Clinical Profiling of BCL-2 Family Members in the Setting of BRAF Inhibition Offers a Rationale for Targeting De Novo Resistance Using BH3 Mimetics

Abstract

While response rates to BRAF inhibitiors (BRAFi) are high, disease progression emerges quickly. One strategy to delay the onset of resistance is to target anti-apoptotic proteins such as BCL-2, known to be associated with a poor prognosis. We analyzed BCL-2 family member expression levels of 34 samples from 17 patients collected before and 10 to 14 days after treatment initiation with either vemurafenib or dabrafenib/trametinib combination. The observed changes in mRNA and protein levels with BRAFi treatment led us to hypothesize that combining BRAFi with a BCL-2 inhibitor (the BH3-mimetic navitoclax) would improve outcome. We tested this hypothesis in cell lines and in mice. Pretreatment mRNA levels of BCL-2 negatively correlated with maximal tumor regression. Early increases in mRNA levels were seen in BIM, BCL-XL, BID and BCL2-W, as were decreases in MCL-1 and BCL2A. No significant changes were observed with BCL-2. Using reverse phase protein array (RPPA), significant increases in protein levels were found in BIM and BID. No changes in mRNA or protein correlated with response. Concurrent BRAF (PLX4720) and BCL2 (navitoclax) inhibition synergistically reduced viability in BRAF mutant cell lines and correlated with down-modulation of MCL-1 and BIM induction after PLX4720 treatment. In xenograft models, navitoclax enhanced the efficacy of PLX4720. The combination of a selective BRAF inhibitor with a BH3-mimetic promises to be an important therapeutic strategy capable of enhancing the clinical efficacy of BRAF inhibition in many patients that might otherwise succumb quickly to de novo resistance. Trial Registrations: ClinicalTrials.gov NCT01006980;ClinicalTrials.gov NCT01107418; ClinicalTrials.gov NCT01264380; ClinicalTrials.gov NCT01248936; ClinicalTrials.gov NCT00949702; ClinicalTrials.gov NCT01072175

The Hippo effector YAP promotes resistance to RAF- and MEK-targeted cancer therapies

“…These data indicate that BCL-xL is a critical effector by which YAP promotes resistance to RAF or MEK inhibition. Consistent with these observations and those of others 28 , pharmacological BCL-xL inhibition using ABT-263 (navitoclax) enhanced the efficacy of treatment with either RAF or MEK inhibitor in several tumor cell lines harboring BRAF V600E, including NSCLC (HCC364), melanoma (A2058) and colon cancer (HT29) models (Fig. 3j).…”

Genomic Classification of Cutaneous Melanoma

“…Triple-WT melanomas with amplifications of MDM2 and overexpression of BCL2 may respond to inhibitors such as AMG 232, nutlin-3, and BH3 mimetics, currently in preclinical or clinical development in melanoma. Such agents may also be beneficial for patients with wild-type TP53 across the genetic subtypes (Frederick et al, 2014; Ji et al, 2013; Sun et al, 2014). Other potentially actionable mutations include recurrent IDH1 R132 (~6%) and EZH2 Y641 mutations (<1%) (Table S2E).…”

Targeted agents and immunotherapies: optimizing outcomes in melanoma

“…In some tumours, BRAF and MEK inhibition has been observed to increase signalling through the YAP pathway 127 , leading to escape from cell death via increased expression of the antiapoptotic protein Bcl-xL 128 (FIG. 4a).…”