 2002;2:117–25. [7] Hofmann W-K, Jones LC, Lemp NA, de Vos S, Gschaidmeier H, Hoelzer D, et al. Ph+ acute lymphoblastic leukemia resistant to
[14]
[15]
[16]
[17]
the tyrosine kinase inhibitor STI571 has a unique BCR-ABL gene mutation. Blood 2002;99:1860–2. Branford S, Rudzki Z, Walsh S, Grigg A, Arthur C, Taylor K, et al. High frequency of point mutations clustered within the adenosine triphosphate-binding region of BCR/ABL in patients with chronic myeloid leukemia or Ph-positive acute lymphoblastic leukemia who develop imatinib (STI571) resistance. Blood 2002;99:3472–5. von Bubnoff N, Schneller F, Peschel C, Duyster J. BCR-ABL gene mutations in relation to clinical resistance of Philadelphiachromosome-positive leukaemia to STI571: a prospective study. Lancet 2002;359:487–91. Corbin AS, La Rosée P, Stoffregen EP, Druker BJ, Deininger MW. Several Bcr-Abl kinase domain mutants associated with imatinib mesylate resistance remain sensitive to imatinib. Blood, 2003. (Prepublished 6 February 2003, DOI 10.1182/Blood 12;2002: 3659.) Mahon FX, Deininger MWN, Schultheis B, Chabrol J, Reiffers J, Goldman JM, et al. Selection and characterization of BCR-ABL positive cell lines with differential sensitivity to the tyrosine kinase inhibitor STI571: diverse mechanisms of resistance. Blood 2000;96: 1070–9. Gambacorti-Passerini C, Barni R, le Coutre P, Zucchetti M, Cabrita G, Cleris L. Role of a1 acid glycoprotein in the in vivo resistance of human BCR-ABL+ leukemic cells to the Abl inhibitor STI571. J Natl Cancer Inst 2000;92:1641–50. Kantarjian HM, Talpaz M, O’Brian S, Giles F, Garcia-Manero G, Faderl S, et al. Dose escalation of imatinib mesylate can overcome resistance to standard-dose therapy in patients with chronic myelogenous leukemia. Blood 2003;101:473–5. La Rosée P, Corbin AS, Stoffregen EP, Deininger MW, Druker BJ. Activity of the BCR-Abl kinase inhibitor PD180970 against clinically relevant Bcr-Abl isoforms that cause resistance to imatinib mesylate (Gleevec, STI571). Cancer Res 2002;62:7149–53. Gorre ME, Ellwood-Yen K, Chiosis G, Rosen N, Sawyers CL. BCRABL point mutants isolated from patients with imatinib mesylateresistant chronic myeloid leukemia remain sensitive to inhibitors of the BCR-ABL chaperone heat shcok protein 90. Blood 2002; 100:3041–4. Liu W-H, Makrigiorgos GM. Sensitive and quantitative detection of mutations associated with clinical resistance to STI-571. Leukemia Res., in press. Traverso G, Shuber A, Levin B, Johnson C, Olsson L, Schoetz Jr DJ. Detection of APC mutations in fecal DNA from patients with colorectal tumors. N Engl J Med 2002;346:311–20.
Paul G. Rothberg Molecular Diagnosis Laboratory Department of Pathology and Laboratory Medicine University of Rochester Medical Center Rochester, NY 14642, USA E-mail address: paul [email protected]
Editorial
Imatinib: resisting the resistance
CML is driven by the activated tyrosine kinase (TK) encoded by the BCR-ABL fusion gene. Inhibition of this activity by imatinib (Gleevec, Glivec, STI571) causes hematologic, cytogenetic and molecular remissions in descending frequency, respectively [1]. Unfortunately, as with many agents utilized in the treatment of cancer, including chemotherapeutic drugs, hormones and antibodies, resistance is an almost inevitable outcome. Refractory disease and acquired resistance is most commonly found for patients in accelerated phase and blast crises, being much rarer for patients in the chronic phase of the disease [1]. Resistance to imatinib in the clinic setting has been attributed to amplification of the fusion gene and point mutations in the TK [2]. Eighteen different candidate gleevec resistance mutations (GRMs) have been reported at 14 different sites, all between ABL codons 244 and 396 [2–9]. Fig. 1 in Corbin et al. [10] shows the relative frequency of these mutations. The most frequently reported GRMs are T315I, E255K, M351T and Y253H. Not all cases of evident drug resistance have been explained with GRM and gene amplification. Other mechanisms have been proposed including overexpression of the multiple drug resistance gene, activation of another oncogenic pathway, overexpression of a single-copy BCR-ABL, and binding of imatinib to overexpressed plasma ␣1 acid glycoprotein [4,11,12]. Overexpression of BCR-ABL in the absence of gene amplification has been seen in several patients who relapsed during imatinib therapy [4]. This suggests that a search for mutations in the promoter region of the fusion gene may be fruitful or possibly a trans mechanism may be at work in which expression of the fusion gene is up-regulated due to a defective regulatory pathway. Not all BCR-ABL GRMs are created equal. Some of the mutations discovered in patients with evidence for clinical resistance, particularly V379I and F311L, have not been substantiated by direct demonstration of resistance in biochemical and cellular assays [10]. This might be due to innocuous variants that are coselected along with a real BCR-ABL GRM or imatinib resistance due to some other mechanism. Other mutant BCR-ABL products have been shown to maintain sensitivity to imatinib at higher doses in cell proliferation assays, suggesting that a dose escalation strategy might be useful [5,6,10]. In a very recent report Kantarjian et al. [13] showed that an increased dosage of
imatinib can be helpful in CML patients resistant to standard doses, but they did not evaluate the patients for GRMs. In any strategy to cope with a GRM, it is important to know the patterns of cross-resistance. For example, PD09808 inhibits ABL TK with most of the known BCRABL GRMs, with the notable exception of T315I [14], while the hsp90 inhibitor 17-allylaminogeldanamycin causes the degradation of BCR-ABL containing this mutation with even greater potency than for wild-type BCR-ABL [15]. For these reasons, the advice given to families with inherited disease, “know your mutation,” is valuable in this situation as well. Knowledge of the patterns of cross-resistance will also be valuable in designing multiagent therapies to prevent the emergence of drug resistance [1]. If it is good to know your mutation, then is it good to know your mutation early, before overt resistance and relapse are evident? I think the answer will be yes, but we cannot be sure until prospective analysis for GRMs demonstrates an ability to predict resistance. We do not know how long it takes for a cell with a de novo mutation, or a preexisting rare variant, to expand and produce a relapse in a treated patient. If this process is slow enough we will find patients with low-level GRM for whom we can develop strategies to alter fate. Should we wait until there is evidence of rising BCR-ABL transcript level by molecular methods, or use mutation testing as a primary means of detecting an imminent relapse? I think mutation testing should be withheld until there is some other evidence of potential resistance. Detection and measurement of the BCR-ABL fusion transcript is sensitive down to one leukemia cell in 10,000–1 million normal cells, which is beyond the sensitivity of most methods for the detection of point mutations. When there is clear evidence of an increase in BCR-ABL transcripts during imatinib therapy, then resistance may be suspected and investigated. What level of sensitivity is needed for the early detection of GRMs? The answer to this question awaits evidence. The need to detect point mutations when present in low levels is a challenge to the molecular diagnostician. The most commonly used methods for detection of point mutations are adequate when the mutation is present in 10% of the cells. In this issue of Leukemia Research Liu and Makrigiorgos present a strategy to detect two of the GRMs down to 0.1% for Y253F and nearly to this level for T315I [16]. Thus, methods are now available to begin working on this problem.
0145-2126/03/$ – see front matter © 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0145-2126(03)00096-1
978
Editorial / Leukemia Research 27 (2003) 977–978
We have an even greater challenge ahead if the proposals above prove true. We will need to detect several GRMs (all?) in a sensitive and cost effective manner. Such methods of mutation detection may be valuable in other clinical situations. Among these are early detection of drug resistance to other chemotherapeutic agents for cancer and infectious disease, and detection of minimal residual disease in malignancies using point mutations as a marker. Perhaps it might become feasible to use such tests as early markers of malignancy for screening purposes [17]. One possible scenario is that after a 10-fold increase in BCR-ABL fusion transcripts in an environment selective for imatinib resistance, the majority of such transcripts may have a GRM. In that case enrichment for the mutation by the BCR-ABL specific RT-PCR itself may provide the needed sensitivity. Other complications include the recent finding of multiple GRMs simultaneously in many relapsed patients, with each mutation present in a fraction of the cells [6]. There is still much to learn about resistance to imatinib and how to exploit mutation detection strategies to gain a benefit in the clinic.
[8]
[9]
[10]
[11]
[12]
[13]
References [1] Druker BJ. Inhibition of the Bcr-Abl tyrosine kinase as a therapeutic strategy for CML. Oncogene 2002;21:8541–6. [2] Gorre ME, Mohammed M, Ellwood K, Hsu N, Paquette R, Rao PN, et al. Clinical resistance to STI-571 cancer therapy caused by BCRABL gene mutation or amplification. Science 2001;293:876–80. [3] Roche-Lestienne C, Soenen-Cornu V, Grardel-Duflos N, La¨ı J-L, Philippe N, Facon T, et al. Several types of mutations of the Abl gene can be found in chronic myeloid leukemia patients resistant to STI571, and they can pre-exist to the onset of treatment. Blood 2002;100:1014–8. [4] Hochhaus A, Kreil S, Corbin AS, La Rosée P, Müller MC, Lahaye T, et al. Molecular and chromosomal mechanisms of resistance to imatinib (STI571) therapy. Leukemia 2002;16:2190–6. [5] Roumiantsev S, Shah NP, Gorre ME, Nicoll J, Brasher BB, Sawyers CL, et al. Clinical resistance to the kinase inhibitor STI-571 in chronic myeloid leukemia by mutation of Tyr-252 in the Abl kinase domain P-loop. Proc Natl Acad Sci USA 2002;99:10700–5. [6] Shah NP, Nicoll J, Nagar B, Gorre ME, Paquette RL, Kuriyan J, et al. Multiple BCR-ABL kinase domain mutations confer polyclonal resistance to the tyrosine kinase inhibitor imatinib (STI571) in chronic phase and blast crisis chronic myeloid leukemia. Cancer Cell 2002;2:117–25. [7] Hofmann W-K, Jones LC, Lemp NA, de Vos S, Gschaidmeier H, Hoelzer D, et al. Ph+ acute lymphoblastic leukemia resistant to
[14]
[15]
[16]
[17]
the tyrosine kinase inhibitor STI571 has a unique BCR-ABL gene mutation. Blood 2002;99:1860–2. Branford S, Rudzki Z, Walsh S, Grigg A, Arthur C, Taylor K, et al. High frequency of point mutations clustered within the adenosine triphosphate-binding region of BCR/ABL in patients with chronic myeloid leukemia or Ph-positive acute lymphoblastic leukemia who develop imatinib (STI571) resistance. Blood 2002;99:3472–5. von Bubnoff N, Schneller F, Peschel C, Duyster J. BCR-ABL gene mutations in relation to clinical resistance of Philadelphiachromosome-positive leukaemia to STI571: a prospective study. Lancet 2002;359:487–91. Corbin AS, La Rosée P, Stoffregen EP, Druker BJ, Deininger MW. Several Bcr-Abl kinase domain mutants associated with imatinib mesylate resistance remain sensitive to imatinib. Blood, 2003. (Prepublished 6 February 2003, DOI 10.1182/Blood 12;2002: 3659.) Mahon FX, Deininger MWN, Schultheis B, Chabrol J, Reiffers J, Goldman JM, et al. Selection and characterization of BCR-ABL positive cell lines with differential sensitivity to the tyrosine kinase inhibitor STI571: diverse mechanisms of resistance. Blood 2000;96: 1070–9. Gambacorti-Passerini C, Barni R, le Coutre P, Zucchetti M, Cabrita G, Cleris L. Role of a1 acid glycoprotein in the in vivo resistance of human BCR-ABL+ leukemic cells to the Abl inhibitor STI571. J Natl Cancer Inst 2000;92:1641–50. Kantarjian HM, Talpaz M, O’Brian S, Giles F, Garcia-Manero G, Faderl S, et al. Dose escalation of imatinib mesylate can overcome resistance to standard-dose therapy in patients with chronic myelogenous leukemia. Blood 2003;101:473–5. La Rosée P, Corbin AS, Stoffregen EP, Deininger MW, Druker BJ. Activity of the BCR-Abl kinase inhibitor PD180970 against clinically relevant Bcr-Abl isoforms that cause resistance to imatinib mesylate (Gleevec, STI571). Cancer Res 2002;62:7149–53. Gorre ME, Ellwood-Yen K, Chiosis G, Rosen N, Sawyers CL. BCRABL point mutants isolated from patients with imatinib mesylateresistant chronic myeloid leukemia remain sensitive to inhibitors of the BCR-ABL chaperone heat shcok protein 90. Blood 2002; 100:3041–4. Liu W-H, Makrigiorgos GM. Sensitive and quantitative detection of mutations associated with clinical resistance to STI-571. Leukemia Res., in press. Traverso G, Shuber A, Levin B, Johnson C, Olsson L, Schoetz Jr DJ. Detection of APC mutations in fecal DNA from patients with colorectal tumors. N Engl J Med 2002;346:311–20.
Paul G. Rothberg Molecular Diagnosis Laboratory Department of Pathology and Laboratory Medicine University of Rochester Medical Center Rochester, NY 14642, USA E-mail address: paul [email protected]