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New directions for drug-resistant breast cancer: the CDK4/6 inhibitors.

ABSTRACT: Many breast cancers are treated with selective estrogen receptor modulators (SERMs) if the cancers are estrogen and progesterone hormone receptor positive. However, some 30% are not responsive or later become resistant to such therapies. There has been continued interest in developing new and more effective SERMs that target the estrogen receptors for therapeutic benefit. This article will focus on therapies directed against other molecular targets to improve outcomes, as preventing growth of breast cancer cells by an unrelated mechanism is most likely to yield success against resistance, or synergize in a combination therapy with SERMs or aromatase inhibitors. New drugs in development that target the cyclin-dependent kinases CDK4/CDK6 have 'breakthrough therapy' designation at the US FDA and may provide an exciting and realistic new avenue to patients in the near future.

SUBMITTER: Nichols M

PROVIDER: S-EPMC4625900 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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New directions for drug-resistant breast cancer: the CDK4/6 inhibitors.

Nichols Mark M

Future medicinal chemistry 20150826 12

Many breast cancers are treated with selective estrogen receptor modulators (SERMs) if the cancers are estrogen and progesterone hormone receptor positive. However, some 30% are not responsive or later become resistant to such therapies. There has been continued interest in developing new and more effective SERMs that target the estrogen receptors for therapeutic benefit. This article will focus on therapies directed against other molecular targets to improve outcomes, as preventing growth of br ...[more]

PMID: 26306734

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Project description:BackgroundAddition of CDK4/6 inhibitors (CDK4/6i) to endocrine therapy significantly increased progression-free survival, leading to their approval and incorporation into the metastatic breast cancer treatment paradigm. With these inhibitors being routinely used for patients with advanced estrogen receptor-positive (ER+) breast cancer, resistance to these agents and its impact on subsequent therapy needs to be understood. Considering the central role of ER in driving the growth of ER+ breast cancers, and thus endocrine agents being a mainstay in the treatment paradigm, the effects of prior CDK4/6i exposure on ER signaling and the relevance of ER-targeted therapy are important to investigate. The objective of this study was to evaluate the anti-tumor activity of elacestrant, a novel oral selective estrogen receptor degrader (SERD), in preclinical models of CDK4/6i resistance.MethodsElacestrant was evaluated as a single agent, and in combination with alpelisib or everolimus, in multiple in vitro models and patient-derived xenografts that represent acquired and "de novo" CDK4/6i resistance.ResultsElacestrant demonstrated growth inhibition in cells resistant to all three approved CDK4/6i (palbociclib, abemaciclib, ribociclib) in both ESR1 wild-type and mutant backgrounds. Furthermore, we demonstrated that elacestrant, as a single agent and in combination, inhibited growth of patient-derived xenografts that have been derived from a patient previously treated with a CDK4/6i or exhibit de novo resistance to CDK4/6i. While the resistant lines demonstrate distinct alterations in cell cycle modulators, this did not affect elacestrant's anti-tumor activity. In fact, we observe that elacestrant downregulates several key cell cycle players and halts cell cycle progression in vitro and in vivo.ConclusionsWe demonstrate that breast cancer tumor cells continue to rely on ER signaling to drive tumor growth despite exposure to CDK4/6i inhibitors. Importantly, elacestrant can inhibit this ER-dependent growth despite previously reported mechanisms of CDK4/6i resistance observed such as Rb loss, CDK6 overexpression, upregulated cyclinE1 and E2F1, among others. These data provide a scientific rationale for the evaluation of elacestrant in a post-CDK4/6i patient population. Additionally, elacestrant may also serve as an endocrine backbone for rational combinations to combat resistance.

Dataset Information

New directions for drug-resistant breast cancer: the CDK4/6 inhibitors.

Publications

New directions for drug-resistant breast cancer: the CDK4/6 inhibitors.

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