Medical Oncologist, Gastrointestinal Malignancies

	The University of Texas Health Science Center at San Antonio

Autophagy is a conserved protein degradation process that involves the vacuolar sequestration of long-lived cytoplasmic proteins and organelles into a structure called an autophagosome.

 Autophagosomes fuse with lysosomes, which results in the proteolytic degradation of the cytoplasmic contents.

In eukaryotic cells, autophagy plays an important role in the disposal of damaged organelles and proteins, and serves to generate alternative sources of energy for cell survival during cellular stress through the catabolization of protein substrates.

 The activation of stress response genes such as tumor protein p53 by anticancer therapies can stimulate autophagy in addition to apoptosis.

		Figure 1. Responses to Autophagy-Targeting Therapy

		Treatment with vorinostat and hydroxychloroquine yielded a prolonged partial response in a patient with refractory renal cell carcinoma that has been durable for more than 50 cycles of therapy. MRI scans obtained at baseline and post cycles 10 and 50 (C10 and C50, respectively) are shown.

Although prolonged autophagy can result in cancer cell death, recent investigations suggest that therapy-induced autophagy is a reversible response that promotes cancer cell survival, and thus may diminish the efficacy of some therapeutic agents.

Therefore, autophagy may significantly contribute to resistance to a number of anticancer therapeutic modalities.

Our institution chose to study the role of histone deactelyase (HDAC) inhibitors, which are known to induce autophagy, to investigate the impact of targeting the process.

CTRC researchers showed that HDAC inhibitor— induced autophagy blunts its anticancer activity.6 Yet, genetic or pharmacologic disruption of autophagy synergistically modulated the proapoptotic and cytostatic effects of the HDAC inhibitor vorinostat in models of imatinib-resistant chronic myeloid leukemia and colon cancer.

 A therapy-induced increase in the levels of lysosomal protease cathepsin D was identified as a key downstream pharmacodynamic mediator of the proapoptotic effects of the combination of vorinostat and the autophagy inhibitor, chloroquine.

		Figure 2. Schema for Phase II Autophagy Study

		HCQ indicates hydroxychloroquine; mCRC, metastatic colorectal cancer; po, by mouth; RGF, regorafenib; VOR, vorinostat.

Investigators at our institution have shown that autophagy inhibition with hydroxychloroquine enhanced vorinostat-induced apoptosis via ubiquitinated protein accumulation in preclinical cancer models.

When this was translated to the clinic in a phase I study of 31 patients previously heavily pretreated with chemotherapeutic agents, the most common treatment-related toxicities were primarily grade 1-2 nausea, diarrhea, fatigue, anorexia, weight loss, anemia, and creatinine elevation.

 Most common significant toxicities were fatigue in three patients, with anemia, thrombocytopenia, and neutropenia in one patient each.

The maximum tolerated dose of the combination therapy is hydroxychloroquine 600 mg by mouth daily with vorinostat 400 mg daily. One patient with renal cell carcinoma who had failed seven lines of prior therapy had a confirmed durable partial response (RECIST 1.0 criteria, active on study with 50+ cycles) 

-mutated colorectal cancer (CRC) had prolonged stable disease (>4 cycles).

The addition of hydroxychloroquine did not significantly impact the pharmacokinetic profile of vorinostat.

These promising data have led to the opening of a phase II randomized study comparing autophagy inhibition with vorinostat and hydroxychloroquine with regorafenib, the current standard in patients with CRC who are failing standard therapies 

 This study, which has a primary endpoint of progression-free survival, is currently open to enrollment. Preplanned pharmacodynamic analyses will help us identify which patients with refractory metastatic CRC benefit from autophagy inhibition versus angiogenic inhibition.

		Table. Open Phase II Clinical Trials of Autophagy Modulation in Malignancies

		CQ indicates chloroquine; HCQ, hydroxychloroquine; IL-2, interleukin-2 (aldesleukin).

If the early clinical finding holds true for survival benefit in patients with advanced CRC with minimal toxicity to patients, then autophagy modulation with vorinostat and hydroxychloroquine could one day become a treatment option for patients with advanced CRC. This study could result in better treatment choices for patients with refractory metastatic CRC and lay the foundation for future studies of a new class of therapeutics in metastatic CRC. In addition to CRC, autophagy modulation has demonstrated the potential to improve the treatment efficacy of other chemotherapeutic and targeted agents in other cancers.

 Many clinical trials of autophagy modulators are currently recruiting cancer patients, with several ongoing phase II studies in refractory malignancies 

Preliminary results demonstrate tolerability of autophagy modulators with chemotherapy. Final survival and pharmacodynamic analyses of these studies will allow us to better understand the therapeutic potential of autophagy modulation across a variety of cancer types.

			Louis M, Rosato RR, Brauit L, et al. The histone deacetylase inhibitor sodium butyrate induces breast cancer cell apoptosis through diverse cytotoxic actions including glutathione depletion and oxidative stress. 

			Li H, Wu X. Histone deacetylase inhibitor, Trichostatin A, activates p21WAF1/CIP1 expression through downregulation of c-myc and release of the repression of c-myc from the promoter in human cervical cancer cells. 

			Kuefer R, Hofer MD, Altug V, et al. Sodium butyrate and tributyrin induce in vivo growth inhibition and apoptosis in human prostate cancer. 

			Strait KA, Dabbas B, Hammond EH, et al. Cell cycle blockade and differentiation of ovarian cancer cells by the histone deacetylase inhibitor trichostatin A are associated with changes in p21, Rb, and Id proteins. 

			Duan H, Heckman CA, Boxer LM. Histone deacetylase inhibitors down-regulate bcl-2 expression and induce apoptosis in t(14;18) lymphomas. 

			Carew JS, Nawrocki ST, Cleveland JL. Modulating autophagy for therapeutic benefit. 

			Carew JS, Medina EC, Esquivel II JA, et al. Autophagy inhibition enhances vorinostat-induced apoptosis via ubiquitinated protein accumulation. 

			Carew JS, Nawrocki ST, Kahue CN, et al. et al. Targeting autophagy augments the anticancer activity of the histone deacetylase inhibitor SAHA to overcome Bcr-Abl-mediated drug resistance. 

			Mahalingam D, Mita M, Sarantopoulos J, et al. Combined autophagy and HDAC inhibition: a phase I safety, tolerability, pharmacokinetic, and pharmacodynamic analysis of hydroxychloroquine in combination with the HDAC inhibitor vorinostat in patients with advanced solid tumors. 

			NIH Clinical Trails Registray. www.ClinicalTrials.gov. Identifier: NCT02316340.

			Galluzzi L, Pietrocola F, Bravo-San Pedro JM, et al. Autophagy in malignant transformation and cancer progression. 

Articles

Although prolonged autophagy can result in
cancer cell death, recent investigations suggest
that therapy-induced autophagy is a reversible
response that promotes cancer cell survival, and
thus may diminish the efficacy of some therapeutic
agents.

Sukeshi R. Patel, MD

Articles

Autophagy Modulation May Be a Novel Approach to Treatment of Advanced Cancers