Targeted therapy and molecular genetics

Targeted therapy

The use of site-specific combinations of surgery, chemotherapy, and radiation therapy in gynecologic malignancies has led to marked improvements in patient survivorship. Unfortunately, over the past 30 years, there has been little improvement in disease-specific mortality rates from the three major gynecologic malignancies ( Table 15.1 ). Furthermore, while the incidence of ovarian and cervical cancer has gradually declined over the past several decades, the incidence of endometrial cancer has been steadily rising ( Table 15.2 ) and disproportionately so among certain ethnic/racial populations. Nevertheless, a uniting demographic among each of the gynecologic malignancies is an increase in disease prevalence, which highlights both the recent successes of contemporary management and the premium for discovery of new active agents. Indeed, to critically affect patient outcome and improve quality of life, the therapeutic armamentarium of modern oncologists must be expanded. Thus the search for novel therapeutic options has focused on an exploration of therapies targeting molecular pathways critical to the survival of cancer cells.

Foundation of targeted therapy

In a pair of seminal papers in 2000 and 2011, Hanahan and Weinberg described the key capabilities acquired by normal cells that lead to the development of cancer. Fig. 15.1 represents the 10 “hallmarks of cancer” implicated in the tumorigenic process. Sustained proliferative signaling and evading growth suppressors relate to the development of cellular autonomy, which is essential for uncontrolled proliferation. Enabling replicative immortality indicates that the cell is unencumbered by two typical processes of senescence: (1) the cessation of growth upon reaching a set number of cellular doublings and (2) crisis, which involves massive cellular death. Resisting cell death is a feature seen in most cancer types, allowing the cells to continue to grow and replicate in the setting of damage that would lead to attrition in a normal cell. The ability to activate invasion of tissues and metastasis is crucial to the continued expansion of tumor when space and nutrients become limited. Inducing sustained angiogenesis describes uncontrolled growth of new blood vessels, which supply oxygen and nutrients to the tumor. Evading immune destruction allows the tumor to avoid detection by immune cells and limit the extent of immunologic killing. Finally, the ability to reprogram energy metabolism allows alignment of energy needs to prioritize tumor growth and survival. Two additional enabling characteristics allow the cancer to leverage the above mechanisms into cellular growth and survival. Genomic instability hampers the cell’s ability to detect and repair DNA errors and damage. Thus mutations accumulate, and genomic integrity is lost. The presence of rich immune infiltrates in the tumor microenvironment (TME) can support tumorigenesis by growth and prosurvival factors. Collectively, these steps enable tumor initiation, growth, invasion, and progression; there has been a large increase in new drugs to target each of these major mechanisms.

Acquisition of survival capabilities by cancer cells is theorized to be directly related to dysfunction of the normal molecular mechanisms and pathways within the cell and surrounding TME. Because these pathways drive the progression of cancer, identifying and targeting the changes in the pathways to treat malignancy is a rational strategy. Thus the field of targeted therapy has flourished in modern cancer treatment, especially among common gynecologic malignancies.

Cytotoxic chemotherapy typically acts primarily on any rapidly dividing cells. Although this may have the desired effects on tumor cells, these drugs do not discriminate between tumor cells and normal host cells, resulting in undesirable side effects in the gastrointestinal (GI) tract, bone marrow, and integumentary and other systems. Ideal targeted therapies provide a more directed approach by acting on targets selectively leveraged in tumor cells or in the TME. These targets are typically members of the pathways involved in tumorigenesis, supporting growth, proliferation, metastasis, and angiogenesis. By homing in on those pathways rather than broad-based activity, normal tissues could be spared, and adverse events may be minimized.

These therapies hold the potential to reduce mortality rates from gynecologic malignancies while concurrently reducing the morbidity associated with cancer treatment by targeting abnormal rather than normal tissue. This chapter provides a broad overview of the pertinent molecular pathways in gynecologic cancer and the targeted agents that are currently being explored as treatment options. In addition, the unique toxicities of these targeted agents are reviewed. As our knowledge continues to expand, there will no doubt be myriad other pathways to exploit along with agents used to treat gynecologic malignancies.

Targeted agents

Targeting molecular pathways that drive tumor progression can be accomplished through a variety of mechanisms. The first is a humanized monoclonal antibody (mAb), which is created to bind cancer-associated antigens or molecules for cancer therapy. mAbs may be directed toward ligands or cell surface molecules that participate in pathways of tumorigenesis. Table 15.3 describes the standard nomenclature of the mAb classes. These agents are classified based on the origin of the antibody. By definition, mAbs have affinity for a single target, which allows for minimal non–tumor-related effects. These agents are administered systemically and have long clearance times, allowing biweekly to monthly administration. One such agent is bevacizumab, which is a mAb to vascular endothelial growth factor A (VEGF-A), a key active ligand in angiogenesis, to be discussed later in the chapter. Engineered antibodies are also being developed that can interact with more than one ligand or binding domain and to deliver one or more cytostatic and/or cytotoxic agents (e.g., antibody-drug conjugates [ADCs]).

Small molecule inhibitors are primarily oral drugs that inhibit the function of molecular receptors through the blockage of tyrosine kinase activity. Tyrosine kinases are enzymes involved in an array of normal and abnormal cellular functions. Their activity causes the transfer of a phosphate group from adenosine triphosphate (ATP) to a downstream protein tyrosine residue, resulting in changes in protein conformation and association, affecting innumerable biologic processes. Two types of tyrosine kinases exist: receptor and nonreceptor tyrosine kinases. Fig. 15.2 demonstrates the typical structure of a receptor tyrosine kinase, exhibiting three major domains: extracellular ligand binding, transmembrane, and cytoplasmic. Currently, more than 100 receptor tyrosine kinases have been identified and classified. Nonreceptor tyrosine kinases are typically present in the cytoplasm or nucleus and interact with transmembrane receptors to phosphorylate downstream substrates. They may also be activated through signals derived from extracellular processes such as ion exchange. Erlotinib is an example of a small molecule inhibitor that targets the epidermal growth factor receptor (EGFR) pathway affecting cellular division and proliferation.

Small molecule inhibitors typically block tyrosine kinase phosphorylation through interaction with the ATP-binding site on the intracellular domain of the tyrosine kinase. Binding to this site may be reversible or irreversible, depending on the agent. These molecules often have short half-lives, which necessitates frequent administration. Secondary to the high degree of homology found at the ATP-binding domain of the various tyrosine kinases, many of these molecules may inhibit one or more receptors within the cellular mechanism. Depending on the pathways affected, this can improve antitumor activity or lead to undesired adverse effects related to “off-target” inhibition.

The use of antisense oligonucleotides (ASOs) and short interfering RNAs (siRNAs) has great promise for expanding targeted therapy through knockdown of expression of specific genes involved in tumorigenesis. RNA silencing pathways are mechanisms within the cell that directly control gene expression. In general, siRNAs are generated from double-stranded RNA (dsRNA) within the cell by an endonuclease called Dicer. The antisense strands of the siRNA then associate with an RNA-induced silencing complex (RISC) that targets a specific messenger RNA (mRNA) for cleavage by Argonaute 2. Cleavage of the mRNA can silence genes involved in cellular survival, proliferation, invasion, and metastasis. Of note, the level of expression of the components of RNA silencing pathways correlates with survival in a variety of cancers.

The delivery of nucleotides such as siRNA in vivo has been challenging. However, local delivery (intranasal or intravitreal) and systemic (intravenous [IV]) approaches have been advanced into clinical trials in nonmalignant diseases such as macular degeneration. Several methods of delivery using biodegradable lipids and polymers have shown safety and efficacy in cancer models. Patisiran is an RNA-based therapy that was approved by the US Food and Drug Administration (FDA) for treatment of peripheral nerve disease (polyneuropathy) caused by hereditary transthyretin-mediated amyloidosis (hATTR) in adult patients. Inclisiran (siRNA therapeutic) has shown robust effects in lowering low-density lipoprotein (LDL) cholesterol in phase III clinical trials. Many other clinical trials are either underway or have been completed. Nanodelivery vehicles for selective delivery can further enhance tumor specificity. The arrival of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based cancer therapy in the clinic offers even more opportunities for aberrant gene-driving disease. These approaches to targeted therapy have the potential to greatly expand the possible targets while reducing undesirable adverse effects.

ADCs combine a highly toxic cytotoxic agent (or agents) with a specific immunoglobulin meant to create a targeted therapy that spares normal tissues that lack expression of the selected target. This is accomplished through use of a high-dose cytotoxic payload linked to a specific receptor that allows for direct delivery of the agent into the cancer cell. Current ADCs in development in gynecologic malignancies are leveraging targets, including HER2/neu, tissue factor, folate receptor α, mesothelin, MUC16, and NaPi2B.

Other unique agents have also been explored as prospective biologic options to disrupt carcinogenic pathways. Decoy receptors that bind key ligands of carcinogenic pathways have been developed. An example of this is AVB-500, which binds GAS6, the ligand for AXL, disrupting this pathway which is responsible for metastasis, drug resistance, and cell survival. Virus-based gene therapies deliver a functional transgene designed to selectively kill cancer cells by taking advantage of the ability of viruses to stimulate the host immune system. Ofranergene obadenovec (VB-111) is an example of this type of agent which has a dual mechanism of action, including antiangiogenesis and stimulation of tumor-directed immune response. There is no doubt that as our knowledge of cellular signaling mechanisms grows, so will the variety of agents available for targeted therapy.

Angiogenesis

Targeting angiogenesis has been markedly successful across the spectrum of gynecologic cancers. Angiogenesis is a key process for the supply of nutrients, oxygen, and growth factors and dissemination of a tumor. Thus the development of new vasculature is an essential process for a tumor to grow beyond 1 mm in size. There are two primary mechanisms for the growth of new blood vessels in both the normal and TME. Sprouting, the dominant means of vessel formation, is the branching of a new vessel from an established blood vessel. The other major mechanism is nonsprouting, which occurs when an existing blood vessel enlarges and splits into two separate vessels. Aggressive tumor cells may also develop microvascular channels to support neovascularization in a process known as vasculogenic mimicry. Finally, existing vasculature in the host tissue may be coopted by the tumors to increase vascular supply.

In normal tissues, the vasculature is organized and uniform in size and shape. Angiogenesis in the TME results in vessels that are more irregular, tortuous, dilated, and leaky. The regulation of angiogenic mechanisms occurs by a complex set of growth factors that stimulate and inhibit vascular growth in response to internal and external stimuli. In general, these factors act on the cells lining the blood vessel (the endothelial cells) to regulate activity within the cellular microenvironment. In the normal cellular microenvironment, the endothelial cells are stable, dividing rarely. Pathologic angiogenesis secondary to an increase in proangiogenic factors results in endothelial cells that demonstrate unregulated division and growth. In fact, high expression of proangiogenic molecules and increased microvessel density (a marker of increased tumor vascularization) are poor prognostic factors in many solid malignancies.

Vascular endothelial growth factors and vascular endothelial growth factor receptors

Fig. 15.3 demonstrates a schematic of the VEGF pathway, a key contributor to the regulation of angiogenesis. Activation of this pathway promotes the proliferation, survival, and migration of endothelial cells leading to vascular growth. In addition, VEGF stimulation increases cell fenestration and vascular permeability, which has been associated with the development of malignant effusions in the lungs and peritoneal cavity. VEGF overexpression has been found in a majority of solid tumors, including all three major gynecologic cancers, and is associated with poor prognosis and tumor progression.

As shown in Fig. 15.3 , the VEGF pathway includes seven different ligands: VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, placental growth factor (PlGF)-1, and PlGF-2. The mediation of the angiogenic effects for each VEGF ligand is accomplished through one of three receptors (VEGF receptors [VEGFRs]), including VEGFR-1, VEGFR-2, and VEGFR-3. These receptors belong to the class III family of tyrosine kinase receptors and are typically expressed on the vascular and lymphatic endothelium. However, these receptors may also be expressed by tumor tissue. The overexpression of VEGF in tumor cells is associated with increased tumor growth and metastasis in several solid malignancies, including ovarian, cervix, and endometrial cancer. Studies have revealed that ovarian cancers expressing VEGFRs have higher mortality rates compared with tumors lacking VEGFR expression. In cervical cancer, human papilloma virus infection can lead to degradation of p53 and subsequent upregulation of hypoxia inducible factor (HIF)-1. This factor can lead to increased neovascularization, supporting the rationale for antiangiogenic therapy in cervical cancer.

Activation of a given VEGFR results in subsequent downstream activation of a variety of known survival, proliferation, and migration pathways in the cell. These downstream pathways include phosphoinositide-3-kinase/akt (PI3K-AKT), Ras and Raf superfamily-MAPK (Ras-Raf-MAPK), focal adhesion kinase (FAK), and v-src sarcoma viral oncogene homolog (SRC). The activity of the VEGFR2 appears to be potentiated by the binding of coreceptors, neuropilin-1 (NRP-1) on arteries, and NRP-2 on venous and lymphatic vessels. NRP-1 and NRP-2 may have intrinsic activity through the binding of small G proteins and regulation of the cytoskeleton also.

Furthermore, VEGF has been found to affect several functions of immune activation and immune effector cells in the TME. Regulation and repolarization of tumor-associated macrophages, infiltration of myeloid-derived suppressor cells (MDSCs), induction of regulatory T cells (Tregs) and decrease maturation of dendritic cells, all can affect the function of tumor-directed cytotoxic T cells, providing favorable conditions for tumor cell survival.

Given the importance of the VEGF pathway, the majority of angiogenesis-related targeted therapies are focused on the VEGF family of ligands and receptors. Current options for therapy include drugs that directly target VEGF and its receptors and vascular disrupting agents that damage existing tumor related blood vessels.

Agents targeting the vascular endothelial growth factor pathway

Bevacizumab

Ovarian cancer.

Bevacizumab, a humanized mAb to human VEGF, was the first FDA-approved drug targeting angiogenesis. In ovarian cancer, bevacizumab has been evaluated both as a single agent and in combination therapy for primary and recurrent disease. After encouraging preclinical studies and multiple case studies, the Gynecologic Oncology Group (GOG) instituted a phase II trial of single-agent bevacizumab (15 mg/kg every 3 weeks) in persistent or recurrent refractory epithelial ovarian cancer. Despite a heavily pretreated cohort, the authors reported 13 of 62 patients (21%) experienced a clinical response, including 11 patients with partial response and 2 patients with a complete response. The median number of cycles was seven, and 25 patients (40.3%) had a progression-free survival (PFS) time of at least 6 months. Overall, toxicity was low, and there were no reports of bowel perforation. Another phase II trial of bevacizumab (15 mg/kg every 3 weeks) in 44 patients with ovarian cancer receiving third- or fourth-line chemotherapy demonstrated a partial response rate of 16%. The median PFS time was 4.4 months, and the median overall survival (OS) period was 10.7 months at study closure. This study was terminated early secondary to five patients (11.4%) experiencing spontaneous bowel perforation. The risk of bowel perforation appeared to be higher in patients with a higher median number of prior treatments and in whom impending bowel obstruction was suspected.

In the setting of relapsed disease, bevacizumab was evaluated in combination with both cytotoxic and biologic therapies. A phase II study of bevacizumab (10 mg/kg every 2 weeks) combined with oral cyclophosphamide (50 mg/day) demonstrated a partial response rate of 24% (17 of 70 patients) at a median follow-up period of 23.2 months. The probability of being progression free at 6 months was 56% in this study. Overall toxicity was acceptable in this study. This combination has also been evaluated retrospectively at several institutions with similar encouraging results (objective response rates, 44% to 53.3%). A phase II trial combining bevacizumab (15 mg/kg every 21 days) and oral erlotinib (150 mg/day) in 13 patients with recurrent müllerian cancer showed an objective response rate of 15% and a stable disease (SD) rate of 54%. However, this trial was stopped early secondary to lack of clear benefit of the combination over single-agent bevacizumab and a higher than expected rate of bowel perforation (15%).

Success in the platinum-resistant recurrent setting and in several phase II trials in the upfront setting led to five major phase III trials in ovarian cancer. In the upfront setting, GOG-0218 and International Collaborative Ovarian Neoplasm (ICON) 7 both include bevacizumab in combination with standard cytotoxic drugs followed by maintenance bevacizumab. Key characteristics of these studies are summarized in Table 15.4 . Data from GOG-0218 revealed a PFS benefit of 3 months in the arm that included bevacizumab treatment upfront and continued as single-agent maintenance (14.1 vs. 11.2 months; hazard ratio [HR], 0.72; P < .001). It is interesting that there was no PFS benefit in the patients who received only adjuvant bevacizumab compared with standard therapy alone. No OS benefit was noted in the arms containing bevacizumab, although this was not a primary endpoint of the study. Although different in design, ICON7 reached similar conclusions. In the arm receiving paclitaxel, carboplatin, and bevacizumab followed by bevacizumab maintenance, the PFS time was improved by 1.7 months (24.1 vs. 22.4 months; HR, 0.87; P = .04). OS was similar between the arms. Importantly, an ancillary study of GOG-0218 provided further data to indicate that bevacizumab should be used with caution in the primary setting in patients with history of inflammatory bowel disease or bowel resection.

TABLE 15.4

Comparison of Trial Design of Gynecologic Oncology Group (GOG) 218 and International Collaborative Ovarian Neoplasm (ICON) 7

	GOG 218	ICON 7
Patients (n)	1873	1528
Type	Randomized	Randomized
	Placebo controlled	Open Label
Primary endpoints	Overall survival	Progression-free survival
	Progression-free survival
Secondary endpoints	Toxicity	Overall survival
	Quality of life	Response rate
	Translational research	Biologic progression-free survival
		Toxicity
		Quality of life
		Economics
Strata	Stage (III ≤1 cm vs. >1 cm vs. IV)	Stage (I–III ≤1 cm vs. >1 cm vs. IV)
	PS: (0 vs. 1–2)	Chemotherapy start (≤4 weeks vs. > 4)
		Enrolling center
Sites	490	142
Opened	September 2005	April 2006
Closed	June 2009	February 2009

PS, Performance status.

As further targeted therapies and immunotherapies have been developed (discussed later), there has been interest in moving these therapies in combination into the frontline setting. IMAGYN050/GOG-3015 was a randomized control trial to assess the benefit of addition of the PD-1 inhibitor, atezolizumab, to chemotherapy with bevacizumab in newly diagnosed advanced ovarian cancer. There was no improvement in PFS in the group treated with atezolizumab (19.5 vs. 18.4 months, HR 0.92, P = .28). We have yet to determine the appropriate patient population for combination strategies; accordingly, a number of additional trials are planned that combine bevacizumab with poly (ADP-ribose) polymerase (PARP) inhibitors and immune oncology agents in upfront advanced ovarian cancer.

More promising results for bevacizumab have been observed in the phase III trials in the recurrent setting. GOG-0213 is a randomized study evaluating two primary objectives: (1) the effect of the addition of bevacizumab to standard carboplatin and paclitaxel and (2) the role of secondary cytoreduction in patients with platinum-sensitive recurrent ovarian cancer ( Fig. 15.4 ). With respect to the first objective, GOG-0213 demonstrated a significant improvement in PFS as well as a trend toward improved OS in the arm containing bevacizumab. In the OCEANS trial, patients with platinum-sensitive ovarian cancer were treated with gemcitabine and carboplatin with or without bevacizumab. This trial aimed to evaluate PFS and potential GI toxicity of this combination. Similar to GOG-0213, the arm containing bevacizumab demonstrated a significant improvement in PFS of 4 months. However, this did not yield a difference in OS. Finally, the combination of liposomal doxorubicin, carboplatin, and bevacizumab yielded improved PFS when compared with the to the OCEANS regimen of gemcitabine, carboplatin, and bevacizumab (13.3 vs. 11.6 months, HR 0.81, P = .012).

In the platinum-resistant setting, the AURELIA trial compared bevacizumab with a physician-choice standard agent, including paclitaxel, liposomal doxorubicin, or topotecan, with the standard agent alone. Bevacizumab provided a statistically significant improvement in response rate and PFS when added to standard chemotherapy. Interestingly, when a subanalysis stratified by each chemotherapy cohort was performed, the greatest PFS benefit (6 months) was found in the cohort that combined weekly paclitaxel with bevacizumab. The high crossover to bevacizumab after trial participation likely influenced the lack of OS difference noted in this trial. The results of this trial yielded an FDA approval for bevacizumab in combination with chemotherapy in platinum-resistant ovarian cancer receiving one or two prior regimens.

Bevacizumab has also shown promise in nonepithelial ovarian cancer. A retrospective review of eight patients with recurrent granulosa cell tumors demonstrated a partial response rate of 38% and SD rate of 25%. This study has encouraged the development of a phase II trial by the GOG evaluating bevacizumab for women with recurrent ovarian sex cord–stromal tumors. Among 36 patients treated, 16.7% had a partial response and 77.8% achieved SD. Certainly, these results are promising in this notoriously chemoresistant disease.

Two important recent follow-up studies have addressed other clinical questions with respect to bevacizumab use in the primary treatment setting: first, MITO-16b addressed the hypothesis that prior bevacizumab use would negatively impact subsequent use in platinum-sensitive recurrent disease and, second, AGO-OVAR17/BOOST trial addressed the role that doubling the exposure to bevacizumab in primary management would have on PFS and OS. In the former trial, no detriment was apparent because the HR for subsequent treatment of gemcitabine, carboplatin, and bevacizumab was similar (HR: 0.51, 95% confidence interval [CI]: 0.41 to 0.64) to the similarly designed OCEANS trial. In the latter, doubling bevacizumab from 15 to 30 months of exposure had no effect on PFS or OS.

Uterine cancer.

VEGF expression has been correlated with adverse outcomes in endometrial cancer, and bevacizumab has demonstrated encouraging results in early-phase clinical settings. The GOG initiated a phase II study of single-agent bevacizumab (15 mg/kg every 21 days) for advanced endometrial cancer demonstrating a 13.5% response rate and 40.4% surviving progression free at 6 months. The median OS time was 10.5 months in this trial. A subsequent trial attempted to maximize this benefit by combining bevacizumab with temsirolimus, an mTORC1 inhibitor described later in this chapter. The combination was deemed active based on reasonable response rate (24.5%) and 47% of patients surviving progression free at 6 months; however, its development has been limited by increased toxicity.

Given the activity of bevacizumab for relapsed disease, this agent was added to chemotherapy in two separate randomized phase II trials. In both the GOG-86P study (discussed in detail later) and the MITO-END-2 study, the addition of bevacizumab did not yield an improvement in PFS. Interestingly, the presence of p53 mutation was associated with better PFS and OS in GOG-86P, indicating this may be a potential biomarker to select combination therapy. In the upfront setting, the addition of bevacizumab to intensity-modulated radiation therapy (IMRT) with cisplatin was evaluated in high-risk endometrial cancer. Overall, toxicity was reasonable, and the OS rate for the cohort was 96.7% at 2 years.

Cervical cancer.

Bevacizumab is the first targeted agent that has demonstrated activity in recurrent cervical cancer. A phase II trial of single-agent bevacizumab (15 mg/kg every 21 days) had promising results in a cohort of patients with fewer than three prior regimens, achieving a median OS period of 7.29 months and acceptable toxicity. Five patients (10.9%) had a partial response, and an additional 11 patients were progression free for a minimum of 6 months. Furthermore, an analysis of six patients treated with bevacizumab in combination with 5-fluorouracil or capecitabine demonstrated a clinical benefit rate of 67%. There are several trials with bevacizumab in cervical cancer actively accruing or completed in the upfront and recurrent settings. GOG 240 combined bevacizumab with standard chemotherapy in four regimens, described in Fig. 15.5 . This study found a significant improvement in OS among the arms that received bevacizumab (17.0 vs. 13.3 months, HR, 0.71, 95% CI: P = .004), which led to an FDA approval for bevacizumab in combination with chemotherapy for advanced and recurrent cervical cancer. These successful results have led to exploration of the addition of immune oncology agents (discussed later) to bevacizumab and chemotherapy in this setting.

Vascular endothelial growth factor-trap (aflibercept)

Aflibercept is a manufactured protein that acts as a decoy receptor for all VEGF-A isoforms and PlGF. This agent was engineered through fusion of the ligand-binding domains from two VEGFRs with the constant region of IgG1, resulting in high-affinity VEGF binding and prevention of VEGF pathway activation. In the in vivo setting, aflibercept was found to improve ascites and reduce tumor growth.

Initial phase I trials of aflibercept for advanced solid malignancy demonstrated acceptable toxicity with clinical benefit approaching 50%. Several partial responses were observed in ovarian cancer. This led to a randomized phase II trial of aflibercept (2 mg/kg vs. 4 mg/kg) in platinum-resistant recurrent ovarian cancer. A response rate of 11% was reported with five partial responses and no mention of SD. Aflibercept has also been studied for the treatment of malignant ascites in ovarian cancer. Colombo and colleagues treated 12 patients with aflibercept (4 mg/kg) every 2 weeks and found successful prolongation in time to repeat paracentesis with minimal adverse advents. A phase I/II, multi-institutional trial reported the activity and toxicity of aflibercept in combination with docetaxel in women with recurrent ovarian cancer. Overall response in the phase II component was 54%, including 11 of 25 responders being complete. Median PFS and OS periods were 6.4 and 26.6 month, respectively. As expected, the most frequent aflibercept-associated toxicity was hypertension (11% grade 1 or 2). In endometrial cancer, the GOG performed a phase II study of aflibercept in the recurrent setting. This agent achieved a 7% response rate, and 23% of patients survived progression free for 6 months.

Agents targeting vascular endothelial growth factor receptors

AZD2171 (cediranib)

Cediranib is a small molecule inhibitor of VEGFR-2, platelet-derived growth factor receptor (PDGFR), and c-kit; it has shown promise in several phase II trials. In a study of 46 patients with recurrent ovarian cancer, the clinical benefit rate of single-agent cediranib was 30%. Eight patients achieved partial response, and six patients had SD, and median PFS for the group was 5.2 months. Hirte and colleagues reported a response rate of 41% in platinum-sensitive and 29% in platinum-resistant ovarian malignancy. Toxicities in both studies included diarrhea, hypertension, mucositis, fatigue, and anorexia. Cediranib was evaluated in the upfront setting in combination with standard paclitaxel and carboplatin as part of ICON6 ( Fig. 15.6 ). Toxicity of the combination was well tolerated and yielded a PFS benefit of 3 months. Importantly, the use of cediranib in the maintenance setting was not associated with a significant improvement in OS. This combination of paclitaxel and carboplatin with cediranib was studied in cervical cancer as well, yielding 2 months of increased PFS at the expense of increased toxicity. Single-agent cediranib in endometrial cancer had promising activity, with a 12% response rate and 30% of patients progression free at 6 months, leading to the development of ongoing combination trials with multiple targeted agents.

Agents targeting multiple vascular endothelial growth factor–related molecules

Sunitinib

Sunitinib is an oral receptor tyrosine kinase inhibitor whose targets include VEGFR, PDGFR, epidermal growth factor (EGF), and the stem cell factor (KIT) receptor. This drug has been evaluated in the treatment of recurrent ovarian cancer in several phase II trials and one phase III trial. A phase II trial of sunitinib (50 mg/day intermittent dosing, 4 of 6 weeks vs. 37.5 mg/day) in recurrent platinum-sensitive and platinum-resistant ovarian cancer demonstrated a 66% clinical benefit with partial response in 1 patient, cancer antigen (CA) 125 responses in 3 patients, and SD in 16 patients. Of note, responses were seen only in patients in the intermittent cohort. Common side effects were hand and foot reaction, fatigue, hypertension, and mucositis. Sunitinib was studied in clear cell ovarian cancer as a single agent in GOG 254 but did not yield sufficient activity to warrant further exploration.

In endometrial cancer, sunitinib demonstrated similar activity to other antiangiogenic agents. Of 33 patients, 18% had response to therapy and 30% had SD beyond 6 months. Mackay and colleagues reported the results from a phase II trial of sunitinib (50 mg/day) in 19 patients with advanced or metastatic cervical cancer. Although they achieved no objective responses, 16 patients achieved SD, with a median duration of 4.4 months.

Pazopanib

Pazopanib inhibits all of the VEGFRs (VEGFR1, VEGFR2, and VEGFR3), PDGFR-α and PDGF-β, and the KIT receptor. This small molecule inhibitor (800 mg/day) has been evaluated in a phase II study of 36 patients with recurrent ovarian cancer by CA 125 and nonbulky disease. This study revealed a 31% response by CA 125 level and a 56% SD rate. Among the 17 patients with measurable disease, 18% had a partial response. Ongoing ovarian cancer studies of pazopanib include combination with liposomal doxorubicin in the recurrent setting and in combination with paclitaxel and carboplatin in the upfront setting. A phase III, placebo-controlled study of pazopanib for consolidation after completion of primary chemotherapy in ovarian cancer yielded a prolonged PFS by 5.6 months when compared with placebo. Adverse events were increased in the pazopanib arm, with 33% of patients terminating this agent early. Unfortunately, pazopanib did not result in benefit in OS in this population. Interestingly, a subset analysis of East Asian women included in this study revealed a negative impact of pazopanib on PFS among this cohort. Further studies are ongoing to understand the mechanism underlying this difference. Pazopanib has also been combined with chemotherapy in the recurrent ovarian cancer setting. One randomized phase II trial comparing weekly paclitaxel with or without pazopanib revealed a 3-month PFS benefit in the setting of moderately increased adverse events, including neutropenia and fatigue. However, another placebo-controlled trial failed to demonstrate a benefit with the addition of pazopanib to weekly paclitaxel in recurrent ovarian cancer. In combination with gemcitabine, pazopanib yielded improved PFS, especially among women with platinum-resistant ovarian cancer. In cervical cancer, pazopanib was explored alone and in combination with lapatinib (a small molecule EGFR inhibitor to be discussed later) in the treatment of advanced and recurrent disease ( Fig. 15.7 ). The combination pazopanib and lapatinib arm was closed early after a futility analysis, leaving the randomized phase II trial to compare pazopanib with single-agent lapatinib. Both PFS (HR, 0.66; 90% CI 0.48 to 0.91) and OS (HR, 0.67; 90% CI 0.49 to 0.99) were superior in the monotherapy pazopanib arm. Median OS was 50.7 weeks versus 39.1 weeks for pazopanib and lapatinib, respectively. Pazopanib has also been evaluated as a treatment for metastatic soft tissue sarcoma. In the PALETTE study, pazopanib yielded improved PFS and OS as compared with placebo. This yielded an FDA approval in this indication.

Nintedanib

Nintedanib is a multikinase inhibitor targeting three key angiogenic receptors: VEGFR, PDGFR, and FGFR. A phase I trial of this agent in patients with gynecologic malignancies revealed a promising response rate, with five of seven patients with measurable disease demonstrating response and two achieving SD. Nintedanib (250 mg/day) was evaluated as a maintenance therapy compared with placebo in recurrent ovarian cancer after response to standard therapy. Although the trial was not powered to compare the two arms, PFS was less in the placebo arm (2.8 months) compared with the nintedanib arm (4.8 months). A randomized phase III placebo-controlled trial compared standard paclitaxel and carboplatin with or without nintedanib in previously untreated primary ovarian cancer patients. The combination arm was associated with significantly prolonged PFS, although clinically, this was a median increase of approximately 2 weeks. There was no improvement in OS in an updated report. Furthermore, there was significant toxicity in the combination arm, including GI and hematologic adverse events. A phase II study of this agent in recurrent endometrial cancer did not provide sufficient activity to warrant further study as a single agent.

Lenvatinib

Lenvatinib is a multikinase inhibitor against VEGFR1–3, RET, FGFR1–3, KIT, and PDGFRα that has been explored alone and in combination with a number of targeted agents in endometrial cancer. As a single agent, lenvatinib achieved similar clinical benefit in recurrent endometrial cancer as other antiangiogenic agents. Objective response rate was 13% and clinical benefit was 38% among 133 patients treated in this phase II study. Importantly, this agent was combined with immunotherapy in recurrent endometrial cancer, achieving impressive clinical benefit (discussed later).

Ofranergene obadenovec (VB-111)

As noted previously, ofranergene obadenovec is a virus-based gene therapy encompassing two targets—vascular disruption and induction of an immune response. This agent has been explored in combination with weekly paclitaxel in recurrent platinum-resistant ovarian cancer. Although objective response was modest at 13%, disease control was achieved in 73% of all patients. This agent is under further evaluation in a randomized phase III trial.

Phosphatidylinositol-3-kinase/AKT pathway

The PI3K/AKT pathway plays a central role in cell survival, growth, and avoidance of apoptosis. Fig. 15.8 demonstrates a simple schematic of this complex pathway that is known to interact with many other cellular growth and survival pathways. This pathway may be activated by a large number of receptor tyrosine kinases, including the EGFR family and the insulin-like growth factor receptors (IGFRs). Thus a variety of mitogenic substances are involved in its activation.

Activation of the pathway starts with the PI3K family, which consists of lipid and serine/threonine kinases composed of heterodimers, including a catalytic and regulatory subunit. Activation of PI3K leads to phosphorylation of phosphatidylionositol-4,5-bisphospate (PIP2) to phosphatidylinositol-3,4,5-triphosphate (PIP3). PIP3 acts as a second messenger to bind a variety of targets and recruit them to the plasma membrane, leading to their activation. One critical downstream mediator of PIP3 is AKT, which on activation acts on a number of different targets that directly affect cellular survival, proliferation through activation of transcription and translation, evasion of apoptosis, and resistance to chemotherapy. One key downstream target of AKT is the mammalian target of rapamycin (mTOR), a serine/threonine kinase. The upregulation of mTOR by AKT leads to activation of downstream regulator protein S6 kinase, which directly affects protein translation and the progression of growth through the cell cycle.

The PI3K/AKT pathway is known to be activated in a variety of cancers, especially in gynecologic malignancies. The phosphatase and tensin homolog on chromosome 10 (PTEN) is a tumor suppressor that encodes for a serine/threonine kinase, which acts directly to dephosphorylate PIP3 to PIP2. In patients with PTEN mutation and loss of function, there is an overaccumulation of PIP3, leading to constitutive activation of the AKT pathway. The PI3K/AKT pathway is also frequently activated through mutations in PIK3CA, which encodes for the activating subunit (110α) of PI3K or through mutations in AKT.

As described in Chapter 04 , the aforementioned mutations are commonly found in endometrial cancer and less frequently in the other gynecologic malignancies. Furthermore, this pathway is thought to be targeted more frequently in cancer than any other pathway aside from p53. Thus PI3K/AKT signaling provides a promising target for the treatment of malignancy and is under active exploration. Currently, the drugs targeting this pathway consist primarily of small molecule inhibitors of key pathway components. The inhibition of only one member of the pathway may not be sufficient to affect tumor growth given the significant pathway cross-talk and feedback loops. For example, mTOR is known to regulate cellular growth and proliferation through activation of several downstream proteins. These proteins also participate in a feedback loop that can lead to subsequent upregulation of AKT phosphorylation. Thus the exploration of combination therapies in this pathway is paramount.