General mechanisms ofresistance to trastuzumab: obstacles fortrastuzumab binding to HER2. A, aconstitutively active truncated form ofHER2 receptor that has kinase activitybut lacks the extracellular domain andthe binding site of trastuzumab isoriginated from metalloproteasedependentcleavage of the full-lengthHER2 receptor (p185; refs. 45, 130).Trastuzumab does not bind to p95HER2and therefore has no effect against it.The remaining intracellular domain ofp95HER2 has operational kinasedomains and can be targeted by the TKinhibitor lapatinib (63)
B, epitopemasking by MUC4 or CD44/polymerichyaluronan complex. MUC4 is a largemembrane-associated mucin producedby epithelia as part of the epithelialprotective mechanisms. MUC4 hasmultiple repeat regions containingserine and threonine. Glycosylation ofthese repeats forces them into a highlyextended, rigid conformation andmakes them hydrophilic (69). MUC4 isnormally present on the apical surfacesof epithelial cells, but overexpressed inseveral carcinomas. MUC4 has closeassociation with HER2 and may masktrastuzumab cognate epitope,interfering with antibody binding andactivity. CD44/hyaluronan polymercomplex activates RAS and PI3Kpathways, but it is not clear if theseeffects depend on HER2. Inhibition ofhyaluronan synthesis in vitro reduceshyaluronan polymer binding to CD44,and increases trastuzumab binding toHER2.
Fig. 4. General mechanisms of resistance to trastuzumab: presence of upregulation of HER2 downstream signaling pathways. PTEN is a tumor suppressor.Trastuzumab binding stabilizes and activates PTEN and consequently down-regulates the PI3K/Akt signaling pathway (39). When PTEN function is lost,PI3K remains constitutively active regardless of binding of trastuzumab to HER2. PTEN loss correlates with clinical unresponsiveness to trastuzumabtreatment. Genomic aberrations in the PI3K pathway are a common event in a variety of cancer types (127). Multiple components of this pathway are affectedby germline or somatic mutation, amplification, rearrangement, methylation, overexpression, and aberrant splicing, but only in a few instances PIK3CAand PTEN mutations are seen simultaneously (86). Genomic aberrations in the PI3K pathway produce constitutive activation of the pathway, which will signaldownstream to the nucleus regardless of trastuzumab binding to HER2. This is the case with activating mutations of PIK3R1 and PIK3CA, encoding genesfor PI3K p85α and p110α, respectively. Increased Akt kinase activity and PDPK1 overexpression have also been implicated with trastuzumab resistance.
Fig. 5. General mechanisms of resistance to trastuzumab: presence of signaling through an alternate receptor and/or pathway. Signaling may continueregardless of trastuzumab binding to HER2 when other receptors remain active on the tumor cell. The activity of certain receptors may also increase as aresult of trastuzumab blockage of HER2, as a cell survival mechanism (see text for details). Trastuzumab-induced growth inhibition in HER2-overexpressingcells can be compensated for by increased IGF-IR signaling, resulting in resistance to trastuzumab. In preclinical models in which HER2-overexpressingtumor cells are cultured in the presence of ligand, resembling what is likely to happen in vivo, trastuzumab does not interfere with HER2/HER3heterodimerization and therefore does not block signaling from these heterodimers (42). c-Met is frequently co-expressed with HER2 in cell lines andcontributes to trastuzumab resistance through sustained Akt activation.
Fig. 6. General mechanisms of resistance to trastuzumab: failure to trigger immune-mediated mechanisms to destroy tumor cells. ADCC is a process inwhich the Fab region of an antibody binds to its cognate antigen present on a target cell (for instance cancer cell), whereas its Fc region engages with the Fcreceptor present on an effector cell from immune system. This process triggers degranulation of cytotoxic granules from effector cell toward the target celland culminates with target cell apoptosis (131). In humans, the Fc receptor family comprises FcγRI (CD64); FcγRII (CD32), with three isoforms FcγRIIa, FcγRIIb(inhibitory), and FcγRIIc; and FcγRIII (CD16), including two isoforms FcγRIIIa and FcγRIIIb (132). There is a correlation between the clinical efficacy oftherapeutic antibodies in humans and their allotype of high-affinity (V158) or low-affinity (F158) polymorphic forms of FcγRIIIa. Epitope masking previouslydiscussed in the obstacles for trastuzumab binding to HER2 section would also play a role by preventing antibody-based cell destruction
The investigational agent, trastuzumab-DM1 (T-DM1), is designed to combine the anti-tumor activity of trastuzumab with a means of delivering highly potent chemotherapy directly into HER2-expressing cells. DM-1 (also known as maytansine) is an inhibitor of tubulin polymerization, binding tubulin competitively with vinca alkaloids. Compared with drugs like vincristine, however, it is 20 to 100 times more potent, said principal investigator Murali Beeram, MD, of the Institute for Drug Development, San Antonio. "DM-1 was developed in 1975 but was found to be too toxic for standard chemotherapy," Dr. Beeram said. "We tagged it in a very small amount to the trastuzumab molecule with a linker. The linker provides a stable bond between the two agents that is designed to prolong exposure and reduce the toxicity of T-DM1. We are, in essence, sending a chemotherapy payload into the cell via the antibody. We get a twofold effect—an increase in the efficacy of trastuzumab and direct delivery of the cytotoxic agent, which reduces treatment toxicity." The compound was well tolerated. The only grade 3-4 toxicity was a rapidly reversible grade 4 thrombocytopenia at the highest dose in one patientA phase II trial of the immunoconjugate is being initiated in HER2-positive metastatic breast cancer patients. Genentech, which is developing the new agent, has enlisted ImmunoGen, Inc. to develop a commercial-scale process for making T-DM1, using ImmunoGen's tumor-activated prodrug (TAP) technology.
ABC1 - G.W. Sledge - Resistance to anti-HER2 therapies
Resistance to Anti-HER2 Therapy George W. Sledge, Jr. MD Indiana University Simon Cancer Center
What Do We Mean by “Resistance”?• ChemoRx resistance Throw away the drug• Targeted therapy resistance: – Is resistance absolute? – Should we maintain selective pressure?
Trastuzumab treatment beyond progression sensitises tumour cells to chemotherapy Initial treatment Treatment beyond progression Control Tumour volume (mm3) Tumour volume (mm3) lgG 30 mg/kg 1000 1000 Trastuzumab Control lgG 30 mg/kg 30 mg/kg Paclitaxe l 60 * Herceptin mg/kg 300 30 mg/kg 300 * Trastuzumab + 100 100 paclitaxel 1 8 15 22 22 29 36 43 50 57 Days after treatment start Days after treatment startMDA-MB-361 tumour xenograft; *p<0.05 by U-testIgG, immunoglobulin; paclitaxelqw iv; Trastuzumab or IgGqwip Shirane et al 2005
Trastuzumab Benefits Beyond Progression GBG 26/BIG 3-05 (Closed Early With Poor Accrual) Capecitabine Progression ontaxane + trastuzumab Capecitabine + trastuzumab von Minckwitz G, et al. J Clin Oncol. 2009:27:1999-2006.
Trastuzumab Remains Effective After Progression 100 90 2-sided P OR: P = .011 CB: 75.3% 80 CB: P = .0068 (95% CI: 64.2-84.4) 70 60 CB: 54.1% % of pts (95% CI: 42.1-65.7) 50 40 NC >24wks 30 20 27.0% 48.1% OR CR: 2.7% CR: 7.7% (95% CI: 17.3-38.6) (95% CI: 36.5-59.7) 10 PR: 24.3% PR: 40.3% 0 X XH OR = overall response = CR+PRvon Minckwitz G, et al. J Clin Oncol. 2009:27:1999-2006. CB = clinical benefit = CR+PR+NC>24wks
Lapatinib + Trastuzumab Upon Progression on Trastuzumab: EGF104900 Lapatinib 1500 mg PO QD (n = 148) Primary endpoint: Heavily pretreated patients PFS Optional crossover towith HER2-positive metastatic trastuzumabarm breast cancer and if PD after 4 wks (n = 77) Secondary endpoints: progression on trastuzumab OS Lapatinib 1000 mg PO QD + ORR (N = 296) Trastuzumab 4 mg/kg loading CBR dose, then 2 mg/kg IV wkly (n = 148) Stratified by visceral disease and hormone receptor status PO, orally; QD, once daily. Blackwell K, et al. SABCS 2009. Abstract 61.
Lapatinib + trastuzumab improves OS compared tolapatinib in patients progressing on or after trastuzumab Blackwell KL, et al. J ClinOncol2010; 28;1124–1130
Conclusion #1:Trastuzumab resistance is incomplete,and both switching chemotherapy andcombined HER2 inhibition benefitpatients progressing on trastuzumab. Resistance is Futile! Locutis of Borg
But Is Resistance Futile? No: Tumors Trastuzumab keep finding novel resistance HER2+ Cancer mechanisms
What are the mechanisms of resistance?• Impaired trastuzumab binding• Altered downstream signaling• Signaling through an alternate receptor• Failure to trigger an immune response• Pharmacokinetic failures
Mechanisms of resistance (1)Impaired trastuzumab binding to HER2:• A constitutively active truncated form of HER2 receptor that lacks binding site of trastuzumab (p95 HER2).• Epitope masking by mucin 4 or CD44/polymeric hyaluronan complex.• Loss of HER2 complex Pohlmann PR, et al. Clin Cancer Res 20
Mechanisms of resistance (2) • Altered HER2 downstream signaling. Increased ligand production (ADAM17) • Signaling through an alternate receptor pathway Pohlmann PR, et al. Clin Cancer Res 2009
Mechanisms of resistance (3)• Failure to trigger immune-mediated mechanisms to destroy tumor cellsFcγRIII F158 polymorphism interfere with antibody-dependent cellular cytotoxicityfunction Pohlmann PR, et al. Clin Cancer Res 2009
Trastuzumab Resistance: The List Grows• HER2 protein expression• Sprouty 2 expression (via PTEN & ERK)• Cyclin E amplification/overexpression; loss of p27Kip1 (downstream HER2 effectors)• Calpain inactivation (via pHER2 cleavage)• miR21 upregulation (via PTEN)• Loss of HER2 amplification (post-adjuvant Trast)• Notch-1 overexpression
Pharmacokinetic Resistance: Inability to Penetrate the CNSLapatinibas 1st-Line Treatment in HER-2+ Advanced Breast Cancer Gomez HL et al, ASCO 2005, abstract #3046 Patient D: Brain Lesion Baseline and 12 Weeks
Lapatinib/RTK Resistance• Many trastuzumab resistance mechanism do not apply: (IGF-1, p95, PTEN, HER3, PI3K/AKT)• Increased pSRC kinase (via PTEN/PI3K/AKT)• Altered antiapoptotic proteins (MCL-1 and survivin)• Activated FOXO3a and increased expression of estrogen receptor• Quasi-resistance: lack of immune reponse
Conclusion #2:There are many mechanisms ofresistance; most affect commonpathways.Resistance mechanisms are complexbut not infinite.
PTEN Impact on Sensitivity or Resistance to Trastuzumab• Preclinical data suggest PTEN loss associated with trastuzumab resistance – O’Brien NA, 2010; Stemke-Hale K, 2008; Saal LH, 2005; Nagata Y, 2004• Clinical data available to date: limited and conflicting – PTEN loss associated with trastuzumab resistance • Dave, 2011; Esteva, 2010, Faratian, 2009 N = 122 – PTEN loss NOT associated with trastuzumab resistance • Fabi, 2010; Gori, 2009; Yonemori, 2009 Faratian et al Cancer Res 69(16):6713–20
DFS by Treatment Arm for Pts with PTEN Negative Tumors: N9831 100 90 AC →T+H → H AC → T → H 80 Arm N Events HR 95% CI p 5yrEvent free (%) 70 DFS AC → T A 176 53 72.3 B 146 38 0.85 0.55-1.30 0.44 77.8 60 A 176 53 72.3 C 138 19 0.47 0.28-0.79 0.005 86.7 50 B 146 38 77.8 C 138 19 0.56 0.32-0.97 0.04 86.7 40 0 1 2 3 4 5 Years from randomization Perez EA, et al. ASCO 2011; Abst 79057
Multifactorial Resistance: Clinical Data Mechanism/Reference Outcome (all significant p values)• p95HER2/CCR 16:4226, 2010 • PFS HR = 1.9, OS HR = 2.2• PTEN/Cancer Res 69:6713,2009 • OS HR = 3.0• HER2 prot exp/Ann Oncol 22: • TTP HR = 3.7, OS HR = 2.0 2014,2011• Sprouty 2/PLOS One 6: • OS HR = 2.28 e23772, 2011• Cyclin E/PNAS 108: 3761, 2011 • Lower RR and PFS• FcR Polymorphisms/JCO 26: • PFS HR = 5.3 1789, 2008
Conclusion #3:Laboratory mechanisms of resistance havenot been confirmed in any meaningfulsense in the clinic: 1. We lack large data sets 2. Most studies are small, lack confirmatory studies, level 4 evidence 3. Adjuvant studies can reject metastatic hypotheses 4. Assays not validated and variable 5. Multifactorial resistance mechanisms not examined
What are the Therapeutic Implications of Resistance Mechanisms?• Since different resistance mechanisms affect different drugs, combined HER2 pathway blockade should be superior.• Multifactorial nature of resistance suggests that no single therapeutic approach will overcome resistance.
What are the Therapeutic Implications of Resistance Mechanisms?• Since many resistance mechanisms have common downstream effectors (e.g., mTOR), downstream inhibition may prove useful.• Improved measurement of resistance mechanisms might improve targeting.
Figure 1 Proposed mechanisms of trastuzumab resistanceNahta R et al. (2006) Mechanisms of Disease: understanding resistance to HER2-targeted therapy in human breast cancer Nat Clin Pract Oncol 3: 269–280 doi:10.1038/ncponc0509
Figure 1 Molecular targets and therapeutic approaches in trastuzumab and lapatinib resistance Esteva, F. J.et al.(2009)Molecular predictors of response to trastuzumab and lapatinib in breast cancer Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2009.216
Trastuzumab-DM1 (T-DM1), isdesigned to combine the anti-tumor activity of trastuzumabwith a means of delivering highlypotent chemotherapy directlyinto HER2-expressing cells.DM-1 (also known asmaytansine) is an inhibitor oftubulin polymerization, bindingtubulin competitively with vincaalkaloids.
Analysis 1 DFS by Treatment Arm for Pts with PTEN Positive Tumors 100 90 AC →T+H → H 80 AC → T → H Arm N Events HR 95% CI p 5yrEvent free (%) 70 DFS AC → T A 425 120 73.9 B 504 106 0.70 0.54-0.92 0.009 81.0 60 A 425 120 73.9 C 413 77 0.65 0.48-0.86 0.003 85.1 50 B 504 106 81.0 C 413 77 0.90 0.67-1.21 0.49 85.1 40 0 1 2 3 4 5 Years from randomization Perez EA, et al. ASCO 2011; Abst 79057
Analysis 1Impact of PTEN on DFS Based for Different Treatment Arm Comparisons: N9831 Adjuvant • Arm C vs Arm A – PTEN+ HR: 0.65 (p=0.003) Interaction p=0.16 – PTEN- HR: 0.47 (p=0.005) • Arm B vs Arm A – PTEN+ HR: 0.70 (p=0.009) – PTEN- HR: 0.85 (p=0.44) Interaction p=0.47 • Arm C vs Arm B – PTEN+ HR: 0.90 (p=0.49) – PTEN- HR: 0.56 (p=0.04) Interaction p=0.08 Perez EA, et al. ASCO 2011; Abst 79057
Table 1 Characteristics and mechanisms of action of trastuzumab and lapatinib Esteva, F. J.et al.(2009)Molecular predictors of response to trastuzumab and lapatinib in breast cancer Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2009.216
Table 3 Efficacy of HER2-directed therapy in trastuzumab-resistant metastatic breast cancer Esteva, F. J.et al.(2009)Molecular predictors of response to trastuzumab and lapatinib in breast cancer Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2009.216
Table 2 Treatment of HER2 breast cancer: trastuzumab-based combinations beyond trastuzumab progression Di Cosimo, S. & Baselga, J.(2010)Management of breast cancer with targeted agents: importance of heterogenicity Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2009.234
Figure 1 Overall response rates in HER2-positive and hormone receptor-positive metastatic breast cancerCortés, J. et al.(2010)HER2 and hormone receptor-positive breast cancer—blocking the right target Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2010.185
Figure 2 Receptor cross-talk and response to therapyCortés, J. et al.(2010)HER2 and hormone receptor-positive breast cancer—blocking the right target Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2010.185