Maria Abbattista

The Bioreductive Prodrug PR-104A Is Activated under Aerobic Conditions by Human Aldo-Keto Reductase 1C3

PR-104, currently in phase II clinical trials, is a phosphate ester pre-prodrug which is converted in vivo to its cognate alcohol, PR-104A, a prodrug designed to exploit tumor hypoxia. Bioactivation occurs via one-electron reduction to DNA crosslinking metabolites in the absence of oxygen. However, certain tumor cell lines activate PR-104A in the presence of oxygen, suggesting the existence of an aerobic nitroreductase. Microarray analysis identified a cluster of five aldo-keto reductase (AKR) family members whose expressions correlated with aerobic metabolism of PR-104A. Plasmid-based expression of candidate genes identified aldo-keto reductase 1C3 as a novel nitroreductase. AKR1C3 protein was detected by Western blot in 7 of 23 cell lines and correlated with oxic PR-104A metabolism, an activity which could be partially suppressed by Nrf2 RNAi knockdown (or induced by Keap1 RNAi), indicating regulation by the ARE pathway. AKR1C3 was unable to sensitize cells to 10 other bioreductive prodrugs and was associated with single-agent PR-104 activity across a panel of 9 human tumor xenograft models. Overexpression in two AKR1C3-negative tumor xenograft models strongly enhanced PR-104 antitumor activity. A population level survey of AKR1C3 expression in 2,490 individual cases across 19 cancer types using tissue microarrays revealed marked upregulation of AKR1C3 in a subset including hepatocellular, bladder, renal, gastric, and non-small cell lung carcinoma. A survey of normal tissue AKR1C3 expression suggests the potential for tumor-selective PR-104A activation by this mechanism. These findings have significant implications for the clinical development of PR-104.

Diflavin Oxidoreductases Activate the Bioreductive Prodrug PR-104A under Hypoxia

The clinical agent PR-104 is converted systemically to PR-104A, a nitrogen mustard prodrug designed to target tumor hypoxia. Reductive activation of PR-104A is initiated by one-electron oxidoreductases in a process reversed by oxygen. The identity of these oxidoreductases is unknown, with the exception of cytochrome P450 reductase (POR). To identify other hypoxia-selective PR-104A reductases, nine candidate oxidoreductases were expressed in HCT116 cells. Increased PR-104A-cytotoxicity was observed in cells expressing methionine synthase reductase (MTRR), novel diflavin oxidoreductase 1 (NDOR1), and inducible nitric-oxide synthase (NOS2A), in addition to POR. Plasmid-based expression of these diflavin oxidoreductases also enhanced bioreductive metabolism of PR-104A in an anoxia-specific manner. Diflavin oxidoreductase-dependent PR-104A metabolism was suppressed >90% by pan-flavoenzyme inhibition with diphenyliodonium chloride. Antibodies were used to quantify endogenous POR, MTRR, NDOR1, and NOS2A expression in 23 human tumor cell lines; however, only POR protein was detectable and its expression correlated with anoxic PR-104A reduction (r2 = 0.712). An anti-POR monoclonal antibody was used to probe expression using human tissue microarrays; 13 of 19 cancer types expressed detectable POR with 21% of cores (185 of 874) staining positive; this heterogeneity suggests that POR is a useful biomarker for PR-104A activation. Immunostaining for carbonic anhydrase 9 (CAIX), reportedly an endogenous marker of hypoxia, revealed only moderate coexpression (9.6%) of both CAIX and POR across a subset of five cancer types.

The Role of Bystander Effects in the Antitumor Activity of the Hypoxia-Activated Prodrug PR-104

Activation of prodrugs in tumors (e.g., by bioreduction in hypoxic zones) has the potential to generate active metabolites that can diffuse within the tumor microenvironment. Such “bystander effects” may offset spatial heterogeneity in prodrug activation but the relative importance of this effect is not understood. Here, we quantify the contribution of bystander effects to antitumor activity for the first time, by developing a spatially resolved pharmacokinetic/pharmacodynamic (SR-PK/PD) model for PR-104, a phosphate ester pre-prodrug that is converted systemically to the hypoxia-activated prodrug PR-104A. Using Green’s function methods we calculated concentrations of oxygen, PR-104A and its active metabolites, and resultant cell killing, at each point of a mapped three-dimensional tumor microregion. Model parameters were determined in vitro, using single cell suspensions to determine relationships between PR-104A metabolism and clonogenic cell killing, and multicellular layer (MCL) cultures to measure tissue diffusion coefficients. LC-MS/MS detection of active metabolites in the extracellular medium following exposure of anoxic single cell suspensions and MCLs to PR-104A confirmed that metabolites can diffuse out of cells and through a tissue-like environment. The SR-PK/PD model estimated that bystander effects contribute 30 and 50% of PR-104 activity in SiHa and HCT116 tumors, respectively. Testing the model by modulating PR-104A-activating reductases and hypoxia in tumor xenografts showed overall clonogenic killing broadly consistent with model predictions. Overall, our data suggest that bystander effects are important in PR-104 antitumor activity, although their reach may be limited by macroregional heterogeneity in hypoxia and reductase expression in tumors. The reported computational and experimental techniques are broadly applicable to all targeted anticancer prodrugs and could be used to identify strategies for rational prodrug optimization.

Reductive metabolism of the dinitrobenzamide mustard anticancer prodrug PR-104 in mice

PurposePR-104, a bioreductive prodrug in clinical trial, is a phosphate ester which is rapidly metabolized to the corresponding alcohol PR-104A. This dinitrobenzamide mustard is activated by reduction to hydroxylamine (PR-104H) and amine (PR-104M) metabolites selectively in hypoxic cells, and also independently of hypoxia by aldo-keto reductase (AKR) 1C3 in some tumors. Here, we evaluate reductive metabolism of PR-104A in mice and its significance for host toxicity.MethodsThe pharmacokinetics of PR-104, PR-104A and its reduced metabolites were investigated in plasma and tissues of mice (with and without SiHa or H460 tumor xenografts) and effects of potential oxidoreductase inhibitors were evaluated.ResultsPharmacokinetic studies identified extensive non-tumor reduction of PR-104A to the 5-amine PR-104H (identity of which was confirmed by chemical synthesis), especially in liver. However, high concentrations of PR-104H in tumors that suggested intra-tumor activation is also significant. The tissue distribution of PR-104M/H was broadly consistent with the target organ toxicities of PR-104 (bone marrow, intestines and liver). Surprisingly, hepatic nitroreduction was not enhanced when the liver was made more hypoxic by hepatic artery ligation or breathing of 10% oxygen. A screen of non-steroidal anti-inflammatory drugs identified naproxen as an effective AKR1C3 inhibitor in human tumor cell cultures and xenografts, suggesting its potential use to ameliorate PR-104 toxicity in patients. However, neither naproxen nor the pan-CYP inhibitor 1-aminobenzotriazole inhibited normal tissue reduction of PR-104A in mice.ConclusionsPR-104 is extensively reduced in mouse tissues, apparently via oxygen-independent two-electron reduction, with a tissue distribution that broadly reflects toxicity.

Pre-clinical activity of PR-104 as monotherapy and in combination with sorafenib in hepatocellular carcinoma

PR-104 is a clinical stage bioreductive prodrug that is converted in vivo to its cognate alcohol, PR-104A. This dinitrobenzamide mustard is reduced to activated DNA cross-linking metabolites (hydroxylamine PR-104H and amine PR-104M) under hypoxia by one-electron reductases and independently of hypoxia by the 2-electron reductase aldo-keto reductase 1C3 (AKR1C3). High expression of AKR1C3, along with extensive hypoxia, suggested the potential of PR-104 for treatment of hepatocellular carcinoma (HCC). However, a phase IB trial with sorafenib demonstrated significant toxicity that was ascribed in part to reduced PR-104A clearance, likely reflecting compromised glucuronidation in patients with advanced HCC. Here, we evaluate the activity of PR-104 in HCC xenografts (HepG2, PLC/PRF/5, SNU-398, Hep3B) in mice, which do not significantly glucuronidate PR-104A. Cell line differences in sensitivity to PR-104A in vitro under aerobic conditions could be accounted for by differences in both expression of AKR1C3 (high in HepG2 and PLC/PRF/5) and sensitivity to the major active metabolite PR-104H, to which PLC/PRF/5 was relatively resistant, while hypoxic selectivity of PR-104A cytotoxicity and reductive metabolism was greatest in the low-AKR1C3 SNU-398 and Hep3B lines. Expression of AKR1C3 in HepG2 and PLC/PRF/5 xenografts was in the range seen in 21 human HCC specimens. PR-104 monotherapy elicited significant reductions in growth of Hep3B and HepG2 xenografts, and the combination with sorafenib was significantly active in all 4 xenograft models. The results suggest that better-tolerated analogs of PR-104, without a glucuronidation liability, may have the potential to exploit AKR1C3 and/or hypoxia in HCC in humans.

Abstract B76: Cellular metabolism, murine pharmacokinetics and preclinical antitumor activity of SN29966, a novel hypoxia‐activated irreversible pan‐HER inhibitor

Hypoxia occurs in most human tumors and is associated with disease progression, resistance to conventional therapies and poor patient outcome. Hypoxia can up‐regulate HER1 by several known mechanisms, including increased mRNA translation (Franovic et al., PNAS,2007;104:13092) and delayed receptor endocytosis (Wang et al., Nat Med.,2009;15:319). We have developed SN29966, a hypoxia‐activated prodrug of the irreversible pan‐HER inhibitor SN29926, to target and exploit hypoxic cells and thereby broaden the therapeutic index of this class of agent. Quaternization of the aminebearing Michael acceptor masks activity SN29926, and one‐electron reduction provides selective release under hypoxia. This prodrug design confers 62‐fold deactivation of inhibitor activity with respect to HER1 autophosphorylation in A431 cells (Smaill et al., this meeting). In a panel of HER1/2 expressing cell lines SN29966 showed hypoxia‐dependent inhibition of proliferation (hypoxic/oxic IC50 ratios of 63, 38, 31 and 19 in BT474, A431, SKOV3 and SKBR3 cells, respectively), a property SN29926 lacked (IC50 ratios 0.7–1.1). SN29926 was generated from SN29966 under hypoxic conditions at a rate of 200–500 pmol/hr/106 cells. Oxic production was ∼1 pmol/hr/106 cells. Plasma and A431 tumor pharmacokinetics (PK) of prodrug SN29966 and inhibitor were measured in nude mice by LC/MS/MS detection (with D6 internal standards) following administration at their respective MTDs (133 and 75 umol/kg; ip). Prodrug SN29966 gave a plasma AUC0‐72h of 2016 umol‐h/L, some ∼110‐fold greater than achieved for administration of inhibitor SN29926 (18 umol‐h/L). The latter gave a tumor AUC0‐inf of 100 umol‐h/kg with a half‐life (t½) of 9 h. In contrast the prodrug SN29966 gave a tumor AUC0‐72h of 2245 umol‐h/kg with a stable tumor tissue concentration of ∼ 30 umol/kg out to 72 h, such that a t½ could not be determined. Consistent with this long prodrug residency, SN29926 released from prodrug had a t½ in tumor tissue of >72h, providing an AUC0‐72h of 464 umol‐h/kg. Thus the AUC of SN29926 in A431 tumors was at least 4.6‐fold higher after administration of prodrug SN29966 than following administration of inhibitor SN29926 itself at equivalent toxicity. In A431 tumor growth delay studies, SN29966 (113 umol/kg, q4dx6, ip) induced tumor regressions (12/12) with no recovery of growth by day 36 (tumor volume 44 ±19 mm3), whereas controls grew rapidly (day 8 tumor volume 1043 ±109 mm3). Comparative administration of inhibitor SN29926 (63 umol/kg, q4dx6, ip) provided tumor stasis, but with rapid growth following cessation of treatment (day 36 tumor volume 642 ±191 mm3), a difference that was significant from prodrug (p Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B76.

Abstract A247: Mechanism of action of the hypoxia-activated irreversible pan-HER inhibitor SN29966.

Hypoxia occurs in most human tumors and is associated with disease progression, treatment resistance and poor patient outcome. We have developed the hypoxia-activated prodrug SN29966, designed to release the irreversible pan-HER inhibitor SN29926, following one-electron reduction by hypoxic cells (Smaill et al, Mol Cancer Ther., 2009; 8(12 Suppl), C46). Pharmacokinetic (PK) studies in nude mice bearing A431 tumor xenografts indicated SN29966 has a long tumor half-life (>3 days) and releases SN29926 in tumors. SN29966 demonstrated single agent activity in nude mice bearing A431 and SKOV3 xenografts, inducing striking tumor regressions in both models (Patterson et al, Mol Cancer Ther., 2009; 8(12 Suppl), B76). PR509 and PR610, clinical candidates developed from SN29966, are currently undergoing comparative evaluation with Phase I trials anticipated in early 2012. The single-agent antitumor activity of SN29966 is arguably counter-intuitive given that it is designed to target hypoxic cells within tumors. This activity may arise from a number of contributing mechanisms including; (i) bioactivity of the unreduced prodrug; (ii) local redistribution of released inhibitor in the tumor; (iii) liver metabolism and circulating inhibitor and (iv) a long tumor half-life allowing for targeting of both chronic and cycling hypoxia. To critically assess the relative contribution of each to the mechanism of action of SN29966 we performed a number of studies. We prepared SN31950, a prodrug of SN29926 designed to be incapable of one-electron fragmentation. In target modulation and anti-proliferative assays SN31950 showed no hypoxia-dependent activity. The murine A431 tumor PK of SN29966 and SN31950 demonstrated that at an equimolar dose (20 μmol/kg, ip), both prodrugs gave comparable tumor exposures (AUC0–72h: SN31950, 50 μmol*h/kg; SN29966, 57 μmol*h/kg). In contrast, the tumor exposure of SN29926 released from each prodrug differed by 40-fold (AUC0–72h: SN29926 from SN31950, 0.3 μmol*h/kg; SN29926 from SN29966, 12 μmol*h/kg). Plasma exposure of each prodrug was comparable, as were levels of SN29926 in plasma (presumed mainly due to hepatic prodrug metabolism). Consistent with the observed lack of inhibitor release in A431 tumors, SN31950 was inactive against A431 tumors in growth delay assays. To confirm the hypoxia-dependent nature of SN29966 inhibitor release in A431 tumors we re-oxygenated tumors in mice breathing 100% oxygen at 2.5 atm in a hyperbaric chamber. Accordingly, mice showed a marked reduction (56%, p Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A247.

Abstract 5358: The hypoxia-activated EGFR-TKI TH-4000 overcomes erlotinib-resistance in preclinical NSCLC models at plasma levels achieved in a Phase 1 clinical trial

Clinical data indicate that mutant EGFR NSCLC is often heterozygous (PLoS ONE 2013; 8: e54170; PLoS ONE 2009; 4: e7464) and the presence of wild type (WT) EGFR allele is associated with limited response to EGFR-tyrosine kinase inhibitor (TKI) therapy (Cancer Sci 2008; 99:929). Tumor hypoxia upregulates WT EGFR protein and its cognate ligand TGFα via several HIF-dependent mechanisms (reviewed in: Curr Pharm Des 2013; 19:907). NSCLC is known to be a hypoxic tumor, and thus hyperactivation of WT EGFR may be an important cause of resistance to EGFR-TKI therapy. TH-4000 (formerly called PR610) is a clinical-stage hypoxia-activated prodrug that releases an irreversible EGFR-TKI under hypoxic conditions and may overcome resistance to conventional TKI therapy. We tested this hypothesis using the heterozygous WT/Δ19 EGFR PC9 tumor model and found it to be resistant to clinically relevant doses of the EGFR-TKI erlotinib; 100% of tumors progressed during treatment with human matched plasma PK exposures of erlotinib. In contrast, the homozygous Δ19 mutant EGFR tumor HCC827 was readily controlled by erlotinib (100% tumor regression). TH-4000 (15 mg/kg) produced 100% tumor regressions in both models. In vitro, PC9 cells exposed to hypoxia had elevated EGFR protein and were more resistant to erlotinib as measured by EGFR phosphorylation. In nude mice, single-dose administration of 15 mg/kg TH-4000 achieved a plasma AUC equivalent to 32 mg/m2 in human subjects, one-fifth of the maximum tolerated dose (MTD) defined in the Phase 1 trial (MTD = 150 mg/m2/week; NCT01631279). A single dose of TH-4000 (15 mg/kg) cleared rapidly from mouse plasma (T½ = 0.37 h) but had durable residency in PC9 tumors (T½ = 39 h), releasing TKI above efficacious levels for 7 days (T½β = 84 h). Consistent with these PK properties, tumor shutdown of EGFR signalling was durable, with no recovery by day 7. To confirm the mechanism of action, TH-4000 was shown to be metabolized efficiently under hypoxia using a panel of human NSCLC cell lines (rate of TKI release 0.4-2.1 nmol/hr/106 cells), a process that was inhibited by oxygen (TKI release 80% (538 vs 99 nmol/kg; p Citation Format: Adam V. Patterson, Shevan Silva, Christopher Guise, Maria Abbattista, Matthew Bull, Huai-Ling Hsu, Charles Hart, Jessica Sun, Angus Grey, Amir Ashoorzadeh, Robert Anderson, Jeff B. Smaill. The hypoxia-activated EGFR-TKI TH-4000 overcomes erlotinib-resistance in preclinical NSCLC models at plasma levels achieved in a Phase 1 clinical trial. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5358. doi:10.1158/1538-7445.AM2015-5358

Abstract C46: Design and identification of the novel hypoxia‐activated irreversible pan‐HER inhibitor SN29966

Several irreversible pan‐HER inhibitors (HKI‐272, BIBW‐2992, PF299) are under development and demonstrate encouraging activity against erlotinib resistant non‐small cell lung cancer expressing mutant forms of HER1. However, dose limiting toxicities mirror that of erlotinib and are attributed to inhibition of HER1 in gastrointestinal and skin tissues. To introduce additional tumor selectivity to irreversible pan‐HER inhibitors and thereby broaden their therapeutic index, we have sought to utilise tumor hypoxia as a physiological target that supports tumor‐selective bioreduction. To achieve this we have developed a series of hypoxia‐activated prodrugs of the known irreversible pan‐HER inhibitor SN29926. Five nitromethylaryl quaternary ammonium bromide (NMQ) prodrugs were synthesised by quaternizing the tertiary amine of SN29926 with five nitroheterocyclic alpha‐methyl bromides. Three further quaternary salts were prepared as Chemical‐Biology Tools (CBTs) designed as controls to probe aspects of the mechanism of action of the NMQ prodrugs. The NMQ prodrugs and CBTs were compared, relative to SN29926, in a range of assays to identify a lead compound that (i) is deactivated under oxic conditions with respect to A431 cellular HER1 target modulation and proliferation, (ii) efficiently fragments following one‐electron reduction in an oxygen inhibited manner to release the irreversible pan‐HER inhibitor, (iii) displays increased anti‐proliferative activity against A431 cells under hypoxia. All of the NMQ/CBT prodrugs were successfully deactivated with respect to inhibition of A431 HER1 autophosphorylation (62‐ to 201‐fold) and proliferation under oxic conditions (12‐ to 294‐fold). Pulse and steady‐state radiolysis under nitrogen determined their one‐electron reduction potentials (−388 to −493 mV) and demonstrated that only two of the NMQ prodrugs (SN29965, SN29966) efficiently fragment following one‐electron reduction (first‐order rate constants of 90 and 130 s−1, respectively). SN29966 alone demonstrated significant anti‐proliferative activity against A431 cells under hypoxia (hypoxic/oxic IC50 ratio 38). Preliminary growth delay screening of SN29966 and the CBTs in advanced A431 xenografts (∼600 mm3; hypoxic fraction of 32% ± 13%) demonstrated that the CBTs lacked efficacy, while SN29966 induced tumor regressions, with greater than 30 days tumor control using a well tolerated three‐dose schedule (133 umol/kg/dose, q4dx3). In summary, prodrug SN29966 is deactivated relative to the parent inhibitor, efficiently fragments following one‐electron reduction, is selective against hypoxic A431 cells and has remarkable single‐agent activity against hypoxic A431 xenografts using a conservative treatment schedule. We therefore identify SN29966 as a “first‐in‐class” hypoxia‐activated irreversible pan‐HER inhibitor that has significant clinical potential. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C46.

Abstract A67: Preclinical efficacy of tarloxotinib bromide (TH-4000), a hypoxia-activated EGFR/HER2 inhibitor: rationale for clinical evaluation in EGFR mutant, T790M-negative NSCLC following progression on EGFR-TKI therapy

Tarloxotinib bromide (T) is a prodrug that releases an irreversible EGFR/HER2 inhibitor (T-TKI) under hypoxic conditions. NSCLC is known to be a hypoxic disease and wild type (WT) EGFR is upregulated by multiple hypoxia-driven mechanisms (Curr Pharm Des, 19:907). Mutant EGFR NSCLC is commonly heterozygous and may result in maintenance of WT EGFR signalling (Can Sci, 103:1946; PloS One 8:e54170). Clinical studies indicate NSCLC patients harbouring WT/mut heterozygous EGFR have significantly poorer ORR, PFS and OS on treatment with EGFR-TKI (Can Sci, 99:929). Other mechanisms of resistance to EGFR-TKI include 50-60% with T790M EGFR mutation, 8-13% with HER2 amplification, while 15-20% lack identifiable mutation/amplification events (Nat Rev Clin Onc, 11:473). The combination of cetuximab/afatinib provides an ORR of 25% and PFS of 4.6 months in T790M-negative NSCLC suggesting the persistence of HER signalling plays a role in resistance. However the high proportion of Grade 3/4 toxicity seen with cetuximab/afatinib indicates an opportunity for dose-intensification with an improved therapeutic index (Can Discov, 4:1). In addition, early clinical data on resistance to the 3rd Gen (WT EGFR-sparing) TKI rociletinib, fails to identify further mutations by NGS in some patients and describes reversion to EGFR-WT (T790) status (Can Discov, 5:713). Collectively these data support the hypothesis that WT EGFR heterozygosity may be a mechanism of resistance to current EGFR-TKI. Current EGFR-TKI lack the therapeutic index to silence WT EGFR signalling in tumors due to on-target skin/GI toxicities (Ann Oncol 18:761). Therefore we sought to examine the potency of T-TKI relative to erlotinib, afatinib and AZD9291 in five human cancer cell lines expressing WT EGFR (H1838, H2073, H1648, H125 and A431). In antiproliferative assays T-TKI was more dose-potent than erlotinib (25- to 110-fold) afatinib (4- to 32-fold) and AZD9291 (120- to 71-fold). This activity correlated with inhibition of WT EGFR phosphorylation and downstream MAPK signalling. We used a prototypic WT EGFR driven xenograft model (A431) to benchmark T activity against each EGFR-TKI by ‘retrotranslation’ of reported plasma exposure for each agent in human subjects back to the xenograft model. Only treatment with clinically relevant doses and schedules of T was associated with tumor regression and durable inhibition of WT EGFR tumor phosphorylation. Consistent with these findings, T treatment can also regress the WT EGFR NSCLC tumor models H125 and H1648, demonstrating T provides the necessary therapeutic index to inhibit WT EGFR in vivo. The transfection of WT EGFR into mutant EGFR NSCLC line PC9 (vs GFP control) conferred TGFα dependent induction of p-EGFR that was supressed by T-TKI but resistant to inhibition by erlotinib, afatinib or AZD9291. This was associated with reduced antiproliferative activity for EGFR-TKIs. Collectively these data indicate T-TKI is a dose-potent inhibitor of WT EGFR signalling and the prodrug T may possess the therapeutic index to silence WT EGFR signalling in xenograft models at plasma exposure levels achieved in a human Ph1 trial. T is under investigation in a Phase 2 clinical trial for EGFR mutant, T790M-negative, NSCLC patients who have progressed on EGFR-TKI (NCT02454842). Citation Format: Shevan Silva, Victoria Jackson, Christopher Guise, Maria Abbattista, Matthew Bull, Angus Grey, Robert Anderson, Amir Ashoorzadeh, Charles Hart, Tillman Pearce, Adam V. Patterson, Jeff B. Smaill. Preclinical efficacy of tarloxotinib bromide (TH-4000), a hypoxia-activated EGFR/HER2 inhibitor: rationale for clinical evaluation in EGFR mutant, T790M-negative NSCLC following progression on EGFR-TKI therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A67.